Radical ring-opening polymerization of five-membered cyclic ketene acetals with the tetraleucine macromonomer toward preparation of self-assembling peptide-grafted polyesters

Abstract

The development of sustainable polymer materials, such as biodegradable aliphatic polyesters and natural polymers, has recently become an important issue because of the environmental impact of plastic waste. In this study, we demonstrate the novel synthesis of self-assembling peptide-grafted polyesters. The graft copolymers were prepared via radical ring-opening copolymerization of 2-methylene-1,3-dioxolane (C5), a five-membered cyclic ketene acetal, and tetraleucine peptide macromonomers (MA-Leu4-Am) with various feed compositions, and their structures were characterized by ¹H NMR, SEC, and FT-IR analyses. The ring-opening ratio (R_op) of C5 units was almost constant at 70–85% regardless of the feed compositions. In contrast, the values of the grafting ratio of the peptide chain (G_r) were remarkably higher than the values calculated from the feed composition of C5 and MA-Leu4-Am (G_r,feed), reflecting their monomer reactivities. To characterize the copolymerization behavior in detail, density functional theory (DFT) calculations were performed to elucidate the copolymerization mechanisms. These calculations demonstrated that radicals derived from C5 preferentially react with the peptide macromonomer, which was supported by the calculated reaction rate constants and monomer reactivity ratios.