Chapter 18 Practical applications

1141

Chapter 18

PRACTICAL

APPLICATIONS

The progress made in the catalytic polymerization of cycloolefins stimulated a variety of applications for both commercial and technological purposes. These applications range from commercial products to small scale manufacture of speciality polymers suitable for top technologies like automotive industry, computer science, microelectronics, fine mechanics, electrotechnique, constructions, optics, etc. In addition, the process opened the way for the synthesis of new compounds with unprecedented structure and architecture which cannot be prepared by conventional methods.

18.1. Commercial Products Whereas hydrocarbon resins dominated the plastics production for several decades, only recently a family of new polymers with remarkable physical-mechanical properties entered successfully the market. These products are suitable to a wide variety of applications in many areas. In the following section the most important representatives of this class will be highlighted.

18.1.1. Hydrocarbon Resins The products commonly known as hydrocarbon resins t are low molecular weight, thermoplastic polymers obtained from cracked petroleum distillates, turpentine fractions, coal tar and various pure hydrocarbon monomers. This class of compounds is used extensively in several industrial fields such as adhesives, rubbers, printing inks, hot-melt coatings, protective coatings, paint, flooring and other areas, z They generally are employed to modify existing materials and are rarely used alone. The average molecular weights of these resins are usually below 2000 and they range from viscous liquids to hard, brittle solids. Hard resins are commercialized in flake or solid form or in solutions according to customer demand. Some of the hydrocarbon resins are also available in the form of cationic, anionic or nonionic aqueous emulsions. The colors range from water-white for resins

1142 produced from pure aromatic vinyl monomers prepared with boron trifluoride to pale yellow and amber, and to very dark brown in the case of some inexpensive petroleum by-product resins. The first hydrocarbon resins to be manufactured on a commercial scale before 1920 were coumarone-indene or coal-tar resins. The next to be produced on the market since the mid-1930s are terpene resins used mostly in adhesives. They are mainly polymers prepared from ot-pinene, [3-pinene, and d-limonene of citrus origin, or dipentene mixtures obtained from sulphate turpentine. Due to the increasing demand for resins, petroleum resins were manufactured as a new type and distributed as commercial products by the mid-1940s. A wide range of petroleum resins is currently available. They have a varying degree of unsaturation and aromatic content and may be used in various fields of application. Resins from pure monomers have been developed and produced from styrene, otmethylstyrene, vinyltoluene, isobutylene, dicyclopentadiene, and other compounds with related structures. 3 These products are very light in color, frequently water-white compounds. Resins prepared from dicyclopentadiene, an important monomer obtained from cracked petroleum stream, have been recently available. Coumarone-indene resins. This type of hydrocarbon resins named also coal-tar resins is derived mainly from coumarone (1) and indene (2) where indene is the major component of the monomer feed. 2

1

2

The feedstock originated from coal-tar contains several other lower and higher boiling components such as styrene, o-, m-, p-methylstyrene, 2methylcoumarone, 2-methylindene, naphthalene which contribute as be resin-formers. The polymerization process of the monomer feed occurred first under the action of sulphurir acid but higher melting, lighter-colored products were obtained with aluminium chloride or boron fluoride and their complexes as catalysts. Though these feedstocks are mixtures of monomers exhibiting fairly wide boiling ranges, product softening points up to 150~

1143 and even higher could be obtained. Usually, the crude feedstock is diluted before polymerization with an aromatic naphtha solvent so that the final resin solution to contain about 30-35% solid products. As the heat of polymerization of indene is ca. 63 kJ/mole (15 kcal/mole), the heat removal is easier from a more diluted and less viscous polymer solution. The catalyst is frequently added to the indene-containing mixture, although the order of reactant addition may be reversed as in the case of other h y d r ~ o n resin processes. When the polymerization reaction is completed, the catalyst may be removed by means of alkaline washing or lime treatment. Subsequently, the solvent is removed from the resin by distillation. Coumarone-indene resins with a softening point of 100~ and higher have been employed extensively in coatings together with filmforming materials such as drying oils. They have also been widely used as process aids and pigment-dispersing agents in the compounding of the natural and synthetic rubber. Terpolymers of indene, cx-methylstyrene and vinyltoluene produced with BF3 have been applied in alkyd-based coatings because of improved compatibility compared with resins derived only from cx-methylstyrene and vinyltoluene. Indene resins have also been used as components of printing inks, adhesives and flooring. Importantly, the polyindene resins reportedly improve the flexural modulus and processability of high molecular weight poly(vinylchloride), polystyrene and other commercially available thermoplastic resins. Terpene resins. Terpene resins are manufactured by cationic polymerization of various terpene hydrocarbons, most of which occur naturally. The most important terpene resins are those prepared from otpinene (3), 13-pinene (4), and limonene or dipentene (5) (Scheme 18.1).

3

6

4

7

5

8

Scheme 18.1

9

1144

Less important resins include those obtained from [}-phellandrene (6), myrcene (7), 3-carene (8), camphene (9), terpinolene, and various other terpinene isomers. Optically active d-limonene is a product derived from citrus-fruit industry, d,l-Limonene or dipentene is sometimes obtained as crude distillate fraction from pulp-mill liquor. It has the same physical properties as d-limonene with the exception of optical activity, d, l-Limonene is formed in addition to other terpenes in the processing of sulphate liquor from kraftpaper production. Polymerization reaction of these monomers has been effected by means of high-energy radiation, Ziegler-Natta 4 catalysts and Friedel-Crafis 5 type catalysts. Of the latter class, wide range of catalysts were evaluated in the following decreasing order of effectiveness: AICI3 = AIBr3, ZrCL, AICI3.OEtz, BF3.OEtz, SnCLs, BiCI3, SbCI3 and ZnCI2. The terpene resins are solids with fairly light colors, ranging from Gardner 1 to Gardner 5. When the polymerization reaction is carried out in solution in the presence of AICI3, 13-pinene and limonene give better polymer yields than r However, dibutyltin dichloride as a cocatalysts in conjunction with AICI3 substantially improves the yield of solid resins from ot-pinene.6 Also, trialkylsilicon halides are effective cocatalysts. 7 Moreover, organogermanium halides and organoantimony halides were reported to produce high yields of terpene resins from otpinene s when used in association with AICI3. The structure and properties of r resins are somewhat different from those of 13-pinene resins. Neither the structure nor the mechanism of ot-pinene resins are completely elucidated. Although ot-pinene can initially form the same carbenium ion as 13-pinene under the influence of cationic initiators, the final products have different molecular weight distributions and infrared spectra and display a distinct behavior in tackifying natural and synthetic rubbers. Significantly, in a comparison of products with a softening temperature of 115~ r resins possess a narrower molecular weight distribution than 13-pinene resins. Relevant differences in solubility profiles and tackifying efficiencies for natural rubber and styrene-butadiene rubber were also reported. 9 Limonene and sulphate dipentene were polymerized with AICI3 to produce high yields of light-colored terpene resins. The structure of these polymers has been thoroughly examined and found to contain two types of repeat units (Eq. 18.1).

1145

2n

+~ n

(18.1)

The polymerization of dipentene is usually conducted in a combination of toluene and high boiling aliphatic naphtha to improve the catalyst effectiveness. In this process the dipentene is gradually added to an agitated slurry of aluminium chloride in the diluent. It was observed that though terpenes may be polymerized by gradual addition of the catalyst to the monomer, the reverse addition procedure afforded a better control of the reaction temperature and usually resulted in higher yields of cleaner products. In the batch process for dipentene polymerization, the reaction mixture is conveniently stirred for an additional 30 min following monomer addition; sometimes, an hour or longer was needed to complete the reaction. Generally, the polymerization temperature is between 30~ and 55~ preferably of 40-50~ For some reactions, the temperature may be as low as 15~ to 20~ and the process can be run continuously. The catalytic system is deactivated with lime and clay at the end of the polymerization. Following the complete removal of toluene by distillation, the mixture of polymer, naphtha, lime and clay is heated for 4 hr at reflux to remove chlorine eliminated as hydrogen chloride. In the polymerization of dipentene and d-limonene the catalyst concentration is of 4-8% AICI3 whereas ]3-pinene requires less catalyst. Following catalyst removal, the final polymer is recovered by distillation of the solvent, the finished product is commercialized in drums containing approximately 182 kg or flaked and packaged in multiwall paper bags containing 22.7 kg. Copolymers of terpenes have been manufactured by copolymerization reaction of a variety of terpene monomers or with other nonterpene monomers. ~~ An efficient process for the preparation of terpene resins with low softening points (0-40~ using AICI3 as a catalyst starts from J3-pinene, dipentene and terpene oligomers (dimers and trimers) as the raw materials. Copolymerization of ]3-pinene with styrene and otmethylstyrene in the presence of AICI3 has been largely explored, the products obtained were true copolymers as evidenced by NMP, and GPC analyses. ~2 Several patents apply resin production from 13-pinene and styrene, from dipentene and styrene and ot-pinene and isoprene. ~3 13-Pinene-

1146

styrene-isobutylene terpolymers with softening points--IO0~ were manufactured in hexane solutions under the influence of ethylaluminium chloride as a catalyst. ~ These resins are successfully applied as tackifiers for pressure-sensitive adhesives and as components of hot-melt coatings or adhesives, m5 Petroleum resins. Petroleum resins are low molecular weight, thermoplastic hydrocarbon polymers manufactured from cracked petroleum fractions. Initially, the petroleum resins were soft, unstable and darkcolored products, but improvements in the methods of preparation have provided products with acceptable color, better stability and higher melting points. Nowadays, petroleum resin colors vary from pale yellow to dark brown. They have practically replaced eoumarone-indene resins in all areas. Large volume applications of petroleum resins are in the rubber industry, printing inks, adhesives and coatings. The raw materials for petroleum resins come from the deep cracking of petroleum distillates and usually exhibit wide boiling range. Three main streams from cracking of petroleum distillates are employed as crude feeds for the resin production namely C4-C6 aliphatic stream, Cs-C~0 aromatic stream and dicyclopentadiene stream. The C~-C6 aliphatic stream contains varying amounts of piperylene, isoprene and various linear and cyclic mono and diolefins in addition to not polymerizable paraflinic compounds. Examples of unsaturated monomers of the C4-C6 aliphatic stream are illustrated in Table 18.1. Table 18.1 Unsaturated monomers of the C4-C6 aliphatic stream from petroleum cracking' Monomer Pentenes Hexenes Heptenes Pentadienes Hexadienes Cyclopentene Cyclopentadiene Cyclohexene Cyclohexadienes Methylcyclopetaadime Data from reference.~

Boiling range, ~ 20-40 41-73 72-98.5 34-38 59-80 44 41.5 83 81.5-88.5

73

1147 The Cs-C~0 aromatic stream contains indene, vinyltoluene isomers, styrene, c~-methylstyrene and dicyclopentadiene in varying amounts in addition to ethyl- and polymethylbenzenes. The unsaturated monomers and boiling range of these compounds are listed in Table 18.2. Table 18.2 Unsaturated nsmomers of the Cs-C~0aromatic stream from petroleum cracking' Monomer Dicyclopentadiene Methylcyclopentadiene dimer Styrene ct-Methylstyrene Vinyttoluenes Indene Methylindenes

Boiling range, ~ 170 200 145.2 164 166-170 182.6 15%199

9 Data from reference. The dicyclopentadiene stream contains 45-75% dicyclopentadiene in addition to other substituted monomers, streams of over 90~ dicyclopentadiene are also employed. The manufacture of petroleum resins from crude streams occurred in the presence of boron trifluoride and aluminium trichloride as catalysts. In early procedures H2SO4 has also been employed to initiate the polymerization reaction. With these catalysts, the reaction temperature varied from below 0~ to ~IO0~ depending on the type of the product prepared and the polymerization conditions. After the reaction time needed to achieve a complete conversion of the monomer, the catalyst was deactivated and removed with water, aqueous alkalies, ammonia, or lime. The polymer product was recovered by distilling the solvent from the "polymerized oil" or polymer solution. Petroleum resins range from liquids with softening points below 10~ to hard, brittle products with softening points up to 180-190 ~ Oicyclopentadiene resins. 1,3-Cyclopentadiene which is formed along with many other hydrocarbon compounds in the cracking of petroleum is removed from C4-C6 fraction by thermal dimerization to dicyclopentadiene (Eq. 18.2).

1148

(18.2)

Dicyclopentadiene feedstocks obtained from petroleum cracking may vary in purity from high (90-95%) to medium (78-80%) and to low purity mixtures of varying dicyclopentadiene content (45-70%). Codimers of cyclopentadiene with other linear dienes, e.g., butadiene or isoprene, and cyclic dienes, e.g., methylcyclopentadiene, are also present in the feedstock. Hydrocarbon resins were prepared from dicyclopentadiene by catalytic and thermal polymerization. ~6 The catalytic polymerization occurred mainly with AICI3 in solution. In this case, the process was conducted at 30~ by adding dicyclopentadiene slowly to half its weight of toluene in which 1% of AICI3 was suspended. After neutralization with aqueous alkali and removal of the solvent, a polymer with a softening point of 152~ bromine number 47 and Gardner color 13 was manufactured. Interestingly, a similar product, also with softening point of 152~ was obtained by the polymerization of the distillation bottoms from isoprene purification, under the same conditions. ~ This finding indicates that cyclopentadiene can increase the softening point when added to Cs monomers polymerized in the presence of AICI3 as catalyst. Hydrocarbon resins with lower softening points may be produced from dicyclopentadiene by an alkylation-polymerization process in mixed xylenes under the action of AICI3. The structure of these products involves aromatic xylyl groups attached to dicyclopentadiene recurring units ~8(10)

,C 10

1

Usually polymers with softening points between 30~ and 130~ are obtained. The lower softening point products are mainly employed as plasticizers.

1149

Applications. The main types of hydrocarbon resin are used widely as component parts in a great number of materials such as adhesives, rubber articles, printing inks, hot-melt coatings, floor coverings, textiles, paints and varnishes, caulks and sealants, and plastics. They are generally compounded with elastomers, plastics, alkyds, waxes and oils to confer special properties for a certain use. Sometimes, they are employed as the sole component in a particular application. For convenience of handling and transportation, hydrocarbon resins are commercialized in several physical forms including solid, bead, flake, crushed, powder or molten as well as water emulsions or dispersions, and solutions in adequate solvents or oils. The largest application of hydrocarbon resins is in the adhesive production. ~ As the conventional elastomers used in the adhesive compositions do not possess all of the desired properties for good adhesive performance, the hydrocarbon resins are incorporated into the formulation to modify the properties of the base elastomer and create the needed characteristics such as tack, resistance to creep, and viscosity control in hot-melt adhesives. The type of resin employed, e.g., indene, terpene or petroleum resin is determined, among other parameters, by the compatibility of the resin with the base elastomer. The main adhesive composition which contain resins are the following types industrial, construction, packaging, transportation, pressure-sensitive and consumer. Of all these types of adhesive, pressure-sensitive adhesives are one of the fastest growing area of the adhesive industry. This adhesive can be produced by resin modification of a large number of elastomers such as natural rubber, styrene-butadiene rubber, butyl rubber, chloroprene rubber, silicone rubber, acrylics, vinyl ether copolymers and ethylene-vinyl acetate copolymer. Terpene resins, particularly the [3-pinene resins, aliphatic C5 resins, and low molecular weight aromatic resins are widely employed for manufacturing pressure-sensitive adhesives from natural rubber. In adhesives based on styrene-butadiene rubber, ~-pinene resins, low molecular weight aromatic resins and aromatic-modified aliphatic hydrocarbon resins are suitable tackifiers. In addition to elastomer and tackifying resin, the adhesive includes plasticizer, filler, pigment, curing resin or cross-linker, and antioxidant. Hydrocarbon resins have also been extensively applied in hot-melt adhesives for markets such as packaging, disposable products, product assembly, bookbinding, and kraft-paper laminating to confer improved adhesion, enhanced hot tack, controlled viscosity and improved heat stability.These adhesives are formulated from polymers or copolymers e.g.,

1150 low molecular weight polyethylene, amorphous polypropylene, ethylenevinyl acetate (EVA) and ethylene-ethyl acetate(EEA). In the hot-melt adhesives derived from EVA copolymers the type of tackifying resin depends on the amount of vinyl acetate in the copolymer. Resins such as terpenes, pure and modified aromatics, and aliphatics have been effectively employed. In addition to the pressure-sensitive and hot-melt adhesives, large quantities of various hydrocarbon resins have been employed in special compositions of caulks, mastics and sealants. These adhesives are primarily solvent-applied or water based, but hot-melt caulks and sealant have been also developed. Polymers suitable for such compositions include neoprene, butyl rubber, natural rubber, polyisoprene, polyisobutylene, styrene-butadiene rubber, acrylics, polyesters, polyamides, amorphous polypropylene and block copolymers. The hydrocarbon resins are widely applied in the production of a variety of rubber-based products such as auto and truck tires, shoe soles and heels, hoses, industrial belting, mats, electric wire insulation, and roll covering. In this production they serve as processing aids, tackifiers and reinforcing agents. For instance, the coumarone-indene and aromatic resins reinforce mineral-loaded styrene-butadiene rubber stock and increase the tensile strength, elongation, and resistance to flex cracking. Also, aliphatir and terpene resins are useful as tackifiers for natural rubber and natural rubber/styrene butadiene rubber compositions used in the formulations of tires and molded goods. In this case, aliphatir resins impart good tack to unvulcanized carcass plies prior to tire building. In addition, resins may be involved in many other applications in tire manufacturing. A great amount of hydrocarbon resins are used in printing inks providing excellent pigment wetting, compatibility with many ink components, good resistance to water and alkali and good solvent release. Significantly, adequate selection of the feedstreams, careful control of the manufacturing processes, and continued quality assurance proc~ures ensure the supply of useful resin products to the printing industry. Thus, hydrocarbon resins with softening point of at least 140~ are usually desired as they provide higher solution viscosity, better solvent release, and improved hardness after drying. The resin may also behave as solubilizer or solid plasticizer when applied in conjunction with certain higher softening rosin ester resin in ink vehicles. Hydrocarbon resins are used extensively in letter press, lithographic and gravure inks. At a reduc~ sere the resins are used in flexographic inks because they are poorly soluble in the more polar flexo solvents. However, the hydrocarbon resins find some use in

1151 publication gravure and packaging gravure inks. In these applications, the resin contributes essentially to good pigment wetting as well as solvent release. Attempts have also been made to develop functional hydrocarbon resins with controlled solubility to preserve low ink-solution viscosity while providing fast ink setting for high-speed printing. A large number of paints and varnishes as protective coatings for industrial and trade-sale applications contain hydrocarbon resins as solid or solutions. Thus, petroleum resins are applied in air-dry and low bake industrial primers containing medium or long oil alkyds, gloss and semigloss industrial and trade-sale enamels to speed up drying, leafing aluminium paints to improve leafing properties and speed dry time, and oil and varnish stains to improve penetrating parameters and impart water resistance. Also, dieyr resins acting as oxidizing resins improve solvent resistance in aged films. Due to their unsaturation, these resins undergo copolymerization in drying oils used in cooked varnishes and alkyds to reduce the dry time in traffic paints. Furthermore, pure monomer resins are used in aerosol can paints where they retain pigments in excellent condition and promote high gloss and fast solvent release. In addition, the low solution viscosity of the resin is helpful in formulating these low solids coatings. Used in 20-30% as component part of the binder portion, the coumarone-indene and styrene modified aromatic resins are applied in the manufacture of light-colored asphalt floor tile. On their turn, some terpene resins are used as tackifiers for the natural rubber and synthetic gum bases employed in the manufacture of chewing gum due to their low odor and acceptable clearance. Block copolymer elastomers of styrene-butadienestyrene modified with parts of styrene or styrene copolymer resins are injection-molded to produce tennis shoes and tubing. Also, poly(vinyl chloride) compounded with styrene or styrene copolymer resins as processing aids is extruded into underground drain pipes. Furthermore, corrugated containers for shipping i c ~ or frozen poultry, fish, and meat are coated or impregnated with certain hot-melt blends composed of aliphatic or terpene resins, ethylene-vinyl acetate resin, and paraffin or microcrystalline waxes. In building technology, in order to control the degree of moisture evaporation and setting time, freshly poured concrete is sprayed with solutions of aromatic, dicyr or aliphatir resins. Economic aspects. Estimation of the total worldwide annual h y d r ~ o n resin production capacity indicated the value of ~1.04 million tons in the year of 1985. The main hydrocarbon resin producers are grouped in the

1152 United States, Japan, France, Netherlands, United Kingdom and Germany. (Table 18.3).

Table 18.3 Hydrocarbon resin manufacturers groupod by country'

United States Amoco Chemicals Corp. Arizona Chemical Co. Beatrice Companies, Inc., Chemfax, Inc. Eastman Chemical Products, Inc. Exxon Chemical Co. Goodyear Chemicals Co Hercules Inc. Hooker Chemical Corp., S.C. Jolmson & Son, Inc.

