Lipase-catalyzed ring-opening polymerization of substituted lactones

Effects of substituted position and ring size of methyl-substituted lactones in their lipase-catalyzed polymerization have been systematically investigated. In the polymerization of 6- and 7-membered lactones using Candida antarctica lipase as catalyst, the reaction behaviors of alpha-substituted lactones were relatively similar to those of the unsubstituted ones, whereas much lower enzymatic polymerizability was observed in the case of omega-substituted lactones. The enzymatic polymerization of gamma-methyl-epsilon-caprolactone also proceeded under mild reaction conditions and the reaction rate was close to that of epsilon-caprolactone. In the polymerization of alpha-methyl-substituted macrolides (13- and 16-membered), the polymerizability decreased by the introduction of the methyl substituent. The enzymatic polymerizability of these lactones was compared with their anionic polymerizability using sodium methoxide as initiator. In case of all the alpha- or omega-substituted lactones examined, the lower anionic polymerizability was observed than that of the unsubstituted ones. These data indicate that the polymerization behaviors strongly depended on the lactone ring size and substituent position as well as type of catalyst (initiator).