Study on the mechanism of anionic polymerization with mixed RLi-R′OK initiators, 1. Polymerization of butadiene

Abstract

SUMMARY: Butadiene polymerization in toluene with n-BuLi/t-AmOK mixed initiator at K/Li molar ratio, x, from 0 to 6 has been studied. The results observed substantially depend on the composition of the initiator. The usual scheme assuming the accumulation of highly reactive organopotassium species due to a metalmetal exchange between the initiator components is qualitatively applicable only at 0 a x a 1, although its quantitative agreement with the experiment still remains disputable. In the overstoichiometric region (x A 1), the general pattern is completely inconsistent with this scheme. At x = 2, the relative constant of chain transfer to toluene is 30 times higher than that with potassium alkyls (RK), and only low-molecular-weight polymer (M -n L 500) is formed, the polymerization rate being 10 times lower than the rate observed at x = 1. At even higher excess of t-AmOK, x The study of several model mixed initiators suggests that these new species are complex aggregates containing simultaneously K, Li, and OR moieties rather than single-metal species. Surprisingly, it was found that neither free RK nor its complexes with excess t-AmOK play any important role in the overstoichiometric region.

Initiation of Styrene Retarded Anionic Polymerization Using the Combination of Lithium Alkoxides with Organometallic Compounds

“…They are known as a practical route for the preparation of various alkyl−metal compounds of the heavier alkali metals . These bimetallic combinations have also been reported as specific initiating systems for vinyl monomer polymerization and copolymerization. − …”