Recent developments in alternating copolymerization

0032-3950]79/1101-2862507.50[0

Polymer Science U.S.S.R. VoL 21, pp. 2862-2878. O Pergamon Press Ltd. 1980. Printed in Poland

RECENT DEVELOPMENTS IN ALTERNATII~G COPOLYMERIZATION* J . FURUKAWA Tokyo University, J a p a n

Properties of alternating copolymers. A study was made of alternating copolymorization of diolefins with acrylic or olefinic monomers to produce synthetic rubber of very high tensile strength, which i~ dependent on the high degree of orientation of macromolecules during elongation. For example, alternating copolymers of propylene and butadiene have properties which are similar to those of n a t u r a l polyisoprene rubber, while alternating copolymers of acrylonitril0 and butadieno retain excellent properties even when immersed in oil. Alternating copolymers of cyclopentene and acrylonitrile were prepared recently. I t was found that Tg is not determined b y the average relative composition of the copolymer, b u t depends on the proportion of diads, i.e. TZ----FAATA~-FBBTB~2FABTAB, where FAR is the proportion of diads AB and TAB, their glass temperature. The difference in Tg of a n alternating eopolymer of 1 : 1 composition and a homopelymer mixture of the same composition is determined b y the proportion of FAR a n d the characteristic value of zl. The value of zt is positive or negative, according to the effect of sterie factors, the same way as the bond energy of monomer units. Alternating copolymers are of interest as polymers with functional groups. Different poly-fl-, 7- or fl,y.aminoacids were obtained during hydrolysis of alternating copolymers of aldiminc with acrylonitrile, vinylisocyanide with acrylonitrile or vinylsuccinimide with maleic anhydride, respectively. A study was made of complex formation between polyamino acids and heavy metal ions. Mechanism of alternating eopolymerization of donor-accepter monomers. Kirooka et al. showed that d u r i n g copolymerization of acrylic monomer with x-olofin an alternating copolymer is formed if Lewis acid is used as complex forming agent for the acrylic monomer. This method was used for the copolymerization of a n acrylic monomer with butadieno, however, crosslinked polymers were obtained, apparently, as a consequence of the interaction of Lewis acid with unsaturated bonds of copolymers. This can be avoided on using small amounts of transition metal compounds. Traces of these compounds reduce the requisite a m o u n t of Lewis acid to a catalytic a m o u n t while a fully sglublo copolymer is formed. The problem arises whether polymerization takes place with the formation of a monomer-donor-monomer-accepter complex, or the monomers are added sequentially. I n the latter case a m a x i m u m is observed in velocity with a monomer ratio of [1KA]/[MB]=(kAB/kBAK[A1])*, while in the former case ([MA]/([MA]+ [MB])={(KI[M]~+ 1)*-- 1}/Kx[M]n ~<{, where [MA], [MB], [M] and [All are the concentra4~ions of monomers, A, B, the overall concentration of monomers and Lewis acid, respectively. I t was shown experimentally that copolymorization takes place with the formation of a donor-accepter complex since the monomer ratio, for which product yield is maximum, is independent of the concentration of the Lewis acid, and is only determined by the concentration of the monomer. NMR spectroscopic results and cryoscopic investigations confirm the formation of various complexes (such * Vysokomol. soyed. A21: No. 11, 2591-2605, 1979. 2862

Recent developments in alternating eopolymerization

2863

as MA-A1, (MA)I-A1 and MA-A1-Mm However, the structure of the latter complex has not finally been established. Stereoregulation in alternating copolymerization is very difficult, however, asymmetrical alternating eopolymerization of acrylic monomer with olefin or diolefin could be carried out using an asymmetric Lewis acid. It is interesting to examine two processes: alternating copolymerization and addition according to Diels-Alders. Both reaction are accelerated by similar means using a Lewis acid of average strength. The difference in these two types of reaction is probably due to a different method of reactivation of the complex; alternating copolymerization is initiated by radical initiators or photochemically, whereas addition according to Diels-Alders is initiated by heat. The stereochemistry of these processes also shows a variation. Alternating copolymerization of mono- and diolefins. Alternating copolymers were obtained of ethylene, propylene and other olefins with butadiene, isoprene or ~ranspentadiene using modified Ziegler-l~atta catalysts based on vanadium or titanium and alkyl-aluminium compounds. Mixing catalyst components at as low a temperature as possible is very important for obtaining slightly associated and nonaggregated catalyst particles with a controllable coordination number. Catalyst structure was examined by potentiometric titration and EPR. The alternating structure of the copolymer was established by NMR (220 Me/s) and ozonolysis. DURr~O the past decade alternating copolymerization was extended to systems such as acrylic monomer-olefin, acrylic monomer-diolefin and olefin-diolefin. However, features of polymerization and properties of copolymers obtained have not been finally explained. A study is made in this paper of results obtained recently. Glass temloerature [•]. I t was found t h a t the glass temperature Tg of copolymers depends to a large extent not only on copolymer composition, but also on the regularity of arrangement of units in the chain. For a butadiene and aerylonitrile eopolymer (1 : 1) Tg is reduced by 12 ° with an increase in the proportion of alternating diads from 85 to 95%. A s t u d y of the effect of composition and the regularity of diads in an acrylonitrile-butadiene (AB) copolymer shows t h a t T~ is not determined either by the composition (eqn. (1)), or the proportion of monomers FA and FB, or square composition FAFB (eqn. (2)), but depends on the proportion of diads FA-A, -~B-B a n d FA-~ (eqn. (3))