Lawter Chemicals, Inc. Neville Chemical Co. Polymer Applications, Inc. Reichhold Chemicals, Inc. Resmall Corp. Saturn Chemicals, Inc. Schenectady Chemicals, Inc.

Japan Arakawa Forest Chemical Hitachi Chemical Co. Mitsui Petrochemical Co. Maruzen Co. Mitsubishi Co., Ltd. Nippon Oil Co. Nippon Zeon Nisseki Plastic Chemical Co. Sanyo Toho Chemical Co. Torten Petrochemical Co. Yasuhara Zyushi Kogyo Co. I ~ . Netherlands AKZO Hercules B.V.

Neville Cindu Synthese Germany France Charbonnage de France (CdF) Chimie Ho~Alst AG Verkaufsveremigung fur Derive Resines Terpeniques (DRT) Teererzeugnisse Esso Chimie Others Granel Camphor and Allied Products, L~. Le Monde Chemicals, Inc. (India) Rousellot S.A. Faime (Italy) DSM, Sheby Hercules do Brazil (Brazil) United Kingdom Kolon Petrochemical Co., Ltd. (Korea) British Steel Corp. Quimica Demieres S.A. (Spare) Imperial Chemical Industries St Lawrence Resin Products, Ltd. (Canada)

' Data from reference. ~

1153

18.1.2. Polyalkenamers At present there are several industrial processes for the synthesis of poly~kenamers with elastomeric or thermoplastic properties. ~9"~ They supply a significant amount of products suitable for important applications in various scientific and technological areas.

18.1.2.1. trans-Polyoctenamer Though at first the research on polyoctenamers concentrated on the polymers rich in cis structure, for economic reasons an industrial breakthrough was achieved only with trans-polyoctenamer. This polymer was introduced as under the trade name Vestenamer by Chemische Werke Htils in 1980 and is at present commercialized as different types of products, depending on the molecular weight and trans contents. 2~23 Production of cyclooctene.The monomer, cyclooctene, is manufactured by partial hydrogenation of 1,5-cyclooctadiene. The latter was formed as a byproduct in the synthesis of 1,5,9-cyclododecatriene or from butadiene via dimerization in the presence of modified Ziegler-Natta catalysts with zerovalent nickel compound 24(Eq. 18.3).

(.)

()

Under these conditions, complete conversion of the starting material and high selectivity at elevated temperatures can be attuned. The crude product in the first step is separated from by-products and catalyst residues by flash evaporation. Purity of >99% can be easily reached. The selectivity of the hydrogenation step to cyclooctene is slightly less than 100% when commercial heterogeneous catalysts are employed. With rigorous temperature control and hydrogen metering a specially developed hydrogenation catalyst gives complete selectivity. However, a small degree of overhydrogenation to cyclooctane must be admitted, otherwise, traces of 1,5-cyclooctadiene can remain in the product that may hinder the sensitive polymerization process as results of its isomerization to 1,3-cyclooctadiene. The latter acts especially as a strong catalyst poison. The monomer with the purity necessary for polymerization contains 95-97% cyclooctene, the remaining being essentially cyclooctane. Synthesis of trans-polyoctenamer. On the industrial scale, polymerization of cyclooctene is performed in hexane as a solvent in the presence of a

1154 WCI6-based metathesis catalyst. 24 High purity monomer and anhydrous conditions are essential. The reaction is carried out adiabatically to complete conversion of monomer in almost 100% yield. The workup involves flash evaporation of the solvent with subsequent recycling. The final product is filtered in the melt, pelletized after cooling, and packed at a purity of >99.5% in bags. The content of impurities and low mass oligomers is very small. Properties of trans-polyoetenamer. Polyoctenamer has been produced over a wide range of molecular weights and cis:trans ratios of the double bonds. 24 The products exhibit bimodal molecular weight distribution with the first maximum corresponding to the low molecular weight oligomers. Depending on the reaction conditions, linear, unbranched polyoctenamers with an ideal poly(l-octenylene) structure in addition to macrocycles are formed in the polymerization process. As one double bond occurs at every eighth carbon atom of the chain or macrocycle, polymers with high chain mobility and low glass transition temperature will result. The crystallinity of the polyalkenamers depends strongly on their microstructure i.e., the ratio of cis:trans double bonds. The double bonds can be arranged in sequences and crystallites with defined melting temperatures will be formed. The crystallinity is thermally completely reversible and has a beneficial effect in blends of Vestenamer and other rubbers. During the mixing and extrusion the temperatures exceeds 50~ and the molten polyoctenamer improves the flow properties of the blend. After cooling the polymer recrystallizes and increases the green strength and shape stability. It was observed that the influence of the trans double bonds on the crystallinity is more pronounced than that of the cis double bonds. It is significant that recrystallization from the melt occurs within seconds; this property is very important in certain applications involving rubber processing. Several polyoctenamer grades are available commercially from Hials AG under the trade name Vestenamer. z5"3~The low molecular weight and crystallinity are chosen specifically so that they provide advantages in rubber processing due to their low melt viscosity. Typical properties of Vestenamer 8012 and Vestenamer 6213 are given in Table 18.4. In addition to these two types, a low molecular weight polyoctenamer has been offered to the coatings industry as Vestenamer L. The molecular weight of Vestenamer is kept intentionally low for a rubber. Due to its thermoplasticity, the viscosity in the molten state is unusually low compared to other solid rubbers. The Mooney viscosity ML

1155 Table 18.4. Properties of Vestezmmer 8012 and 6213' Property

Molecular mass, g/mol Glass transition temperature Tg, ~ Crystallmity (at 23 ~ % Melting point, ~ Startof d~osition, ~ Ratio trans:cisdouble bonds, % Mooney viscosityM L (l+4)(at I00 ~ Viscositynumber J(at23 ~ mL/g

Density,g/cm 3

Vestenamer

Vestenamer

8012

6213

100000 -65 30 54 275 80:20 <10 120 0.91

120000 -75 12 <36 250 60:40 <10 130 0.89

' Data from reference.24 (1+4) at I O0~ is between 5 and 8. Interestingly, it was found that polyoctenamer with 55% trans content and rather low viscosity exhibited surprisingly high elastomeric characteristics when compared with a cispolybutadiene of the same viscosity (e.g., tear strength 120 vs. 60 kp/cm 2, rebound elasticity at 22~ 43 vs. 30 %, modulus at 300% elongation 105 vs. 50). In contrast to common baled rubbers, the handling of polyoctenamers is simplified because they are delivered as pellets. Vulcanization and processing. ~3. Vestenamer can be vulcanized with all the cross-linking agents commonly used in the rubber industry such as sulphur, sulphur donors and accelerators, peroxides and vulcanization resins. Its cure rate with sulphur is comparable to that of a slow curing styrene-butadiene rubber. In blends with faster curing rubbers like natural rubber, isoprene rubber, butadiene rubber the accelerator level can be slightly increased. Blends of EPDM with Vestenamer are normally cured with peroxides since sulphur curing can deteriorate the vulcanizate properties. Vestenamer has two important functions when used as a blend component in 5 to 20 parts in the rubber compounds; first, due to its low viscosity, Vestenamer acts as a plasticizer or processing agent in compounding and molding and second, after vulcanization it is cross-linked like all other rubbers, completely incorporated into the network, and can no longer be extracted. It is interesting to note that the ring molecules in

1156 Vestenamer permit good rubber properties at low molecular weight. In vulcanizates the same amount of cross-linking agent (e.g., sulphur) binds long polymer chains as well as medium-sized tings (Figure 18. l, A, B and C) to an effective polymer network but fails to do so with short or medium length chains. (A)

(B)

(c)

S-bridges

S-bridges

S-bridges

\

Figure 18.1. Different network types in rubber vulcanizates (Adapted from Ref.23). These network types can explain the good elastic and thermodynamic properties of vulcanizates from a polymer with low molecular weight. Addition of Vestenamer in rubber compounds affords a series of significant advantages. These imply a lower overall energy consumption for the mixing process, easier filler incorporation, better filler dispersion and a smaller temperature increase during mixing. In the extrusion process the mass pressure and die swell are decreased and the surface finish of the extrudates, e.g., profiles and tubing, is improved. Furthermore, the high rate of crystallization of Vestenamer leads to a significantly higher green strength of the compounds. Examples on the improvement in the green

1157 strength of the natural rubber and of polybutadiene or polyisoprene rubber in rimstrip compounds or carcass compounds in tire building are illustrated in Figures 18.2 and 18.3. Green Strength, Mp. 10 1

06

/ 06

,X,,..~...X,,--'X.~,~o,,~ '" ' ' ' ~ ' ' ' ' ~ ' ' ' ' ~ ' ~ ' ' " .... ~''" "'~''''~ 2

ts S

04

.~. o*

' O " "" ~* ' ' ~ ~ ' " 0 ' " ' ~ "" ~

' ' 0 ' ' ' ~* ~ ~ * "" 0 ~* ' "' " 0 "' ' ' 3

02

Elongation, % Figure 182 lnfluen~ of Vestenamer on green strength m rimstrip compounds (Curve 1 NR/BR/TOR = 10/70/20 ; Curve 2 NR/BR/TOR = 20/70/10; Curve 3 NR/BR/TOR = 70/70/0) (Adapted from Ref3~ As it can be seen, the replacement of natural rubber by small amounts of Vestenamer 8012 improved the green strength considerably what helps to avoid overstretching during the tire building operations. Significantly, such effects can be obtained with the more crystalline Vestenamer 8012 and not with Vestenamer 6213. It was also found that the rigidity and dimensional stability of extrudates, which are stored before vulcanization, are increased markedly; examples are tire bead and apex compounds, profiles and braided hoses. Due to the improved flow properties of these compounds, the mold-filling process can be improved and shortened in the production of molded articles

1158 Green Strength, MPo ! /

4.5

9

J

3 /

/

t

/

t/"

3.0

.,.--

1.5

/

/

7

0

2

4

6

8

10

12

Elongation, % Figure 18.3.. Influence of Vestenamer (TOR) on green strength in carcass compounds (Curve 1 NRfTOR = 50/50; Curve 2: NRfFOR = 80/20; Curve 3" NRfrOR 90/10; Curve 4" NR = 100; Curve 5" IRfI'OR = 80/20; Curve 6" IRfFOR = 90/10, Curve 7" TOR = 100) (Adapted from Ref.3~ and complicated mold geometries are cleanly manufactured. As result of the rapid recrystallization of Vestenamer 8012, the anisotropy of the calender shrinkage is considerably reduced; even very thin sheets can be calendered without defects. Moreover, the tack of the compounds is reduced due to the completely unbranched polyoctenamer molecules in conjunction with their crystallinity.

1159 The vulcanizate properties of rubber-polyoctenamer blends are barely affected compared to compounds without Vestenamer. Tensile strength and tear resistance are decreased somewhat as a consequence of the low molecular weight of the polyoctenamer. The elongation at break decreases while the modulus increases. The hardness is also increased because the crystallinity is substantial after cross-linking. In addition, the ozone resistance is not changed. It was also observed that in blends of polar and nonpolar (NBR-EPDM) rubbers or emulsion and solution rubbers (NRBR), the use of small amounts of Vestenamer (5-10 phr) increased dispersion of the otherwise mutually not very compatible rubbers and processing can thus be improved. The dynamic properties of the natural rubber compounds are improved on blending with Vestenamer and reversion is suppressed at the same time. These results open up new possibilities for tire compounding and manufacture. Applications and economic aspects. Vestenamer has been used in all areas of rubber industry, z;'z4 At present it is predominantly used in blends with the following rubbers: NR, SBIL EPDM, NBR, CIL CSM and precross-linked rubbers. Thus, the improved flow with Vestenamer often provides smoother extrudates and higher output, while the swell is diminished. This allows the extrusion of the very hard compounds which otherwise could not be achieved by conventional ways. Moreover, by improving the flowability of the compounds, Vestenamer facilitates mold filling by decreasing the pressure build-up and affords a better shape precision. In this way, even poorly flowing hard compounds may be injection molded by the addition of Vestenamer. During calendering process Vestenamer decreases the shrinkage and improves the surface quality particularly of coated fabrics. In many cases, in the hose production, the improved green strength of the uncured hose core enables savings by eliminating the costly cooling operation, usually necessary before braiding the core. It was found that covering of the metal rolls with unvulcanized rubber sheets is made easier by the improved green strength given by Vestenamer. The good compatibility and covulcanization properties of Vestenamer with other rubbers improves the peel strength between the layers. Vestenamer also improves the processing of very hard roll coverings making thus the injection molding of e.g., type-writer rolls and rice hulling rolls possible. It allows to manufacture rolls consisting of natural rubber and EPDM mixtures which are otherwise incompatible. The pronounced thermoplasticity and low melting point of

1160

Vestenamer permit the use as a carrier material for filler batches. In this case, the filler incorporation is high and the rapid recrystallization from the melt allows granulation of the batches. Of interest are uses of Vestenamer as carrier material in combination with dyes, accelerators, peroxides and very fine powders. Vestenamer is mainly used in the bead area and in the sidewall of passenger and truck tires. This facilitates the building process by increased green strength which also contributes to a better tire uniformity. At the same time, the processing is improved especially for highly filled compounds. Unlike other processing aids, Vestenamer is used to replace the base rubber, normally at 5-20 phr. Interest is also increasing in the use of Vestenamer as the only rubber component for the manufacture of extremely hard but readily processible tire apex compounds and golf balls. Vibration damping sheets for steel plates based on butyl rubberpolyoctenamer blend have been developed and commercialized. Recent development is the application of Vestenamer-oil mixtures as coating and binding agents for ground rubber waste powder. This technique can be employed for recycling rubber waste, which is technically rather difficult. Vestenamer production began at Hills Company in a pilot plant in 1980 and in 1989 a large plant with a capacity of c a . 12000 to/year was put in operation. Of interest, in 1991 the following quantities of Vestenamer were consumed in different areas of the rubber industry (Table 18.5).

Table 18.5. Uses of Vestenamer in the rubber industry'

Industrial Area

Tires Profiles Molded articles Tubing Calendered articles Roll covers Other ' Data from reference.~

Vestenamer amount % 34 27 15 3 2 1 18

1161 Toxicology. ~ trans-Polyoetenamer and its precursors have been thoroughly investigated with regard to their toxic properties. Toxicology studies on 1,5-cyclooetadiene indicated that this precursor has an LDs0 (oral) of 1900 mg/k 8 in rats and LDs0 (dermal) of >10000 mg/k 8 in rabbits. This compound shows a slight irritant effect on the skin but has no sensitizing effect in the corresponding test according to Magnusson and Kligrnan. It has no irritating effect on the eyes or mucous membranes. Cyelooctene has an LDs0 (oral) of 4550 mg/kg in rats and an LDs0 (dermal) of >10000 mg/kg in rabbits. This compound exhibits a slight irritant effect on the skin but has no sensitizing effect in the corresponding test according to Magnusson and Kligman. It shows no irritating effect to the eyes and mucous membranes. Studies on trans-polyoctenamer indicated an LDs0 (oral) of > 12500 mg/kg in rats. The product exhibits no irritating effect on the skin or on rabbit eyes. Experiments on rats showed that a 90-d oral administration at concentrations up to 4000 mg/kg did not result in any toxic effect. The polymer showed no mutagenic effect in the Ames test (m vitro) on Salmonella typhimurium and the micronucleus test (in vivo) on mice.

18.1.2.2. Polynorbornene Polynorbornene is the frequently used name for poly(1,3cyclopentylenevinylene) obtained by the ring-opening polymerization of bicyclo[2.2.1]hept-2-ene (norbornene) though polynorbornene designates also the product obtained by vinyl polymerization of norbornene. Since 1940 this highly strained reactive monomer has been subjected to numerous polymerization investigation using various types of catalytic systems. As result of intensive studies on the polymerization of norbornene, the polymer has been produced in France by CdF Chimie under the trade name of Norsorex since 1976. The final products are copolymers of norbomene with ethylene and propylene and possess the structure of a trans-poly(l,3cyclopentylene-l-vinylene) with ethylene and propylene units. They are characterized by an unusual high molecular weight (>3x106 g/mole) and a glass transition temperature T s of 37~ being intermediate between elastomers and thermoplastics. The materials are compatible with plasticizers and acquire elastomeric properties by incorporation of these substances. At present, the worldwide production capacity of polynorbomene is 5000 to/year (Norsorex)in the French plant of Elf Atochem (Carling).

1162 Consumption of pure polynorbomene was about 1000 to in 1991, corresponding to 5000 to of compounded elastomer. Norsorex product was introduced in North America by American Cyanamid in 1977 and in Japan by Nippon Zeon in 1978; the product price was of $3.00-4.00/kg in 1987. Production of 2-norbornene. The monomer, 2-norbornene, is synthesized by Diels-Alder reaction of cyclopentadiene with ethylene. Cyclopentadiene is itself obtained by cracking of dicyclopentadiene at a temperature higher than 160~ (Eq. 18.4).

