Synthesis Of Block Copolymer Nanoparticles With Different Topological Architectures By RAFT-mediated Dispersion Polymerization

Reversible addition-fragmentation chain transfer（RAFT）-mediated polymerization-induced self-assembly（PISA）has attracted considerable attention due to its significant advantages such as simple operation,high solids concentrations and directly preparation of block copolymer nanoparticles.Almost all macromolecular chain transfer agents（macro-CTAs）used in PISA are linear polymers,leading to the formation of linear block copolymers.In contrast,the use of non-linear macro-CTAs in RAFT-mediated PISA has rarely been reported.Many previous researchs have demonstrated that topological architectures of block copolymers have significant effects on the self-assembly process and morphologies of the formed self-assembled nano-objects.In this thesis,macro-CTAs with different topological architectures were used to prepare a series of block copolymers with different topological architectures.The PISA behavior of these block copolymers was also investigated in detail.The main results of the research are as following:1.Photoinitiated polymerization-induced self-assembly（Photo-PISA）has emerged as an efficient and facile method for the preparation of linear block copolymer nanoparticles.However,light penetration is an important issue that should be addressed,which may limit the application of Photo-PISA on a large scale.Herein,aqueous photoinitiated RAFT dispersion polymerization of 2-hydroxypropyl methacrylate（HPMA）in a flow reactor was investigated using a RAFT agent-functionalized poly（ethylene glycol）monomethyl ether as macro-CTA in the presence of glucose oxidase（GOx）and glucose.The polymerization kinetics was investigated in detail with different concentrations of GOx.In the absence of GOx,It was found that the final monomer conversion was low,which can be attributed to the oxygen-inhibition.As increasing the concentration of GOx,the polymerization rate was increased gradually.When the concentration of GOx was 0.5 μmol/L or higher,100%monomer conversion could be achieved within 30 min,exhibiting excellent oxygen-tolerant properties.Gel permeation chromatography（GPC）results indicated that good RAFT control was maintained in the enzyme-assisted Photo-PISA in a flow reactor.Effects of reaction conditions（monomer concentration,degree of polymerization（DP）of PHPMA and reaction temperature）on morphologies of block copolymer nanoparticles were investigated,and corresponding morphological phase diagrams were constructed.Moreover,it was found that the addition of nonfunctionalized mPEG to the polymerization system could promote the formation of higher-order morphologies.The small diameter of the pipe in the flow reactor makes light irradiation of the reaction mixture relatively uniform,which solves the light penetration problem in Photo-PISA and provides a new method for the continuous preparation of linear block copolymer nanoparticles with different morphologies at room temperature.2.Segmented hyperbranched macro-RAFT agents were synthesized by self-condensing vinyl polymerization（SCVP）by using R-type or Z-type CTM.These macro-RAFT agents were then used to mediate RAFT-mediated dispersion polymerization of styrene（St）in methanol/water（80/20,w/w）at 70 ℃,allowing the synthesis and in situ self-assembly of amphiphilic segmented hyperbranched block copolymers（SHBCs）.The results showed that colloidally stable SHBC assemblies with well-defined morphologies were obtained by RAFT-mediated dispersion polymerization using Z-type macro-RAFT agents.Compared with the corresponding linear Z-type macro-RAFT agent,higher-order morphologies were more likely to form in the case of SHBCs（synthesized by using the Z-type segmented hyperbranched macro-RAFT agent）.Linear branches could be cleaved from SHBCs（synthesized from using Z-type macro-RAFT agents）by removing the trithiocarbonate groups via 1-hexanamine,providing proof of the segmented branched structure.A series of macro-RAFT agents were also synthesized by using a binary mixture of R-type and Z-type CTMs.The ratio of solvophobic block in the inner and periphery of SHBC was controlled by changing the ratio of the Z-type CTM and the R-type CTM,allowing the control over PISA behaviors.Finally,a CTM was also added into the RAFT-mediated dispersion polymerization to further tune structures of SHBCs and morphologies of SHBC assemblies.3.Core cross-linked star（CCS）polymers were first synthesized by heterogeneous RAFT polymerization.The CCS polymers were then used as macro-CTAs in aqueous Photo-PISA of HPMA to prepare a series of CCS block copolymer nanoparticles.The Photo-PISA exhibited a high polymerization rate with 100% monomer conversion being achieved within 1 h.TEM results showed that spherical CCS block copolymer nanoparticles with rough surface were formed.Sizes of the CCS block copolymer nanoparticles were increased gradually as increasing DPs of PHPMA.Finally,the morphology of CCS block copolymer nanoparticles was further controlled by changing the reaction temperature.It was found that non-spherical morphologies were likely to form at high reaction temperatures.