Tg-~FATA+.FBTB

(1)

T g : F~T A~- IV~TB+ 2F AFBTAB

(2)

Tg:FAATA~-FBBTB~- 2FABTAB

(3)

This fact is of interest firstly because transition at glass temperature involves intermolecular motion in the isoviscous state and may, therefore, be described by eqn. (2). However, Tg is determined by the proportion of diads and the r61e of eqn. (3) m a y be significant in view of the existence of microdomains such as AA, BB, or AB. For the simple case of binary copolymer of composition 1 : 1 eqn. (3) is transformed to eqn. (4), which indicates t h a t the deviation of Tg from the arithmetical mean is proportional both to the deviation of glass temperature of an alternating copolymer TAB from the arithmetical mean

2864

J. Fu~ug~WA

and the degree of alternation FAB

T, TA+TB-~ (TAB TA~TB)FAB

(4)

YAB values are determined from NMR analytical results or calculated using relative activities of monomers rl and r=. On the other hand, TAB is a typical parameter of an alternating copolymer determined not only by the energy factor, but also the entropy factor in the glass temperature region. o',k$/cm2 300-

2OO

IOO

.....

0

1-. . . . .

500

3 1

I000 e.,%

l~ig. ]. Dependence of deformation on stress for acrylonitrile-isoprene copo]ymcrs with a content of acrylonitrile units of 49.7 (1), 51"6 (2) and 45.2% (3); ]--alternating,

2, 3-- statistical copolymers. Using formula (5), which is similar to the equation for the crystallization process (5)

T,=H/~S,

where H is enthalpy, AS, entropy variation on transition through the glass transition temperature. If H and AS is expressed by the geometric mean values of these parameters for homopolymers, i.e.

HAB=,/ff-- HB and then

TAB-- TA+TB 2


I f the arithmetic mean is used, i.e.

HAm-= HA+HB and ASAB= ASA+ASB 2

(s)

Recent developments in alternating eopolymerization

2865

then

TA+TB TAB--"--

2

1 ~

(ASA--ASB)(TA--TB)

--

~8A+~SB

2

1 (ASA--ASB)(HA

HB~=

= 2 ~SA+dSB \~-S~

~S~/< 0

(7)

In fact, there are several systems showing positive, or negative deviations in TAB (Table 1).

Fio. 2. X-ray photograph of a butadiene-acrylonitrile elongated, crosslinked alternating copolymer. According to AS values calculated from eqn. (7), polymer systems may be arranged in the following order: CHs

CHI--CH

~

"~ CHI-CH

N

N CHz--CH-~

'

c1__o

~ CHz--CH

c'

I

O. I

CHs

I

CIt, CHs

CHs

I CH~--C~,

I

CH,

~, C H s - - C H

I ~

CH~--C

0

I ~

C

.

N

2866

J. FURUXAWA

This, apparently, points to a slight change of entropy during glass transition for systems with bulky substituents. For a combination of monomers having the same order of Tg and AS, AT is positive, whereas for a combination of monomers having the opposite order, AT is negative. .Rubbery alternating copolymers. The authors of this study obtained two types of synthetic rubber--alternating copolymers of acrylonitrile with butadiene and propylene with butadiene. Both alternating copolymers have excellent properties, particularly deformation strength properties. For vulcanized propylene-butadiene alternating copolymers [1] a very significant increase was observed in tensile strength in limiting elongations, the same way as observed for natural or synthetic 'natural' rubber, compared, for example, with cis-polybutadiene or a styrene-butadiene copolymer. A similar effect is also observed for a copelymer of acrylonitrile with butadiene (1 : 1), vulcanized with different quantities of dicumyl hydroperoxide [1]. Alternating copolymers with a high degree of alternation have higher tensile strength, in spite of a lower modulus with low elongation, compared with the same parameters for a copolymer having a lower degree of alternation (e.g. 80%). A similar effect was also observed in unvulcanized raw rubber [1]. Compared with styrene-buta~liene rubber, propylene-butadiene copolymers have hi~aer strength and deformation characteristics. Figure 1 shows curves of elongation of alternating and statistical copolymers of acrylonitrile and isoprene. It can be seen that orientation in elongation is observed in alternating copolymers, which is not the case for statistical copolymers [2]. Orientation in elongation was confirmed experimentally by X-ray using an alternating copolymer of butadiene and acrylonitrile (Fig. 2) [3]. Statistical copolymer macromolecules contain longer or shorter bulk sequences of units and have a high modulus even with low deformation. In alternating copolymers molecular interaction is comparatively low with low deformation, however, it increases considerably during orientation. Breaking elongation generally reaches a maximum at a temperature high enough for rubber capable of undergoing orientation. For an elastomer of alternating structure based on acrylonitrile and butadiene this temperature is fairly high, the same way as for natrual rubber [4]. The high flexibility and tensile strength of butadienenitrile alternating copolymers is shown in their\considerable stability to the extension of cracks in notched bending tests [5]. The v~lcanizate of an equilibrium mixture of cis-polybutadiene and an alternating butadiene-nitrile copolymer is 1000 times more stable in these notched bending experiments than the same vulcauizate in a mixture with a conventional statistical copolymer. Alternating copolymers sometimes have a l~Agh glass temperature. We developed methods for preparing alternating copolymers of acrylonitrile (AN} and cyclic olefins such as cyclopentene and cyclohexene. Cyclopentene eopolymers are stable to deeolourization at high temperature, while eyclopentadiene

