Coexistence of Active Species in Anionic Polymerization of Ethyl Methacrylate by Butyllithium

Abstract

Polymerizations of ethyl methacrylate were carried out in toluene with butyllithium at various temperatures. The polymer obtained at −78°C could be fractionated into methanol-insoluble and methanol-soluble fractions. The former was rather syndiotactic. The latter was found by gel-permeation chromatography and 1H NMR spectroscopy to be composed of highly isotactic polymer and isotactic oligomer. These three fractions were formed simultaneously at the beginning of the polymerization and the amounts and molecular weights of the isotactic and syndiotactic fractions increased during the polymerization, while the amount of oligomeric fraction remained almost constant after the initial rapid increase. These results indicate the coexistence of three different active species for isotactic and syndiotactic polymers and isotactic oligomer, respectively, at the initial stage of the polymerization and two propagating species during the polymerization. The amounts of syndiotactic fraction and oligomeric fraction decreased with an increase in the polymerization temperature and only the isotactic polymer was obtained above −20°C. When the polymerization was initiated with 1,1-diphenylhexyllithium, only an isotactic polymer was produced. In the polymerization initiated with butyllithium, an appreciable amount of lithium ethoxide formed at the initial stage of the reaction, but no formation of the ethoxide was observed in the case of 1,1-diphenylhexyllithium. This indicates that the multiplicity of the active species in the polymerization with butyllithium is strongly related to the lithium ethoxide formed.