High CIS-1,4 polybutadiene—I The catalyst system nickel diisopropylsalicylate, boron trifluoride etherate, butyl lithium

European PolymerJournal, 1970, Vol.6. pp. 1359-1370. PergamonPr~s. Prkntedin England.

HIGH CIS-1,4 POLYBUTADIENE--I THE CATALYST SYSTEM NICKEL DI-/SOPROPYLSALICYLATE, BORON TRIFLUORIDE ETHERATE, BUTYL LITHIUM C. DIxoN, E. W. DucK, D. P. GRIEVE, D. K. JENKINS and M. N. THOR_',,'BER Research and Development Laboratories, The International Synthetic Rubber Co. Ltd., Brunswick House, Southampton, SO9 3AT

(Received 7 November 1969) Abstract--Butadiene is polymerized by the catalyst system nickel diisopropylsalicytatei~ooron trifluoride etherate/butyl lithium to high cis-l,4-configuration. A description is given of the effects of (a) changing catalyst component ratios; (b) order of catalyst addition; and (c) change of solvent, on microstructure, molecular weight and conversion. INTRODUCTION THE NUMEROUS catalysts for solution polymerization o f butadiene to high cis-l,4 polymer can be roughly grouped into three categories: (1) Cobalt or nickel c o m p o u n d s and complexes with aluminium alkyls (~) or alkyl halides; (2) Alkyl-free systems based on cobalt and nickel (E) e.g. COC12 -+- A1CI3; and (3) Catalysts based on titanium c o m p o u n d s (s) plus reducing agents, usually aluminium alkyls, where either a titanium iodide is used or iodine in some form is added to the catalyst. The catalyst reported here is a three c o m p o n e n t system consisting of a soluble nickel (II) complex, a Lewis acid complex and a lithium alkyl. A similar system was later found to be simultaneously under development by the Bridgestone Tyre Co. of Japan, (~) but their catalyst used aluminium alkyl reducing agents. At this time the lithium alkyl catalysts were unique since other high cis catalysts using lithium alkyls required a transition metal containing a halogen, as cocatalyst. Nickel diisopropyl salicylate (nickel DIPS) was used t h r o u g h o u t the w o r k as the two isopropyl groups conferred an extremely high solubility o f the nickel complex in aliphatic and aromatic hydrocarbons, c o m p a r e d to the simple salicylate or nickel acetylacetonate. It will be shown that the nickel diisopropyl salicylate molecule contains co-ordinated water when prepared by the usual methods. A l t h o u g h a range of metal halides and metal halide complexes was studied, b o r o n trifluoride etherate (BF3 etherate) gave by far the best results and was used in all the w o r k reported in this paper. EXPERIMENTAL 1. Purification of materials Nitrogen. Air Products' white spot nitrogen (99" 98 per cent) was passed over hot copper at 200° to remove traces of oxygen, and then dried in a column containing magnesium perehlorate and molecular sieves type 4A. The final moisture content was less than 10 ppm. Copper tubing was used to distribute the dry nitrogen round the laboratory, and the system sealed from the atmosphere when not in use. Hexane. A crude petroleum hexane fraction containing approximately 20 ppm water was dried by refluxing over powdered calcium hydride for about 10 rain followed by fractional distillation under E.P.J. 6/10---~ 1359

1360

C. DIXON, E. W. DUCK, D. P. GRIEVE, D. K. JENKINS and M. N. THORN'BER

nitrogen from butyl lithium. The butyl lithium was present as a 1-2 per cent solution in the hexane prior to distillation. The fraction boiling at 62"-68 ~ was collected in a solvent storage bottle. Whenever possible, the liquid was re-distilled immediately before use. Benzene, toluene, mesitylene. A R grade materials were purified in the same way as hexane. The fractions boiling at 80- 1~-80 • 2 ~ for benzene, 110" 6~-110" 8 ° for toluene and 136" 1~-136- 3 ° tbr mesitylene were collected and stored under nitrogen. 1:3 butadiene. Commercial butadienes (99-4--99.6 mole % purity) and high purity butadienes (99-9 mole ~o) were stored in stainless steel bombs and dried in the gaseous phase by passing through three 3-ft drying columns containing either: (1) Anyhydrous calcium sulphate and soda asbestos. (2) Silica gel. (3) Molecular sieves type 4A; or (I) Potassium hydroxide pellets. (2) Activated alumina. (3) Molecular sieves type 4A. Both purification trains dried the monomer equally well, i.e. to less than 10 ppm moisture. The purified butadiene was always passed through stainless steel or polythene tubing into the polymerization vessels. Analysis of the butadiene was carried out by GLC, using a Perkin-Elmer FI 1 instrument. The liquid phase consisted of 27 per cent propy[ sulphide on firebrick. The column operated at 25" with a nitrogen carrier gas flow rate of 10 ml/min. A 0" 5 ml gas sample of butadiene was used for analysis.