Recent developmenim in alternating copolymerization

286T

eopolymers are unstable [6].

CN-EtA1CI~ +Cr(AA)3

•

\

~

~/

I CN.EtAlCh

+

[~/]=0-14 (DMF) Traeu~---135-155°; '~ Tg--~-88°

~ l /\ - - \ / ~ CN]

+Cr(AA)3

L\~

[e]=0.13 (DMF);

J n Traelt---~145-157°

CH~=CH I

CN'EtA1C12

> or --~-CH,---CH ~']

O ÷

[~]=0.65-0.8 (DMF); Tmelt=155 ° (turned brown)

[

Alternating copolymer as a polymer with func'tional groups.

Alternating:: eopolymerization is a convenient means of preparing fl- or 7-polyamino acids from malele acid or an acrylic monomer with vinylsuccinimide, aldimine or vinyl isoeyanate [7]. CH HC CH / ,[ ], ~ttC--CH-~ CO + HC CH-* I ] \/ \/ c c 0 0 o 0 o 0 H H CH HC=CH~ ,-- HC--CH--HC--CH2~ ([3,"~-type)

HC

&

HC \

/'

OC

\/

CO

+ / OC

0

--*

\C0

H3C=CH

HC=N

I

N

i

+

Ph CH3 H~C=CH

I +

NCO

[ CN

AIC~.

H2C=CH i

CN

C C NH2 0 0 o 0 H H ,~ HC--N--HoC--CH ~ ([3-type) I Ph

I CHs

"

I C00H

,-, H~C--CH--H2C--CH ~ (y-'type) --,

I

NH~

I

COOII

Compared with conventional homopolymers, copolymers have an increased: ability to form complexes with heavy metal ions (Table 2). To obtain copolymers containing phosphorus, alternating copolymerization of a phosphorus derivative of vinyl phenol and maleic anhydride should b e carried out without complex forming agents. Copolymers are fireproof a n d have curious properties of combining metal ions (Tables 4 and 3).

:.~868

FURU'KAWA

J.

TABLE 1.

D E V I A T I O N S OF T A B FROM

T H E A R I T H M E T I C M E A N *VALUE OF

T g OF H O M O P O L Y M E R S

Monomer A

Monomer B

Aerylonitrile

T¢ of copolymer AB

a -Methylstyrene Styrene Vinyl chloride Vinylidene chloride Vinyl acetate ~-Methylstyrene Styrene Vinyl chloride Vinylidene chloride Vinyl acetate ~-Methylstyrene Styrene Vinyl chloride Vinylidene chloride Vinyl acetate

Vinyl acetate

Methyl methacrylate

--26----28.7 12-18 --21---20.6 3.5-6-3 9.5-11 --26-+3 48.5-58

18

TABLE 2. EQUILIBRiUm CONSTA~rrs K OF COMPLEX FORMATIOlqOF M~TAL IONS W.TH A MAT.EICANHYDRIDE--VINYLAMINE (MA-VA) AI~D ltfAT~EIC A.lffHYDRIDE--VINY-L SUCCINIMIDE (MA-VSI) COFOT.X~mR Equilibrium constant K MA-VA I MA-VSI

Reference electrode

pH

Ion

Cu*+

2 × 105

7.2

J

None

3 × 10'

4 × 102 4 × lO s

lm NaNO, None 1M NaN0s

4 × 10' 3 × 104

3× 10' 7 × 10a

2× 104 2 × 10' 1 × 10' 3 × 10e

3× 1× 1× 4×

i

Hg 2+ ] I

None

l~t KC1 1M KC1 None

102 102 102 10'

D u r i n g a l t e r n a t i n g c o p o l y m e r i z a t i o n of p h e n y l a c e t y l e n e w i t h o t h e r a c e t y l e n e ' m o n o m e r s a Copolymer is f o r m e d w h i c h c o n t a i n s c o n j u g a t e ~ double b o n d s in t h e m a i n chain a n d donor, or a c c e p t e r g r o u p s in t h e side chain (Table 5) [8]. X

X

\

CH--C+CH--C

.~

\

C--C

C=C

/

/

Y 'where X: - - H , - - C H s - - O C H , , - - ~ ;

Y: --COOCH 8, --CN.

