JOURNAL OF POLYMER SCIENCE: Polymer Chemistry Edition VOL. 14, 1213-1219 (1976)

Preparation of Copolymer of Acetylene and Butadiene

JUNJI FURUKAWA, TAKAHIRO KAWAGOE,* and EIICHI KOBAYASHI, Department of Synthetic Chemistry, Kyoto University,

Kyoto 606, Japan

Synopsis

Conditions for preparation of acetylene-butadiene random copolymers were investigated. Only a combination of organonickel compound and dialkylaluminum halide was able to copolym- erize acetylene and butadiene to give soluble, linear, random copolymers in high yield. Toluene and xylene were the preferred solvents for the copolymerization. The catalyst activity and co- polymer composition were influenced by the Al/Ni molar ratio, polymerization temperature, po- lymerization time, and conditions of preparation of catalyst.

INTRODUCTION

The random copolymerization of acetylene and butadiene with the use of nickel naphthenate-diethylaluminum chloride catalyst1 and the random co- polymerization of acetylene or methylacetylene with butadiene, isoprene, chloroprene, or 2,3-dimethylb~tadiene~ were previously reported. Random copolymers of acetylene and butadiene possess diallyl methylene groups com- ing from the acetylene-butadiene dyad. The preparation of copolymers is an interesting research field because the copolymer is very reactive toward oxy- gen and various chemical reagents and has possible applications as a new type of drying

In the course of the previous investigations1-3 it was found that the catalyst activity and the copolymer composition were markedly influenced by the conditions of mixing of catalyst components and aging of the catalyst. The present report deals with a detailed investigation of conditions of preparation of these copolymers.

EXPERIMENTAL

Copolymerization was performed under an oxygen-free dry nitrogen atmo- sphere. The nickel compound and solvent were placed in a glass flask, and then a n-hexane solution of alkylaluminum compound (2 mole/l.) was added. The aging of catalyst was performed for a definite time at a constant temper- ature with agitation prior to the monomer charge. The gas mixture (purified acetylene and butadiene) was bubbled into the catalyst solution at a constant flow rate with agitation until the copolymerization stopped.2 The reaction

* Present address: Tokyo Research Laboratories, Bridgestone Tire Co., Kodaira 187, Japan. 1213

0 1976 by John Wiley & Sons, Inc.

1214 FURUKAWA, KAWAGOE, AND KOBAYASHI

TABLE I Effect of Catalyst Componenta

CHC1,-soluble polymer

Catalyst

Al Ni

Total polymer yield, g

Et,AICl Ni stearate Ni benzoate 3H,O Ni formate Ni naphthanate Ni cyclohexylbutylate Ni acetylacetonate Nickelocene

Et,AlBr Ni naphthenate

2.78 5.45

16.36 11.98

6.24 2.83 1.09 2.08

~~

Acetylene content,

Yield, g mole fraction

1.60 0.374 3.86 0.291

15.10 0.110 8.37 0.296 5.43 0.268 2.69 0.181 0.86 0.324 1.09 0.164

a Polymerization conditions: Al component, 15 mmole; Ni component, 3 mmole; toluene, 7 0 ml; acetylene, 0.1 2 mole; butadiene, 0.39 mole; polymerization tempera- ture, 20°C; time, 3 hr. Catalyst reaction: 25"C, 10 min.

mixture was poured into a large amount of methanol containing a small amount of 2,6-di-tert- butyl-p -cresol as stabilizer. The liquid polymer isolat- ed in the lower layer was washed with methanol containing the stabilizer. The liquid polymer recovered was dissolved in chloroform and the soluble polymer was separated from the insoluble part by filtration. The solvent chloroform was then evaporated, and a yellowish viscous liquid or waxy poly- mer was obtained.

The microstructure of copolymers was determined by infrared spectrosco- p ~ . ~ The copolymer composition and its sequence distribution were evalu- ated by 60-MHz NMR spectra.' The intrinsic viscosity [7] was measured in toluene a t 30 f 0.05OC with an Ubbelohde viscometer.

RESULTS

Various kinds of catalyst systems were tested in preliminary efforts to co- polymerize acetylene and butadiene. For instance, halides, alkoxides, acetyl- acetonates, or organic acid salts of Ti, V, Cr, Mo, W, Mn, Fe, Co, Ni, Rh, and T h were examined, together with R3A1, RzAlCl, RAlClz, or R2A1- (OR'). However, only a particular combination of a nickel compound and an alkylaluminum compound was able to copolymerize acetylene and butadiene to soluble, linear and random copolymers, as shown in Table I. From the point of high catalytic activity and preparation of soluble copolymer, nickel formate or nickel naphthenate are among the most suitable transition metal compounds. According to the NMR and infrared results, the sequence dis- tribution of the copolymers was quite random, and the microstructure' of the double bonds was composed of about 83% cis, 10% trans, and 7% vinyl link- ages, irrespective of the acetylene content of copo1ymer.l

