Copolymerization of Butadiene and Styrene with n-Butyllithium and Methyl Substituted Pyridine Mixture

Abstract

The effects of some methyl substituted pyridine compounds (including prydine, quinoline and β-collidine) on n-butyllithium (BuLi)-initiated copolymerization of butadiene and styrene were examined at 40°C or 50°C in n-hexane (solvent). The weight ratio of butadiene to styrene was 75: 25 and that of the monomer to solvent was 1: 4 in all cases.Addition of a small amount of pyridine (or quinoline) retarded the rate of polymerization but did not change the styrene inclusion profile. When more than equimolar pyridine (or quinoline) was added to BuLi, polymerization did not occur. Addition of 2, 6-lutidine or 3, 4- lutidine was effective in increasing both the rate and the styrene content. Addition of 3, 4- lutidine with same 1, 2-addition content gave far more styrene content than that of 2, 6-lutidine when conversion was less than 60%. A detailed comparison of rates of polymerization with copolymer structures obtained was carried out when 2, 4, 6-collidine, β-collidine and triethylamine (TEA) were used as additives to BuLi. The rate of polymerization and the 1, 2-addition content of copolymer decreased in the following order: 2, 4, 6-collidine>8-collidine>TEA, while the order of effectiveness for inclusion of styrene in the copolymer chain was 8-collidine > 2, 4, 6-collidine > TEA.From the oxidative degradation it was found that addition of 2, 4, 6-collidine, β-collidine or 3, 4-lutidine was effective to produce a random butadiene styrene copolymer. Grass transition temperatures (Tg) of these copolymers were also examined.Butadiene-styrene copolymerizations were carried out bs7 using fifteen methyl substituted pyridines as additives to BuLi under the same conditions. It was found the polymerization rate showed as a whole negative correlation with pKb of each compound and the plots of the 1, 2-addition content vs. the styrene content of copolymer (10∼50% conversion) split into three lines because of a steric effect of the additives (cf. Fig.6).