2aaa

Recent developmenbs in alternating eopolymerization

During polymerization taking place in the presence of transition metal complexes such as vanadium, chromium, iron, cobalt, magnesium, or tungsten a low molecular weight alternating copolymer, soluble in methanol, is formed. I t was established by I R and NMR spectroscopy that the chain microstructure is mainly of cis-form. TABLE 3. E Q U I L I B R I U M CONSTANTS K OF COMPLEX F O R M A T I O N O F M E T A L IONS w I T H P O L Y M E R S C O N T A I N I N G P

~ CHIICH ~

0 I X----P~OEt, where XO(I), S(II)

Metal ion

Hg*+

pH

4

2 × 10 6

5 X 10 5

7

2 × 10' 3 × 10' 2 × 10 ~

5 × 10 5

9 3

UOJ +

Equilibrium constant K copolymer I homopoly, homopoly- with maleic mer II mer I

5'5 4 3

C u $+

4

F o 3+ Ca s+

7 9

2 X 10 ~ 4 × 10' 3 × l0 s $ × 10 5 3 × I0 s 3 × 10 s

Note. Reference electrode 1 K KCI, only for U 0 ] + - I

6 X 10 6 5 X 10 ~ 8 X 10 7 7 X 10 ~ 8 X 10 8

4 x l0 s 3 × l0 s 4 X 6x 7× 5× 2 X

l0 s 106 10 6 10 5 10 8

1 X 10 6 2 X 10 6 2 X 10 6 M NAN0,.

An alternating butadiene-acetylene copolymer was also prepared with an active methylene group between two double bonds. A copolymer with a controlled amount (about 10~/o) of acetylene may, apparently, be of interest either as a drying oil, or a colouring coating if it is modified b y styrylation or maleination. The copolymer readily undergoes lithium treatment and m a y t h e n be used as a material for graft copolymerization of acrylic monomers. Grafting of 4-vinyl pyridine and maleic anhydride was carried out, for example; the reaction was carried out at 100 ° in the presence of benzoyl peroxide a n d at room temperature with cobalt aeetylacetonate. The weight increase o f ~he sample as a result of grafting was 12-39%. Treatment using lithium metal was carried out at 80 ° in dimethoxy e t h a n e

~870

J. F U R U r ~ W A

f o r 1 hr; 24% active methylene groups were subjected to the treatment, which w a s evaluated by carboxylation [9].

Alternating copolymerization in the presence of modified Ziegler catalysts.

It,,

w a s found that Ziegler type catalysts prepared at a temperature of --70 ° ini-

tiate alternating copolymerization of butadiene and propylene. In every case, TABLE 4. FIRE RESISTANCE OF VARIOUS COPOLYMERS (Improved methods J I S K6705-1952)

Copolymer*

Induction period of ignition, see

Duration of eombustion, see

Phosphorus content,

wt. % PMMA II-MMA I-MMA

20 50 Does not ignite

PMA II-MMA I-MA

17 80 Does not ignite

PS II-styrene I-styrene

48 80 Does not ignite

120 Dies down rapidly Undergoes carbonization 120 Dies down rapidly Undergoes carbonization 120 Dies down rapidly Undergoes carbonization

* H A - m e t h y l acrylate; I and I I - h o m o p o l y m e r s , as in Table 3.

independent of the composition of the initial monomer mixture, eopolymers of 1 : 1 composition are formed. The molecular weight of the product is comparatively low, it may be increased, however, if a third catalyst component e.g. TABLE 5.

C O P O L Y M E : R I Z A T I O N OF P H E N Y L A C E T Y L E N E A N D P R O P A R G Y L

A C E T A T E Ii~ T H E

PRESENCE

OF A/~

EtA1CI,+X

CATALYTIC SYSTEI~I

(Monomers--9 mmoles each, catalyst 4.5-6.8 mmoles; 15°; 20 hr) X

Co(AA), VO(AAh Cr(AAh Fe(AA) s Co(DMG) Mn(AA)s WCle WCle" 1/2Me0H Benzoyl peroxide

Yield, % 59.3-49.8 10.1-9-4 26-1 23.4 68.6

i~8-o 64.5-~ 5.5* Traces t None

• 1 : 1 composition, mainly c~-form. t insoluble in MoOH.