2. Polymerization technique Small scale polymerizations were carried out in 8 oz and 16 oz hydrogen peroxide bottles fitted with screw aluminium caps and neoprene gaskets. All glass apparatus was thoroughly cleaned and dried at 170 ° for at least three hours, and the polymerization bottles were left at 170 ° overnight. The bottles were removed from the oven immediately before use and flushed with nitrogen while still hot. The bottles were capped and weighed, and then flushed for a further 15 or 20 min with nitrogen passing through hypodermic syringe needles inserted through the neoprene gaskets. The bottles were then cooled to - 4 0 ° to --45 ° in an acetone-dry ice bath and filled with the required amount of butadiene which entered as a gas through a syringe needle in the gasket. A slow stream of nitrogen was maintained through the bottles while they were being filled and the efl]uent connected to a waste gas line. The bottles were finally weighed and the solvent, catalyst and any other additives were injected from hypodermic syringes. The neoprene gaskets were self-sealing providing that the syringe needles were not passed through the gasket i n t h e same position more than once. The bottles were then placed in wire cages in the water bath at the required temperature. After polymerization, an aatioxidant such as phenyl/] naphthylamine or 2:6 ditertiary butyl para cresol was added to the viscous polymer cement from which the polymer was isolated by pouring into methanol. The polymer was washed twice with methanol and dried at 45 ° for I or 2 days, and then weighed to obtain the percentage conversion. The rates of polymerization were determined from the total solids content of small samples withdrawn from the bottles during polymerization, with a hypodermic syringe.

3. Polymer evaluation Microstructure. Polybutadiene contained the three isomers vinyl 1:2, trans 1:4 and cis 1:4. The vinyl 1:2 and trans 1:4 isomers gave peaks at 10-98~ and 10- 35v. on the Grubb-Parsons GS4 spectrophotometer. The heights of the peaks were a measure of the concentration of each isomer; the cis 1 :4 was calculated by difference from 100. A 2 per cent solution of the polymer in carbon disulphide was used in this method developed by Hampton. Inherent Viscosities. Inherent viscosities were determined with 0" 1 per cent polymer solutions in benzene at 25 °. For calculation of molecular weights from the Mark-Houwink equation, L V. = K,VI~ the following constants were used. (Inherent ~- Intrinsic viscosity at this dilution): Potybutadiene (high-cis) K = 1"0 x 10--4, ct = 0"77. RESULTS ( A ) P r e m i x o f nickel D I P S and boron trifluoride etherate in the absence o f butadiene

1. Determination o f the optimum catalyst ratios T h e m o s t i m p o r t a n t v a r i a b l e s in a m u l t i - c o m p o n e n t

catalyst system are the ratios

High cis-l,4 Polybutadiene--I

136l

o f the c o m p o n e n t s . F o r this w o r k the most convenient m o l a r ratios (and their abbreviations) were" Nickel D I P S

(i)

Boron trifluoride etherate (ii)

