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

摘要

epsilon-Caprolactone was polymerized in bulk at 80 degrees 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 degrees C. Regardless of the M/I ratios and of the reaction time the polydispersities were nearly constant. Number average molecular weights ((M) over bar(n)'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 beta-D,L-butyrolactone. References: 13