| Controlled/living radical polymerization(CLRP)is an effective way to synthesize polymers with tailored structures,such as block copolymers.Halogenated monomers like vinyl chloride(VC)and vinylidene fluoride(VDF)are less active monomers,and chain transfer to monomer is prominent in VC polymerization,and few methods could be used for CLRP of both halogenated monomers and hydrophilic monomers.It is still a challenge for the CLRP of VC and VDF,as well as the synthesis of amphiphilic block copolymers containing PVC or PVDF blocks and hydrophilic blocks.Thus,studies on the structures and performances of PVC and PVDF based amphiphilic block copolymers are rare.In this thesis,the reversible addition-fragmentation chain transfer(RAFT)polymerizations of VC mediated by xanthates were proposed,and synthesis of block copolymers of poly(vinyl chloride)-b-poly(vinyl acetate)(PVC-b-PVAc),poly(vinly chloride)-b-poly(vinyl alcohol)(PVC-b-PVA)and poly(vinyl chloride)-b-poly(ethylene glycol)-b-poly(vinyl chloride)-b-poly(vinyl chloride)(PVC-b-PEG-b-PVC),and poly(vinylidene fluoride)-b-poly(N-vinylpyrrolidone)(PVDF-b-PVP)were investigated.Furthermore,effects of amphiphilic block copolymers of PVC-b-PVA,PVC-b-PEG-b-PVC and PVDF-b-PVP on the permeation and antifouling performances of PVC or PVDF microfiltration membrane were investigated.Firstly,a xanthate RAFT agent(XI)with leaving group of perflurinated octanol propionic ester was designed and synthesized.The living character and RAFT mechanism of X1 mediated VC polymerization were confirmed by density function theory calculation,kinetics investigation,structure analysis of PVC by nuclear magnetic resonance and matrix assisted laser desorption ionization time of flight mass spectrum.The effect of polymerization ways and X1 concentration on the kinetics of polymerization were investigated.It was found that polymerization rates of miniemulsion and suspension polymerization were greater than that of solution polymerization,with final monomer conversion above 85%.Both the final monomer conversion and polymerization rates of VC miniemulsion and suspension polymerizations were independent on X1 concentration.Number average molecular weight(Mn)of PVC was increased with the increase of conversion,and decreased with the increase of X1 concentration.PVC synthesized by miniemulsion and suspension polymerization exhibited greater PDI than that of solution polymerization at close Mn,which could be attributed to the two phase(monomer-rich phase and polymer-rich phase)polymerization of miniemulsion and suspension polymerizations.PDI of PVC synthesized by miniemulsion polymerization was slightly greater than that of suspension polymerization,which could be attributed to the monomer diffusion between monomer droplets and desorption-adsorption of primary radicals in the monomer droplets in the miniemulsion polymerization.X1 was further used to control the RAFT miniemulsion polymerization of VAc,and living PVAc latex(PVAc-X)with small polydispersion index(PDI)(<1.20)could be obtained.The synthesis of PVC-b-PVAc copolymer were conducted by miniemulsion polymerization using both PVAc-X and living PVC latex as RAFT agents and "seeds" for the miniemulsion polymerization of VC or VAc.Since PVC-X could only be swollen by VAc,the VAc polymerization mediated by PVC-X was less controllable and exhibited samaller polymerization rates.Due to the solubility of PVAc-X in VC,the VC polymerization mediated by PVAc-X could be well controlled an achieved greater polymerization rates.With the increase of VC conversion,PVAc-b-PVC became less soluble in VC,and the polymerization system became heterogeneous,leading to the broadening of PDI of copolymers.PVAc-b-PVC copolymers with different block ratios exhibited micro-phase separation morphologies.After 48 h of acid hydrolysis,PVC-b-PVA copolymers with about 70%hydrolysis degree could be obtained.Secondly,PEG macro xanthate(X-PEG-X)was synthesized and used as RAFT agent to mediate the VC solution and suspension polymerizations,to synthesize PVC-b-PEG-b-PVC tri-block copolymer.Mn of copolymers synthesized by VC solution polymerization mediated by X-PEG-X were increased with the increase of polymerization time,with PDIs smaller than 1.65.X-PEG-X could be dissolved both in water and oil(partition ration 0.12:0.88)and decrease the interfacial tension between oil and water.Thus,X-PEG-X could act not only as RAFT agent,but also as the suspending astabilizer to achieve the self-stabilized suspension polymerization of VC.Mn of the resulted PVC-b-PEG-b-PVC copolymer was increased with the increase of polymerization time,and their PDIs were larger than that of solution polymerization.PVC-b-PEG-b-PVC copolymers exhibited micro-phase separation morphologies.Thirdly,iodine terminated(PVDF-I)was synthesized by iodine transfer polymerization(ITP)of VDF mediated with C6F13I,and used to mediate ITP of tert-butyl acrylate(tBA).Poly(vinylidene fluoride)-b-poly(acrylic acid)copolymer was obtained by the hydrolysis of as prepared PVDF-b-P(t-BA)copolymer.However,poly(acrylic acid)content in the block copolymer was low(about 5%).ITPs of VP mediated by PVDF-I were also conducted and it was confirmed by 1H and 19F NMR spectra that PVP blocks could be effectively inserted into PVDF-I,resulting the formation of PVDF-b-PVP copolymers.It was found that the insertion of PVP block would decrease the order of PVDF chain and change the crystal structure of PVDF from single a phase to the co-existence of a and ty phases in PVDF-b-PVP copolymers,and the crystallization temperatures and crystallinities of PVDF decreased with the increase of PVP content.PVDF-b-PVP copolymers exhibited small micro-phase separation size and good miscibility.Finally,PVC microfiltration membranes(MFs)modified by PVC-b-PVA and PVC-b-PEG-b-PVC copolymers,as well as PVDF MFs modified by PVDF-b-PVP block copolymers were frabicated by non-solvent induced phase separation:method.The effects of molecular structure and adding contents of these block copolymers on the morphologies,permeation and antifouling performances of MFs were investigated.It was found that adding of the above copolymers could improve the pore formation,the hydrophilicity,permeation and antifouling performances of MFs.Moreover,modification effect could keep longer than that of PVA,PEG and PVP homopolymers,respectively.PVC-b-PEG-b-PVC copolymer with low Mn(<7000)would be drained during membrane preparation due to their micelle formation feature.The best comprehensive modification effects were achieved when 30wt%PVC-b-PEG-b-PVC copolymer with Mn of 7070,or 20wt%PVC-b-PVA copolymer with Mn of 25000 and PVC/PVA block ratio of 80/20,was added in PVC casting solution(based on added polymer).PVC-b-PVA copolymer was more effective in improving the permeation and antifouling performance of PVC MFs than PVC-b-PEG-b-PVC copolymer at the close hydrophilic segment content in the casing solution.The best comprehensive modification effect was achieved when 30wt%PVDF-b-PVP copolymer with PVP content of 23.1 wt%was added in the casting solution for fabrication of PVDF MFs. |
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