Butyl lithium B o r o n trifluoride etherate

=

Ni/BF3

=

Li/BF3

W h e n the existence o f an active catalyst f r o m nickel DIPS, b o r o n trifluoride etherate and butyl lithium had been established, a systematic e x a m i n a t i o n was carried out to determine the o p t i m u m or m o s t efficient catalyst ratios for p o l y m e r i z a t i o n . Hexane was used as solvent for the p o l y m e r i z a t i o n s and also for the solutions of nickel D I P S and butyl lithium. B o r o n trifluoride etherate was dissolved in benzene as it was only sparingly soluble in hexane. The nickel D I P S and b o r o n trifluoride were premixed under nitrogen in the desired m o l a r ratios and allowed to react together for a b o u t 5 min before being a d d e d to the b u t a d i e n e / h e x a n e mixed feed. The butyl lithium was a d d e d last. T a b l e 1 lists the results o f experiments in which the Ni/BF3 mole ratio was varied between 0 a n d 1.0 [constant Li/BF3 ratio o f 1-0 a n d BuLi = 0.1 parts per h u n d r e d m o n o m e r (phm)]. All three catalyst c o m p o n e n t s were essential for catalytic activity. A n y c o m b i n a t i o n of two o f the three c o m p o n e n t s did not give p o l y b u t a d i e n e . The results (see Fig. 1) TABLE 1.

Expt. No.

POLYMERIZATION OF BUTADIENE W I T H VARIOUS Ni/BF3 MOLE RATIOS, SHOWING THE EFFECT ON THE MICROSTRUCTURE AND THE CONVERSION

Ni/BF~

Ni DIPS mM

1

0

0

2 3 4 5 6 7 8 9

0-I0 0"15 0"20 0-25 0"30 0"45 0-60 1.00

0"04 0"06 0"08 0"10 0.12 0"18 0.24 0'40

~ conversion 0

100 96 85 77 67 44 30 0

~

~

cis t :4

trans

. 96"3 96"7 95"7 95"7 94"3 90"1 83'1 .

.

.

. 2-5 2"0 3-0 3"0 4-8 8"9 15"5 .

vinyl

I.V.

1.2 1"3 1"3 1"3 0"9 1"0 1"4

2"1 2"2 1"7 1'6 1'6 1"3 0"7

.

.

Conversions measured after 2 hr Bath temperature; 55 ° BuLl concentration constant at 0" 1 phm. Li/BF~ mole ratio = 1-0. Butadiene, 25 g; hexane, 70 g. show that the m a x i m u m conversion in 2 h was o b t a i n e d using a Ni/BF3 ratio of 0.1 to 0.15. The cis 1:4 content o f the p o l y m e r c o n t i n u e d to increase with decrease in Ni/BF3, and was close to its m a x i m u m at the o p t i m u m N i / B F a ratio. Similar experiments were carried out to give the o p t i m u m Li/BF3 ratio, and Fig. 2 shows curves for two N i / B F a ratios. V a r i a t i o n o f Li/BF3 between 0-9 and 1-3 did n o t have a very m a r k e d effect on the reaction. A value o f 1 -0 was chosen for subsequent experiments. The experiments carried out with Ni/BF3 ratios between 0 and 1-0 were isolated after 2 hr when the actual conversions were lower t h a n the limiting values. A wider

1362

C. DIXON, E. W. DUCK, D. P. GRIEVE, D. K. JENKINS and M. N. THORN'BER

ioo 90 8O 70

°

5c c o

4C

3O 2O 10 0

I

0-1

I

I

0,2

0-3

I

0.4

r

I

,05

0.6

I

0,7

P

I

0-8

0.9

""b

1.0

N i / B F 3 mole ratio

Fro. 1. The effect of Ni/BFs mole ratio on the conversion (measured after 2 hr) and ~/o cis 1:4 content of high cis polybutadiene. [Active butyl lithium = 0-1 phm, Li/BF3 -----1.0, po!ymerization temperature = 55' (130°F)].

3.0

(a)

2.5

n

2"0

z.5

i.O

T 0"4

I

I

0,8

1.2

1.6

Li / BF s mole ratio

FIG. 2. The effect of a variation in the Li/BF3 ratio on the molecular weight of high cis polybutadiene. Ni/BF3 ratio constant. [Active butyl lithium = 0"09 phm, (a) Ni/BFs = 0" 1, T~ = 35 °, Co) Ni/BF3 = 0.2, Tp = 355 (95°F)1.

H i g h cis-l,4 P o l y b u t a d i e n e - - I

1363

range of Ni/BF3 ratios, between 0-05 and 0.35 gave final conversions greater than 95 per cent when the polymerizations were continued for several hours before isolation. The fastest polymerizations, however, were obtained with Ni/BF 3 ratios between 0- 1 and 0.2. A value of 0.1 for this ratio was preferred, as Fig. 3 shows that molecular weight increased with decrease in the Ni/BF3 ratio from 1-0 to 0.1 and it was obviously advantageous to polymerize with the lowest nickel concentration. During the course of this work, the catalyst ratios were periodically checked as the purity of the materials varied or as the efficiency of the catalyst was improved. Ratios of 0.1 and 1.0 were generally used for Ni/BF3 and Li/BF3 respectively.

