Degradation of poly(vinyl sulfone carbonate) in aqueous media

Abstract

A cyclic vinyl sulfone carbonate monomer has previously been developed and used to prepare degradable polymers through ring-opening copolymerization with cyclic ester monomers such as L-lactide. The resulting polymers have the advantage of being functionalized by reaction of the pendant vinyl sulfone moiety. However, the hydrolytic susceptibility of repeating units of the vinyl sulfone carbonate was never examined. Herein, we demonstrate that block copolymers prepared with this monomer and using methoxy poly(ethylene glycol) and 4-arm poly(ethylene glycol) as initiators are readily hydrolysable in micelle form in pH 7.4 phosphate buffer, whereas non-water soluble poly(vinyl sulfone carbonate) is resistant to hydrolysis, exhibiting little mass loss over 32 weeks. A degradation mechanism was proposed for the block copolymer micelles wherein the backbone carbonate linkage is susceptible to nucleophile attack by a hydroxyl ion due to the metal ion coordinating with the pendant thioether-vinyl sulfone group allowing access of hydroxyl ions to the carbonyl carbon of the carbonate group. The non-water soluble poly(vinyl sulfone carbonate) is only very slowly hydrolyzed due to restricted water access to the polymer backbone. Further, the block copolymers remained hydrolytically degradable following reaction of the pendant vinyl sulfone. These findings should prove useful for the broader application of this monomer in developing functionalized biodegradable polymers.