Preparation Of Block Copolymer Nano-objects Via Aqueous Enzyme-catalyzed Polymerization-induced Self-assembly

In recent years,the development of polymerization-induced self-assembly（PISA）method based on reversible addition-fragmentation chain transfer polymerization（RAFT）allowed the large-scale preparation of polymer nano-objects with different morphologies and has attracted extensive attention.However,most PISA formulations are initiated by thermal initiation,which is not beneficial for the preparation of thermo-sensitive or bio-related polymer nano-objects.Enzyme catalysis controlled/”living”radical polymerization is a new developed technology that has several advantages including high rate of polymerization,mild reaction conditions,high selective ability and oxygen tolerance,which is particularly beneficial for the preparation of new polymer materials.The combination of enzyme catalysis with PISA will greatly expand the scope of PISA for overcoming the current problems of PISA and provided a new strategy for the preparation of novel polymer nano-objects.In this thesis,a series of polymer nano-objects with different morphologies are synthesized by enzyme-catalyzed RAFT dispersion polymerization.The applications of the obtained polymer nano-objects are explored.The main contents are as follows:1.Peroxide horseradish enzyme（HRP）was used as the catalyst to initiate RAFT dispersion polymerization in water at room temperature to synthesize poly（ethylene glycol monomethyl ether）-b-poly（2-hydroxypropyl methacrylate）(mPEG₁₁₃-PHPMA)diblock polymer nano-objects.Kinetic studies show that rate of polymerization is high with more than99%monomer conversion being achieved within 30 min.GPC measurement demonstrated that good control was maintained during the polymerization process.A phase diagram was constructed by varying the degree of polymerization（DP）of PHPMA and monomer concentration,which is important for reproducible preparation of well-defined polymer nano-objects.By adding SiO₂ nanoparticles/bovine serum proteins（BSA）at the beginning of the enzyme catalyzed RAFT dispersion polymerization,SiO₂ nanoparticles or BSA-loaded polymer vesicles were prepared.Taking advantage of the room temperature feature of enzyme catalyzed RAFT dispersion polymerization,pure worm-like micelles could be readily prepared by monitoring the viscosity of the reaction mixture.Using the glucose oxidase（GOx）-HRP cascade catalysis,the RAFT dispersion polymerization could be conducted in open vessels at different volumes（including 96-well plates）.GPC measurement and kintic studies demonstrated that good control was still maintained and polymer nano-objects with different morphologies（including spheres,worms,vesicles）could be prepared.2.Using HRP as the catalyst,poly（glycerol monomethacrylate）-b-poly（2-hydroxypropyl methacrylate）（PGMA-PHPMA）diblock copolymer vesicles were first prepared via enzyme-initiated aqueous RAFT dispersion polymerization at 32℃,and subsequently served as seeds for the chain extention of glycidyl methacrylate（GlyMA）via enzyme-initiated seeded RAFT emulsion polymerization.Framboidal triblock copolymer vesicles were obtained due to the insolubility between PGlyMA and PHPMA.Since the enzyme-initiated aqueous RAFT polymerization was carried out at a lower temperature,more than 97%of the epoxy groups were retained after polymerization and it still contains about 80%of the epoxy groups after 45days.Due to the strong hydrophobicity of PGlyMA,the morphology of PGMA-PHPMA-PGlyMA triblock copolymer vesicles can be maintained in the SDS surfactant aqueous solution.The triblock polymer vesicles were further used as Pickering emulsion stabilizers to obtain stable hexane in water Pickering emulsion.Finally,the cross-linked triblock copolymer vesicles were prepared by the reaction of epoxy group with ethylene diamine,and the silver nanoparticles were loaded on cross-linked vesicles which were then tested for catalytic performance.3.Through catalytic deoxygenation with GOx enzyme,a series of cross-linked poly（glycerol monomethacrylate）-b-poly（（2-hydroxypropyl methacrylate）-co-（2-（dimethylamino）ethyl acrylate）-co-（methylacrylate allyl））（PGMA-b-（PHPMA-co-PDMAEMA-co-PAMA））polymer vesicles with CO₂-response characteristic were prepared via photo-initiated aqueous RAFT dispersion polymerization.By regulating the content of DMAEMA,the swelling degree of copolymer vesicles treated with CO₂ can be controlled.In order to maintain the integrity of the swollen vesicular membrane with high PDMAEMA content,the cross-linking degree of copolymer vesicles were adjusted.Exploring the CO₂response behavior of vesicles,it was found that the swelling equilibrium was reached within5 min,and the controllable transformation of the swelling/recovery state of polymer vesicles can be achieved by cyclic purging with CO₂/N₂.The polymer vesicles were further used as Pickering emulsion stabilizer and toluene in water Pickering emulsion with uniform particle size was obtained.By adding diisocyanate crosslinking agent to the oil phase,the vesicles can be cross-linked on the surface of the emulsion droplets to form polymer capsule.After the centrifugal separation,the polymer capsule was then used for adsorption of the dye.