2. Factors controlling molecular weight and rate of polymerization Earlier work (Table 1) had indicated that the polymer molecular weight depended upon the Ni/BF3 mole ratio (see Fig. 3). However, the polymerization temperature was the most important parameter controlling the molecular weight, such that the lower the temperature the higher the molecular weight obtained. Figure 4 shows an almost

2.5 o

2-0--

>,

"~o

o

o

o

o

O 0

~. 5 --

0

:>

.~ ~0-

0.5-

0

O'

"

O"

-4

0-5

0.6

0.7

0-8

0.9

t.O

Ni/BF-~ mole ratio FIG. 3. T h e d e p e n d e n c e o f t h e m o l e c u l a r w e i g h t o f h i g h cis p o l y b u t a d i e n e o n the N i / B F 3 m o l e r a t i o .

linear relationship between the inherent viscosity and temperature, between --18: and 4-55 °. A polymerization temperature of 20°-25 ° was chosen for high purity butadiene as it provided the most satisfactory balance between a fast polymerization and acceptable molecular weight. Low temperatures resulted in very slow polymerizations. The overall polymerization time to full conversion ranged from approximately one hour at +55" to several days at -- 18 °, with a catalyst concentration based on 0-1 phm butyl lithium. Reduction in the catalyst concentration also decreased the rate of polymerization, but had no sig-nificant effect on the molecular weight of the polymer. Fig. 5 shows typical rate curves for the polymerization of pure butadiene at various catalyst concentrations and temperatures.

1364 C. DIXON, E. W. DUCK, D. P. GRIEVE, D. K. JENKINS and M. N. THORNBER

6-0

5"0 i

O

o

40 u ~" c

3.0

=:

2.0

1.0

o

T -20

I

I

l

I

t

I

t

~

I

I

-I0

0

I0

2.0

30

40

50

60

70

80

Polyrnerisation temperolure,

*C

FIG. 4. The effect of polymerization on temperature on the molecular weight of high cis polybutadiene. Ni/BF3 = 0" 1. Li/BF3 = 1"0. Active butyl lithium = 0'08 phm. Phillips butadiene.

3. Factors controlling the microstructure o f the polymer Figxtre 1 shows the variation of p o l y m e r cis i : 4 content with Ni/BF3 mole ratio. This was the only variable which affected the microstructure. The m i c r o s t r u c t u r e was i n d e p e n d e n t of the p o l y m e r i z a t i o n t e m p e r a t u r e a n d overall catalyst c o n c e n t r a t i o n a n d cis 1:4 contents between 95 and 97 p e r cent were always obtained. In practice, this was the easiest variable to c o n t r o l since it was a l m o s t insensitive to changes in r e a c t i o n conditions. Vinyl 1:2 contents between 1 and 2 p e r cent were generally o b t a i n e d for p o l y m e r s with cis contents greater than 85 per cent, the balance being m a d e up by an increase in the trans 1 : 4 content of the polymer. F o r e x a m p l e a typical p o l y m e r m i c r o s t r u c t u r e c o r r e s p o n d e d to 9 6 . 2 per cent cis 1:4, 1.7 per cent vinyl 1:2 and 2. I per cent trans 1:4. A sample with a lower cis content w o u l d show a m i c r o s t r u c t u r e c o r r e s p o n d i n g to 92.1 p e r cent cis 1 :4, 1 • 6 per cent vinyl 1 : 2 a n d 6 . 3 per cent trans 1 :4. (B) Premix o f nickel D I P S and boron trifluoride etherate in the presence of butadiene

1. The effect of order of addition of the catalyst components A l l the experiments described involved the reaction o f the nickel D I P S a n d b o r o n trifluoride etherate p r i o r to their a d d i t i o n to the b u t a d i e n e and hexane. This premix, as an a p p r o x i m a t e l y 1 per cent solution in the h e x a n e - b e n z e n e solvent, became cloudy

High cis-l,4 Polybutadiene--I

1365

(a}

lOO 90

(b)

80 ¸

70 *~

60

c .£ ,,n

50

¢

40!

