RAFT Polymerization Of Vinyl Chloride,Synthesis And Self-assembly Of Vinyl Chloride Block Copolymers

Controlled/living radical polymerization(CLRP)can mediate the molecular weight and structure of polymers,and be used to design and synthesize complex topological copolymers,such as block copolymers.Reversible-addition fragmentation chain transfer(RAFT)polymerization was a kind of CLRP method with mild polymerization conditions and applicability for low activity monomers,such as vinyl chloride(VC)and vinyl acetate(VAc).In this thesis,RAFT polymerizations of VC were conducted by employing xanthates as chain transfer agents.PVC-b-PDMAEMA,PVAc-b-PVC and PVA-b-PVC copolymers were further prepared by using xanthate-terminated PVC as macromolecular RAFT agent.The self-assembly behaviors of PVC-b-PDMAEMA and PVA-b-PVC in bulk and aqueous phase were also investigated.Firstly,three xanthate RAFT agents with different structures were designed and synthesized to control the polymerization of VC.Effects of the structure of Z and R groups in the RAFT agents on the control of VC polymerization were investigated,and the best RAFT agents were selected.The influences of polymerization methods(solution and miniemulsion)on the kinetics of VC RAFT polymerization were studied.It was found that both RAFT solution and miniemulsion polymerizations of VC showed obvious living natures.The rate of RAFT miniemulsion polymerization was obviously greater than that of solution polymerization,and the conversion of VC reached 91%after 12h miniemulsion polymerization.However,the molecular weight distributions of PVC resins prepared by miniemulsion polymerization were wider than that of PVC prepared by solution polymerization,which could be explained by the different phase behavior and reaction species distributions in miniemulsion and solution polymerizations.NMR and UV-Vis absorption analysis confirmed that the prepared PVC had a xanthate-based terminated structure.Furthermore,the chain extension reaction showed that PVC prepared by using xanthate RAFT agent possessed the living characteristics.Secondly,PVC-b-PDMAEMA copolymers were prepared by RAFT polymerizations by employing xanthate-terminated PVC as macromolecular RAFT agents.A series of PVC-b-PDMAEMA copolymers with different molecular weight and block ratio were synthesized by varying the molecular weight of xanthate-terminated PVC and controlling the reaction time.The block structure of copolymers was confirmed by GPC and NMR analysis.Due to the thermodynamic incompatibility between PVC and PDMAEMA,the microphase separation would be occurred in the bulk state,confirming by AFM and TEM analysis PDMAEMA segments were irregularly distributed in the continuous phase of copolymers with a width of about 40-100 nm.The size of separated phase was increased as the mass fraction of PDMAEMA block in the copolymer increased.The aqueous micelle solutions of PVC-b-PDMAEMA copolymers with different compositions were prepared by solvent evaporation method,and the features of micelles were characterized by fluorescence spectra,DLS and TEM.With the increase of the PDMAEMA segment content in the block copolymer,the critical micelle concentration(CMC)of PVC-b-PDMAEMA copolymer was increased and the copolymer micelle size was decreased.The pH and temperature responsive self-assembly behaviors of PVC-b-PDMAEMA copolymer micelles were also investigated.As the solution temperature increased,the hydrogen bond action between PDMAEMA chain and water were weakened,resulting the shrinkage of the PDMAEMA segment and the decrease of the micelle size.As pH value of solution increased,the copolymer micelle size was initially increased and reached a maximum size at pH value of about 5.As pH value further increased,the copolymer micelle size tended to decrease.Finally,PVAc was synthesized by RAFT suspension polymerization,and a series of PVAc-b-PVC copolymers with different compositions were synthesized by controlling reaction time in solution and suspension polymerization system.The solution polymerization system was uniform and the molecular weight distribution of PVAc-b-PVC copolymer was narrow.However,the suspension polymerization system exhibited two-phase feature since PVAc-b-PVC copolymer with great PVC mass fraction was insoluable in VC.Thus,the molecular weight distribution of the prepared PVAc-b-PVC copolymer was wider,and the copolymer particles had a porous structure.PVA-b-PVC copolymers were obtained by acid-catalyzed alcoholysis of PVAc-b-PVC copolymers.After alcoholysis for 12 h at 50?,the alcoholysis degrees of PVA29-b-PVC62?PVA57-b-PVC86 and PVA66-b-PVC-05 copolymers were reached 92.3%,92.4%,and 92.9%,respectively.The self-assembly behaviors of PVA-b-PVC copolymers were analyzed by means of AFM and TEM.With the increase of the PVA block content,the size of separated phase of block copolymers decreased.PVA-b-PVC copolymers contain hydrophilic and hydrophobic blocks and can form core-shell structure micelle with hydrophobic PVC core and hydrophilic PVA shell in water.The CMC of PVA-b-PVC copolymer was increased from 1.65 mg/L to 2.68 mg/L with the increase of PVA content.The copolymer micelle size was distributed between 50 to 80 nm.When the molecular weight of the hydrophobic PVC segment was fixed,the copolymer micelle size was decreased as the molecular weight of hydrophilic PVA segment increased.In conclusion,this research provides guidance for the synthesis of PVC and its block copolymers by CLRP.The prepared PVC block copolymers exhibit application prospects in using as compatibilizers for PVC alloys and as dispersant(or emulisifier)in polymerization.