Peculiarities of the Anionic Copolymerization of Styrene and Dienes in Non-Polar Solvents with Li+ as Counter-ion mvb

The anionic copolymerization of styrene and butadiene in hydrocarbon solvents initiated by lithium alkyls was first studied by Korotkov, who reported that the polymerization starts slowly and initially consumes butadiene. On exhaustion of this monomer, the reaction speeds up and then styrene polymerizes rapidly. This peculiar behaviour, which was originally explained by Korotkov by treating the monomers as solvents, butadiene being a preferential solvent for the Li+ cation, was later accounted for by considering the cross-over reactions. In this paper an in dept further explanation is given by admitting that the polymerization reactions occur through coordination of the Li+ cation by the monomer followed by insertion of the monomer into the polymer chain. A preliminary MOPAC 93 (PM3) calculation seems to confirm this interpretation.