,,0.c.

o §

(18.4)

II

-~ Dicyclopentadiene is extracted from the Cs streams from naphtha steam cracking. The addition reaction occurs without catalyst at a high temperature and a high pressure. The impurities contained in the commercial dicyclopentadiene (about 5%) and the by-products formed by reaction of 2-norbomene with the raw materials are removed by a thorough purification of 2-norbomene after the synthesis step. The polymefizable monomer has 99.7% purity. Pure 2-norbomene is solid at room temperature (Mp = 47~ and has to be protected from air oxidation. Manufacture of polynorbornene. Commercial polynorbomene (Norsorex) is produced by ring-opening polymerization of norborrlerle 31'32 in the presence of RuCI3 in butanol~C131'32 (Eq. 18.5).

n

i~~

RuCI3 C41..IoOH/HC ~-

(18.5)

The chemical structure of the polymer corresponds to poly(1,3cyclopentylenevinylene) preserving one double bond per repeat unit with mainly t r a n s configuration. The polymerization reaction is extremely rapid and highly exothermic. A special technology provides a polynorbomene with a convoluted and porous structure. After cooling and drying, the polymer appears as a white, free flowing and easily processible amorphous powder, with an irregular surface area having a grain size of <0.8 mm and an apparent density of 0.3 g/cm. 3 It rapidly absorbs oils typically employed

1163 in compounding formulations. The porous structure and the presence of double bonds render polynorbornene very sensitive to air oxidation; therefore, a non-staining antioxidant is added during its manufacture. Several grades of Norsorex are produced which contain various concentrations of aromatic and naphthenic processing oils; these products are available in slab form. Properties and processing. Polynorbomene possesses remarkable properties due to its particular chemical structure, uncommonly high molecular weight and unusual transition temperature. Relevant physical properties of the pure polymer are given in Table l8.6. Table 18.6. Physical properties of polynorbomene ~

Property

Value

Microstructure, % t r a n s Appearance Molecular weight, g/mole Glass transition, T s, ~

80 white amorphous powder >3x10 s 37 ~ 0.96 1.534 19.8 2.09 218 0.285 2.5 10.4 7x1016

Dens y, g/cm3 Refractive mdex Solubility parameter, Mpa 1/2 Heat capacity, J/(g.K) Heat of formation, J/g Thermal conductivity, W/(m.K) Dielectric constant (1 MHz) Dissipation factor (l MHz) Volume resistivity f2.cm 9 Data from reference. 33"35

The thermal behavior of pure polynorbomene classifies it as a thermoplastic product with a very low transition temperature. Because of its high molecular weight, polynorbornene does not melt under usual conditions and decomposes at >200~ without real fluidization. Interestingly, the polymer exhibits a "shape memory effect": when heated to more than 37~ it recovers its memorized shape. The pure product is used

1164 in only a few minor applications. The pure polymer has a very high attinity for liquid hydrocarbons promoted by its extremely porous structure. Due to its ability to absorb and gel about ten times its weight of common hydrocarbons, pure polynorbomene is considered a highly efficient antipolluant. Because of the compatibility of polynorbomene with various extension oils that act as plasticizers, the transition temperature of the polynorbornene-oil mixture is lowered thus converting the plasticized polymer into an elastomer (Figure lS.3). Ts, ~ 10

-10

-20

-30

-40 0

I 5O

i IO0

i 150

I 2OO

Oil, phr Figure 18.4. Influence of various plasticiz~rs on Ts of polynorbomene (Curve l aromatic, Curve 2, naphthenic; Curve 3, paraf~ic) (Adapted from Ref.S~). Moreover, the presence of double bonds in the structural unit allows further vulcanization of the polymer with common peroxides or various sulphur vulcanization compounds. Pure polynorbornene has good aging and heat resistance (up to 90~ excellent mechanical strength, low compression set, and high compatibility with most other rubbers. When unprotected, polynorbornene rubbers exhibit poor ozone resistance, however, efficient protection is obtained by addition of antiozonants or small amounts of EPDM rubber.

1165 Polynorbornene rubbers allow a high level of palsticizers and filler to be incorporated. Plasticizers can be applied at up to 500 parts per 100 parts of polymer while fillers up to 200 parts. Most usual polynorbornene rubbers contain on average 20~ pure polynorbomene so that the properties of the resulting vulcanizates will vary over a wide range depending on the formulation. The amount of plasticizer incorporated in the polymer determines the soRness of the vulcanizates, usually low hardness values of products clown to 10 Shore A can be reached in combination with good mechanical properties. The type of plasticizer affects substantially the cold resistance, energy absorption capability and compatibility with other rubbers. The dependence of the cold resistance (brittle point) of the polynorbornene v u l ~ t e s on the type and level of plasticizer is illustrated in Table 18.7. Table 18.7. Influence of plasticizer on the brittle point of polynorbomene vulcanizat~~ Plasticizer level, ph'r

Plasticizer type

Aromatic oil Naphthenic oil Paraifmc oil Dioctyl adipate Brittle point, ~

160

180

180

180 180

20 40

-30

-42

-49

-38

-52

9 Data from reference.2' As Table 18.6 shows a wide range of brittle points result for various groups of plasticizer and different levels of incorporation. Several types of mineral fillers and carbon blacks can be used with polynorbornene rubber. The type of filler will influence mainly physical properties such as strength resistance, abrasion and tear resistance, electrical properties and dynamic damping parameters. The degree of their effect depends essentially on their concentration in the rubber compound. Values of the mechanical properties of a given polynorbornene rubber compound containing 200 parts of naphthenic oil and 200 parts of various fillers are listed in Table 18.8.

1166

Table 18.8 Effect of filler type on polynorbomene rubber' Property ~itin B

MT

sal

Type of filler GPF

FEF

HAF

28 l 0.5 525 55

35 l I. 8 507 56

43 14.r 369 45

57 15. l 276 34

61 16.9 268 22.5

Hardness, Shore A Tensile strength, Mpa Elongation, % Rebound at 20 ~ %

53 14.8 322 35

9 Data from reference,z4 Highly filled polynorbomene vulcanizates can be employed where the ability to accept ultrahigh Ioadings provides excellent damping characteristics, which are little affected by the temperature. It was observed that the glass transition T s of the polynorbomene rubber is determined by the oil selection and the damping above 20~ can be adjusted by the type and amount of filler. Remarkably, small-particle-size carbon blacks provide both reinforcement and damping. Two formulations of low and high damping are presented in Table 18.9. Table 18.9 High and low dampmg formulations for polynorbomene' Ingredient

Low damping, parts

High darnpmg, parts

Norsorex polynorbomene Mediun viscosity napl~enic oil Dioctyl adipate N-990 thermal black N-774 furnace black N-220 fumace black N-octyl diphenylamme Zinc oxide Stearic acid N-Isopropylbenzothiazole-2-sulphenamide Sulphur

100 150 50 100 100

100 250 50

Data from reference. ;a

2 5

2OO 2 5

I

1

5 1.5

5 1.5

1167 The effect of temperature on the damping parameter (tan ~i) for the two polynorbornene formulations for low and high damping characteristics is illustrated in Figure 18.5. Tan 8 1.00

0.30

0.25

0.10 -40

9 -20

, 0

9

9

t

t

t

20

40

SO

80

100

Temp., ~ Figure 18.5. Effect of ten'~rature on damping parameter (tan 6) for polynorbomene formulations (Curve 1" high damping characteristics; Curve 2" low damping characteristics) (Frequency 110 Hz, Stram amplitude 3%) (Adapted from Ref.35). It is relevant that formulations with good aging characteristics include a microcrystalline wax with a p-phenylenediamine antiozonant for ozone resistance. For non-staining applications, blends of polynorbornene with EPDM rubber are employed. The best results are recorded with high unsaturation, oil-extended EPDM rubbers. These formulations give better dispersions in the high molecular weight polynorbomene and provide a better match of cure rates for the respective compounds. Matching of the cure rates will give satisfactory ozone resistance with a 25:75 blend of polynorbornene-EPDM rubber. Interesting results on the effect of various compounding ingredients such as oil, filler, curative, antioxidant on hot-air aging of polynorbornene vulcanizates have also been reported. It is noteworthy that, because of its high molecular weight, polynorbornene rubbers can be blended with large amounts of extenders and fillers without affecting their processability or mechanical properties. For instance, compounds that contain 100-400 parts each of oil and carbon

1168 black varied in 200% modulus from <2 to >20 MN/m z (2900 psi) (Figure

18.6). Oil, phr

Oil, phr 5004Oo

0

200

100

300

30O

300

/'~3o.o as.o t

100

|

2OO (a}

200

loo I

'

30O

100

,

!

2OO Co)

2"04.0

30 4050

7.0 300

10.0

i

3OO

3OO

6O

12.0 150 200

2OO

100

I00

100

200

300

(c)

i

i

I

100

2OO

30O

(d)

Carbon black, phr Figure 18.6. Effect ofoil and carbon black on properties ofpolynorbomene vulcanizates (a) Tensile strength, M N / m 2, Co) Elongation at break, %; (c) 200% Modulus, MN/mZ; (d) Shore A hardness (1 MN/m z = 145 psi) (Adapted from Ref.').

Other properties such as tensile strength and Shore A hardness changed correspondingly. As Figure 18.6 shows, modulus was also affected greatly by the type of reinforcing carbon black, thus, high surface carbon blacks provide the greatest increase. Significantly, high concentrations of nonreinforcing fillers (qv), e.g., mineral fillers, afford low cost compounds that

1169 are remarkably soft, yet possess low permanent set under compression. Processing of polynorbornene rubber ~ r s in common equipment used for rubbers under usual conditions. Both internal mixers and open mills can be employed for polynorbomene rubber compounding. Preferably, the equipment must be preheated at c~z 80~ to avoid possible degradation of the long polymeric chains at lower temperature due to mechanical rupture. The process always involves a preliminary absorption of oil (i.e. plasticizer) by the powdered polynorbornene, so that it becomes an elastomcric material that can be submitted to she~ng. For the manufacture of very soft compounds, a masterbatch with a limited amount of oil (150 parts) is mixed first and then the additional ingredients are introduc~ in a second mixing step. Further processing is carried out with common equipment in the rubber industry. In addition, the polynorbornene compounds can be produc~ as free-flowing dry blends in a high-speed powder blender. Moreover, the dry blend may be extruded or injection molded. Applications and economic aspects, polynorbornene rubber is a specialty elastomer which is used widely in areas where its unique properties are in demand. The most important applications are in the field of low-hardness solid parts and elastomers with tailore~ damping properties. These properties are exploited in very different industries such as automotive, appliance, office equipment and leisure industries for the production of moldext or extruded goods. Thus, high density sheet material is used for noise control under the hood in Diesel-powered cars, and body mounts based on polynorbornene provide a smooth fide. Other automotive applications, e.g., gaskets and seals, require soft, durable and moisture resistant products. Special nonautomotive vibration-isolation applications include railway cushions and seismic equipment pads as well as audio Ioudspe~er seals and cushioninserts for running shoes. The ability of polynorbornene to absorb great amounts of oil rapidly is applied to control oil spills. The advantage is that the polymer floats on water and soaks up the spill in a few minutes. The resulting product may form a cohesive, continuous sheet, which will be easily removed and dispose~ of. Toxicology and explosion hazard, z4 Polynorbornene powder is non-toxic and non-mutagenic to Salmonella (Ames test). Acute oral toxicity for rats is 11 g/kg. However, the product is flammable and can create a potential explosion hazard as an airborne dust. The high concentration of allylic,

1170 tertiary hydrogen atoms in the polymer requires that products be stabilized against oxidative aging. Polynorbornene is currently supplied with a protective antioxidant, but, because of the high surface area, antioxidant depletion and subsequent autoxidation can pose some problems. The storage of the powder beyond one year is not recommended. The main photooxidative degradation behavior is similar to that observed with polydienes, however, there are other possible degradation pathways. Zeonex 280. Since 1991 Nippon Zeon commercialized a hydrogenated ROMP polymer from norbornene-like polycyclic monomers under the trade name of Zeonex. A new commercial product manufactured by Nippon Zeon Co. by ring-opening metathesis polymerization of norbornene monomers and subsequent hydrogenation is Zeonex 280. The product has remarkable physical and chemical properties what makes it of interest for many applications in optical, electrical and medical fields. Some of its properties compared to traditional resins for optical uses such as polycarbonate (PC) and polymethylmethacrylate (PMMA) are given in Table 18.10. Zeonex 280 is an amorphous, colorless and transparent polymer. For its application potential, it is remarkable that the transmittance of Zeonex 280 is comparable to polymethylmethacrylate in the visible light region, but is superior to polycarbonate and polymethylmethacrylate in the near ultraviolet region. This behavior is illustrated in Figure 18.7. Transmittance, % 100 I

~ ' -

.....

2

80 3

60

40

y;

20

0

L.at

200

400

600

800

Wavelength, run Figure 18.7. Transmittance curves for Zeonex 280, PC and PMMA (8 mm thick; l-Zeonex; 2-PC; 3-PMMA) (Adapted from Ref.~).

1171 Table 18.10. Physical properties of Zeonex 280 con~ared with polycarbonate (PC) and polymethy~acrylate (PMMA) ~b

Property

Unit

Specific gravity % Water absorption % Moisture absorption 8/m2.24hr Water permeability % Transmittance 25 nd Refractive index r Photoelastic coefficient nlTI Retardation of birefrmgence of disk ~ Glass transition temp. ~ Heat defloction tenq3. cal/sec.cm Thermal conductivity .~C Lmear expansion ~ c i e n t deg"1 Solubility parameter Melt-flow index

Bending modulus

Bending strength Tensile modulus Tensile strength Elongation Impaa strmgth Pencil hardness

~/10min k~cm z kgfcm ~ k~crn 2 k~cm 2 %

kgf.cm/cm

Zeonex 280

PC

PMMA

1.01 <0.01 <0.01 <0.01 91

1.20

1.19 0.30 0.50 1.14 91

0.20 0.24 1.53

90

1.53

1.59

1.49

6.3.10"13 <25

72.10 "13 <60

6.0.10 "13

140 123 4.7.104 7.0.I0 "s

140 121 4.5.104 7.0.10 "~

105 90 4.6.104

6.2 15

57

24,000 1,010 24,000 643 10 3,0 H

24,000 930 24,000 640 90 6.0 B

8.0.10 "~

30,000 1,150 31,000 730 5 1.6 3H

|

'Data from reference.3~

In addition to this behavior, it is noteworthy that Zeonex is an optically stable polymer and shows a minimal thermal dependency of the refractive index. The dependency of the refractive index with the temperature is illustrated in Figure 18.8.

1172 Refractive index, nk

1 ! .535

1.530

1.525

"~X.......~x

1.520

~ 5--L~~.,~_..~ ~x~'~X

1.515

0

I

l

10

20

,

l

&

30

40

,,

9

&

50

60

X m

9

70

80

Temp., ~ Figure 18.8. Thermal dependencyof refractive index of Zeonex 280 (Adapted from Ref~S). Interestingly, Zeonex 280 shows one tenth less optical elasticity than polycarbonate and is nearly equal to polymethylmethacrylate. Thus, when molded into optical disks, for instance, this polymer provides extremely small retardation and minimal sub-retraction difference on any incident beam angle. Because Zeonex has no polar groups, it provides extremely low water absorption and moisture permeability. Disks made from this polymer show good durability under high humidity. Zeonex 280 is easy to mold and provides good groove transfer rate. In addition, its thermal decomposition temperature is 420~ approximately 100~ above its molding temperature. Consequently, there is a considerable less risk of thermal decomposition during the molding process for Zeonex as compared to polymethylmethacrylate. Likewise, Zeonex 280 has excellent electric properties such as low dielectric constant, low dielectric loss tan/5 and high dielectric breakdown strength. Furthermore, the polymer dissolves completely in aromatic or cyclic hydrocarbons but exhibits a high resistance to alcohols, ketones and cellosolves.

1173 Due to its outstanding properties including dimensional stability, low water absorption, high transmittance and low retardation as well as high heat resistance, Zeonex 280 is efficiently employed in various areas and particularly for optical lenses and prisms of cameras, CD and CD-ROM players, laser beam printers, and optical link modules, etc. It can be a proper substitute of the traditional resins applied in optics such as polycarbonate (PC), polymethylmethacrylate (PMMA), and regular polyolefins. In medical field Zeonex is used for prefilled syringes, vials and cells for blood analysis systems because of high purity, low adsorption of medicines, low water permeability and high tolerance to steam sterilization. In electrical field, due to its low tan/5 and dielectric constant, Zeonex 280 is used for the insulator of coaxial connectors

18.1.2.3. Poly(dicyclopentadiene) Recently, poly(dicyclopentadiene) prepared by ring-opening metathesis polymerization of dicyclopentadiene gained an important role on the market of thermoset polymers due to its wide range of valuable physical-mechanic~ properties. The product is manufactured mainly by reaction injection molding (RIM) process and commercialized under various trade names. Manufacture of poly(dieyclopentadiene) ~. In the currently applied RIM process for the manufacture of poly(dicyclopentadiene), the monomer is split into two parts which serve as carriers for catalyst components. The two solutions are stable enough to be mixed in the mixing head of the RIM machine and react after their injection into the mold. The first composition contains the transition metal compounds, typically WCI6 whereas the second part contains a cocatalyst such as an organoaluminium compound. The second composition can also contain esters or ethers, which control reaction rate and induction time. Modification of the first part with oxygenated compounds such as phenols is beneficial for increased catalyst solubility and activity. As with most metathesis reactions, strict exclusion of air and moisture is necessary. In addition, the purified dicyclopentadiene has to be free of traces of conjugated dienes and polar impurities which are strong catalyst poisons. The monomer portions may contain additives that facilitate the reaction or modify the product properties. Certain dissolved polymers, for instance, increase the viscosity of reactant streams, improve pumping characteristics, and may increase the impact resistance of the polymer.

1174 Reinforcing fillers such as glass, mica, carbon black, and talc increase hardness and reduce mold shrinkage, whereas chopped fibers improve dimensional stability, flexural modulus and heat-distortion temperature. Usually dicyclopentadiene is polymerized in conventional urethane RIM equipment. Since the process effected at a low pressure, molds can be of light weight constmctiort, allowing low cost, short production runs. The low viscosities of the two monomer solutions permit filling of rather complex shapes and allow molding of large parts. Articles up to several tens kg could be manufactured by this efficient technology. The polymerization reaction of dicyclopentadiene in the presence of these catalytic systems is exothermie, with an estimated heat of reaction of about 41.85 kJ/mole (10 kcal/mole). As a result, the temperature increases about 170-190~ under adiabatic conditions. This temperature increase will promote cross-linking as well as complete reaction of dicyclopentadiene. These factors, in turn, will influence hardness, glass transition temperature and heat distortion temperature as well. In actual practice, the temperature rise will vary with mold geometry and part thickness, and process conditions have to be carefully controlled. Polymerization of dicyclopentadiene by the RIM process leads to gel formation at a very early stage, although soluble polymers are readily attainable with other catalyst systems. It is well documented that, under these conditions, dicyclopentadiene reacts as a difunctional monomer, leading first to linear and then to cross-linked structures (Scheme 18.1). RIM

~

Scheme 18.1

RIM

1175 However, in view of the fact that norbomene also yields gelled polymers with this procedure, it is likely that cationic side reactions are involved in the gelation process. In addition, the high reaction temperatures encountered in dicyclopentadiene polymerization might favor reversible formation of low strained tings rather than ring-opening reaction. Properties of poly(dicyclopentadiene), as Poly(dicyclopentadiene) as manufactured in the Metton RIM process has several remarkable properties what makes the polymer of a wide use in many industrial fields. Some of the most relevant physical properties of the polymer are listed in Table 18. l I.

Table 18.11 Physical properties of poly(dicyclopentadiene)' Physical property

Flexural modulus, MPa b Flexural strength, MPab Tensile modulus, MPab Tensile strength, Mpab Tensile elongation, % Plate impact strength, J at 23 ~ at -29~ Glass transition, Ts, ~ Coefficient of linear expansion Mold shrinkage, cm/cm

Orientation

parallel perpendicular parallel perpendicular parallel parallel

parallel parallel perpendicular

Unfilled polymer 1790 62 1620 34 80 13-16 11-13 90,119,127 37 0.035

.

Milled Mi glass (20%) 2620-2900 2480 62-76 62 31 25 11-13 11-13 127 17 0.008-0.014 0.012-0.021

'Data from reference 3,; hi,o convert Mpa to psi, multiply by 145.