In contrast, cationic catalysts composed of alkylaluminum dihalide and a nickel compound yielded highly cyclized polymers of butadiene and/or acetylene, while trialkylaluminum-nickel compound catalyst afforded insolu- ble black powdery polymers of acetylene. Consequently, the catalyst systems of dialkylaluminum halide and organonickel compound but not nickel halide

ACETYLENE-BUTADIENE COPOLYMER 1215

TABLE I1 Effect of Catalyst Component on the Nature of Polymer

Aluminum compounds

Ni compound R3Al R,AlX RAlX,

Ni salt of organic Almost insoluble Linear and random Highly cyclized acid or organic black powdera copolymer copolymer complex

Nix, Almost insoluble Butadiene polymer Butadiene polymer black powdera with cyclizationb with cyclizationb

a No evidence of presence of butadiene units. b No evidence of copolymerization.

TABLE I11 Effect of Solvent on the Copolymerizationa

CHC1,-soluble polymer

Total Acetylene polymer con tent,

Solvent yield, g Yield, g mole fraction [77 1 - n- Hexane 0.35 0.30 0.153

Benzene 1.67 0.49 0.231 Toluene 11.98 8.37 0.296 0.12 Ethylbenzene 2.62 1.41 0.458 Xylene 11.01 7.42 0.250

Chlorobenzene 1.31 0.94 0.459

-

- -

1,2-Dichloroethane 8.79 5.78 0.357 0.11 -

a Polymerization conditions: diethylaluminum chloride, 15 mmole; nickel naphthe- nate, 3 mmole;solvent, 70 ml; acetylene, 0.12 mole; butadiene, 0.39 mole; polymeriza- tion temperature, 20°C; time, 3 hr. Catalyst reaction: 25"C, 10 min.

are preferable for the random copolymerization of acetylene and butadiene. (Table 11).

The effect of solvent on the copolymerization is shown in Table 111. Hy- drocarbon and chlorinated hydrocarbon solvents could be used successfully

.G - 0.2 5

AI/NI. Molar ratio

Fig. 1. Effect of Al/Ni molar ratio on the monomer unit in the copolymers. Polymerization conditions: nickel naphthenate, 3 mmole; toluene, 70 ml; acetylene, 0.12 mole; butadiene, 0.39 mole; polymerization temperature, 20°C; time, 3 hr. Catalyst reaction: 2OoC, 10 min.

1216 FURUKAWA, KAWAGOE, AND KOBAYASHI

TABLE IV Effect of PreDaration Condition of the Catalvsta

CHCl ,-soluble polymer

Catalyst reaction Microstructure Total content, Monomer Temp, Time, polymer mole Cis, Trans, Vinyl,

present "C min yield, g Yield, g fraction % % [a1 20 10 25 10 30 10 30 20 40 10

A 20 10 BD 20 10 A + B D 20 b

- - - - -

3.01 11.98 17.61

7.35 3.40 9.44

26.31 14.39

1.63 8.37

14.71 4.86 2.05 6.97

23.60 9.61

0.441 0.296 0.180 0.382 0.481 0.323 0.144 0.352

81.0 11.1 7.9 83.7 10.0 6.3 83.6 11.1 5.3 82.2 9.9 7.9

- 0.12 -

- 0.13

0.09 -

a Polymerization conditions: diethylaluminum chloride, 15 mmole; nickel naphthe- nate, 3 mmole; toluene, 70 ml; acetylene, 0.12 mole; butadiene, 0.39 mole; polymeriza- tion temperature, 20°C; time, 3 hr.

b The catalyst reaction time is not defined, as it is included in polymerization time.

for the copolymerization. Of these, toluene and xylene were the most suit- able.

The catalyst activity and the copolymer composition are affected by the molar ratio of diethylaluminum chloride and nickel naphthenate. At an AlINi ratio of 7, both acetylene and butadiene reacted at a maximum rate, af- fording maximum product yield, as shown in Figure 1.

The catalyst activity is also influenced markedly by the conditions of cata- lyst aging, as illustrated in Table IV.

The most active catalyst was prepared by mixing the catalyst components in the presence of butadiene monomer. This catalyst produced a greater amount of soluble linear copolymers than the other catalyst systems. How- ever, the acetylene content of the copolymer was rather low.

Polymerization temperature also influences not only the reaction rate but also the product composition. Figure 2 indicates maxima at 40°C for butadi-

Polym. Temp., "C

Fig. 2. Effect of polymerization temperature on the monomer unit in the copolymers. Po- diethylaluminum chloride, 15 mmole; nickel naphthenate, 3 mmole;

Catalyst lymerization conditions: toluene, 70 ml; acetylene, 0.12 mole; butadiene, 0.39 mole; polymerization time, 3 hr. reaction in the presence of both monomers.