Mw

lO3"O, 760 1350 1310" 2110 1545 1960 2160(2550) t

Recent developments in alternating copolymerization

~71

~arbonyl compounds are used; this was done by the research team of Maruzen Petroleum Co [10].They developsd for industrialapplication various co-catalysts such as metal alkoxides, acyloxides and halide compounds: Catalysts A1RnX3-n---VX;

Co-catalysts AI(OPr)s, Zn (O---i~Pr) s, Ca(CRaCO0)~

A1R~Xa-. "VO(OR)3-,X. ;

tert. BuCll, I2, SOClm EtA1C12, SnC14, CrOzCI~, TiBrd.

A1RnXa-n--VO(OR)a;

Alternating eopolymer structure was confirmed by ozonolysis. For example, adipic acid without succinic acid impurities was only formed in practice from a n ethylene-butadiene copolymer* [1]. A propylene-isoprene low molecular weight alternating copolymer is of interest, as it provides information about t h e structure of internal and end groups. It appeared that 80% diads are alternatAng forming 4-methyl-5-aeetylpentanal during ozonolysis; this fact confirms t h a t polymerization takes place via position 1 of isoprene and the a-position of propylene. The formation of 107/o acetylaeetone is evidence of the fact that hydrogen a t o m transfer takes place in the propylene end unit. Furthermore, products were formed in a small amount as a result of the 'head to head' addition units and the existence of butadiene homodiads. This can easily be explained by the mechanism" of anionic polymerization and (or) the formation of a u-allyl end unit with an isoprene methyl group of minimum steric hindrance. The authors proposed a mechanism of alternating copolymerization involving the alternate coordination of isoprene and propylene. Two centre coordination takes place with a propylene end unit, this, however, does not take place with the u-allyl isoprene end, if the coordination number of the catalyst is controlled; concentric coordination of propylene takes place instead. Chain transfer occurs by the transfer of a hydrogen atom with a propylene end unit. This was confirmed by NMR when studying signals of the methyl group formed in deuterated butadiene on adding hydrogen. It was also found that similar coordination is very hindered for olefin with a bulky lateral group, e.g. 3-methylbutene, or 4-methylpentene [1]. A similar effect of steric hindrance due to a lateral methyl group in diolelin was observed for dimethylbutadiene and cis-pentadiene, which do not form a n alternating copolymer. It is interesting to note that trans-pentadiene forms a n alternating eopolymer with dimethylbutadiene, in which, however, 50% of all pentadiene units are of trans-configuration and 50% of remaining units are added according to the 1,2 type. This is, apparently, the consequence of steric hindrance in the ~-allyl structure of the pentadiene end unit; an anti-form is * Propylne-butadiene copolyIners have similar structures.

~872

J. FIr~VXAWA

formed from the cis-monomer and a syn-form from the trans-monomer. The latter is more likely; polymerization, apparently, takes place both in the a and y-position, resulting in the formation in equivalent proportions of 1,4- and 1,2polymer, respectively. In the case of 4-methylpentadiene a polymer of exclusively 1,2-structure is'formed. This position is satisfactorily illustrated by the system

v

C l C--C=C \

c\ C\ C=C

/C=C

C:C\

C=C

C:C

Two types of crossed chain extension [11] are possible during alternating eopolymerization. These are evaluated from the stationary condition bearing in mind crossed extension. The value which is inversely proportional to reaction rate, shows a linear relation with inverse concentrations of butadiene and propylene. The rate of polymerization R~ is proportional to the concentration of the polymer with a propylene end unit P~ or with a butadiene end unit P~ and monomer concentration (butadiene [B] or propylene PP)), according to the formulae:

Rp=kp~B[P~] [P]+kBrKr [B~] [PP] kpBKB [P~] [B]=kBpKp [P~] [PP]

2 [P*] .Bp

1 = kpBK~]

1 -F kBpKp[PP]

Constants kpB'/CB and/~p./~p were calculated from these linear ratios and found to be 67.4 and 9.6 l./mole.min, respectively. Alternating copolymerization of donor-acceptor monomers. It has been known for a long time that an alternating copolymer is formed during copolymerization of maleie anhydride with styrene. The acrylic monomer is copolymerized with q-oleiin, but the copolymer obtained is not fully alternating in structure. Hirooka has shown, however, [12] that if the acrylic monomer forms complexes with alkylalnminium halide, an alternating copolymer is formed. The author et al. copolymerized butadienc with acrylonitrile in the presence of ethylaluminium dichloride as complexing agent, l~owever, reaction rate was very low and a highly crosslinked insoluble copolymer was obtained, apparently, as a consequence of subsequent conversions at the double bond of the eopolymer formed, the processes being catalysed by a Lewis acid. An excellent co-catalyst was later prepared from a transition metal [13], tracer concentrations of which enable the requisite amount of Lewis acid to be reduced from the equimolecular