As it can be easily observed, the combination of high modulus and high impact strength, even at -30~ affords outstanding properties for poly(dicyclopentadiene). In addition, the polymer has excellent creep resistance. As Figure 18.9 illustrates, after 105 hours under equal loads, poly(dicyclopentadiene) creeps 1/5 as much at 38~ as nylon-6 at 23~

1176 Stram, % 3

m

1

2 3

0

iL

9

I

"

"

0.1

1

10

100

1000

9

9

10000

100000

Figure 18.9. Creep behavior of Metton (100~ vs. Nylon-6 (75~ (1- Nylon 6, 1000 psi; 2-Metton, 2000 psi, 3-Metton 1500 psi; 4-Metton 100 psi, 5 Nylon 6, 435 psi) (Adapted from Ref.3=). Surprisingly, unlike most polymers, the impact strength of poly(dicyclopentadiene) increases as the square of the thickness, rather than linearly (Figure 18.10). Plate impact strength, J 180 r 160 140 120 100 80 60 40 20 0

Ik.

0

2

4

6

8

10

12

Thickness, mm Figure l 8. l O. Plate impact strength of poly(dicyclopemadiene)

as a function of thickness (Adapted from Ref.3=).

1177 Another significant property, considering the polymer's high degree of unsaturation, is the high resistance to oxidation, it appears to undergo surface oxidation to form a oxygen-impermeable film at air exposure. This characteristic improves the product paintability. Paint adhesion was reported to be excellent, with no need for priming. Outstanding properties were also reported for the poly(dicyclopentadiene) products Telene RIM or RTM. These specialty polymers provide an excellent combination of stiffness, impact strength and heat deflection temperature with a low specific gravity. They have superior hydrolysis resistance to water, acids and bases, remarkable electrical insulating properties and give paintable products with good painting adhesion. The formulations can be easily processed on high pressure impingement mixing gIM or low pressure RTM type equipment. A wide range of viscosity values, between 50 and 1000 cps is provided at room temperature. Some physical properties of the standard formulation of Telene are included in Table 18.12.

Table 18.12. Physical properties of standard Telene formulation*

Physical Property

Value

Specific gravity Tensile yield strength, MPa Flexural modulus, MPa Notched Izod impact, J/cm +25 ~

1.03 45 1850

-40 ~ Heat deflection temperature, ~

load 18.5 kg/cm2 Coefficient of thermal expansion, cm/cm.~ Weight change after 7-d, % 100~ in water Dielectric constant, 1 MHz Dissipation factor, 1MHz 9 Data from reference. 39

5 1.6 110 8.2x10 "~

+0.75 2.66 8.15x10 "3

1178 Insolubility of poly(dicyclopentadiene) has hindered for some time the accurate determination of the chemical structure. Infrared methods have indicated a high concentration of open-chain cis vinylene units, as well as the retention of most of the fused cyclopentene tings present in the monomer. Also, it is estimated that in the polymer prepared under RIM conditions one cross-link occurs for every five monomer units. The double bond geometry is about 60:40 cis:trans. Traces of norbornene units also survive under some conditions, probably due to the presence of unreacted monomer or reaction of fused cyclopentene ring. Applications and economic aspects. Poly(dieyclopentadiene) has been produced since 1982 by BF Goodrich under the trade name of Telene and since 1984 by Hercules Inc. under the trade name of Metton. Telene RIM/RTM products include a standard formulation, an FR grade and a fiberglass reinforced glass mat to service a variety of applications. 39 These specialty polymer finds wide uses in leisure vehicles, automotive and truck industry, industrial and agricultural equipment, lawn and garden equipment, marine and aerospace equipment. Leisure vehicle applications concern golf carts, jet skis, snowmobile hoods, motorcycle and moped fenders and cowlings whereas automotive and truck areas refer to truck wind deflectors, fairings and shields, van conversion parts-running boards, cargo box for pick-up trucks. Industrial and agricultural equipment will comprise corrosion resistant blowers and fans, photographical chemical tanks, underground electrical junction boxes, material handling pallets and containers, tractor fenders and hoods, seed and fertilizer hoppers. Lawn and garden equipment implies lawn tractors and tiding mowers, fenders and hoods, clipping containers and snow blowers. Interesting applications in the marine and aerospace fields will produce marine propellers, small boats, water intake strainer grates and jet skis. The first reported use of Metton was for snowmobile hoods, where good low temperature impact resistance is very important. 4~ Other applications of Metton product include golf carts, water crafts, one-piece cabs for farm machines, satellite receiver dishes, seamless plastic pipes. Seamless pipe could be manufactured in situ since the RIM technology is not energy-intensive and could be portable. Automotive industry will benefit by the polymer's high impact strength for the production of car bumpers, hoods and other car parts. Especially good chances seem to be in the molding of very large parts (up to 700 lb. presently) as well as in various composites. 4t

1179

18.1.3. Cycloolefin Copolymers A great number of copolymers derived from ot-olefins e.g., ethylene and propylene with norbornene-like cycloolefins e.g., norbomene, dieyclopentadiene, tricyclopentadiene etc. have been manufactured using binary Ziegler-Natta type catalysts such as TiCldorganoaluminium compounds, VOClflorganoaluminium compounds, metalloeene/methylaluminoxane. '2 Of these products, copolymers under the trade name of Topas have found interesting applications in various areas.

18.1.3.1. Topas Copolymers of ethylene with norbomene-type cycloolefins produced with metalloeene/methylaluminoxane catalysts are commercialized under the trade name of Topas (Thermoplastic Olefin Polymers of Amorphous Structure) by HOchst Company in conjunction w i t h Mistui Petrochemicals. 43 Starting materials. The main starting monomers for Topas production include ot-olefins such as ethylene and propene and bieyclie olefins such as norbornene and substituted norbornenes. The standard catalysts used derive from metallocenes and methylaluminoxane. Polymerization procedures. The copolymerization reaction is carried out under the standard conditions of Ziegler-Natta polymerization using metallocene catalysts. Several patents published by H0chst Company describe the main procedure applied for the synthesis of copolymers. Specific data of Topas technology are proprietary. Structure and properties. The structure of Topas products corresponds to olefin/cycloolefin copolymers of the following general formula (11)

Rl/

\R2

11 where R, R~ and R2 call be hydrogen or alkyl groups. The physical and mechanical properties of these products vary as a function of the composition of the copolymers. Due to the random

1180

distribution of ethylene and norbornene units, Topas is an amorphous compound in which the crystallization is suppressed. The high transparency in the visible and near ultraviolet regions (transmission above 90% up to 300 nm) is coupled with low optical anisotropy and an inherently low birefringence. Generally, the products display a low density, extremely low water absorption, a thermal stability up to 170~ good resistance toward acids, bases and hydrolysis, high electric insulating propensity, high hardness and weathering. Due to the aliphatic character, Topas is resistant to polar solvents such as methanol and acetone but non-polar solvents like toluene do attack the polymer. The product is water-repellent and exhibits negligible swelling when immersed in water. Water uptake is only 0.01% after 24 hr at a temperature of 23~ Besides that, water vapor permeability is extremely low, giving excellent water vapor barrier properties, even superior to polyolefins like polypropylene. It is noteworthy that the glass transition temperature of Topas can be shifted in a wide range by simply adjusting the ratio between the two comonomers. As the amount of norbornene component increases, the polymer chain is stiffened and thus mobility decreased. Therefore, glass transition temperature will be increased. The influence of norbornene content on the glass transition temperature of Topas, Ts, can be observed in Figure 18.11. Tg,~ 250 200

150 100 50 a

10

l

l

9

20

9

30

,

9

40

9

a

,50

9

9

6O

9

a

70

9

J

80

Norbomene, mole % Figure 18.11. Influence of the norbomene content on the glass transition temperature m Topas polymers (Adapted from Ref.43). Glass transition temperatures well above 200~ are available but currently grades with T s between 80~ and 180~ are preferred.

1181

The products can be easily processed under normal conditions. As flowability is correlated to the molecular weight, flow behavior can be tailored to the customer's requirements for any given T 8. Interestingly, the mechanical properties are retained over a wide temperature range from 50~ to near glass transition temperature. This behavior is usually observed for an amorphous thermoplastic polymer. Topas is a plastic material with high modulus and high stif~ess. Tensile modulus is about 3 Gpa, tensile strength varies from 40 to 70 Mpa. Elongation at break is in the range from 3% up to 10%. The behavior under long-term stress is excellent. Stress relaxation test revealed the very low creep tendency; even after several hundreds of hours, flexural creep modulus is decreased by a small amount only. Applications and economic aspects. ~ Four types of commercial products are at present available on the market: Topas 8007, 5013, 6015 and 6017, the first two numbers indicating the product viscosity and the last two indicating the thermal stability. A global output of 3000 t/year Topas products has been foreseen for 1996 to be manufactured in an industrial plant in Japan by H6chst Company (Germany) in conjunction with Mitsui Petrochemicals (Mitsui Sekka). Topas products find direct application in several modern technologies such as data processing machines, optical devices, as parts of elements in construction, electronics, electrotechnique, illuminating devices etc. Special applications are particularly for production of optical lenses, optical storage media such as compact discs and CD-ROMs, films for capacitors. The chemical purity of Topas products allows them to be also used for medical articles, for steam- and gamma-sterilization techniques. 18.2. Products of Interest for Industry

Though not applied on an industrial scale, many polyakenamers have been developed due to their easy availability and attractive physicalchemical properties. Some of these are potential products for interesting applications in various fields. 18.2.1. trans-Polypentenamer

Due to the easy accessibility of cyclopentene and the excellent properties of trans-polypentenamer as a general purpose rubber, the synthesis and properties of this polyalkenamer have been extensivley

1182 studied by many research groups. The abundant results obtained in these studies constitutes a valuable reference source for the vast ring-opening metathesis polymerization chemistry. Starting materials. Significant amounts of cyclopentene are obtained from refinery C5 fractions. Cyclopentene itself is a minor recoverable component of these streams, but larger amounts can be obtained by hydrogenation of the more abundant component eyclopentadiene. Several routes are known for the hydrogenation of eyclopentadiene. Of these, two particularly attractive procedures utilize titanium- or nickel-based catalysts. "'~5 These methods appear to be over 97% selective for the production of cyclopentene at quantitative conversion of cyclopentadiene. According to a process developed jointly by BASF and Erdolchemie, cyclopentadiene is first isolated as dicyclopentadiene, this is then cracked, hydrogenated and recombined with the initially separated C5 fraction which contains some cyclopentene. Ultimate separation and recovery of monomers consists of extractive distillation. ~ Cyclopentene is a colorless, pungent liquid product under normal conditions. It is quite volatile and highly flammable. In contact with air for extended periods forms a relatively stable hydroperoxide. Importantly, samples that have not been treated to remove peroxides should not be distilled to dryness. The oral LD50 is 2.14 g/kg in rats. The relevant physical properties of cyclopentene are summarized in Table 18.13. Table. 18.13 Ph~!cal properties of cyclcl~ntene* ' Physical Property

Value

Molecular weight Freezing point Boilmg point rla2O d2~ g/mL

68.11 -135.076 44.242 1.42246 0.77199 1.837 233/4.79 20.5,28.5 d

Cp20, J(g.oC)b

Critical temperature, ~ Ring strata, kJ/mole b

~

9 Data from reference47, b To convert Id to cal, divide by 4.184, ~To convert MPa to atm, divide by O.101 ~ Different data from reference,a

1183

Polymerization procedures. Cyclopentene polymerization has been carried out in bulk and more conveniently in solution where the control of the reaction exotherm of ca. 4.5 kcal/mole (19 kJ/mole) is better accomplished. Suitable inert solvents include aromatic and aliphatic compounds such as benzene, toluene, chlorobenzene and methylene chloride. Usually, the polymerizations have been conducted at room temperature or below, because polymer yields decrease substantially at elevated temperatures. This is a consequence of the rather low ceiling temperature of cyclopentene polymerization. As the majority of p r ~ u r e s employed classical metathesis catalysts derived from metal halides e.g., WCI6, MoCI5 and organometaUic compounds, e.g., organoaluminium compounds, organotin compounds, strict precautions for the control of monomer and solvent purity are required to maintain the catalyst activity. Usually, allenes, conjugated dienes and acetylenes which may be present as impurities in the starting material must be removed. Moreover, polar impurities such as oxygenated compounds have also be removed. On the other hand, adventitious traces of some polar contaminants such as water, or the easily formed cyclopentene hydroperoxide, can serve rather to enhance reaction rate as catalyst modifiers. A wide range of binary homogeneous catalytic systems have been developed for cyclopentene polymerization including a large variety of transition metals ranging from zero-valent coordination complexes to salts of the metals in their highest oxidation states. In association with the transition metal compound, a great number of coc,atalysts have been employed that are typically organometallic compounds or Lewis acids. The activity of binary catalyst systems has been often substantially enhanced by the addition of a third component known as promoter, activator or modifier. The three-component catalysts form the basis for many excellent catalytic systems which are well suited for economically commercial polymerization processes. Oxygen-compounds such as alcohols, phenols, haloalcohols, ethers, peroxides, hydroperoxides, epoxides, c,arboxylic acids, esters, molecular oxygen, and water have been preferably employed as catalyst modifiers. Generally, the catalytic systems were prepared by precomplexation of catalyst components or in situ in the presence of the monomer. It was observed that addition of catalyst components is crucial for the optimum activity; particularly, the reaction of promoter or activator with the transition metal component should ~ r prior to the addition of the organometallic cocatalyst. Reaction termination and catalyst deactivation were carried out by quenching with alcohols or adequate

1184 oxygen-containing compounds. Polymer separation and characrterization were performed by standard methods known from polymer chemistry. Structure and properties, trans-Polypentenamer has a fairly low melting point (18~ very close to that of the natural rubber. The low glass transition temperature (-97 ~ close to that of 1,4-polybutadiene, imparts good processability and elastomeric properties. Practically, transpolypentenamer does not crystallize at room temperature within a limited period of time. However, under strain it will crystallize readily and the polymer acquires good processing qualities. Polypentenamers with a high trans content, ranging normally from 75 to 85%, as determined by IR and NMR spectroscopy, were usually obtained using trans-specific catalytic systems. The content of trans structure varied markedly with catalyst, reaction temperature, solvent and reaction time. The steric content has also been obtained by variation of the ratio transition metal/organometallic compound or other catalyst components in the base system, trans-Polypentenamer appears to exhibit higher intrinsic viscosities than cis polymers of comparable molecular weight, suggesting stiffer, more extended chains.~s Compounding and processing. Due to its special structure and properties, trans-polypentenamer exhibits a good compounding and processing behavior. 49 This refers to mill banding, filler and ingredient dispersion, extrusion, calendering, tire building, and other operations with compositions of any Mooney range between 30 and >150. These outstanding properties were attributed not only to the chemical structure, but also to a wide molecular weight distribution of a special type. The presence of low molecular weight fractions imparts to transpolypentenamer the plasticity needed for easy processing whereas high molecular weight fractions provide good vulcanizate properties and the steep shear gradient necessary for ready filler and ingredient dispersion. Such a compromise is generally unfavorable in view of the mechanical properties of the v u l ~ z a t e s , however, solution polymerization of cyclopentene leads to a large molecular weight distribution of a special type due to the particular polymerization mechanism and to the use of special catalytic systems. From a comparative examination of the molecular weight distribution of trans-polypentenamer, polybutadiene and polyisoprene, it is obvious that trcms-polypentenamer is essentially characterized by a large fraction of high molecular weight polymer and by small fractions of products ranging down to very low molecular weights. (Figure 18.12).

1185

[~], % lO0-

1

50-

/

lOII

0.5

0.I

II

II

9

1.0

5

I0

log [11],toluene, 25~ Figure 18.12. Molecular weight distributions of trans-polypentenamer (1), cis-polybutadiene (2) and cis-polyisoprene (3) (Adapted from Ref.*9). Extensive studies carried out by Haas and Theisen s~ showed that the processability of trans-polypentenamer is equivalent to that of the natural rubber, as indicated by the Mooney viscosity/temperature relationship (Figure 18.13). Mooney viscosity, ML-4' 120 1

100 M &

80

6O

2060

8O

100

12.0

140

160

Temp., ~ Figure 18.13. Mooney viscosity/temperature dependence for trans-polypentenamer and diene rubbers (Adapted from Ref.S~

1186

As it can be seen, trcms-polypentenamer exhibits the highly desired strong viscosity as a function of the temperature gradient, which at room temperature provides low cold flow while at the processing temperature (80-130~ combines sufficient plasticity for extrusion with mechanical strength for rapid filler and ingredient dispersion. It was found that transpolypentenamer can be easily compounded on the open mill and in Banbury without premastication, the mix is rapidly blended to a smooth and compact band. The favorable compounding behavior of trans-polypentenamer evidenced by the energy absorption and temperature profiles during filler incorporation has been illustrated by G0nther and coworkers 5~ for tire tread formulations of different elastomers. It is worth noting that trans-polypentenamer may be loaded with exceptionally large amounts of carbon black and oil. Black Ioadings of 110125 phr and oil levels of 75-90 phr are tolerated by trans-polypentenamer without extensive drop in mechanical properties. Taking tensile strength as a criterion for comparing the response of trans-polypentenamer and natural rubber to heavy Ioadings, it may be inferred that even at 160 phr black and 100 phr oil loading good mechanical properties are retained. Interestingly, microscopic examination of the trans-polypentenamer mixes revealed that black dispersion in the polymer is at least as perfect as in the natural rubber and definitely superior to that in polybutadiene rubber and styrenebutadiene copolymer. It is relevant that the extrusion behavior of trans-polypentenamer is substantially better than that of polybutadiene rubber and close to that of styrene-butadiene rubber (Table 18.14). Also remarkably, trans-polypentenamer mixtures display a very high building tack, much higher than that of any other general purpose rubber. This is another highly desired processing property of trans-polypentenamer which was ascribed to the rapid stress crystallization of the polymer. This property is reflected in the excellent rubber-to-fabric adhesion of highly loaded trans-polypentenamer stocks as compared to natural rubber. One of the most important properties of trans-polypentenamer is the rapid stress crystallization of the unvulcanized polymer, resulting in strong self-reinforcement or green strength of the product. This outstanding property is a significant advantage of the polymer for all processing operations, including carcass build up. Haas and Theisen s~ showed that tire tread stocks of trans-polypentenamer exhibit exceptionally high green strength, even higher than that of natural rubber (Figure 18.14).

1187 Table 18.14. Garvey Die extrusion radices for trans-polypentenamer cJs-poly~utadiene~) _and ,st~'ene--butadiene rubber ~ ElasWn~r Rate, Rate Rating m/mm g/min t ra ns- P o l ypentename r

38.5

113

2434

37

102

3433

27

I00

1342

35

80

3444

ML 1+4 (100~ = 30 40 phr IS AF black t rans-P ol ypentenamer

ML 1+4 (100~ = 70 65 phr ISAF black, 40 phr Paraflux oil cis-Poly(butadiene) ML 1+4 (100~ = 40-50 40 phr IS AF black Styrene-Butadiene Rubber ML 1+4 (100~ = 50 65 phr ISAF black 40 phr Paraflux oil 9 Data f r o m reference. 49

Stress, kg/cm z 4O

1

30

20

2

10

0 0

100

200

300

400

500

eO0

700

Elongation, % Figure 18.14. Green strengthof uncured 50 phr HAl: black loaded tiretread stocks (at 23~ l_trans.polypentenamer; 2-natural rubber; 3-styrene-butadiene rubber (Adapted from Ref.S~

1188

Vulcanization and vulcanizate properties, trm~-Polypentenamer can be easily vulcanized with sulphur and sulphur donors. Compared to other highly unsaturated hydrocarbon polymers, the vulcanized products show substantial cross-linking structures and consequently require low vulcanizing agent and accelerator consumption to attain high tensile and modulus values. Interesting studies carried out by Dall'Asta and coworkers 49 on the black and oil loaded trans-polypentenamer mixes using conventional sulphur and accelerator or sulphur donor and accelerator formulations showed high cure rate up to a pronounced plateau with only very low reversion (Figure 18.15). in/lb J| r

m/lb I

~

/

3_

/ |

o

Tm~e,

(A)

~o

~

30

18

~0

Time, mm

(B)

Figure 18.15. Rheometer curves for sulphur cured (A) and sulphur donor cured (B) carbon black and oil loaded trans-polypentenamer at d~fferent temperatures (Adapted from Ref.*9).

