Control of Mn, Mw/Mn, end-groups, and kinetics in living polymerization of cyclic esters

Abstract

Factors affecting molar mass, molar mass distribution, end-groups, and kinetics control in polymerization of ε-caprolactone (CL) and L,L-dilactide (LA) initiated by covalent alkylmetal alkoxides, metal alkoxides, and metal carboxylates are discussed. First, an importance of the reliable molar mass measurements of the resulting polyesters is stressed. Then, it is shown that R2AlOR', Al(OR)3 Sn(OR)2, and Sn[(O)OCR')]2/ROH initiators provide living polymerization of cyclic esters, in spite of the extensive aggregation phenomena. In LA polymerization Sn(II)-alkoxides appeared to be particularly effective, allowing Mn control in the range from 102 up to 106. Conditions enabling side chain transfer reactions to be eliminated are also discussed.