SYNTHESIS OF REDUCTIVELY DEGRADABLE COMB-LIKE CATIONIC POLYMER

A reductively degradable cationic polymer with comb-like architecture was synthesized by a combination of polycondensation and reversible addition and fragmentation chain transfer radical polymerization (RAFT). First, the direct polycondensation of decanediol, 3, 3'-dithiodipeopionic acid and malic acid was carried out using scandium triflate as catalyst. Due to the chemoselectivity of scandium triflate for esterification, the secondary hydroxyl groups of malic units were not esterified during the polycondensation process,resulting in functional polyester with numerous disulfide bones and hydroxyl groups. Then the pendant hydroxyl groups were modified into dithioester form in the presence of N,N'-dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP),to give a macromolecular chain transfer agent, which could be used as multifunctional backbone to prepare comb-like polymer by "grafting from" method. Finally, the poly (2-(dimethylamino) ethyl methacrylate) (PDMAEMA) side chains were attached to the backbone via RAFT polymerization of 2-(dimethylamino) ethyl methacrylate. The comb-like architecture of the copolymer was characterized by H-1-NMR and GPC. The reducible degradation of the comb-like polycation was studied in the presence of tributylphosphane as reducing agent, which demonstrated the cleavage of disulfide bonds in the backbone under reductive environment, resulting in low molecular weight PDMAEMA oligomers. This comb-like cationic polymer may have potential applications in gene delivery, which is being investigated in our research group.