Radical Ring Opening Polymerization of Cyclic Ketene Acetals Derived From d-Glucal

Abstract

A cyclic ketene acetal (CKA) derived from d-glucal was synthesized, and its polymerization using free radicals has been investigated. NMR analysis of the resulting polymers revealed the formation of polyacetal–polyester copolymers, with up to 78% of ester linkages formed by radical ring-opening polymerization (rROP). Conversely, the polymerization of the monomer-saturated analogue only produced acetal linkages, demonstrating that the alkene functionality within the d-glucal pyranose ring is essential to promote ring-opening and ester formation, likely via the stabilization of an allyl radical. The thermal properties of the polymers were linked to the ratio of the ester and acetal linkages. Copolymerization with methyl methacrylate (MMA) afforded statistically PMMA-rich copolymers (66–98%) with linkages prone to hydrolytic degradation and decreased glass-transition temperatures. The retention of the pseudoglucal alkene function offers opportunities to functionalize further these bioderived (co)­polymers.

Quantitative, Regiospecific, and Stereoselective Radical Ring-Opening Polymerization of Monosaccharide Cyclic Ketene Acetals

“…Cyclic ketene acetals (CKAs) are one of the most extensively studied monomer classes for the synthesis of degradable polymers thanks to their ability to introduce degradable ester groups into the polymer backbone via radical ring-opening polymerization (rROP). − , Despite the pioneering works by Bailey et al, Dove et al, − Nicolas et al, − Sumerlin et al, , and others, − , existing CKAs still suffer from two major limitations: (1) the ring-retaining side reaction that leaves nondegradable motifs in the polymer backbone and (2) low reactivity in the copolymerization with vinyl monomers, which leads to uneven incorporation and necessitates a high feeding ratio of CKA (Figure A). For example, in a recent example reported by Buchard et al, 50% CKA in the feed was needed to achieve 11.9% incorporation of the ester group, with 21.1% nondegradable motifs derived from ring-retaining side reactions of the CKA also incorporated in the resulting polymer.…”