Preparation Of Triblock Copolymer By RAFT Polymerization And Its Application In UV-Controlled Drug Delivery Emulsion System

Photodegradable block copolymers have the ability to respond to external stimuli and self-assemble in selective solvent and thus have a broad application prospect in smart materials,especially in controlled release drug delivery system.The Reversible Addition-Fragmentation Chain Transfer polymerization(RAFT)offers approaches to synthesize polymers with complex structure and multiple function,and make it possible to controll the structure and photodegradation behaviors of photodegradable polymers.In RAFT polymerization,tail-type radicals produced by head addition of monomers will react with RAFT agents to produce non-active RAFT agents(DDS),leading to impurity and the decrease of block efficiency.In this article,gradient polymer elution chromatography(GPEC)and RAFT block chain extension reaction were combined to investigate this side reaction in the RAFT system of acrylate.The mathematical relationship between the content of DDS and polymerization parameters,like the incidence of head addition,degree of polymerization,conversion and chain transfer constant of RAFT agents to tail-type radicals,was deduced based on the kinetic model of RAFT polymerization.The benzyl N-carbazolecarbodithioate(BCBD),which has specific UV absorption,was chosen as RAFT agent to mediate the RAFT polymerization of benzyl acrylate(BzA),and the PBzA-BCBD was chain-extended with methyl acrylate(MA).The homopolymers were separated from block copolymers by GPEC,and the existence and content of DDS was determined by UV absorption,~1H NMR and MS.By changing the polymerization degree of PBzA,the incidence of head addition of BzA is estimated to be 0.14%.Based on the photodegradation ability of PVK,amphiphilic triblock copolymers PDMAEMA-PPVK-P(2-EHA)were prepared by RAFT polymerization using dimethylaminoethyl methacrylate(DMAEMA)and 2-ethylhexyl acrylate(2-EHA)as hydrophilic and hydrophobic monomers,respectively.And their application in the emulsion with photo-controlled drug release character was investigated.The degradation behaviors of PPVK and poly((4-methoxyl)phenyl vinyl ketone)(PMPVK)was compared and concluded that the degradation rate of PPVK is faster than PMPVK.Ethyl oleate was employed as oil phase to prepare an environmental-friendly W/O emulsion using PDMAEMA-P(2-EHA)as emulsifier,and the influences of volume ratio of oil and water,the structure and dosage of emulsifier and the pH of water phase on stability of emulsion were investigated.The results show that the emulsion can achieve good stability under the condition that the volume ratio of O/W is 2:1,the polymerization degree ratio of hydrophilic/hydrophobic segments of the block copolymer is 1:5,the dosage of block copolymer is 0.03 g/mL and the p H of water phase is 5.Later on,PDMAEMA-PPVK-P(2-EHA)was employed to prepare photosensitive emulsions,and the influence of the type of photodegradable polymers,the chain length of photodegradable segments and the dosage of emulsifier on the demulsification rate and drug release rate was investigated.The rate of demulsification and drug release was proved to increase by lengthening photodegradable chain length and decrease by raising emulsifier dosage.These results provide guidance for the preparation of photosensitive emulsion and drug release system of glyphosate.