Controlling the synthesis of degradable vinyl polymers by xanthate-mediated polymerization

The copolymerization of vinyl acetate (VAc) and 2-methylene-1,3-dioxepane (MDO), as well as the homo-polymerization of MDO in the presence of a p-methoxyphenyl xanthate chain transfer agent (CTA) is reported and comparison of the homopolymerization of MDO with other known xanthates was also investigated. In depth investigation showed loss of the xanthate functionality was a result of Z-group fragmentation leading to the formation of carbonodithioate groups, as confirmed by C-13 NMR spectroscopy. The use of the xanthate with a substituted phenyl Z-group drastically reduces fragmentation through the Z-group and hence significantly increases chain-end retention during the polymerization using the RAFT/MADIX technique. Post-polymerization modification of the chain-end of poly(MDO) was achieved by in situ aminolysis and base-catalyzed Michael addition of propargyl methacrylate onto the terminal thiol to form alkyne functional poly(MDO).