Recent deve~pments in alternating copolymerization

2873

to the catalytic amount. I n the presence of this co-catalyst alternating copolymerization takes place at increased rate even without the formation of a crosslinked product. For example, VOC13 or TiC14 are satisfactory co-catalysts enabling the Lewis acid to be recovered. A similar effect was also observed during alternating copolymerization of cyclo-olefin with acrylonitrile; chromium compounds have a satisfactory co-catalytic effect. I t was shown [14] t h a t the strength of the Lewis acid is an important factor. During alternating copolymerization, the same way as during the addition of butadiene and acrylonitrile according to Diels-Alders, eopolymer yield reaches m a x i m u m with average strength of the acid. This means t h a t the same intermediate compound is formed in both cases and the course of the process is determined by reaction conditions: alternating copolymerization is initiated by radical initiators or UV radiation, while the Diels-Alders reaction takes place during heating. The temperature coei~cient is different for both these reactions [14]. During copolymerization of vinyl acetate with acrylonitrile the composition of the copolymer formed becomes near 1 : 1 if a Lewis acid with average tendency to complex formation is used. This is because some average stability of the donor-aceeptor complex is required both for its formation and for achieving the requisite reactivity [15]. The formation of a donor-acceptor complex between butadiene and the acrylic monomer t h a t had formed a complex with EtA1C12 (or A1) was established by I~MR from the chemical shift of proton signals of acrylic ester, the m a x i m u m of which is observed exactly with a copolymer composition of 1 : 1 [16]. The existence of a donor-acceptor complex was also established by UV absorption a t 340 nm; the rate of alternating copolymerization reached a m a x i m u m by the action of light of the same wave length [17, 18]. Kinetic investigations show t h a t the overall rate of the reaction, the rat~ of initiation and chain extension are proportional to [All 1"5, [All °'~ and [All, respectively. This means t h a t the intermediate product contains one mole of aluminium component [19]. At the same time different orders of reaction rate were observed for the monomer, particularly those proportional to [AN] -2 or [MMA] °. * This fact m a y be explained if we assume t h a t various types of monomer, e.g. A1 : AN, combnied in a complex, m a y be formed in a ternary mixture com, posed of an alumiuium (AI) compound--acrylic monomer (A)--butadiene (B), as well as the A1. AN. B ternary complex detected cryoscopically, the concentration of which m a y be expressed by the Langmuir equation [19] [AI.A.]~] =

k~[~] [A] [B]

1+ K1 [A]"+

[A] [B]

(s)

I t is assumed t h a t for acrylonitrile K1 ~<1 and for methyl methacrylate K 1. [A] ~ /> 1 and K~[A] [B]. Another mechanism is also possible, however, according to. * Methyl methacrylate.

:2874

J. ~FuI~U'KAWA

which alternating addition takes place of butadiene and the acrylic monomer .that forms a complex with the Lewis acid without the formation of a ternary complex. We examined the effect of the amount of Lewis acid on the rate of ~copolymerization R~

[P*] k~2"k.~ [A. A1]. [B] hi2 [A.A1]q-k21 [B]

(9)

f o r the mechanism without the formation of a ternary complex and

bpK1K, [P*] [A] [B] R~~ 1-FKI [A]~-K~ [A] [B]'

(10)

w h e n the reaction takes place with the formation of a ternary complex. Rates Teach a maximum with .a ratio of monomers

(11) [A]

(

1 Mj) "

i+g,[

(12)

W i t h both mechanisms rates are maximum with a given composition of the -monomer mixture which, according to the mechanism without the formation of an intermediate complex, depends on the amount of Lewis acid and is independent of ¢his factor when the mechanism involves complex formation. According to the first mechanism, the ratio of actual monomers, i.e. butadiene and the acrylic -ester-Lewis acid complex depends on the amount of Lewis acid; according to the second mechanism, the composition of the monomer mixture contributing to maximum complex formation, is independent of the Lewis acid and is described b y a Langmuir type equation. The composition of the monomer mixture explaining maximum reaction rate, depends on the overall concentration of monom e r s and not the on proportion of Lewis acid and from this point of view the pattern is similar to the reaction mechanism involving the formation of an intermediate complex [20]. There are cases, which may be explained using a simple approach. For example, during copolymerization of AN a n d vinyl chloride (VC) or vinyl acetate •an alternating copolymer is only formed when using an eqnimolecular amount of :Lewis acid; in other cases a copolymer is obtained containing an increased amount of acrylonitrile. This may be explained using a mechanism assuming the participu t i o n in alternating copolymerization of free acrylonitrile that has not formed a complex with Lewis acid. Assuming that the concentration of the donor-acceptor complex is proportional to [A1].[VC].[AN]/[AzNr]n and the concentration of free ~acrylonitrile [AN] to [A1], formula (13) m a y be readily derived. Concentrations of

Recent

developments in alternating copolymorization

2875

the ternary [VC.AN.A1] complex and free [AN]o are [VC.AN.AI]=

K,[A1] [VC] [AN] K2[A1] [VC] _~ I-~KI[AN]S+Ks[A_N] [VC] - KI[AN]