I

o

(o 30 20;

0

i

I

I

!

2

1

3 Time,

4

1

5

!

6

hr

FIG. 5. Rate curves for the polymerization of high purity butadiene to high cis polymer. Polymerization temperature = 25° (77°F). 25 per cent solutions of butadiene in the mixed feed. (a) Butyl lithium = 0.12 phm. (b) Butyl lithium = 0.06 phm. (c) Butyl lithium = 0.045 phm. a few minutes after the two components had reacted and a fine precipitate slowly settled on standing. This precipitate could not be redissolved by addition of up to ten times the amount of solvent and was added to the butadiene as a suspension. Coagulation of the catalyst at this stage was undesirable, since the coagulated catalyst tended to give gelled polymer. The reaction between nickel DIPS and BFa Et:O in the polymerization bottle was not affected by the presence of butadiene, and furthermore the BF3Et20-NiDIPS-butadiene complex was much more soluble in hexane than the premix alone. Reaction between the nickel DIPS and BF3Et_,O was sufficiently rapid to enable the butyl lithium to be added almost immediately. Either the nickel DIPS or the boron trifluoride could be added as the first catalyst component to the mixed feed, with butyl lithium as the third. If atl three catalyst components were mixed in the absence of butadiene a black suspension of over-reduced nickel was formed and a catalyst of reduced activity was obtained. The following orders of addition were desirable for high catalytic activity: (I) (2) (3) (4) (5) (6) (7)

(8)

NiDIPS BF3Et/O : NiDIPS : BF3Et20 NiDIPS : Monomer Monomer BF3Et20 : Monomer : NiDIPS Monomer : BF3Et20 BuLl : Monomer NiDIPS/BFaEt20 premix: Monomer: BuLi

Monomer: BuLi Monomer:BuLi BF3Et.,O:BuLi NiDIPS:BuLi BF3Et_,O:BuLi NiDIPS:BuLi NiDIPS/BF3EtaO premLx

1366

C. D I X O N , E. W. D U C K , D. P. G R I E V E , D. K. J E N K I N S a n d M. N. T H O R N B E R

These orders of addition gave substantially soluble catalysts for gel-free high cis polybutadiene, and (3) was preferred. When butyl lithium was reacted with boron trifluoride etherate either in the absence or in the presence of butadiene, a flocculent white precipitate was produced. (s) When the nickel DIPS was added, the overall concentration of the catalyst seemed to govern its activity, i.e. based on 0.09 phm butyl lithium no polymer was obtained at 30 ° in 16 hr, but a double catalyst charge gave a 50 per cent yield of polymer containing appreciable quantities of gel. When butyl lithium was reacted with nickel DIPS either in the absence or in the presence of butadiene, a dark brown solution was obtained, with no precipitate. Addition of boron trifluoride etherate gave a catalyst of reduced activity, characterized by slow rates of polymerization and/or appreciable induction periods. These high cis polymers, however, were substantially gel free. The solcent effect Although hexane was the preferred solvent for this polymerization, experiments were carried out in which the hexane was replaced by a range of benzene, cyclohexane, toluene and mesitylene concentrations. (a) Benzene. Technical LR benzene (dried and degassed) and AR benzene (dried, degassed and distilled from butyl lithium) were both evaluated. Benzene replaced the standard hexane solvent between 0 and 200 cm 3 benzene per 100 g butadiene. High purity butadiene was used with catalyst ratios of Ni/BF3 = 0.1, Li/BF3 = 1.0,

90 80 "tO

-~" 5o

~" 30 8 2O {0 40

80

120

160

200

Volume (¢m 3) benzene / IOOg bu'tadiene

FIG. 6. T h e effect o f benzene o n the molecular weight of hi~'l eis polybutadiene. H e x a n e as cosolvent. B a t h temperature 27 ° (80°F) Phillips butadiene. Active butyl lithium = 0 . 0 9 p h m . Ni/BF3 = 0.1. Li/BF3 = 1 "0. (a) Pure (AR) benzene. (b) Technical benzene.

