Macrocycles 2. Living macrocyclic polymerization ofε-caprolactone with 2,2-dibutyl-2-stanna-1,3-dioxepane as initiator

Abstract

ε-Caprolactone was polymerized in bulk at 80°C with 2,2-dibutyl-2-stanna-1,3-dioxepane (DSDOP) as initiator. The reaction time was varied for monomer/initiator molar ratios of 20, 100 and 500. A rapid and complete conversion of the monomer and only slight transesterification or back-biting degradation were found after longer reaction times. However, significant acceleration of these side reactions was observed at 180°C. Regardless of the M/I ratios and of the reaction time the polydispersities were nearly constant. Number average molecular weights (M̄n's) as obtained from GPC measurements are larger than the values obtained from end-group analyses by 15–25% and increase with increasing molar ratio M/I (at 100% conversion). The living character of the SnO “end-groups” was demonstrated by acylation with 4-nitrobenzoyl chloride and by the synthesis of a macrocyclic block copolyester containing β-D,L-butyrolactone.