Lipase-Catalyzed Ring-Opening Polymerization of Substituted Lactones

Abstract

ABSTRACT: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 α-substituted lactones were relatively similar to those of the unsubstituted ones, whereas much lower enzymatic polymerizability was observed in the case of ω-substituted lactones. The enzymatic polymerization of γ-methyl-ε-caprolactone also proceeded under mild reaction conditions and the reaction rate was close to that of ε-caprolactone. In the polymerization of α-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 α-or ω-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).KEY WORDS Enzymatic Polymerization / Lactone / Lipase / Polyester / Ring-Opening Polymerization / Ring-opening polymerization of lactones has been extensively studied, since it provides a facile synthetic route of biodegradable polyesters with controlled structure and molecular weight. 1 So far, a variety of catalysts have been developed for the precise polymerization of lactones. Recently, lipase has received much attention as new catalyst for production of biodegradable polyesters. 2 Lipase catalyzed ring-opening polymerization of unsubstituted lactones in various ring-sizes under mild reaction conditions, yielding high molecular weight polyesters. 3 Furthermore, lipase catalysis exhibited unusual polymerizability of lactones in comparison with that of conventional chemical catalysts. Our recent report showed that macrolides possessed much lower reactivity in the polymerization catalyzed by zinc octanoate than δ-valerolactone (1a) or ε-caprolactone (2a). 4 In the Pseudomonas fluorescens lipase-catalyzed polymerization, on the other hand, the reverse tendency was observed. 5 This is due to the stronger recognition of the macrolides by lipase catalyst.So far, there have been many studies concerning ring-opening polymerization of various 4-membered substituted lactones by chemical catalysts. 1a Lipase also induced the polymerization of such lactones, 6 and the enantioselection took place to give optically active polyesters under selected conditions. 6b,6d,6e In contrast, the ring-opening polymerization of sub- † To whom correspondence should be addressed. stituted lactones of other ring sizes using chemical catalysts has little been reported.For example, α-n-propyl-δ-valerolactone and δ, δ-dimethyl-δ-valerolactone showed no polymerizability using sodium catalyst. 7 Aluminum isopropoxide catalyst polymerize...

Enzymatic Synthesis of Polyesters via Ring-Opening Polymerization

“…On the other hand, the polymerizability of ω-methyl substituted ε-caprolactone significantly decreased compared to the unsubstituted ε-caprolactone [65] (Scheme 6).…”

“…The polymerization behaviors of the macrolides were dependent on the position of the substituent as well as the ring size. The polymerizability of the α-methyl-substituted macrolides (13-and 16-membered) decreased by the introduction of the methyl substituent [65]. The bulk polymerization of the macrolide produced relatively high-molecular-weight polyesters, i.e., the polymerization of 15-pentadecanolide (PDL) using lipase CA produced the corresponding polyester with a molecular weight (M n ) of 34 400.…”

Chiral Polymers by Lipase Catalysis

“…The advantage of ROP over condensation polymerization is that no condensation product needs to be removed and as a result, higher molecular weight polymers can be formed. The ROP of α -methyland ω -methyl -substituted lactones of varying ring size to polymers with a M n of 0.9 -13 kg mol − 1 (PDI 1.4 -2.8) has indeed been described in literature using Candida antarctica lipase ( CAL ) or Mucor miehei lipase ( MML ) as catalyst [36] . However, no information on the degree of enantioselectivity of the polymerization was given.…”

Organocatalyzed ring-opening copolymerization of α-bromo-γ-butyrolactone with ε-caprolactone for the synthesis of functional aliphatic polyesters – pre-polymers for graft copolymerization

“…Therefore, much effort has been conducted, as early as 1999, εCL with a halogenated motif at the γ-position was synthesized [22]. Subsequently, α-, γ- and ω-substituted εCL were synthesized and used as functional monomers for lipase-catalyzed ring-opening polymerization [23]. However, synthesis of functional monomers often involves multiple steps, which increase the cost and limit the application of aliphatic polyesters.…”