High

cis-l,4

Polybutadiene--[

1367

active butyl lithium concentration 0.09 phm and a polymerization temperature of 80 :. Figure 6 shows an almost linear drop in Mooney viscosity with increase in the benzene concentration, indicating that the benzene concentration must be kept to a minimum for maximum molecular weight. The amount of benzene normally added with the boron trifluoride etherate was only I - 2 cm 3 per 100 g butadiene and its effect on the molecular weight of the polymer can almost be neglected. There was no really significant difference between the rates of polymerization in hexane and hexanebenzene mixtures. (b) Cyclohexane. High purity butadiene was polymerized under the same conditions as in the previous section (a) with mixtures of cyclohexane and hexane, giving the following results: TABLE 2. THE POLYMERIZATION OF HIGH PURITY BUTADIENE IN A MIXED HEXANE-CYCLOHEXANE SOLVENT SYSTEM

Expt No. 49 50 51 52 53 54 55

Vol. % hexane

Vol. % cyciohexane

% conversion

Time (hr)

ML~

100 I00 75 50 50 ---

--25 50 50 100 100

98 98 90 91 97 96 99

8 8 8 8 8 8 8

76 74 73 70 78 78 72

The replacement of hexane by cyclohexane as a solvent for the polymerization had no significant effect on the molecular weight, final conversion or rate of polymerization of the butadiene. (c) Toluene. A mixed solvent of A R toluene and hexane gave molecular weights similar to the A R benzene-hexane solvent system. With 17, 50 and 76 vol. % toluene on the butadiene, the Mooney viscosity corresponded to 80, 72 and 63 respectively. (d) Mesitylene. A mixed solvent of A R mesitylene and hexane gave molecular weights similar to the A R benzene-hexane solvent system. With 16 and 49 vol. % mesitylene on the butadiene, the Mooney viscosities corresponded to 74 and 71 respectively. (C) Reactions of the catalyst components in the absence of butadiene (a) The reaction of butyl lithium with BF3 etherate. It has previously been reported (5 that the reaction of butyl lithium with BF3 etherate is according to the equation: 4 LiBu + 4BF3 etherate -+ 3LiBF~ + LiBBu~ + 4Et20. The isolated LiBBu4 was identical with that synthesized from butyl lithium and Bu3B and contained no ether. Lithium tetrabutyl boron is itself an active catalyst component, equivalent to butyl lithium, in the system nickel DIPS-BF3 etherateLiBBu4 as will be shown in a subsequent paper. Unlike butyl lithium, however, it does not catalyse the simple anionic polymerization of butadiene. (b) The reaction of nickel DIPS with BF3 etherate. The reaction between these two materials was less easily defined. When nickel DIPS and excess BF3 etherate in the

1368 C. DIXON, E. W. DUCK, D. P. GRIEVE, D. K. JENKINS and M. N. THORNBER catalytically active ratios (i.e. considerable excess BF3 etherate) were mixed in benzene, a pale g e e n precipitate and green solution were obtained. From i.r. data, analysis and pyrolysis, the precipitate was identified as Ni(BF~)26H20, (found Ni = 16.9%, B = 4.9%, F = 35.2%, H = 3"42~o;requiredNi = 17.2%, B = 6 - 4 % , F = 44.5 %, H = 3.52 ~) contaminated with traces of organic material which could not be washed out. It is therefore assumed that the original nickel complex might have the approximate formula--Nickel (DIPS), 2 H 2 0 although Thermal Gravimetric Analysis measurements indicated about 1- 5 moles of water and the material was polymeric. The benzene soluble material could be separated into two ill-defined products, one soluble in benzene only, with N i : B : F = 1:2:6 and containing about 50 per cent carbon, and the other soluble in hexane and benzene with N i : B : F ---- 1:4:7 again with about 50 per cent carbon. It is known (s~ that methyl salicylate reacts with BF3 etherate to give (methyl salicylate) BF2 4- HF. It can therefore be postulated that the soluble products of the reaction are of a similar nature, formed (i) from free diisopropyl salicylate, eliminated in the formation of Ni(BF4)26H_,O, and BF3 etherate; and (ii) from the reaction of BF3 etherate with the hydroxyl groups on the intact nickel complex. The material appro,,dmating to Ni(BF,d26H,O showed no polymerization activity with either butyl lithium or butyl lithium 4- BF3 etherate unless the lithium butyl was TABLE 3. TYPICAL G L C

