Incorporation of disulfide bonds into polymer backbones is an effective strategy for the synthesis of degradable polymers. In this research, controlled synthesis of degradable lipoate-vinyl copolymers by xanthate-mediated reversible addition–fragmentation chain transfer (RAFT) polymerization is investigated. Lipoates, including methyl lipoate (LpMe), butyl lipoate (LpBu), and benzyl lipoate (LpBz), are copolymerized with a series of vinyl ester monomers and N-vinyl monomers. Vinyl acetate (VAc) is used as a typical vinyl ester monomer for the RAFT copolymerization with LpMe. The polymerization kinetics study demonstrates that the xanthate-mediated RAFT system enables the controlled copolymerization of VAc and LpMe. The monomer reactivity ratios of LpMe (rLpMe) and VAc (rVAc) are calculated to be around rLpMe = 10.75 and rVAc = 0.19. Similarly, N-vinylformamide (NVF) is used as a typical N-vinyl monomer for xanthate-mediated RAFT copolymerization with LpMe. The polymerization kinetics study demonstrates the controlled synthesis of P(NVF-co-LpMe) copolymers. The monomer reactivity ratios of LpMe (rLpMe) and NVF (rNVF) are determined as rLpMe = 5.32 and rNVF = 0.19, demonstrating the ideal copolymerization behavior. Furthermore, xanthate-mediated RAFT copolymerizations are carried out between lipoates and a variety of vinyl ester monomers or N-vinyl monomers, and copolymers with low dispersities are synthesized. In addition, the xanthate-mediated RAFT strategy affords well-defined degradable diblock copolymers (DBCPs) with LpMe units in one or both block backbones. The successful synthesis and degradation of the DBCPs are confirmed by 1H NMR and size-exclusion chromatography.
Liu et al. (Mon,) studied this question.