1189

Relevant data on the reversion in trans-polypentenamer have been recorded by Jahn. ~z Some of these results together with comparative data obtained with natural and polyisoprene rubber are given in Table 18. I 5. Table 18.15 Reversion (R) in trans-polypentmamer~PR), natural rubber(NR) and polyisoprene rubber(IR)'

NR

IR "rPR ISAF black Oil Sulfur CBS b

100

100 100

50 6 2.3 0.7

50 6 2.3 0.7

100 100 50 12 1.8 0.3

MOW TMTD ~ R' 160~ 180~

52.8 58.8

46.5 57.3

16.0 16.8

50 6

50 6

100 50 12

I

I

1

2 0.1 21.5 39.4

2 0.1 16.2 34.0

2 0.1 9.3 13.2

'Data from reference s2; ~'N-Cyclohexyl-2-benzothiazole sulphenamide;'~lMorpholmyl-2-benzc~iazole sulphenanude; d~retramethylthiuram disulphide; "R=[ I - o ~.,o'.,6o o, ,,ooclo 3oo ~

,,~.c].

It may be noted that both at 160~ and 180~ the reversion in the transpolypentenamer cure was much smaller than for natural and polyisoprene rubber. On the other hand, Dall'Asta ~3 found that special formulations containing very low sulphur and accelerator levels induced rapid cure without appreciable reversion and simultaneously yielded vulcanizates characterized by high tensiles and moduli and low heat buildup (Table 18.16). Even lower heat build up have been recorded by employing low levels of sulphur donor/accelerator formulations with the same carbon black and oil load (Table 18.17). Using a computed regression analysis method, Haas and Theisen ~~ examined the influence of different vulcanization parameters on the vulcanizate properties of the tire tread stocks. In the course of their studies they calculated the tensile strength, the elongation at break, the compression set, and the abrasion resistance as functions of the dosage of

1190 Table 18.16 Physical-nmdmnical and dynamic propertiesof trans-polypemenamer rubber (TPR) v u l c a n ~ at different times of cure ~b Time of cure t min

20

40

60

80

12(

TS, kg/cm 2 EB, % 200% Mod., kg/cm 2 300% Mod., kg/cm 2 H(IRHD) Tear strength, kg/cm H B U AT, ~ (I00~

188 460 47 103 62 43 22

178 400 50 108 64 40 20

180 420 50 108 64 40 22

170 380 50 114 64 42 22

17( 40( 50 11( 64 38 22

9 Dat~a from reference"; b Recipe: TPR 100, PBNA 1.5, Stearic acid 2, ZnO 5, Circosol 4240 oil 30, ISAF black 50, MBTS 0.7, TMTD 0.7, S 0.75, ML 1+4 (100~ 72, cure at 140 ~

Table 18.17 Physical-mechanical and dynamic properties of trans-polypentenamer rubber (TPR) vulcanizates at different times of cure ~b Time of cure~ mm

20

40

60

80

120

TS, kg/cm 2 EB, % 200% Mod., kg/cm~ 300% Meal., kg/cm ~ H(IRHD) Tear strength, kg/on HBU AT, ~ (100~

77 540 16 31 39 21

179 360 61 132 65 44 19

178 360 60 134 64 42 21

183 360 65 139 64 44 19

175 360 62 128 64 44 19

==

9 Data from reference53, ff Recipe: TPR 100, PBNA 1.5, Stearic acid 2, ZnO 5, Circosol 4240 oil 30, ISAF black 50, MBTS 0.5, TMTD 0.5, Sulphasan R 1.5, ML 1+4 (100~ 72, cure at 140 ~ zinc oxide and stearic acid on the vulcanization temperature, at constant sulphur and accelerator levels. The above authors calculated simultaneously these properties as a function of the dosage of sulphur and CBS accelerator

1191 on the vulcanization temperature, both at constant zinc oxide and stearic acid content. The most important result deduced from this approach was that the optimum properties for trans-polypentenamer vulcanizates are obtained at a high vulcanization temperature (170~ with low zinc oxide, stearic acid, and accelerator, and medium (2 phr) sulphur content. By studying the vulcanizate properties, Meissner 5~ observed that trans-polypentenamer cured with dicumyl peroxide exhibited very high cross-linking efficiency, as compared to other elastomers. This result is in agreement with previously reported data on the sulphur cure of transpolypentenamer. He ascribed the high efficiency to an exceptionally high content of physical bonds in the polymer. Accordingly, Meissner found also a very high Mooney-Rivlin (C2) constant. Significant kinetic results on the strain-induced crystallization of a dicumyl peroxide cured trans-polypentenamer as a function of temperature and strain were published by Kraus and Gruver. ~5 Interestingly, they employed a combined birefringence and stress relaxation technique which showed to be more reliable for rapidly crystallizing materials than the stress relaxation technique alone. From their data the above authors confirmed the high crystallization rate of trans-polypentenamer already observed for unvulcanized material. They found that both the rate and degree of crystallization strongly depend on temperature, on the strain rate, and on the degree of undercooling. Elevated tensile strength results to be a consequence of the strain induced crystallization. Typical stress-strain curves at different strain rates are given in Figure 18.16. kg/~:rn2

1

3

~

140 \

"'-,,,

120

\,,

\

I O0

80

B

~

60 4O 2O ~

T

0 I

2

3

*

il

9

9

9

&

4

5

6

7

8

9

Figure 18.16. Influence of strata rate (a) on stress-strata curves (~.) for trans-polypentenamer(at 10~ (1- R = 0.002 sot"; 2 - R= 300 sec"~) (Adapted from Ref.~).

1192 It was inferred that the degree of crystallization does not exceed 10 per cent and, consequently, the tensile strength is not as high as that of natural rubber. This result was assigned to the relatively low trans content of the polymer. Also, the Avrami indices found by Kraus and Gruver were generally low, thus indicating prevalence of linear crystallite growth from pre-existing nuclei. Measurements on the stress-temperature dependence were carried out by Flisi et al.56 in their studies of the stress-induced crystallization of trwLs-polypentenamer vulcanizates. In addition to gums, also reinforced and pigment-filled materials have been investigated. In these studies, dicumyl peroxide or two different conventional sulphur formulations characterized by mono- and polysulphide cross-links, respectively, have been employed. Interestingly, the plot of melting points as a function of elongation and the thermodynamic parameters (fusion enthalpy and entropy) were found to be independent of the curing formulation and of the presence of fillers. Also, it Stress,kg/cm2 2

200 ... .~ . . . . . . .o....-~

100

i

.....-

...~

50

1

2

3

4

~5

6

7

e

....

9

(I

Figure 18.17. Stress-strain curves of peroxide cured 85% trans-polypmtenamer gum at various temperatures (Adapted from Ref.~.

1193 was observed that high crystallization tendency confers an undesired stiffness to trans-polypentenamer at low temperatures. This fact is dearly pointed out by the stress-strain curves at various temperatures illustrated in Figure 18.17. It was outlined that the upturn of the stress-strain curves at high elongations, characteristic of stress-crystallizing elastomers, was in the reported ease much weaker than for natural rubber at the same temperature. This finding was attributed to the relatively low trans content of the polypentenamer and consequently to the low degree of crystallization. In similar studies, carried out by Natta, Dall'Asta and Mazzanti, s7 it was found that trans-polypentenamer gum vulcanizates show steep upturns of the stress-strain curve and high tensile strength provided that very high trans content is present in the polymer (Figure 18.18). Stress, k ~ c m 2

250 -

200

I

-

/ t

150

-

J

t

I

I / /

2

/

/

f

I

'

/

IOO

/ ~ J ft i/ /

jf /

f/

!

50 ~d O I~

2~

3~

4~

500

~0

7~

8~

~10

2

Figure 18.18. Stress-strata curves of sulphur vulcanized 90% trans-polypmtenamer (1) and vulcanizate reinforced with 50 phr HAF black (2) (Adapted from Ref.~7). However, such a strong crystallization tendency is not always desired because of the resulting stiffness below room temperature. Therefore, a compromise is necessary to conciliate good mechanical and processing properties with acceptable low temperature characteristics. To solve this

1194

problem three approaches have been proposed by Haas and Theisen s~ (i) an intermediate trans content of the polymer, (ii) use of the crystallizationhindering plasticizers and (iii) high trans content of the unvulcanized polymer to be used in the compounding and processing operations where rapid stress crystallization is necessary followed by lowering of the trans content by any way during the vulcanization process. In this connection, Gunther and coworkers s~ showed that trans to cis isomerization of the double bonds in the polymer occurred to a certain extent when zinc stearate was employed as the activator in sulphur vulcanization. The strong reinforcing effect induced by carbon black on the transpolypentenamer vulcanizates can be readily pointed out if stress-strain values of pure 90~ trans-polypentenamer gum and filled vulcanizates are compared. It is significant that even at high oil and carbon black loads a set of remarkable physical-mechanical and dynamic properties of the transpolypentenamer rubber are retained as illustrated in Table 18.18. Table 18.18 Influence of oil and carbon black loadmgs on the physical and mechanical properties of trans-polypentmamer vulcanizates ~b

Values

Component/Property

Circosol 4240, phr ISAF black, phr Sulphur, phr MLMB 1+4 at 100~ TS, kg/cmz EB, % M~oo, kg/cmz M~3o, kg/cm2 H, IRHD HBU at 100~ At, ~

25 50 0.75 82 194 380 48 122 70 25

25 50 1.0 82 185 380 52 138 71 24

50 75 0.75 63 176 390 47 l l6 74 37

50 75 1.0 63 181 380 5g 133 74 32

75 100 0.75 57 146 410 43 92 60 36

75 100 1.0 57 154 400 48 lOl 60 30 |

9 Data from reference ~; b Recipe: Polymer (ML 1+4 = 72) 100, PBNA 1.5, Stearic acid 2, Zinc oxide 5, Circosol 4240 oil and ISAF black as indicated, MBTS 0.7, TMTD 0.7, Sulphur as mdic,atod, cure 40 mm at 140~ As already mentioned

above, tram-polypentenamer vulcanizates

1195 undergo a certain amount of static crystallization when stored at low temperatures. In order to evaluate how far this phenomenon could affect the low temperature performances of trans-polypentenamer, Jahn 52 investigated the behavior of several rubbers at low temperature. Data recorded on the variation of the Shore hardness of tire tread formulations of trans-polypentenamer, butadiene rubber and styrene-butadiene rubber with temperature are illustrated in Figure 18.19. Shore A

1oo1"~'hx', 9~ 1

~176

70 ,,,.m

o

~

~

~

~

Q'O e O B 0 0

-60

-40

-20

0

20

40

60

80

!00

120

,

o

~

~

BIP 9 O O O O l l ,

140

160

Temp., ~ Figure 18.19. Variation of Shore hardness with ten'~mture for trans-polypentenamer(1), cis-polybutac~me(2) and styreno-butadiene rubber (3). Recipe polymer 100, ISAF 75, aromatic oil 40 (Adapted from Ref.S2). As it can be noted, the increase of hardness below O~ was much stronger for trans-polypentenamer than for cis-polybutadiene but similar to that of styrene-butadiene rubber. Analogous results were recorded on the dependence of rebound and compression set on the temperature for trans-polypentenamer and butadiene and styrene-butadiene rubbers. The variations of rebound resilience with temperature for trans-polypentenamer, cis-polybutadiene and styrene-butadiene rubber are represented in Figure 18.20 whereas the dependence of the compression set with temperature for these three polymers in Figure 18.21.

1196

% 50

40

30 20 10

O

-40

40

80

120

160

Temp., ~ Figure 18.20 Variation of rebound resilience with temperature for trans-polypemenamer (1), cis-polybutadieae (2) and styrene-butadiene rubber (3). Recipe: polymer 100, ISAF 75, aromatic oil 40 (Adaptod from Ref.n).

% 100 -

2

I

/

,r

.

9

f

10"'k

-60

-40

-20

0

"

m'

20

9

9

9

40

60

80

i

9

l

9

100 120 140

--

180

Temp., ~ Figure 18.21. Compression set as a function of te~erature for transpolypentenamer (1), styrene-butadiene rubber (2) and cas-polybutadiene (3)

(Adapted from Ref.S2).

1197

From inspection of Figures 18.20 and 18.21, it is obvious that these properties are better for trtms-polypentenamer than for butadiene and styrene-butadiene rubbers above 10~ It is important for its application in tire building that transpolypentenamer is a highly abrasion resistant rubber. On comparing tire tread stocks for several rubbers, trans-polypentenamer appears definitely superior to natural rubber, isoprene robber, or styrene-butadiene rubber, similar to styrene-butadiene~utadiene rubber (1:1) and somewhat inferior to butadiene rubber. Conversely, the wet skid resistance of transpolypentenamer tire treads is inferior to that of natural rubber, isoprene rubber, and styrene-butadiene rubber, but exceeds that of butadiene rubber or styrene-butadiene/styrene rubber (1:1). Surprisingly, trans-polypentenamer exhibits a low air permeability as compared to other rubbers. However, according to Jahn, 52 air permeability of trtms-polypentenarner decreases considerably with increasing filler content. Thus, at very high extension degrees, the value of air permeability for trans-polypentenamer are lower than those of ethylenepropylene-diene rubber, isoprene rubber, and butadiene rubber and approaches that of butyl rubber. Another remarkable property of trans-polypentenamer is the fairly good aging resistance. Relevant data on the variation of tensile strength and elongation at break of trans-polypentenamer at prolonged heating under air were reported by Dall'Asta 49 (Table 18.19). Table 18.19 Tensile strength (TS) and elongation at break (EB) during air aging of t r a n s pol~~Jmamer butadiene rubber and styrene-butadiene rubber vuleanizates~~ Polymer S phr Initialvalue 2 Days ~ 4 Days~ 8 Days' 20Daysd TS EB TS EB TS EB TS EB TS EB TPR 1.0 204 480 103 71 105 63 108 62 101 50 1.4 210 400 105 75 99 67 84 52 93 50 BR 1.0 190 520 83 63 83 58 83 52 49 27 1.4 220 500 77 60 78 54 73 44 50 24 SBR 1.4 295 590 103 78 100 68 93 61 92 51 2.0 320 480 90 73 83 60 81 56 74 42 'Data from rerfOl'~ee49, bAt 100~162 Polymer 100, Flectol H 1.5, Stearic acid 2, Zinc oxide 5, HAl: black 50, CBS 1.0, Sulphur as m d i ~ , Cure: TPR and BR 40 mm at 150~ SBR 60 min at 150~ as percent of initial value.

1198

It is noteworthy that comparison of the black reinforced transpolypentenamer, butadiene rubber and styrene-butadiene rubber stocks, vulcanized with two sulphur amounts, revealed a much better behavior of trans-polypentenamer with respect to butadiene rubber and at least equivalent to styrene-butadiene rubber. This behavior was assigned to the trans structure of the double bonds rather than to the lower content of double bonds if compared to butadiene rubber. Also, of great significance is the considerable stability of transpolypentenamer to UV irradiation. 5s In contrast to 1,4-polybutadiene, which undergoes trans/cis isomerization as well as chain mission under the action of UV irradiation, trans-polypentenamer shows only trans/cJs isomerization, but no appreciable chain mission. This particular behavior was attributed to the fact that the mission of the bond between two ormethylene groups yields two allylic radicals in the case of 1,4polybutadiene, but only one in that of polypentenamer, thus conferring higher bond strength to the latter. Most interestingly, trans-polypentenamer exhibits ozone and weathering resistance, both of which are exceptionally high for a largely unsaturated polymer. It is remarkable that crack formation under static ozone attack or under outdoor weathering, in the presence or in the absence of antiozonants and antioxidants respectively, occurs in transpolypentenamer after very much longer times than in natural rubber and nearly at as long times as for chloroprene rubber. Significantly, the resistance of trans-polypentenamer rubber to dynamic crack formation under ozone attack (De Mattia dynamic flex cracking) obviously turns out best as compared to natural rubber, butadiene rubber, natural~utadiene rubber, styrene-butadiene rubber or styrene-butadiene/butadiene rubber, in the presence as well as in the absence of anitozonant compounds. Of particular significance for its application, trans-polypentenamer is compatible and covulcanizable with several other diene rubbers, including natural rubber, isoprene rubber, butadiene rubber and styrene-butadiene rubber, as well as even with ethylene-propylene-diene terpolymer. Using light scattering combined with diffiasion techniques, H o f f m a n n s9 examined the compatibility of trans-polypentenamer with cis-l,4-polybutadiene whereas Schnecko and Caspary~ applied a viscosimetric method for this study. Despite the different configurations of the double bonds in these polymers, both methods revealed a high compatibility between the two rubbers. Of a special interest are trans-polypentenamer/isoprene rubber and trans-polypentenamer/ethylene-propylene-diene rubber blends. In the first

1199

of these two blends, trans-polypentenamer confers green strength to isoprene rubber which is lacking to the latter, whereas, conversely, isoprene rubber improves the tear strength of the trtms-polypentenamer blend. On the other hand, trans-polypentenamer in the second blend may solve some difficult problems which still hinder the application of ethylene-propylenediene terpolymer in the tire field. Thus, it was found that small amounts of trans-polypentenamer in ethylene-propylene~ene terpolymer improve building tack of the latter, this effect being markedly more than additive in the blend. However, a proper adjustment of the vulcanization formulation is needed to achieve good covulcanizability of transpolypentenamer/ethylene-propylene-diene rubber blends. This propensity has been evidenced by following the reciprocal equilibrium swelling of the two components as a function of the blend composition. Applications and economic lspects. Due to the excellent properties of trtms-polypentenamer, this product has a large area of applications as general purpose rubber, including tires and rubber articles. Here the polymer displays a high tack, green strength and abrasion resistance as well as good processability and extendability. trans-Polypentenamer can be applied in compositions with various diene rubbers exhibiting good compatibility and co-vulcanizability. Thus, it is compatible with natural rubber, polyisoprene, polybutadiene and butadiene-styrene copolymer as well as ethylene-propylene--diene terpolymer yielding various compositions suitable for tire and rubber industry, trat~-Polypentenamer confers to these blends high abrasion and aging resistance, superior elasticity and low air permeability. Reversion and aging resistance make it a good candidate for various applications at higher temperatures. Its characteristics open a very promising field of application as a rubber basis for high impact polymers such as polystyrene, ABS copolymers and poly(vinyl chloride). Several companies pursued development programs at pilot and semiindustrial plant level aimed toward tire applications but changes in petroleum feedstock availability and costs resulted in the discontinuation of these programs. Notwithstanding, at present, studies for improving the costs and technologies for cyclopentene production are in course in many research groups. Moreover, the wealth of information about the synthesis, structure and properties of trans-polypentenamer renders this polyalkenamer of a special interest for its application in various technologies in the near future.