Butene-1 Butene-2 Isobutene 1:2 butadiene N-butene Propane 1:3 butadiene

0-007 0"070 0'330 0"031 0.005

0.005 0" 140 0.204 0"028 0.006

99"557

99"617

ANALYSES OF BUTADIENES

0"310 0"051 0'114 0"015 0.003 0-002 99"505

0.206 0" 130 0-046 0- 127 0" 002 0.001 99"469

0-371 0-036 0"011 0"083 0- 003 0.006 99"50

0.14 Trace 0.01 0"03 99"82

0-07 0"02 Trace

99"91

Butyl lithium. This material was supplied by Hans-Heinrich Hutte, Langelsheim, Germany as a 38 per cent (wt./vol.) solution or by the Foote Mineral Company, U.S.A. as a 10 per cent (wt./vol.) solution in a mixed aliphatic hydrocarbon solvent. Inorganically bound lithium content was approximately 1-3 per cent on the butyl lithium. Boron trifluoride etherate. The material was supplied by B.D.M. and re-distilled before use. Allene. Analysed by GLC 97.7 ~o allene, 1" 5 ~ propylene 0" 8 % 2:3 dimethylbutene-1.

in considerable excess, when polymer with the microstructure expected for a normal anionic butyl lithium catalysis was obtained, i.e. 50 % cis, 40 % trans, 10 ~o vinyl. Both soluble materials were inactive alone for polymerization of butadiene but in combination with butyl lithium gave high cis 1,4 polymer in moderate yield.

DISCUSSION The more recent theories on polymerization of butadiene with transition metal/ aluminium alkyt complexes are based on the concept of chain g o w t h from active catalytic sites on the transition metal. Thus, although it has been suggested (7) that chain growth occurs at an organoaluminium compound, the work of Matsuzaki (s. 9) and Yasukawa shows that changing the transition metal has a profound effect on both microstructure and yield, and that these effects can be correlated with change in atomic

High cis-l,4 Polybutadiene--I

1369

radii and ligand field effects of the electronic field round the transition metal. There are many instances in which both ethylene and butadiene have been oligomerized in the absence of a l u m i n u m or organo aluminium compounds, particularly with zerovalent ,-r allyl systems, and both ethylene, with high surface area TIC13, (t°) and butadiene, with low concentrations of Ni(PC13), and TiCI4, (~ ~) have been polymerized in the absence of aluminium compounds. The actual mechanism for high cis polymerization is open to question. Natta (~2) suggested that an essential step on initiation was the rr co-ordination of butadiene in the cis configuration, 7r complexing being the commonest mode of olefin co-ordination for Group VIII metals. Furukawa (t3) proposed that butadiene is a-bonded to the transition metal and that the cis content alters with atomic radius of the metal. Nickel and cobalt have the most favourable atomic dimensions for co-ordinating in the cis configuration. Matsuzaki has used crystal field considerations to show that irrespective of 7r or c~ bonding, the formation of a transition metal complex with butadiene in the cis configuration is aided by the screening effect of non-bonding electrons, which reaches a maximum in the case of low valent Group VIII metals with full or nearly full 3 d orbitals. ~r allyl nickel halide polymerization of butadiene is accelerated by the addition of halides, particularly A1C13, TIC14, and by electron acceptors. (t4) Natta (tS> has reported that complexes such as [rr allyl NiC6H6] + [AIBr~]- can be isolated when working with A1Br3 and that similar complexes are formed with BF3. In the catalyst system nickel DIPS-BF3 etherate-butyl lithium, we have shown that BF3 etherate and butyl lithium, in the absence of nickel, can react to form the -BBu4 anion and that an insoluble nickel compound containing the -BF,~ anion is inactive in polymerization. It therefore seems reasonable to suggest that the active catalyst is a [~ allylic nickel] + [BBu4]- type of complex formed by alkylation of the nickel and insertion of butadiene into the nickel alkyl bond. Polymerization takes place by co-ordination of further butadiene in the cis configuration followed by bonding with the allyl group. I f this type of system is involved, the function of BF3 may be two-fold. It could partly react to form LiBBu~ and also complex with the DIPS ligand, one of which at least is removed from nickel in the formation of the 7r complex. The action of butyl lithium may also be two-fold. It takes part in the reaction to form LiBBu4 and also reduces the nicke complex, probably via an unstable butyl nickel intermediate to form the lower valency ,-r complex. Although the temperature dependence of molecular weight follows the trend shown by cationic polymerizations, styrene and isobutene, both of which are readily polymerized by cationic catalysts, are not polymerized by the catalysts described here. Since molecular weight is largely independent of catalyst concentration, simple anionic polymerization associated with butyl lithium is also unlikely.

