DILITHIUM INITIATORS BASED ON 1,3-BIS(1-PHENYLETHENYL)BENZENE - TETRAHYDROFURAN AND LITHIUM SEC-BUTOXIDE EFFECTS

The adduct (3) from 2 moles of sec-butyllithium with 1,3-bis(1-phenylethenyl)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 MBAR(n) < 150 x 10(3) g/mol and for polystyrenes with MBAR(n) < 50 x 10(3) 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 MBAR(n) = 26.2 x 10(3) g/mol polybutadiene and at MBAR(n) = 10 x 10(3) 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.