Preparation Of Stimuli-responsive Block Copolymer Assemblies By Photoinitiated Polymerization-induced Self-assembly

Stimuli-responsive block copolymer assemblies can exhibit mutations in certain physical or chemical properties conditions（e.g.photo,p H,temperature,etc.）,which have attracted widespread attention for a variety of applications such as drug delivery,sensor,hydrogels,and so on.Stimuli-responsive block copolymer assemblies are mainly prepared by self-assembly methods such as solution self-assembly,and there are problems such as low solid content（<1%）and the need for post-treatment,which limits its large-scale preparation.In recent years,our group has developed photoinitiated polymerization-induced self-assembly（Photo-PISA）mediated by reversible addition-fragmentation chain transfer（RAFT）.Photo-PISA provides a new method for the efficient and controllable preparation of stimuli-responsive block copolymer assemblies due to its ease of operation,mild reaction conditions,fast polymerization speed,and high solids content（up to 50%w/w）.In this thesis,we focus on the efficient and controlled preparation of stimuli-responsive block copolymer assemblies by photo-PISA.Block copolymer assemblies with thermal-responsive,oxidation-responsive,and reduction-responsive are efficiently prepared by using different molecular designs,and stimuli-responsive behaviors of assemblies are explored in detail.The primary research results are as follows:1.To solve the problem of low productivity for PNIPAM thermal-responsive assemblies,thermal-responsive block copolymer assemblies with morphologies of spheres,worms,and vesicles are rapidly prepared by aqueous Photo-PISA of NIPAM,and polymerizations in all cases are achieved within 60 minutes.Assemblies with different structures such as spheres,worms,and vesicles can be obtained.Morphologies of assemblies can be regulated by changing reaction temperature,degree of polymerization for macro-CTA,degree of polymerization for PNIPAM,amount of crosslinking agent,and solids content.The influence of different reaction conditions on the morphologies of assemblies is also studied in detail.The obtained thermal-responsive block copolymer assemblies can be further surface-modified by seeded dispersion polymerization,and the thermal-responsive block copolymer assemblies with different surface charges can be prepared.Finally,these thermal-responsive block copolymer assemblies can be used as fillers for hydrogels,and the tensile fracture properties of hydrogels can be tuned by changing the addition amount of assemblies and reaction temperature.2.Taking advantage of the mild reaction conditions and fast polymerization speed of aqueous Photo-PISA,PNIPAM block copolymer vesicles loaded with enzyme are efficiently prepared,and enzymatic activities of enzyme-loaded vesicles at different temperatures are also explored.Enzyme-loaded poly（ethylene glycol monomethyl ether mesylate）-poly（2-hydroxypropyl methacrylate）（m PEG-b-PHPMA）vesicles are prepared by photo-PISA,and then the third block of PNIPAM is introduced to the vesicles by seeded Photo-PISA to obtain thermal-responsive enzymatic nanoreactors.Since PNIPAM exhibits mutations in hydrophilic/hydrophobic properties near the lower critical solution temperature（LCST）,the membrane permeability of the enzymatic nanoreactor can be regulated by changing the temperature,thereby regulating the enzymatic reaction rate of the nanoreactor.By adding N,N-dimethylacrylamide（DMA）,or diacetone acrylamide（DAAM）to the seeded Photo-PISA for copolymerization with NIPAM,the LCST of the third block can be changed to synthesize enzymatic nanoreactors with a different phase transition temperature.Finally,an enzyme-loaded non-crosslinked nanoreactor is prepared,and the morphology of the nanoreactor can change at a low temperature so that the enzyme can be released from the nanoreactor and the enzymatic reaction efficiency can be significantly improved.3.Using a monomer containing a thioether group（methylthioethyl methacrylate（MTEMA））,block copolymer vesicles with a thioether group are efficiently prepared by Photo-PISA or seed Photo-PISA,imparting the oxidation-responsive property to vesicles.When MTEMA is introduced into the nucleating block by copolymerization,the increase in MTEMA ratio restricted the formation of vesicle morphology,and the obtained vesicles are difficult to exhibit morphology transformation under oxidative conditions.When MTEMA is introduced into the block copolymer vesicles by seed Photo-PISA as a third block,framboidal vesicles are obtained due to the separation of PMTEMA from the second block.Oxidation-responsive behaviors of triblock framboidal vesicles are investigated in detail,PMTEMA₂₀₀and PMTEMA₃₀₀framboidal vesicles can exhibit morphological transformation after hydrogen peroxide treatment.Kinetic studies show that the seeded Photo-PISA can achieve 100%conversion of monomers within 15 min.Oxidation-responsive triblock framboidal vesicles loaded with silica nanoparticles are successfully prepared.Under the treatment of hydrogen peroxide,silica-loaded triblock framboidal vesicles can exhibit the vesicle-to-worm morphology transition,allowing the release of loaded silica nanoparticles.Finally,the application of triblock framboidal vesicles in Pickering emulsions is also explored,and the results showed that the framboidal vesicles can be used as efficient emulsifiers to stabilize Pickering emulsions.4.Two macro-CTAs containing disulfide bonds,m PEG₁₁₃-SS-CEPA and m PEG₄₅-SS-DDMAT are synthesized,and a series of block copolymer assemblies with different morphologies are prepared by aqueous Photo-PISA and alcohol-phase thermal-initiated PISA.Solvophilic blocks and solvophobic blocks of assemblies are connected by a disulfide bond.Assemblies can exhibit reduction-responsive property.Assemblies morphology can be regulated by changing the monomer concentration,and degree of polymerization for solvophobic blocks.A detailed morphological phase diagram is drawn.The polymerization process of Photo-PISA using m PEG₁₁₃-SS-CEPA as a macro-RAFT agent is explored.The kinetic study showed that full monomer conversion can be achieved within 16 min.GPC traces confirm that reaction had control-living polymerization characteristics.After treatment with a reductant,the solvophilic block of assemblies can be cleaved.Assemblies are prepared by simultaneously using a disulfide-linked macro-RAFT agent(m PEG₁₁₃-SS-CEPA)and disulfide-free macro-RAFT agent(m PEG₁₁₃-CEPA),the reduction-responsive behavior of assemblies can be regulated by adjusting the ratio of two macro RAFT agents.