Copolymerization of Butadiene and Styrene with n-Butyllithium and Alkaline-earth Metal Compoud Mixture

Abstract

Copolymerizations of butadiene and styrene were investigated by using n-butyllithium (BuLi) and alkaline-earth metal compound as a catalyst. The weight ratio of butadiene to styrene was 75: 25 and that of the monomer to solvent was 1: 4 in all cases.Calcium compound retarded the rate of BuLi-initiated copolymerization but did scarcely change the microstructure of the copolymer. The addition of strontium t-buthoxide (B⋅Sr) to BuLi somewhat increased styrene inclusion and the trans-1, 4-addition content. The addition of barium compound, especially barium t-buthoxide (B⋅Ba), was the most efficient in accelerating the styrene incorporation and in increasing the trans-1, 4-addition content, whereby there was a negligible change in the 1, 2-addition content. For example, the microstructure of the copolymer obtained with BuLi-B. Ba mixture (BuLi: B⋅Ba=5: 1∼2: 1) contained about 65% trans-1, 4-addition, about 25% cis-1, 4-addition and about 10% 1, 2-addition. The polymerization rate was always markedly increased by elevating polymerization temperature. As the results shown above, the features of butadiene-styrene copolymerization by using BuLi-B⋅Ba mixture [1] as catalyst agreed well with those by bariumzinctetrabutyl as a catalyst. Accordingly, the presence of common catalyst species such as dibutyl-barium was suggestible.Time vs. conversion, conversion vs. styrene content and conversion vs. inherent viscosity were plotted for copolymerizations in n-hexane, benzene and toluene with [1]. Oxidative degradation and glass transition temperature showed that random copolymers, were produced in these cases.The styrene sequence distribution for a random copolymer obtained with [1] was discussed on the basis of NMR and far-infrared spectroscopic measurements, where it seemed that the copolymer with [1] contained more microblocks of styrene than a random copolymer obtained with a BuLi-tetrahydrofuran mixture [2]. Molecular weight distribution by gel permeation chromatography of the copolymer with [1] was far more broad than that of the copolymer with [2].