Dilithium initiators based on 1,3‐bis(1‐ phenylethenyl)benzene. Tetrahydrofuran and lithium sec‐butoxide effects

Abstract

AbstractThe adduct (3) from 2 moles of sec‐butyllithium with 1,3‐bis(1‐phenyl‐ethenyl)benzene has been prepared and evaluated as a hydrocarbon‐soluble, dilithium initiator for butadiene and styrene polymerization in cyclohexane or benzene solution. Under high vacuum conditions with purified reagents, bimodal molecular weight distributions are observed for polybutadienes with Mn < 150 × 103 g/mol and for polystyrenes with Mn < 50 × 103 g/mol; monomodal distributions are observed only for higher molecular weights. Addition of tetrahydrofuran ([THF]/[Li] = 14 to 32) or preformed lithium sec‐butoxide ([LiOBu]/[3] = 1·1) produces narrow, monomodal molecular weight distributions even at Mn = 26·2 × 103 g/mol polybutadiene and at Mn = 10 × 103 g/mol for polystyrene. Added lithium sec‐butoxide is the preferred additive since high 1,4‐polybutadienes are obtained. These results provide an explanation for the contradictory results reported previously; under less rigorous experimental conditions, oxygen and hydroxylic impurities can form lithium alkoxides in situ.