1200 18.2.2. c/s-Polypentenamer

The compounding and processing properties of cis-polypentenamer considerably differ from those of trans-polypentenamer, but markedly resemble that of cis-polybutadiene and of cis-polyoctenamer. Thus, cispolypentenamer is not easily compounded at room temperature. The bank is largely tacky and lacy with tearing edges. At slightly higher temperature it becomes dry and brittle. It was found that only when operating at 80-100~ are common fillers and ingredients incorporated and homogeneously dispersed. This compounding and processing behavior was ascribed to the conformations around the cis double bonds and the adjacent single bonds rather than related to glass and melting temperatures. 6~ Analogously, the vulcanization behavior and vulcanizate properties of cis-polypentenamer rubber differ substantially from those of transpolypentenamer. The absence of stress crystallization at room temperature, owing to the low melting point (-41~ and to the slow crystallization kinetics, fails to confer to cis-polypentenamer adequate properties, like green strength and tack, characteristic of trans-polypentenamer. For this reason, the green properties have not been investigated in detail. Vulcanization of cis-polypentenamer occurs with conventional sulphur and sulphur donor compounds. It was observed that the rubber is fast curing and, even with small amounts of sulphur, it reaches a pronounced level in reasonable times (Table 18.20).

Time min

Table 18.20 Cure rate of ci.s, ,olyoctenamer~b 3OO% 200% Elongation Tensile % Modulus Modulus streagth

IRHD

kg/cm 2

kg/gm 2

10 20 40 60 80 120 180

Hardness

1040 530 490 490 520 510 560

113 147 144 149 154 147 164 9

22 66 71 72 72 68 65

15 37 37 38 38 37 35 |

49 63 63 63 63 63 62

|J

' Data from reference6'; b Recipe: Poi ner ]oo, PBNA 1.5, 'Stearie acid 2, Zinc oxide 5, ISAF black 50, C i r r i 4240, 40 CBTS 0.8, S 1.25, Cured at 1500C.

1201 Examination of the physical-mechani~l properties of cispolypentenamer revealed that, generally, the polymer properties are not as good as those of trans-polypentenamer at room temperature. However, Minchak and Tucker 6z showed that cis-polypentenamer of high molecular weight exhibits good physical properties when extended with high levels of oil dilution and of carbon black reinforcement. The best performances are usually attained by cis-polypentenamer at low temperatures. Some relevant physical-mechanical properties of carbon black reinforced cispolypentenamer vulcanizates are compared in Table 18.21 for various temperatures in the range from +23~ to -90~ 6z

Table 18.21

Physical properties of cis-polypentmamer vulcanizate at various teng>eratures*

Temperature, ~

Tensile, kg/cm2 Elongation, % 100% Modulus, kg/cm2 200% Modulus, kg/cm2 300% Modulus, kg/cm2 Tear strength, kg/cm

+23

-20

-50

-70

-90

168 500 24

148 420 25 53 93 50

225 490 32 64 113 53

284 490 37 79 142 82

392 495 61 126 213 133

48 88

51

9 Data f r o m reference. 6z

It is noteworthy that the strong increase of the tensile strength and moduli is not accompanied by appreciable variation of the elongation at break, this fact indicating high elastomeric performances rather than stiffening of the material. The excellent properties of cis-polypentenamer at low temperatures are fully illustrated when comparing the dependence of the 100% modulus (Figure 18.22), the compression set (Figure 18.23), and the plot of hardness (Figure 18.24) as a function of temperature for various rubbers (e.g., transpolypentenamer, styrene~utadiene rubber 1500, polypropylene oxide,/allyl glycidyl ether and cis-1,4-polybutadiene). 63

1202 M ,oo, kg/cm2

200

/ t ./

100

4

5O

-70

-40

-20

-0

20

Temp., ~ Figure 18.22. Variation of 100% modulus with temperature for various elastomers (1-trans-Polypentenamer; 2- Styrene~utadiene Rubber 1500; 3-Polypropylene Oxide/Allyl Glycidyl F~er; cis-l,4-Polybutadiene; 5-cis-Polypentenamer) (Adapted from Ref.63). Compression, % 4

loo

80

60

I

1 / "

40 I

I

20

O

/

9

-80

9

-70

9

-60

a

-50-40

9

a

-30

f

9

-20

9

9

,,

-10

0

!0

9

20

A

30

Temp., ~ Figure ] 8.23. Dependence of compression set as a function of temperature for different rubbers (]-cis-Polypentenamer; 2-cis-Po]~outadiene 80%; 3-Smok~

Sheet; 4-Styrene/Butadiene Rubber). Conditioning 22 hr, Relaxation 30 mm (Adapted from Ref.63).

1203 Shore A 100

4

90

80

2

7O 6O

50 -80-70 -60-50-40-30

-20 -10

0

10

20

30

Ten~., ~ Figure 18.24. Variation of Shore A hardness with temperature for various rubbers

(l-cis-Polypemenamer; 2-cis-Polybutadiene; 3-Smoked Sheet; 4-StyreneJButadiene Rubber); Conditioning 70 hr (Adapted from Ref.63). It is obvious that cis-polypentenamer exhibits a much better low temperature behavior than general purpose rubbers, like natural rubber, styrene-butadiene rubber, or trans-polypentenamer, and displays even superior properties to the known low temperature rubbers, like cis-l,4polybutadiene and propylene oxide/allylglycidyl ether copolymer. 18.2.3. c/s-Polyoctenamer

cis-Polyoctenamer displays a series of particular physical properties. Thus, high cis-polyoctenamer has the same melting temperature as transpolypentenamer but exhibits a considerably higher crystallization rate at room temperature." To diminish the excess crystallization at room temperature, it is preferable to reduce the proportion of cis configuration to about 75-80%. Furthermore, the glass transition temperature (T o is lower (- 108~ than that of the trans-polypentenamer. cis-Polyoctenamer has poor processing properties, especially at temperatures below 100~ In these conditions, and particularly when the

1204 intrinsic viscosity of the polymer markedly exceeds [11] = 2, the material is dry and brittle and it is difficult to be processed. However, at temperatures between 100~ and 120~ it can be compounded with fillers, ingredients

and oil and the mixes are quite homogeneous. Significantly, sulphur cure is fast even at low sulphur doses. The influence of different oil loading on the vulcanization behavior and on some of the physical and dynamic properties of cis-polyoctenamer is illustrated in Table 18.22.

Table 18.22 Influence of oil loadmg on the cure behavior and physical-mechanical properties of cis-polyoctenamer '~b

Parameter

Sundex 790, phr Compound ML 1+4 at 100~ T2, mm T90, mm AL, m.lb Tensile, kg/cm2 Elongation, % M~0, kg/cm2 M3oo, kg/cm~ D1,% HIRHD HBU at 100~ A~

Value

72 7.5 32.5 95 182 340 77 160 5 75 26

5 62 10 37.5 90 189 370 76 152

I0 54 10 28.5 84 172 370 61 131

20 41 12.7 32.5 74 165 400 45 100

4

4

4

74 23

71 20

68 19

'Data from reference~9; I' Recipe: Polymer i00, SWC 0.5, ~;tearic acid'2, zinc oxide 5, ISAF black 50, Sundex 790 as indicated, Santocurr 0.8, Sulphur 1.0, Monsanto rheometer at 150~ Vulcanization 40 mm at 150~

Examination of the physical and dynamical properties of the reinforced cispolyoctenamer shows that the performances are similar to those of the conventional general purpose rubbers. The dependence of the elastomeric properties of cis-polyoctenamer with temperature is illustrated in Table 18.23.

1205 Table 18.23 Variation of physical properties of cis-polyoctenamer vulcanizates with temperature ~b Temperature ~

Tensile strength kg/cm2

Elongation %

M200 k~n 2

M200

M300

kgcm

kg/. 2

70 50 23 0 -10 -20 -40 -50

117 139 161 157 192 207 300 310

360 360 360 360 360 370 380 360

24 25 23 22 27 41 115 135

57 59 60 70 93 123 200 218

104 107 119 136 168 193 256 283

'Data from refermce~ b Recipe:Polymer 100, SWC 0.5, Stearic acid 2, Zinc oxide 5, Nocton 10, I S , ~ 50, Sant~ure 0.8, Sulphur 1.0, Vulcanization 40 ~ at 150~ It is relevant to note that like cis-polypentenamer, cis-polyoctenamer does not exhibit significant variation of the elongation at break with temperature in the range of +70~ to -50~ However, unlike cis-polypentenamer, as it can be noted from the above data, the 100% modulus of cis-polyoctenamer considerably increases below -10~ this fact indicating rubber stiffening. Also, it is of interest to compare the aging resistance of cispolyoctenamer with that of several rubbers such as trans-polypentenamer, cis-1,4-polybutadiene and styrene-butadiene copolymer (Table 18.24). Table 18.24 Aging resistance of cis-polyoctenamer(COR)and several rubbers L~' |

Aging

TPR

COR

BR

SBR 15O0

days TS 4 8 16

93 86 83

69

TS

E

105 108 96

63 63 50

TS

E

TS

E

83 58 114 72 50 83 52 110 63 45 66 38 108 60 ' Aging resistance m air at 100~ ' Values of TS

' Data from reference' (tensile) and E (elongation) are percent of the original values.

1206 It is obvious that the behavior of cis-polyoctenamer is intermediate between that of cis-l,4-polybutadiene, on one hand, and trans-polypentenamer and styrene-butadiene copolymer, on the other hand. The higher aging resistance of cis-polyoctenamer compared to that of butadiene rubber was attributed to the lower content of double bonds in the former polymer while the lower aging resistance compared to that of trans-polypentenamer was assigned to the different configurations of the double bonds of the two polymers. From careful examination of the physical-mechanical properties of cis-polyoctenamer, it may be concluded that this rubber is to be considered as a special purpose rubber of the butadiene rubber type. However, in comparison to butadiene rubber, it displays poorer low temperature performances, but better aging resistance and stress crystallization (green strength).

18.2.4. Cyclorene Rubber A new flame resistant chlorine-containing elastomer that can be readily vulcanized with sulphur-based curatives has been developed since 1973 using as a monomer the Diels-Alder product of hexachlorocyclopentadiene with 1,5-cyclooctadiene. 65 This compound was copolymerized with additional 1,5-cyclooctadiene to give a family of copolymers with variable microstructures, chlorine content, melting points and glass transition temperatures as well as with a high solvent resistance (Eq 18.6). O

Due to its good solvent and weathering resistance, this product appeared to be capable of replacing polychloroprene (Neoprene) in many applications. Importantly, the copolymers thus manufactured showed to be compatible with conventional diene elastomers and could be vulcanized by sulphur and common sulphur donor curatives.

1207

18.3. Potential Applications Conventional and new polymers have become more and more accessible with the development of the versatile processes of ring-opening metathesis polymerization of cycloolefins.

18.3.1. Synthesis of Monodispersed Polyethylene Linear, monodispersed polyethylene is an extremely important practical and synthetic goal and provides the challenge of preparing essentially monodispersed, linear 1,4-polybutadiene. At present low polydispersity polyethylene is produced by the hydrogenation of 1,4polybutadiene prepared by the anionic polymerization of butadiene. However, this approach results in a somewhat branched polyethylene, since the 1,4-polybutadiene prepared by anionic polymerization generally contains C2 branches as a result of low levels of 1,2-polymerization of butadiene. With the advent of well-defined transition metal alkylider~e and metallacyclobutane complexes for living ring-opening metathesis polymerization (ROMP) of cycloolefins, synthesis of monodispersed, linear 1,4-polybutadiene by ring-opening metathesis polymerization of cyclobutene became feasible. Interesting studies by GnJbbs and coworkers ss showed that 1,4-polybutadiene with a polydispersity index of 1.03 can be manufactured by ring-opening polymerization of cyclobutene under the action of the alkylidene complex W(=CH'Bu)(=NAr)(O~Bu)2 (Ar=2,6diisopropylphenyl) in the presence of PMe3. Further hydrogenation of 1,4polybutadiene in the presence of appropriate hydrogenation catalysts will produce linear, low polydispersity polyethylene (Eq. 18.7).

18.3.2. Synthesis of 1,4-Polybutadiene 1,4-Polybutadiene is produced on a large industrial scale by anionic polymerization of 1,3-butadiene, under various conditions. The polymer obtained by this procedure contains generally a low level of C2 branched as a result of 1,2-polymerization of the monomer. An alternative, efficient route to prepare linear, monodispersed 1,4-polybutadiene, with a high steric

1208 purity, is available by ring-opening metathesis polymerization of cyclobutene, 1,5-cyclooctadiene and 1,5,9-cyclododecatriene 67 (Eq. 18.8). - -

(18.8)

The reaction is promoted selectively to cis-l,4-polybutadiene by TiCI,/Et3AI. 6~" Other catalysts such as TiCI4/(~-C,HT)4Mo, 6~ V(acac)3fEt3Al, 67c Cr(acac)3/Et3Al, 67c MoCI3/Et3AI,67c VCI4/BuLi, 67d MoCIs/(Tt-CaHT)4W,67e MoCIs/(Tt-C4H7)2Mo,67e WCl6/(~-c4n7)4W, 67e RuCI3,6?f Ph(MeO)C=W(CO) 5,67g Ph2C=W(CO)56"th and Mt(=CH'Bu)(=NAr)(O'Bu)2 (Mt = Mo or W, Ar=-2,6-diisopropylphenyl) 67iJ may give trans- or cis-l,4-pelybutadiene, depending on the catalyst and reaction conditions. With the availability of 1,5-cyclooctadiene and 1,5,9cyclododecatriene on the industrial sc~e by cyclodimerization and cyclotrimerization of butadiene, respectively, this method becomes of a great commercial interest.

18.3.3. Synthesis of 1,4-Polyisoprene Due to its outstanding elastomeric properties, synthesis of 1,4polyisoprene has stimulated intensive research work for a long period of time. Recent developments in the ring-opening metathesis polymerization catalysts prompted interesting studies for the synthesis of 1,4-polyisoprene by ring-opening metathesis polymerization of l-methylcyclobutene 68 and 1,5-dimethyl- 1,5-r 69 (Eq. 18.9).

(18.9)

1209 Polymerization of l-methylcyclobutene in the presence of the tungstencarbene catalyst Ph2C=W(CO)5 has been conducted by Katz and coworkers 6t" to appreciable yields of 1,4-polyisoprene having cis configuration at double bonds of ca. 90%. More recently, Wu and Cn'ubbs6~' prepared polyisoprene having an exclusively cis and head-to-tail structure by polymerization of l-methylcyclobutene with the well-defined alkylidene complexes of the type Mt(=CH(CH3)2R)(=NAr)(OC(CH3)n(CF3)3.~)2 (At = 2,6-diisopropylphenyl, Mt = Mo, R - Ph, n = 2). The polymer thus prepared showed properties similar to natural rubber. Unfortunately, at present the manufacture of 1,4polyisoprene through this procedure is limited by the availability of the starting materials, 1-methylcyclobutene and 1,5-dimethyl-1,5cyclooctadiene.

18.3.4. Alternating Copolymers Ring-opening metathesis polymerization of substituted cycloolefins afford a unique method for the synthesis of perfectly alternating copolymers of olefins. Starting from a substituted cyclobutene, a substituted polybutenamer can be prepared in a first step which by subsequent hydrogenation will provide the corresponding copolymer of the linear olefins. Thus, by ring-opening polymerization of 3-methylcyclobutene, in the presence of classical WCl6-based catalysts, poly(3-methylbutenamer) is obtained which by subsequent hydrogenation in the presence of Pd/C catalysts will form the alternating copolymer of ethylene and propylene 7~ (Eq. 18.10).

\ n U

[V l "-

~"-

(18.1@

Similar reactions of 3-ethylcyclobutene will produce the alternating copolymer of ethylene and l-butene whereas those of 3-propylcyclobutene will give rise to the alternating copolymer of ethylene and l-pentene. Alternating diene copolymers have been readily prepared by ringopening polymerization of monosubstituted 1,5-cyclooctadienes (R= CH3, C2H5, CI) in the presence of the ternary metathesis catalysts based on WCIffEtOH/EtAICI2.69 Interestingly, when the substituent was a CH3 group, the alternating copolymer of butadiene and isoprene was formed

1210 (Eq. 18.1 l) n

=

(18.11)

whereas when it was a chlorine atom, the alternating copolymer of butadiene and chloroprene was produce~ (Eq. 18.12). n

Cl

ROMP

(18.12)

If the starting material is 1,2-disubstituted 1,5-cyclooctadiene, an alternating copolymer of butadiene and disubstituted butadiene can be prepared. Obviously, the ring-opening reaction occurs at the more reactive, unsubstituted double bond of the cycle, due to the strong steric hindrance exerted by the substituents at other double bond.

18.3.5. Block Copolymers There are at present several experimental techniques which can be used to produce block copolymers from cycloolefins. The most straightforward synthesis that uses living systems derived from well-defined transition metal alkylidene and metallacyclobutane complexes involves growing the homopolymer with a desired molecular weight of one monomer and continuing the process with a second monomer until a final structure and molecular weight of the copolymer is obtained. A large number of diblock and triblock copolymers with very low polydispersities have been prepared by this method. Some examples are selected from the extensive work by GnJbbs and coworkers 7~ on the synthesis of diblock and triblock copolymers of norbornene with exo-dicyclopentadiene and benzonorbornadiene under the action of titanacyclobutane catalysts (Eq. 18.13-18.14). [ri] ...-~..--~

(18.13)

1211

[Til

"-----.--!~

(18.14)

as well as by Schrock and coworkers ~ on the synthesis of diblock and triblock copolymers of norbornene with substituted norbomene or polycyclic olefins in the presence of Ta, W and Mo catalysts (Eq. 18.15).

nf .m t

(1815)

l

Of a special interest are the block copolymers from halogen-n or ferrocene-containing monomers 74 in the presence of the Mo-alkylidene complex Mo(---CH'BuX=NAr)(OtBuh (Eq. 18.16-18.17).

[Mo] n

+

m

--

F3C

(18.16)

CF3 F3C

9 rn

Fe

, p

CF3

(1817)

1212 By this procedure, copolymerization of norbomene-like monomers having transition metals or main group metals, electroactive groups, etc. leads to products of potential use. Thus, block copolymers prepared from 5(ferrocenyl)-norbornene and 5-(trialkoxysilyl)norbomene were attached to electrode surfaces; redox-active materials with specific morphologies and prescribed dimensions were manufactured by this way. Block copolymers could be prepared by grafting living ring-opened polymers onto polymers that contain carbonyl groups, a method that takes advantage of the Wittig-like alkylidene transfer reactions 75 (Eq. 18.18).

According to several procedures, blocks that are not prepared by ring-opening metathesis polymerization could be added to ring opened polymers to provide a wide range of block copolymers with varying properties. Relevant examples reported GnJbbs and Risse, ~6 for instance, by growing a second block on a ring-opened polymer of norbornene by the use of group transfer polymerization (Eq. 18.19).