REFERENCES (1) M. Gippin, Ind. Engng Chem., Prod. Res. Dev. 1 (1), 32 (1962); J. G. Balas and L. M. Porter, U.S. Patent 3,040,016 (Shell); Montecatini British Patent 916,693 and others; H. Tucker U.S. Patent 3,094,514 (Goodrich-Gulf); A. I. Diaconescu and S. S. Meclvedev,J. Polym. Sci. A3, 31 (1965). (2) H. Scott, R. E. Frost, R. F. Belt and D. E. O'Reilly, J. Polym. Sci. A2, 323 (1964); J. G. Balas, H. E. de la Mare and D. O. Schissler. J. Polym. Sci. A3, 2243 (1965).

1370 C. DIXON, E. W. DUCK, D. P. GRIEVE, D. K. JENKINS and M. N. T H O R N B E R (3) P. H. Moyer and M. H. Lehr, J. Polym. Sci. A3, 217 (1965); Belgium Patent 551,851 (Phillips Petroleum Co.); Belgium Patent 612,732 (Farbenfabrike-Bayer A.G.); British Patent 910,216 (Phillips Petroleum). (4) British Patents, 905,099 and 906,335. (5) D. K. Jenkins and C. Dixon, Chem. Ind. 1887 (1966). (6) N. M. D. Brow-n and P. Bladon, J. chem. Soc. (A) 526 (1969). (7) G. Natta, P. Pino et al., J. Polym. Sci. 26, 120 (1957). (8) K. Matsuzaki and T. Yasukawa, J. Polym. Sci. 5, 511 (1967). (9) K. Matsuzaki and T. Yasukawa, Polymer Lett. 3, 907 (1965). (10) G. F. D'Alelio and T. J. Miranda, J. Polym. Sci. A3, 3675 (1965). (I1) E. W. Duck, D. K. Jenkins and D. G. Timms, Polymer 7, 419 (1966). (12) G. Natta and L. Porri, 148th A. C. S., Chicago (1964). (13) J. Furukawa, Bull. chem. Res., Kyoto Univ. 40, 130 (1959) (14) O. K. Sharaev, A. V. Alferov, E. I. Tinyakova, B. A. Dolgoplosk, V. A. Kormer and B. D. Babitskii. Dokl. Akad. Nauk S S S R 177, 140 (1967). (15) G. Natta, M. C. Gallazzi, L. Porri. Preprint p. 494, LU.P.A.C. International Symposium on Macromolecules, Prague (1965). R~sum~--La polym6risation du butadi6ne par le syst~me catalytique diisopropylsalicylate de nickel, 6th6rate de trifluorure de bore, butyl lithium conduit b. une forte proportion de la configuration cis1,4. On ddcrit les effets produits par (a) le cbangement des proportions des constituants du catalyseur Co) l'ordre dans lequel on ajoute ceux-ci et (c) Ia variation du solvant sur la microstructure, la masse moldculaire et la conversion. Sommario--Del butadiene viene polimerizzato con il sistema catalitico (salicilato diisopropilico di nichel, eterato di trifluoruro di boro, litio butilico) in una elevata configurazione cis-l,4. Si descrivono gli effetti ottenuti, sulla microstructtura, peso molecolare e conversione, cambiando (a) i rapporti tra i componenti dei catalizzatori, (b) l'ordine di aggiunta dei catalizzatori, e (c) il solvente. Zusammenfassung--Butadien wird durch das Katalysatorsystem Nickel-diisopropylsalicylat/Bortrifluorid-~.therat/Butyllithium zu einem hohen Gehalt an cis-l,4-Konfiguration polymerisiert. Der Einflu13 (a) des Verh/iltnisses der Katalysatorkomponenten, (b) der Reihenfolge der Katalysatorzugabe und (c) der ,~.nderung des L6sungsmittels, auf die Mikrostruktur, das Molekulargewicbt und den Umsatz werden beschrieben.