Branched polyesters from radical ring-opening polymerization of cyclic ketene acetals: synthesis, chemical hydrolysis and biodegradation

Herein, we report a new synthetic route to the cyclic ketene acetal, 2-methylene-4-methyl-1,3-dioxepane (Me-MDO) as a way to expand the tool box of synthesis procedures for cyclic ketene acetals and actualize them as realistic alternatives for synthesizing biodegradable polymers. In this work, 2-methylene-1,3-dioxepane (MDO) and Me-MDO were polymerized by radical ring-opening polymerization to synthesize degradable polyesters. NMR and SEC were used to monitor the polymerization while DSC was used to study the thermal properties. Poly(2-methylene-1,3-dioxepane) (PMDO) showed increased degree of branching with higher conversion, subsequently decreasing crystallinity. The effect of branching and the introduction of side-groups on the chemical hydrolysis rate and biodegradability of the polyesters was assessed using a chemical hydrolysis test and the OECD 301D ready biodegradability screening test, respectively. A significant reduction in the chemical hydrolysis rate and biodegradability was observed upon the introduction of a side group in the poly(2-methylene-4-methyl-1,3-dioxepane) (PMe-MDO) polyester. Less obvious effects on the hydrolysis rate and biodegradability were observed as a result of the polyester branching.