The Synthesis And Propersties Of Stimulus-responsive Polymers

The research on the polymers with stimulus-responsive behavior is one hot topic in recently years. The combination of living polyemrizaiton with some high efficient chemistry reaction could easily synthesize the well-defined stimulus-response polymers. The totally hydrophilic polymer and intelligent hydrolgel have the potiential to be used in drug delivery system due to their excellent biocompatibility. Based on the research of the precursors, this dissertation describes the synthesis and application of stimulus-response polymer. The main results of this thesis are as follows.1. Well-defined dually responsive block-brush copolymer of poly(ethylene glycol)-b-[poly(N-isopropylacrylamide)-g-poly(N,N-dimethyl-aminoethyl methacrylate)], [PEG-b-P(NIPAM-g-PDMAEMA)] was successfully prepared by the combination of atom transfer radical polymerization (ATRP) and click chemistry based on azide-capped PDMAEMA and alkyne-pending PEG-b-PNIPAM copolymer. Azide-capped PDMAEMA was synthesized through ATRP of DMAEMA monomer using an azide-functionalized initiator of azidoethyl 2-bromoisobutyrate. Alkyne-pending PEG-b-PNIPAM copolymer was obtained through ATRP copolymerization of NIPAM with propargyl acrylate. The final block-brush copolymer was synthesized by the click reaction between these two polymer precursors. Because of characteristics of three different blocks, the copolymer exhibited dually thermo- and pH-responsive behavior. The dually responsive behaviors of block-brush copolymer were studied by laser light scattering, temperature-dependent turbidity measurement and micro-differential scanning calorimetry. The phase transition temperature increased with the decrease of pH value, and the copolymer displayed weak thermo-responsive behavior at low pH, due to the formation of intra-molecular micelles. In basic and neutral solution, the block-brush copolymer aggregated into the micelles during the phase transition above their low critical solution temperature.2. Reducibly degradable hydrogels of poly(N-isopropylacrylamide) (PNIPAM) and poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) were synthesized by the combination of reversible addition-fragmentation chain transfer (RAFT) polymerization and click chemistry. The alkyne-pending copolymer of PNIPAM or PDMAEMA was obtained through RAFT copolymerization of propargyl acrylate with NIPAM or DMAEMA. Bis-2-azidyl-isobutyrylamide of cystamine (AIBCy) was used as the crosslinking reagent to prepare reducibly degradable hydrogels by click chemistry. The hydrogels exhibited temperature or pH stimulus-responsive behavior in water, with rapid response, high swelling ratio and reproducible swelling/shrinkage cycles. The loading and release of ceftriaxone sodium proved the feasibility of the hydrogels as the stimulus-responsive drug delivery system. Furthermore, the presence of disulfide bond in AIBCy favored the degradation of hydrogels in the reductive environment.