Preparation Of Block Copolymer Nanomaterials Based On RAFT-mediated Emulsion Polymerization

Block copolymer nanomaterials have been widely used due to their unique structures and properties.The recent development of polymerization-induced self-assembly（PISA）allows the preparation of block copolymer nanomaterials with different morphologies at high concentrations.In particular,reversible addition-fragmentation chain transfer（RAFT）-mediated PISA provides a powerful method to efficiently prepare block copolymer nanomaterials with precise composition and functionality.As one of the most studied heterogeneous polymerizations,RAFT-mediated emulsion polymerization has been widely used for the preparation of block copolymer nanomaterials due to its tolerance toward various monomers,high polymerization rate,low viscosity,simple procedure and nanoconfinement effect.However,spherical polymeric nanomaterials were obtained in most RAFT-mediated emulsion polymerization.It was found that the aqueous solubility of monomers and the glass transition temperature of polymers are two key factors that affect the formation of higher-order morphologies during RAFT-mediated emulsion polymerization.Although significant progress has been made in RAFT-mediated emulsion polymerization,mechanistic investigations of RAFT-mediated emulsion polymerization have rarely been reported.In this thesis,we will focus on the mechanistic investigations of RAFT-mediated emulsion polymerization from the following three aspects:1.Currently,almost all RAFT-mediated emulsion polymerizations focus on the preparation of linear block copolymer nanomaterials.However,in situ preparation of cross-linked block copolymer nanomaterials by RAFT-mediated emulsion polymerization has rarely been reported.Cross-linked block copolymer nanomaterials such as worms and vesicles were prepared by redox-initiated RAFT-mediated emulsion polymerization of glycidyl methacrylate（GlyMA）mediated by poly（poly（ethylene glycol methyl ether methacrylate））（PPEGMA）-based macro-RAFT agents using cross-linkers with different water solubility,symmetry,and number of functional groups.The effect of different cross-linkers on the polymerization kinetics of RAFT-mediated emulsion polymerization and the morphology of block copolymer nanomaterials were investigated.It was found that the use of symmetric cross-linker could promote the formation of higher-order morphologies,while the use of asymmetric cross-linkers could maintain the morphology.When using hydrophobic cross-linkers,the cross-linker along with monomer diffuses from monomer droplets to micelles gradually.When using hydrophilic cross-linkers,the cross-linker is prone to stay in water rather than diffuse into hydrophobic micellar cores.Polymerization kinetics and ~1H NMR analysis confirms the consumption behavior of cross-linker and monomer in RAFT-mediated emulsion polymerization.2.Currently,the preparation of AB diblock copolymers using monofunctional macro-RAFT agents dominates the research of RAFT-mediated emulsion polymerization,while the effects of macro-RAFT agents with reactive end groups on RAFT-mediated emulsion polymerization have not yet been reported.The effect of reactive end groups of the macro-RAFT agents on the redox-initiated RAFT-mediated emulsion polymerization of GlyMA（morphologies of block copolymer nanomaterials and the polymerization process）was investigated by using three macro-RAFT agents with different reactive end groups.The results showed that the use of bifunctional macro-RAFT agents with reactive end groups could promote the formation of higher-order morphologies.Kinetic studies showed that high monomer conversions（>97%）and good RAFT control were achieved in all cases.Gel permeation chromatography（GPC）results indicated that higher block efficiency could be achieved by using a symmetric bifunctional macro-RAFT agent.Finally,the large number of unreacted RAFT end groups on the surface of worms provide a landscape for grafting poly（N-isopropyl acrylamide）（PNIPAM）.The obtained PNIPAM-grafted worms exhibited reversible thermo-responsive property.3.The current research on RAFT-mediated emulsion polymerization mainly focuses on the synthesis of block copolymers with narrow molecular weight distributions.In contrast,the control over molecular weight distribution of block copolymers by RAFT-mediated emulsion polymerization has rarely been reported.The effect of reaction temperature on molecular weight distrbutions of block copolymers prepared by photoinitiated RAFT-mediated emulsion polymerization was studied.It was found that molecular weight distributions of block copolymers became narrower as increasing the reaction temperature.The effect of ethanol/water ratios on molecular weight distributions of block copolymers was further investigated.It was found that molecular weight distributions of block copolymers became narrower as increasing ethanol/water ratios.The evolution of molecular weight distributions of multiblock copolymers synthesized by photoinitiated seeded RAFT polymerization was also studied.In addition,effects of the degree of polymerization of the core-forming block,reaction temperature,and ethanol/water ratio on morphologies of block copolymer nanomaterials were investigated,and corresponding morphological phase diagrams were constructed.It was found that increasing the degree of polymerization of the core-forming block,reaction temperature or water/ethanol ratio could promote the formation of higher-order morphology.