(18,10) I

I

-2,-2

The silyl vinyl ether block can be modified by cleaving off the silyl groups. Treatment with tetrabutylammonium fluoride results in the formation of the hydrophobic-hydrophilic AB-diblock copolymer with poly(vinyl alcohol) as hydrophilic segment (Eq. 18.20). H

H

-S-

-S-

H

H

CH

O-t

1213 These block copolymers can potentially be applied as emulsifiers, flocculants, wetting agents, foam stabilizers and as polymeric dispersants for the stabilization of polymer blends. On coupling the anionic polymerization with ring-opening metathesis polymerization, Amass and coworkers ~ prepared block copolymers of styrene and cyclopentene (Eq. 18.21)

n

euLi

.=

Bu

"

mo

B

WCl6=

'[VV] (18.21)

and Feast and coworkers 7s grafted block copolymers of norbornene dicarboxylate with styrene (Eq. 18.22). o~ng:n,johcn~og~

Furthermore, changing the reaction mechanism from Ziegler-Natta polymerization to ring-opening metathesis polymerization, Cmabbs and coworkers ~9 prepared block copolymers of norbornene with ot-olefins in the presence of modified titanium catalysts (Eq. 18.23).

--- Cp2Tt-

,. yc.2H4

(

08.23)

CIMa

Graft copolymers of practical interest could be readily produced by the ring-opening metathesis polymerization of cycloolefins in the presence of unsaturated polymers bearing unsaturation in the side chains (Eq 18.24). P,,~tl +

rn x

(182,4)

1214 Thus, Medema e t al. so grafted cyclooctene on the unsaturated branches of the natural rubber in the presence of ReCIs/EhAI, Pampus and coworkers s~ obtained graft copolymers by ring-opening polymerization of cyclopentene with 1,2-polybutadiene, butadiene, styrene-butadiene copolymer and ethylene-propylene-dicyclopentadiene terpolymer whereas, Scott and Calderon 82 prepared graft copolymers from ethylene-propylene-diene terpolymer and 1,5-cyclooctadiene. 18.3.6. Comb and Star Copolymers

Comb copolymers can be produced by ring-opening polymerization of mono- and disubstituted cycloolefins with moderate to long side chainss3 (Eq. 18.25).

coA

n

lc

M

~D.

~

(18.2b~

Icth H3C,(O42I

CO2(O4 I OH3

Such products behave like hydrogels and can take up a moderate amount of water. Synthesis of a large number of star copolymers s4 is possible by ringopening metathesis polymerization using well-defined metathesis initiators and a cross-linking agent (Eq. 18.26) p

p

P

Reactive alkylidenes such as living poly(5-cyanonorbomene) can be quantitatively converted into living star polymers, which upon treatment with relatively unreactive monomers like 2,3bis(trifluoromethyl)norbornadiene give "heterostar" copolymers, since all the sites in the star core serve as initiators.

1215

18.3.7. Amphiphilic Star Block Copolymers Synthesis of amphiphilic star copolymers that consist of a hydrophobic polynorbornene "core" and hydrophilic functionalized polynorbomene "shell" has been effected by Schrock and coworkers s5 (Eq. 18.27). p.

P

[MI

A variety of star copolymers can be made by this procedure with functional groups in the shell, in the core, or in both, to suit whatever application is desired. Such amphiphilic star copolymers behave as model micelles in aqueous solution.

18.3.8. Macrocyclic Compounds Ring-opening metathesis polymerization affords an elegant and simple way to prepare macrocyclic compounds of the carbocyclic type from cycloolefins. This method has several advantages as compared to multi-step conventional methods. In the presence of metathesis catalysts cycloolefins produce macrocyclic compounds of various size as a function of the nature of the cycloolefin, catalytic system and reaction conditions ~~ (Eq. 18.2S). R

(

--~ ( ~ ~ .

R .... ._~ ,,

F [1~

R = ( ~ _ . ~ . .......

. . _ /(CH2)x (18.28)

(CH2)x

Thus, starting from cyclooctene, Wassermann and coworkers ~s prepared unsaturated carbocycles having up to 120 carbon atoms in the molecule. The reaction proceeded under mild metathesis conditions, in the presence of the catalytic system WCIdEtAICIJEtOH at 5-20~ in benzene as a solvent. By subsequent catalytic hydrogenation, the corresponding saturated

1216 carbocycles were synthesized. Carbocyclic oligomerization products were also obtained by Calderon and coworkers s~ in the ring-opening metathesis polymerization of cyclooctene with the WCIdEtAICI2 catalyst under special conditions. Interestingly, the higher unsaturation degree in 1,5-cyclooctene and 1,5,9-cyclododecatriene as compared to cyclooetene led to a higher amount of carbocyclic compounds. Significantly, the carbocyclic nature of the oliogomeric compounds produced in cyclooctene metathesis was elegantly demonstrated by Hocker and Musch ss by detailed chromatographic and spectrometric investigation of the reaction products. A wide range of unsaturated carbocycles were also produced by Wolovsky and Nirs9 by the metathesis reaction of cyclododeeene in the presence of WCl6-based catalysts. The unsaturated oligomers separated in the first stage were subsequently reduced to the corresponding monoolefins which were further subjected to oligomerization in the presence of the same catalytic system. Carbocycles with 24, 36, or 48 carbon atoms were readily synthesized by this procedure.

18.3.9. Conducting Polymers Synthesis of poly(p-phenylene) (PPP), a remarkable material with good thermal stability, chemical resistance and electrical conductivity when doped, has been reported by Caubbs and coworkers 9~ to occur from stereoregular precursors made by transition metal catalyzed polymerization. Thus, cis-5,6-bis(trimethylsiloxy)-l,3-cyclohexadiene was polymerized by the Ziegler-Natta-type catalyst bis[(allyl)trifluoroacetatonickel(ll)] to give exclusively 1,4-poly(cis-5,6-bis(trimethylsiloxy)-l,3-cyr which after deprotection to the corresponding hydroxy polymer, followed by acylation to the acetoxy polymer, produced high-quality poly(p-phenylene) by the pyrolysis of the acetoxy compound (Eq. 18.29). (18.29) TMSO ~

TM~

OTt~

HO

CH

/k~

O~

As ring-opening metathesis polymerization of cycloolefins produces directly polymers with carbon-carbon double bonds in the backbone, this reaction is an attractive and powerful synthetic route for the preparation of materials with desired electrical and optical properties. One interesting example is the synthesis of the new product poly(diisopropylideneeyclobutene), a cross-

1217 conjugated polymer, by ring-opening metathesis polymerization of 3,4diisopropylidenecyclobutene 9~ (Eq 18.30).

n

--•

rri] ._ MeOH'-

(18 30)

The polymer could be spin-cast, formed flexible films, and, upon doping, exhibited moderate conductivities (10 .3 S cm~). The doped material was brittle and insoluble, but these undesirable properties could be altered by forming block copolymers. It is of interest that blocking this product with polynorbornene yielded a rubbery material with more desirable mechanical properties, though the electrical properties after doping were similar to the homopolymer (Eq. 18.31). t~'li +

m--~

65=C

(18.31)

Two major approaches were developed for the synthesis of polyacetylenes by ring-opening metathesis polymerization of cycloolefins. A first approach is the ring-opening polymerization of suitable monomers such as cyclooctatetraene and substituted cyclooctatetraenes in the presence of the tungsten alkylidene complex W(=CHtBu)(-NAr)[OCMe(CF3h]2, reported by Grubbs and coworkers 92 (Eq. 18.32). R n

R ~

These reactions, especially that from substituted cyclooctatetraene, produced interesting and potentially useful materials, which might have valuable applications.

1218 Another important route, discovered by Feast and coworkers, 93 involves the preparation of a "precursor polymer" in a first step followed by "polyacetylene" synthesis upon thermal treatment in a second one. For instance, 7, 8-hi s(tri fluoromet hyl)t ricyclo [4.2.2.02"s]dec.a-3,7, 9-t riene (TCDT-F6] could be ring-opened by classical olefin metathesis catalysts to give a precursor polymer from which hexafluoro-o-xylene was eliminated upon heating to produce polyacetylene (Eq. 18.33).

n

CFa

[Mr]

CF3

A

F3

(18.33)

CF3

n F3C

CFa

Of a significant synthetic value is the finding of Schrock and coworkers 94~ who demonstrated that it is possible, by using the tungsten and molybdenum alkylidene metathesis catalysts, to prepare a homologous series of polyenes that contain up to 15 double bonds by the ring-opening polymerization of TCDT-F6 in a controlled manner (Scheme 18. l).

n

F3 [Mt]

[Mt]

F3

I

r

F3C

CF 3

F3C

nQ F3C

CF 3

nQ

CF3

F3C

Scheme 18.1

CF3

1219 The first double bond was trans, and warts propagation mechanism dominated (~75%). When pivaldehyde was used in the Wittig-like reaction, a series of "odd" polyenes containing 2x+ 1 double bonds resulted. If 4,4dimethyl-trans-2-pentanal was employed, then the resulting polyenes contain 2x+2 double bonds. Since evidence was accruing that relatively short conjugated sequences could sustain a soliton and could have significant third-order nonlinear optical properties, it was of fundamental interest to produce well-defined unsubstituted polyenes. Interesting variations have been imagined, including capping with para-substituted benzaldehydes, and di-or trialdehydes. Polyenes can be manufactured in diblock or triblock copolymers combined with polynorbomene or similar polymers. For example, Stelzer et al. 97 prepared a block copolymer of polyacetylene and polynorbomene from benzotricyclo[4.2.2.02"5]deca-3,7,9-triene (benzoTCDT) and norbornene using a titanacycle catalyst (Scheme 18.2).

011

Schen~ 18.2

The living polymer obtained from the Feast monomer could be further blocked with polynorbomene. Thermolysis of this product eliminated naphthalene to give rise controllable block lengths of polyacetylene within a polynorbornene matrix. Schrock and coworkers 98 prepared triblock copolymers by adding norbornene to W(=CH'Bu)(=Nar)(OtBu)2, followed by TCDT-F6, and norbornene again. Further heating generated the polynorbornene/polyene/polynorbomene triblock. Interestingly, between 10

1220 and 30 of these macromolecules "aggregated" when the polyene block contained more than approximately 20 double bonds, a phenomenon that was ascribed to cross-linking of polyene chains. When enough TCDT-F6 monomer was employed to generate a 50-ene in the triblock, then all of the macromolecules cross-link to yield dichloromethane-soluble red polymers with molecular weights approaching 500000 (vs. polystyrene). This process opened the possibility to control the size of the cross-linked portion of such copolymers and to prepare polyenes in the block copolymers that contain a wide variety of functionalities, redox centers (for self-doping), etc. Another application of living TCDT-F6 technique could be the generation of isolated polyenes diluted in a host polymer. 99 For this purpose, low concentration of polyTCDT-F6 in homopolymer should be homogeneously dispersed, as should the polyene chains generated from polyTCDT-F6 if the retro-Diels-Alder reaction is carried out in the solid state. If such films can be oriented by stretching before the retro-DielsAlder reaction is carried out, then an anisotropic distribution of polyenes with a known distribution of chain length could be produced. Such products would be valuable in the fundamental and applied third-order nonlinear optical fields. An alternate polymeric precursor route to polyaeetylene that did not involve elimination of molecular fragments was developed through the ringopening metathesis polymerization of the highly strained monomer, benzvalene (a valence isomer of benzene). The polymer precursor which was prepared from benzvalene using the tungsten alkylidene complex W(=CH'Bu)(=NAr)(O'Bu)2 formed soluble, tastable films and could be isomerized to polyacetylene upon treatment with mercury salts ~~176 (Eq. 18.34).

--~D. ~

(18.34)

A new interesting precursor route to high-quality poly(l,4phenylenevinylene) (PPV) by ring-opening metathesis polymerization of substituted bicyclo[2.2.2]octadienes reported recently C~ubbs and coworkers. ~~ Thus, starting from the bis(~xylic ester) of bicyclo[2.2.2]octa-5,8-diene-cis-diol, the precursor polymer was prepared by living ring-opening polymerization under the action of the molybdenum

1221 alkylidene complex Mo(=CHCMe2Ph)(=NArXOCMe2(CF3)h which by subsequent pyrolytic acid elimination provided poly(l,4-phenylenevinylene)

(Eq 18.35).

~OC(O)OO'l.sROMP O ) ~ H3CO(

A -~~

(18.35)

OC(O)OO'h

Significantly, the living metathesis polymerization of the starting bis(carboxylic ester) of bicyclo[2.2.2]octa-5,8-diene-cis-diol permitted direct control over the structure of poly(1,4-phenylenevinylene), and particularly the degree of polymerization, the narrow molecular weight distribution, the end group, and the sequence structure of the final copolymer. By a similar route poly(cyclopentadienylenevinylene) has been prepared by ring-opening metathesis polymerization of bis(carboxylic esters) of bicyclo[2.2.1 ]hept-5-ene-l,2-diol and subsequent thermal elimination reaction from the precursor polymers ~~ (Eq. 18.36).

n

~

A v-~ ~

(18.36)

The temperature needed for thermal elimination was reasonably reduced to <100~ by using organic acids as catalysts. An efficient procedure of high technological value would be the use of photo-acid generators to catalyze the elimination reaction because this seems to enable not only low conversion temperatures but also the production of structures via photoresist technology. 18.3.10. Semiconductors and Metal Ousters.

At present, the manufacture of small semiconductor microstructures and microcrystallites (nanoclusters or nanoparticles) is of considerable importance because of the potential exploitation of quantization effects for the production of optical signal processors and switches. ~~ Several

1222 techniques have been devised to synthesize semiconductor clusters or metal clusters of a predictable size. The manufacture of stable semiconductor clusters of controllable sizes in amorphous polymer films seems to be the most desirable in terms of device fabrication. Recently, one elegant and sophisticated approach involving living ring-opening metathesis polymerization of metal-containing monomers to produce nanoparticles within microphase-separated diblock copolymers has been disclosed by Schrock and coworkers. ~~ The monomers are mainly metal norbornene derivatives that contain metals bound to a cyclopentadienyl group. The initiators suitable for these polymerizations have been the wellcharacterized molybdenum ~~ and tungsten ~~ alkylidene complexes used in the living ring-opening polymerization of cycloolefins. The molybdenum complexes appeared to be more useful as they tolerate functionalities to a greater extent than the tungsten catalysts. This approach took advantage of the ability of block copolymers to self-assemble to form lamellae, cylinders, and spheres with dimensions of the order of 50-200A. !~ Ultimately, the nature of the morphology and to some degree the domain size could be altered by varying the amount and ratio of monomer in each copolymer block. A significant application concerns the manufacture of lead sulphide semiconductors, a material that exbibits a high dielectric constant and a large exciton radius. It has a narrow-bandgap semiconductor with an infrared bandgap (0.41 eV) and an ionic crystal structure (cubic rock salt). According to a procaxlure, small particles of PbS have been obtained by H2S treatment of block copolymer films wherein aggregates of poly[(C~HgCH2CsI'~)-zPb] reside as microdomains distributed throughout a polynorbornene matrix. The block copolymer was prepared by sequential addition of norbomene and (CTH9CH2CsI-L)2Pb to Mo(=CH'Bu)(=NArXO'Bu)z followed by quenching with benzaldehyde l~ (Eq. 18.37).

[Col

(18.37)

The interdomain spacings (320-480A) before and after HzS treatment were determined by small-angle X-ray scattering (SAXS)technique.

1223 Average cluster diameters (20-40A) were measured by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) methods. The clusters were identified as PbS by X-ray fluorescence analysis performed on the STEM and by wideqmgle X-ray powder diffraction. In another procedure, m a lead(II) norbomene derivative, Pb(CpN)OTf (Cp N = 2-(cyclopentadienylmethyl)norbom-5-ene) (OTf = CF3S(h) has been employed along with methyltetracyclododecene (MTD) to produce diblock copolymers via living ring-opening metathesis polymerization with Mo(=CHCMe2PhX=NAr(O'Bu)~_ (Eq. 18.38).

(18.38) ~ c ~ ~

The living copolymer was capped in a chain-transfer reaction by adding 1,3pentadiene (a mixture of isomers) to yield a ~polymer terminated with a methylene group and the corresponding vinylalkylidene complex. Films of these block copolymers were prepared from benzene solutions which upon treatment with H2S under nitrogen atmosphere at a temperature of 100~ provided PbS clusters in lamellar/wormlike and regular spherical morphologies. In one case the PbS dusters ranged in size from 16A to 25A. A new approach for the synthesis of metal clusters makes use of block copolymers to first produce stable clusters and subsequently to interconvert reversibly between one type of cluster and another. The clusters were synthesized in poly[bTAN] domains within poly[MTD] matrix, where bTAN = 2,3-trans-bis(tert-butylanfidomethyl)norbom-5-ene and MTD = methyltetracyclod~tecene. In one ex~unple, Zn clusters were manufactured by sequential addition of monomers to W(=CH'BuX=NArXO'Buh initiator in benzene with MTD added first and [bTAN(ZnPh)2] second ''~ (Eq. 18.39).

n

+m

(18.:3e)

~

4-

,

1224 The benzene solution of the copolymer was dried slowly in a nitrogen atmosphere resulting in thick films. Zinc fluoride clusters were produced by exposing the films to hydrogen fluoride-pyridine (HF-Py) complex containing 70% HF. Further analysis by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) indicated the formation of ZnFz clusters within spherical domains in the copolymer film. Wide-angle X-ray scattering (WAXS) showed the formation of crystalline ZnF2, the peaks in the spectra corresponded to those expected for bulk ZnF2 in the futile form. Interconversion of ZnF2 cluster to ZnS cluster is ready possible by reaction with HzS within the nanoscale domain of the copolymer with the equilibrium shifted toward ZnS at higher temperatures (above ~ 120~ and toward ZnF2 at lower temperatures (at room temperature) (Eq. 18.40). ZrkS

+

2HF

_..

~

ZrhC2

+

H2S

(18.40)

Several kinds of clusters can be produced by this general approach from a given starting material. For instance, thermodynamic data indicate that PbS clusters can be synthesized by treating PbF2 clusters with HzS at temperatures above 70~ while for the interconversion CdF2/CdS this process can be accomplished well below room temperature. ~ Significantly, this approach has generated ZnS quantum clusters which are superior in quality (WAXS) to other available techniques. Metal nanoclusters in lamellar or cylindrical microphase-separated precursor diblock copolymer films in which metal complexes initially were attached to the monomer comprising one block of the block copolymer have been synthesized with silver, ~2 gold, ~2 platinum ~3 and palladium. ~ The organometallic palladium derivative, Pd(NBECpXaUyl), which is relatively stable thermally, but which reacts with hydrogen gas to give Pd(0), could be polymerized smoothly to give block copolymers containing MTD. Cast films showed the expected morphologies and could be treated with hydrogen gas at 100~ to generate palladium clusters having ~25 to 50A diameter in polyMTD matrix. However, the greatest control over the number of atoms or molecules in clusters is possible in spherical microdomains. Synthesis of metal clusters in spherical microdomains is connected to production of metal and metal sulphide (semiconductor) clusters in solution within micelles ~4 and vesicles.~5 Work on this line by Schrock and coworkers ~6 showed that polymer films containing evenly-dispersed silver spherical microdomains can be prepared, and that upon heating these films a single

1225 silver cluster (diameter
n

,

m

(18.41)

-------~

/ The diblock was dissolved in benzene, and the copolymer reacted with Ag(HfacacXCOD) (Hfacac=[CF3C(O)CHC(O)CF3]; COD= 1,5cyclooctadiene). Poly[MTD] was then added to form a polymer mixture and films were cast by evaporating the solvent under nitrogen. Analysis by TEM showed silver-containing microdomains of ca. 180A diameter while X-ray fluorescence on a scanning transmission electron microscope(STEM) indicated the presence of silver and phosphine within the spherical microdomains only. Upon heating to 90~ spherical silver clusters having mean diameters of 55A with a standard deviation of ca 20% were produced. Palladium nanoclusters ~7 within polymer film that display a spherical morphology have been manufactured in polymer films prepared by blending a palladium-containing diblock copolymer of the general formula [Pd(C pN)(P A)] ~-[MTD ]m (CpN = endo- 2(cyclopentadienylmethyl)norbom-5-ene, PA = TI3-l-phenylallyl, and MTD = methyltetracyclododecene) with polyMTD homopolymer (Eq. 18.42).

