Polylactones 54:: ring-opening and ring-expansion polymerizations of ε-caprolactone initiated by germanium alkoxides

Et3GeOMe-initiated polymerizations Of E-caprolactone were studied at six different temperatures, but even at 180 degreesC the conversion was below 50% after two days. Ge(OEt)(4) proved to be more reactive and a temperature of 120 degreesC was found to allow for a nearly quantitative conversion after two days. All four ethoxy groups were active in the initiation process, but a broad molecular weight distribution was found and a low percentage (presumably <1 mol%) of cyclic oligomers was formed. Ring-expansion polymerization initiated with a spirocyclic germanium alkoxide was feasible at 140 degreesC and yielded a molecular weight distribution quite different from that obtained with Ge(OEt)(4). The monomer/initiator (M/I) ratio was varied, and it was found that the average degree of polymerization (DP) did not agree with the M/I ratio for M/I's above 200. Addition of 4-nitrobenzoyl chloride to the hot virgin reaction mixtures yielded poly(epsilon-CL) chains having functional endgroups but the degree of functionalization never exceeded 80%. (C) 2002 Elsevier Science Ltd. All rights reserved.