ACETYLENE-BUTADIENE COPOLYMER 1217

TABLE V Effect of Additivesa

Additive CHCl ,-soluble polymer 'Total

Amt, polymer Acetylene content, 5 P e mmole yield, g Yield, g mole fraction ~

None 17.61 14.71 0.180 0.5 12.75 9.81 0.256

0.228 0 2 0.5 14.96 12.36 (CH3)ZC0 1.0 7.88 7.03 0.395

HZ 0

a Polymerization conditions: diethylaluminum chloride, 15 mmole; nickel naphthe- nate, 3 mmole; toluene, 70 ml; acetylene, 0.12 mole; butadiene, 0.39 mole; polymeriza- tion temperature, 20°C; time, 3 hr. Catalyst reaction: 30"C, 10 min, in the presence of additive.

ene and 2OoC for acetylene. High polymerization temperature tends to favor cyclization of the copolymers. The optimal polymerization temperature is in the range 20-40°C.

The course of polymerization is not simple, as shown in Figure 3, because an accelerating phenomenon was observed in the middle stage, where the acetylene content of the copolymers decreased markedly. The intrinsic vis- cosity of the copolymers is rather low, lying in the range 0.08-0.13 dl/g, corre- sponding to molecular weights of 1900-2400.

The effect of additives on the copolymerization is illustrated in Table V. The copolymers obtained were linear and random. However, in the presence of a rather large amount of water the copolymerization was suppressed mark- edly and copolymer containing a large amount of gel was produced. In either case, the additives diminished the copolymer yield, while the acetylene con-

Polym. Tim'e , hr

Fig. 3. Effect of polymerization time on the yield and acetylene content of the copolymers. Polymerization conditions: diethylaluminum chloride, 75 mmole; nickel naphthenate, 15 mmole; toluene, 350 ml; acetylene, 0.20 molebr; butadiene, 0.82 molehr; polymerization temper- ature, 3OOC. Catalyst reaction: 3OoC, 10 min.

1218 FURUKAWA, KAWAGOE, AND KOBAYASHI

0.G

C .- ; 0.4 0 L ”- - b ’ P a 0.2

tent of the copolymers was mainly controlled by the copolymer yield. Thus, compounds including monomer added for the catalyst preparation as well as the mode of preparation have a great influence on the catalyst activity and also on the nature of the catalyst. However, a simple relation was observed between the selectivity of monomer, i.e., acetylene content of the copolymer, and the catalyst activity, i.e., yield of copolymer, as shown in Figure 4. The higher the catalyst activity, the lower is the acetylene selectivity.

-

’

’

DISCUSSION

From the experimental data it was found that the nature and activity of the catalyst nature change in the course of polymerization and are so affected by the polymerization temperature. Moreover, the nature of the catalyst is affected not only by the catalyst composition (Al/Ni ratio), but also by the compounds such as acetylene, butadiene, and additives present in the course of catalyst preparation. The effect of additives on the nature of the catalyst is correlated with the catalyst activity. These observations suggest that the catalyst is not merely the reaction product of nickel compound with alkylalu- minum compound but that it reacts further with acetylene and/or butadiene. These reactions are greatly influenced by the reaction conditions, such as temperature. The change of the catalyst nature in the course of polymeriza- tion may be explained by the reaction with monomers, which is affected by the polymerization temperature.

The effect of additives such as water, oxygen, and ketone is complex; these compounds react with the catalyst to alter the activity as well as the coordi- nation ability of the catalyst. It seems that the additives tend to decrease the coordination of monomers, especially butadiene, yielding copolymers of low butadiene content.

CONCLUSION

A low molecular weight copolymer of acetylene and butadiene is prepared by catalyst composed of nickel compound and alkylaluminum compound. A typical example is the reaction of nickel naphthenate or formate and di-

t 01 I

0 t o 20 30 Yield, g

Fig. 4. Effect of yield on the acetylene content of the copolymers.

ACETYLENE-BUTADIENE COPOLYMER 1219

ethylaluminum chloride, at a molar ratio of 1:7, at 2OoC for 10 min in the presence of butadiene in toluene. The reaction products can be used as a catalyst for polymerization of a gaseous mixture of acetylene and butadiene at lower than 4OOC.

References

1. J. Furukawa, E. Kobayashi, and T. Kawagoe, J. Polym. Sci. Polym. Letters Ed., 11. 573

2. J. Furukawa, E. Kobayashi, and T. Kawagoe, in preparation. 3. J. Furukawa, E. Kobayashi, and T. Kawagoe, in preparation. 4. D. Morero, A. Santambrogio, L. Porri, and F. Clampelli, Chim. Znd. (Milan), 41,758 (1959).

(1973).

Received July 28,1975 Revised October 2,1975