§ m

~ ~

(18.42)

1226 Small palladium clusters (
1227 method (Eq. 18.43).

n

+ m

.~

(18.43)

All polydispersities were low (<1.10) and ~H NMR spectra confirmed that the block-to-block ratio of repeat units was that expected of a well-behaved living polymerization. Copolymers from M-S monomer and MTD were thus prepared and micrograph of a section of a film showed lamellar morphology. Zn nanoclusters were manufactured by adding diphenylzinr to the (M-S)(MTD) copolymer and then treating the film with HzS in order to convert the ZnPhz to [ZnS]x and benzene. Analysis by TEM indicated the expected lamellar microstructure with interdomains spacing similar to those observed for the film of (S-M)(MTD) alone. Furthermore, X-ray fluorescence in a STEM measurement showed that the ratio of zinc to sulphur in the lamellae was that expected. Similar results were reported by Schrock and coworkers ~s employing block copolymers containing M-O monomers. A well-defined lamellar morphology was found in a film of (MO)(MTD) that had been static cast from benzene in the presence of ZnPh2 as well as of Cd[3,5-(CF3hC6H3]2. The latter products had been treated with H2S to afford (ZnS)x and (CdS)x, respectively, within the lamellar microdomains.

18.3.11. Functionalized Polymers Nowadays, there is a great variety of functionalized polymers prepared by ring-opening metathesis polymerization of r bearing functional groups. Generally, the functional group is situated into a remote position with respect to the double bond, rarely it is in an adjacent position. With the discovery of well-defined transition metal alkylidene and metallacyclobutane catalysts largely tolerable to functional groups, the number of functionalized polymers increased considerably. ~9 The polymers thus prepared possess totally different properties and can be used in a variety of fields depending on their structure and the nature of the functional group.

1228 Polymers containing halogen are of practical importance owing to their particular elastomeric properties that make them to be used as special rubbers. Usually, monomers bearing halogen at the double bond deactivate strongly the catalytic system and the reaction is practically suppressed. Thus, l-chlorocycloolefins are found to be inert in the ring-opening polymerization reactions with classical catalysts. However, it was observed that metathesis polymerization would readily occur under these conditions if halogen atoms are present in a remote position. For instance, l-chloro1,5-cyclooctadiene polymerizes by opening of the unsubstituted double bond to give poly(5-chloro-l,5-octadienamer) which is the perfectly alternating copolymer ofbutadiene with chloroprene. 69 Synthesis of a great number of chlorinated and fluorinated polyalkenamers has been effected by Feast and coworkers re~ using both classical and well-defined metathesis catalysts. These products were derived from several series of substituted bicyclic and tricyclic olefins such as norbomene, norbomadiene, benzonorbomadiene, dimethanohexahydronaphthalene, bicyclo[3.2.1 ]octa-2,6-diene, tricyclo[4.2.2.02"5]deca-3,7,9-triene. Such highly chlorinated and fluorinated products are of major technical importance since they display high thermal stability associated with good mechanical properties. Halogen-containing polyalkenamers have been manufactured that seem to be suitable flameretardant and solvent-resistant materials. Several polymerization procedures have been reported that made use of norbornene derivatives containing halogen, hydroxyl, ester, ether, amide, acid, anhydride and nitrile substituents. TM Polymers manufactured from adducts of cyclopentadiene with vinyl acetate, methyl methacrylate, and dimethyl fumaratr are hard, brittle plastics with low heat-distortion temperatures. Re, Ru, Ir and Rb salts have been employed as catalysts with or without reducing agents in polar media such as water and alcohol, which are normally poison for classical catalysts. Polar norbomene monomers have been widely evaluated in a variety of applications. By reaction of polar monomers, including ester and nitrile derivatives of norbomene, polymers of 5-cyanonorbomene have been manufactured with a desirable balance of chemical and mechanical properties. Some of them have been successfully compounded with various vinyl polymers. These amorphous, solventresistant products possess good heat, weathering and solvent resistance as well as excellent impact and shock resistance, properties that suggested valuable applications in pipes, automotive parts, bottles, food wrap films, and other materials.

1229 Development of.new, well-defined ROMP catalysts, tolerant to functional groups, allowed ring-opening polymerization of less grained cycloolefins bearing .various functional groups. Thus, the tricyclohexylphosphine complex of the stable vinylcarbene complex of ruthenium can polymerize cyclooctene and its derivatives ~z2(Eq. 18.44).

X

a,.~m

x

x

This reaction opened a new way to manufacture the interesting class of terpolymers of butadiene, ethylene and vinyl monomers. Polymerization of organoborane monomers, e.g., (5cyclooctenyl)diethylborane or norbomenyl-9-borabicyclononane and further conversion of novel organoborane polymers to hydroxyl-containing materials with different structural parameters and particular physical properties were reported by Chung and coworkers ~23(Eq. 18.45).

n

>

(~

(18.45)

v

B

OH

It is noteworthy that some of these polymers were thermally stable and began to lose weight only at temperatures above 400~ compared to poly(vinyl alcohol), which undergoes weight loss at temperatures as low as 300~ Interesting polymers have been produced by polymerization of cycloolefins with pendant silane or stannane functionalities, these products showed promise for special applications. An attractive example is the metathesis polymerization of 1-trimethylsilyleyclobutene to a perfectly invariant substituted cis polyalkenamer reported by Katz and coworkers TM (Eq. 18.46).

1230 The reaction occurred readily in the presence of the tungsten carbene complex W(CO)s(=CPh2) to produce a perfect head-tail structure which was unaffected by the catalyst. The pendant trimethylsilyl groups could be easily replaced by other functional groups which otherwise are not tolerated by the catalyst. For instance, a sulphur-containing polymer was obtained via substitution of the silyl groups by thio groups. Related examples include norbornene and norbomadiene monomers bearing silane groups such as trimethylsilyl-norbornene or dimethylsilyl-norbornadiene. ~zs The last type of carbosilane polymers containing Si-H bonds in the backbone appear to facilitate the formation of silicon carbide. This probably results from the ability of these polymers to undergo cross-linking via thermal hydrosilylation. Cross-linking by such Si-bonds seems to be an essential requirement for the high yield conversion of linear preeeramic polymers to ceramic materials. Also, polymers containing Si-H bonds appear to crosslink giving rise to films and gels via hydrosilylation. Several polymers have also been produced from cycloolefins possessing trichlorosilyl substituents. Suitable monomers are 5-trichlorosilylnorbomene, 5trimethyloxysilylnorbornene, 10-trichlorosilyl-l,5-cyclododec~diene. When associated with unsubstituted cycloolefins, the silicon-containing monomers confer new properties to the copolymers. Thus, the copolymer manufactured from cis, cis-l,5-cyclooctadiene with 10 mole % 5trichlorosilylnorbornene and 15 mole % 4-vinylcyclohexene is an efficient adhesion promoter for coupling rubber to siliceous fillers. Furthermore, silicas and other mineral fillers may serve as reinforcing agents for these materials because of specific chemical interactions with these type of polymers. Polymers with biocidal properties were prepared from cycloolefins bearing stannyl groups in a remote position with respect to the double bond. ~26 For instance, cyclooctene, norbornene and tricyclo[8.2, l]tridecene substituted with tributylstannyl were found to be suitable monomers (Eq. 18.47). ROMP

(18.47)

n

Bu3Sn

Products thus prepared find applications as marine antifouling coatings, in wood preservation, etc.

1231

18.3.12. Polymers from Heterocyclic Olefins A new class of acyclic polymeric ionophores prepared by polymerization of oxygen-containing monomers was reported by Novak and Grubbs. ~z7 Thus, poly(ethenylidenetetrahydrofuran) compounds were synthesized by ring-opening metathesis polymerization of 7-oxanorbomene derivatives (Eq. 18.48).

0

These materials are capable of forming helical structures with ion-binding cavities, analogous to the cyclic crown ethers and cryptands. Such products which can be cast into thin films might find potential applications as ion-selective permeable membranes. Metathesis polymerization of unsaturated lactones afforded unsaturated polyesters having interesting properties. Ast and coworkers ~28 synthesized a rubber-like polyester by the polymerization of the lactone of 16-hydroxy-6-hexadecenoic acid in the presence of WCldMe~Sn catalyst (Eq. 18.49). n II

I

--

CH(CH CO0(

(18.49)

The product was a fibrous, non-tacky polymer having an average molecular weight of about 95000. Likewise, polymerization of 2,3-dihydrofuran in the presence of tungsten and chromium carbene complexes, as reported by H6cker and coworkers, ~29 gave rise to a polyether structure having a c J s : t r a n s configuration of the double bonds of ca. 1 (Eq. 18.50).

1232 n

-~

ROMP

~--

=[=C H-O-CH2CH2--C H==~ I

O

(18.50)

I

The availability of the new class of tolerant, well-defined metathesis catalysts allowed ring-opening metathesis polymerization of a wide range of heterocyclic olefins. ~30

18.3.13. Telechelic Polymers Ring-opening metathesis polymerization of cycloolefins provides a new, efficient route for the manufacture of telechelic polymers, macromolecules with one or more reactive end-groups which are useful materials for chain extension processes, block copolymer synthesis, reaction injection molding and network formation. Several applications for the production of this class of compounds by cross-metathesis of cycloolefins with a,~difunctional olefins in the presence of metathesis catalysts have been described. TM An interesting example consists of synthesis of hydroxytelechelic polybutadiene by ring-opening polymerization of 1,5cyclooctadiene in the presence of protected cis-l,4-butenediol as the bis(tert-butyldimethylsilyl)(TBS) ether with W(=CHAr)(-NPh)[OCCHs(CFs)2](THF) as the catalyst t32 (Eq. 18.51).

0 Removal of the TBS end-groups from the polymer was performed by the reaction with excess tetra_nobutylammonium fluoride in tetrahydrofuran. The hydroxytelechelic polybutadiene obtained by this procedure has entirely 1,4 repeat units and only one type of hydroxy end-groups. The functionality of the hydroxytelechelic polybutadiene thus prepared is close to 2.0. The synthesis of hydroxytelechelic oligomers of norbornene has been also performed by the reaction of norbornene with u,~difunctional olefins bearing ester groups in the presence of WCL/Me4Sn catalyst ~33 (Eq. 18.52).

1233

R3M~ YX=/_ Y Y=(33C~

Reduction of the ester groups to hydroxytelechelic oli80mers were carried out quantitatively with LiAIH4. The functionality of the hydroxytelechelic product was found to be-~ 1.9.

18.3.14. Liquid Crystalline Polymers An important application of the ring-opening metathesis polymerization of cycloolefins is the synthesis of side-chain liquid crystalline polymers (SCLCPs), products of interest for modem technologies in electronics and optics. Several norbornene derivatives with mesogenic groups have been polymerized during the last six years. A first series of SCLCPs was manufactured by Schrock and coworkers TM from monosubstituted norbornenes by living ring-opening metathesis polymerization under the action of Mo alkylidene complexes of the type Mo(=CH~Bu)(=NAr)(O'Buh (Ar=2,6-C6H/Pr~). Thus, reactions of norbomene derivatives containing laterally attached mesogens, e.g., [(4'methoxy-4-biphenylyl)oxy] and 2,5-bis[(4'-n-alkoxybenzoyl)oxy] and various spacers produced in high yield SCLCPs with variable molecular weight and narrow molecular weight distribution. Variation in the mesogenic group allowed nematic (parallel) and smectic (perpendicular) mesophases to be obtained. Furthermore, AB type copolymers that contain a side-chain liquid crystalline block and an amorphous polymer block were also prepared from n-[((4'-methoxy-4-biphenyl)yl)oxy)]alkyl bicyclo[2.2.1 ]hept-2-ene-5-carboxylates (n=3,6) and norbomene, 5-cyano2-norbomene, and methyltetracyclododeccne ~35(Eq. 18.53).

n

9

m

RDIVP Not =

(18.53)

X

1234 Another series of SCLCPs with a high density of mesogenic groups per monomer unit prepared Stelzer and coworkers m36 starting from 2,3disubstituted norbornenes in the presence of Mo alkylidene complexes (Eq.

18.54).

m

oo(c8. ,r

[uo] ROMP

(18.54)

~ ~ , .

CoO(CH

mCH ).O0(# 89

In this case, the increase of the number of mesogenic groups brought some remarkable differences in the structure of the liquid crystal phases. Significantly, the liquid crystal phases changed from nematic to smectic with spacer length of n - 6 or 7, also depending on the Mo catalyst employed. Through copolymerization with norbornene esters of a , ~ i o l s , the above authors were able to produce liquid crystalline elastomers by "m situ" cross-linking during the ROMP reaction. Significantly, the crosslinking yield depended greatly on the spacer unit ~37Y (Eq. 18.55).

m

.,. n

O~u

~

(la56)

/

0

X0

They observed that these liquid crystalline polymers were weakly crosslinked in the first step during polymerization, but oriented in a second step by mechanical drawing and finally fixed by a second cross-linking step, e.g., by peroxides or irradiation. By this procedure, materials with anisotropies in their physical properties could be obtained. When such materials are optically clear, they may be employed for the production of biofocal contact lenses.

1235

18.3.15. Optically Active Polymers. Synthesis of optically active polymers became an area of large practical interest over the last decade for several reasons. First, these polymers find special applications as chiral phases in liquid or gas chromatography. Second, synthesis of optically active polymers would mimic the synthesis of enantiomericaUy pure natural compounds of relevance in biochemistry. Third, such polymers are of great importance in the investigation of reaction mechanisms and stereochemistry. However, presently, the main disadvantage of many chiral stationary phases prepared for liquid or gas chromatography is their limited stability towards certain solvents as results of the lack of cross-linking. In order to circumvent some of the existing disadvantages and, primarily, to improve their stability toward solvents, optically active polymers with unsaturation in the main chain, suitable to provide crosslinking, would be suitable for desired applications. Such polymers can be easily manufactured by stereoselective ring-opening polymerization of chiral cycloolefins in the presence of well-defined metathesis catalysts. Polymerization of 2-substituted chiral bicycloalkenes affords such polymers where the ring is embedded between two cross-linkable vinylene groups. A first example is the synthesis of optically active polymers prepared by the ring-opening metathesis polymerization of enantiomerically pure 2acyloxybicyclo[2.2, l]hept-5-enes with Mo(-~H~Bu)(=NAr)(O'Buh in chorobenzene or K2[RuCIs(H20)] in aqueous solvents reported by Stelzer and coworkers m3s(Eq. 18.56).

m

ROMP

._

OCCI-U

o

OCCH3 II 0

The acyl substituent was selected from acetyl, butyryl or benzoyl groups. These optically active polymers could provide appropriate double bonds in the chain for further cross-linking.

1236 Another interesting example is the polymerization of N-(amethylbenzyl)-2-azanorbom-5-ene-3-carbowlates having two chir~ substituents with different Mo alkylidene initiators ~39(Eq. 18.57).

m

~

COOCH3

ROMP __ [Mo]

' '

w

~

.

.

.

..N~'"

.

(18.57)

.

~;OOCH3

The resulting polymer, poly(vinylene-N-(ct-methylbenzyl)pyrrolidine-3,5ylene-2-methylcarboxylate), is a derivative of a poly(ct-amionoacid). Further hydrolysis gives free poly(aminoacid). The formation of helices was expected for highly ordered polymers of this type, for e.g., all-cis, isotactic polymer, the amino acid groups are to point toward the outer surface of the helix. Olefinic bonds could be used for further derivatizing or cross-linking reactions, so the stereoregular optically active polymers may be useful for analytical and chiral inducing purposes. Significantly, for such optically active polymers a high separation power for use in the separation of enantiomers is expected.

18.3.16. Miscellaneous Applications A significant application of the ring-opening polymerization of cycloolefins is the synthesis of a new type of blue-light-emitting electroluminiscent polymer from a norbomene monomer that contains a phenylenevinylene oligomer unit as a side-chain, NBTPV-C~ (Eq. 18.58). ONe

OMe OMe

MeO

[Mo]

0 ~ 0 . ~ ~OMe

(18.58)

1237 Using Mo(=NAr)(=CHCMe~PhXOtBuh as the initiator, Schrock and coworkers ~4~ prepared a polymer of NBTPV-Cs in 95% yield. Electroluminiscent devices were manufactured with single layers of polyNBTPV-C5 with ITO as the anode and Ca as the cathode, both by itself and in blends containing the electron transport material, biphenyl-tertbutylphenyloxadiazole. Interesting applications w i l l f i n d ring-opening metathesis polymerization of cycloolefins in the redox chemistry. Thus, monomers that contain redox-active frrocenes, e.g. FeNBE, have been polymerized along with monomers that contain other redox-active groups such as phenothiazine to give small block copolymers74 (Eq. 18.59).

§

[IV

~

(18.59)

The solution chemistry of these materials showed them to be well-defined and well-behaved. Analogously, more elaborate polymers that contain several redoxactive groups along with several equivalents of trialkoxysilylmethylnorbornene have been obtained and shown to derivatize Pt electrodes with well-defined monolayers. In one example, the molybdenum complex M(=CHFcX=NArXO'Buh (Fc = ferrocenyl) has been employed as the initiator and octamethylferrocenylaldehyde as the capping agent TM (Eq. 18.60).

F~

1238 Polymers terminated with pyridyl or bromobenzyl groups, introduced in the capping reaction employing the appropriate aldehydes, reacted with electrodes pretreated with benzyl chloride or pyridine groups, respectively, to produce special polymer-derivatized surfaces. Appealing well-defined redox chemistry was observed for all redox-active groups in the polymer, both in solution and bound to an electrode surface.

18.4. Future Outlook

Catalytic polymerization of eycloolefins has proved to be an efficient method for the synthesis of a wide variety of polymers. The broad class of catalysts allow the successful application of this process to various monomers, under different conditions, from high vacuum technique to high pressure, in the presence or absence of oxygen and water, in aprotic and protic solvents and sometimes under the influence of Lewis and BrOnsted acids as initiators. Monomers of different structures and re,activities will enable synthesis of new block copolymers, graft and star copolymers as well as dendritic polymers with particular shapes and architectures, of relevance in supramolecular chemistry. A promising trend in the near future is the polymerization of metal-and heteroatom-containing monomers which opens new ways to create and manufacture specialty polymers of interest for semiconductor technology. Polymers and copolymers prepared by this way will find broad applications to refined technologies for many areas such as automotive, construction, fine mechanics, electronics, computer science, optics, telecommunications, etc. A special attention for the future work deserves the design of water soluble ruthenium with quaternary amine groups that creates the possibility for living polymerization in aqueous solution and the synthesis of water soluble polymers in the absence of surfactants or organic solvents. Moreover, the synthesis of functionalized polymers bearing biological entities as pendant groups with potential applications in medicine and biology is a challenging subject for future studies. An area of interest for macromolecular and biological chemistry is the synthesis of macrocyclics, e.g., carbocyclic and heterocyclic compounds, by means of back-biting metathesis reactions of appropriate monomers. Combination of the living polymerization processes with other type of polymerization mechanisms will open the possibility to synthesize copolymers of unprecedented structures with useful applications.

1239 18.5. References

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