(13)

[AN]0: [AN]-- [Al] respectively. Consequently, if k 0 and kc are rate constants of polymerization for free acrylonitrile and the ternary complex. d[A.N] __d[AN] -~dgVC'.A.N'A1]=I_}_ d [VC] d [VC. AN. AI]

k(~. KI~[A.~]--[AI]~([AN]~ Kz] [ [AI] ) \ [VC]/

(14)

The ratio of the consumption of AN to VC is related in a linear manner to the value of [AN]/[VC] and [AN]/[A1]--I, which is confirmed experimentally [21]. A study was recently made [22] of ternary eopolymerization of acrylonitrile with two types of styrene derivatives in the presence of EtA1C1s as complex forming agent. In every case the eopolymer contained g0°/o acrylonitrile and the ratio of two types of styrene derivative shows an indirect proportionality to the ratio of monomers in the initial monomer mixture. It is difficult to explain this fact within the framework of the simple mebhanism of formation or the lack of formation of a donor-accepter complex; the existence of some combined mechanism should be assumed. As in this case two types of styrene derivative are added to the same AN end unit, the effect of the end unit cannot be anticipated. Deviation from the simple mechanism is explained by the mixed mechanism described. Two simple mechanisms, i.e. with and without a monomer complex, may be described by equations (16) and (15), respectively d [M1] : kl[M~l]

d [Ms] d [M1] d [Mz] --

(15)

ks[Ms]

k'~KI[M1]/(K,[MI]+Ks[M2]) k~KI[M1] k[K,[Mz]/(KI[M1]--[-Ks[Ms]) k[Ks[Mz]'

(16)

where kl, ks, kl, k[ are rate constants for the first and second mechanisms, k~ and Ks are constants of complex formation for both monomers. In a combined case polymer composition is determined according to the equation d [M1] d[M,]

klX-~-k~glX/{(Kl--gs) X-}-gs} kz(1--X)-bk'~Ks(1--X)/{(K1--Ks) X+Ks} X k I (KI--Ks) X~kilks+k~K1 1--X

ks (K1--Ks) X-}-ksK~+kzK2

where [Mz]=[M] X, [Mz]=[M~ (l--X).

(17)

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J. FURVKAWA

Ratio kl/k2 m a y be calculated from the gradient of curves (d[Mi] : d[M2]): ([M1] : : [Ms] ) with high X values and the other constants, from the gradient of these curves with low X values. TABLE 6. R E L A T I V E

Method oftionPOlymerizaTerpolymerization Same Radical copolymerization Terpolymerization Same

Radical copolymerization Terpo|ymerization Same Radical copolymerization

ACTIVITIES

IN TERPOLYMERIZATION

A N D COPOLYMERIZATIOI~T

• Product of polymerization

I

kl : k~ [kl+k~(kl/k'~)] : (k2Jr k2)

AN-styrene-p-chlorostyrene MMA-styrene-p-chlorostyrene Styrene-p-chlorostyrene

0.75 0.75 0-75

2.45 2.45

AN-styrene-p -methylstyrene MMA-styrene-p-methylstyrene Styrene-p-methylstyrene

1-05 1-05

1.85 1.85

0.95

Al~-p-methylstyrene-p-chlorostyrene MMA-p-methylstyrene-p-chlorostyrene

0.60 0.60

p-Methylstyrene-p-chlorostyrene

0.65

4.30 4.30

We examined copolymerization of styrene, p-methylstyrene, p-chlorostyrene a n d p-methoxystyrene and the values obtained are shown in Table 6. As anticipated, the ratio of ki : k2 shows fair agreement with the ratio, b u t evaluated from results of conventional radical copolymerization of two styrene derivatives and if polymerization takes place with the formation of a monomer-monomer complex, constants are arranged in accordance with the order for monomers: methylstyrene~p-methoxystyrene>p-styrene>p-chlorostyrene; this is evidence of the fact that the overall rate is determined not only b y the f~rmation of the complex, b u t also its reactivity and maximum rate is observed for a certain average stability of this complex. Accordingly, Mikawa et al. [23] prOl~osed a similar combined mechanism for alternating copolymerization of maleic anhydride and olefin monomer without a complex forming agent. They compared the equation of rate, which allows for monomolecular reaction of each monomer and the equation of rate bearing in m i n d bimolecular reaction of both types of monomer forming a donor-acceptor complex. I t is interesting to investigate b y E P R the type of polymer radical using radical traps [24, 25]. Results in the literature prove in most cases that alternating eopolymerization takes place with the formation of a donor-acceptor complex. Studies of these complexes b y NMR confirm the formation of a catalytic complex of not very clear structure [26]. The complex readily dissociates to a monomer a n d (or) a radical after the reaction of the first monomer molecule in the complex. Whether the reaction takes place with the formation of a donor-acceptor

