Thioester-rich degradable copolymers from a thionolactone and S-vinyl and P-vinyl monomers

The recent advent of the radical thiocarbonyl addition–ring-opening (TARO) copolymerization of thionolactones with vinyl monomers enables the production of degradable thioester backbone-functional vinyl copolymers promising for recycling and biomedical applications. To better understand the copolymerization behaviour of the prototypical thionolactone, dibenzo [c,e]oxepin-5(7H)-thione (DOT), copolymers with three S- and P-vinyl comonomers, phenyl vinyl sulfide (PVS), phenyl vinyl sulfone (PVSO), and diethyl vinylphosphonate (DEVP) were prepared through free and RAFT radical polymerizations. In all cases, DOT was incorporated faster than the vinyl comonomers which led to copolymers with up to 89 mol-% DOT content—surprising in light of past reports of significant retardation for high DOT feeds. All copolymers proved readily degradable. A postpolymerization oxidation enabled the conversion of a DOT–PVS copolymer into a corresponding DOT–PVSO species that remained degradable and offered a synthetic strategy to prepare copolymers with compositions not accessible through a direct copolymerization.