MACROCYCLES 2 - LIVING MACROCYCLIC POLYMERIZATION OF EPSILON-CAPROLACTONE WITH 2,2-DIBUTYL-2-STANNA-1,3-DIOXEPANE AS INITIATOR

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 r apid and complete conversion of the monomer and only slight transester ification or back-biting degradation were found after longer reaction times. However, significant acceleration of these side reactions was o bserved at 180 degrees C. Regardless of the M/I ratios and of the reac tion time the polydispersities were nearly constant. Number average mo lecular 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 acyla tion with 4-nitrobenzoyl chloride and by the synthesis of a macrocycli c block copolyester containing beta-D,L-butyrolactone.