Recent developments in alternating copolymerization

2877

complex, or without complex formation, or b y a mixed mechanism m a y depend on the stability or reactivity of these complexes. The strength of this generally unstable complex was determined from the temperature dependence of chemical shift in N M R spectra. I t is known that stereo-regulation in alternating copolymerization is not too strongly expressed, however, we were able to carry out asymmetric alternating copolymerization of AN and acrylic ester with olefin, or diolefin using an asymmetric complexing agent. This only appeared possible to some extent with cyclic diolefin, or a rigid cyclic olefin [27]. I f during copolymerization with acrylonitrile, methacrylonitrile or COD /-menthol ([~]D------50) or amyl alcohel ([~]D~--4"6) is added to the system, the copolymers formed appear to be optically active. For example, for the copolymer

C--r;C----N prepared in the presence of /-menthol, [0f]DZ-- 7"97, in the presence of amyt alcohol [ a l P : ~-l'l, for the copolymer

C~---N these values are -- 4.74 and ~- 1.17, respectively. Conclusion. Alternating copolymers have typical properties in the glass temperature range, or under conditions of maximum elongation when orientation, or aggregation of macromolecular segments are of significance. Interest is attached to functional copolymers, in which adjacent units have a cooperative effect. Alternating copolymerization taking place with the formation of intermediate complexes m a y be a very interesting type of process if new types of intermediate product can be obtained. Translated by E. SEMERE REFERENCES

1. 2. 3. 4.

J. FURUKAWA, J. Polymer Sci., Polymer Symp., No. 51, 105, 1975 R. IRAKO, Dissertation of Dr. Irako, 1975 Taken by Dr. Tadokoro of Osaka University J. FURUKAWA and T. KOTANI, International Conference on Mechanical Behaviour of Materials, v. 3, 1972

:2878

J. FURUKAWA

5. I n t e r n a l I n s t i t u t e of Synthetic R u b b e r Producers Association's Conference in Mfmchen, Abstracts 6. J. F U R U K A W A , E. KOBAYASHI and M. W A K U I , Annual Meeting of Society P o l y m e r Science, Nagoya, 1978 7. J. F U R U K A W A , E. KOBAYASHI and T. DOT, J. Polymer Sci., Polymer Chem., Ed. in press. 8. J. F U R U K A W A , Unpublished. 9. J. F U R U K A W A , E. KORAYASHI and T. KAWAGOE, J. Appl. Polymer Sci. 21: 597, 1977 10. MARUYAMA, Dissertation. 11. M. TANIGUCHI, Dissertation. 12. M. HIROOKA, H. YABUUCH], S. MORITA, S. KAWASUMI and K. NAKAGUCHI, J. Polymer Sci. R 5: 47, 1967 ]3. J. F U R U K A W A , Y. ISEDA, K. HAGA and N. KATAOKA, J. Polymer Sci. 8, A - l : 1147, 1970 14. J. F U R U K A W A , E. KOBAYASHI, ~ . HAGA and Y. ISEDA, Polymer J. $: 475, 1971 115. J. F U R U K A W A , E. KOBAYASHI and J. YAMAUCHI, Polymer Preprints (Japan) 4: 1964, 1972 16. J. F U R U K A W A , Y. ISEDA and E. KOBAYASHI, Polymer J. 2: 337, 1971 17. J. F U R U K A W A , E. KOBAYASHI and Y. ARAI, J. Polymer Sci. B 9: 805, 1971 18. J. F U R U K A W A , E. KOBAYASHI and Y. ISEDA, Polymer J. 1: 155, 1970 19. J. F U R U K A W A , E. KOBAYASHI, Y. ISEDA and Y. ARAI, Polymer J. 442:1970 20. J. F U R U K A W A , Y. ARAI, E. KOBAYASHI, J. Polymer Sci., Polymer Chem. E d . 14: 2243, 1976 2~1. J. F U R U K A W A , E. KOBAYASHI and J. YAMAUCHI, Polymer J. 2: 407, 1971 22. J. F U R U K A W A , E. KOBAYASHI, M. W A K U I , unpublished. 23. Y. SHIROTA, M. YOSHIMURA, A. MATSUMOTO a n d H. M I K A W A , Macromolecules 1: 482, 1968 24. V. B. GOLUBEV, V. P. ZUBOV, G. S. GEORGIYEV, I. L. STOYACHENKO and V. A. KABANOV, J. Polymer Sci., Polymer Chem. Ed. 11: 2463, 1973 25. T. SATO, K. HIBINO and T. 0TSU, J. Macromole. Sci. Chem. A 9: 1165, 1975 26. J. F U R U K A W A , Ionic Polymerization, U S - J a p a n Seminar, Mareel-Dekker Inc., 227, 1976 .27. J. F U R I f K A W A , E. KOBAYASHI a n d S. NAGATA, J. P o l y m e r Sci., P o l y m e r Chem. Ed., in press