Controllde Synthesis Of Block Copolymers From More-Activated Monomers And VAc Or NVP Based On RAFT Polymerization And SET-LRP

Nowadays,reversible-deactivation radical polymerization(RDRP)has already become an important tool for the synthesis of polymers with precise structure,controlled molecular weights and molecular weight distributions.Block copolymers have attracted increasing attention due to their special properties and utility in many application fields,and they can be precisely synthesized by different RDRPs such as atom transfer radical polymerization(ATRP),nitroxide-mediated polymerization(NMP),reversible addition-fragmentation chain transfer(RAFT)polymerization and single electron-transfer living radical polymerization(SET-LRP).However,it is still a challenging task for the synthesis of well-defined block copolymers from both "more-activated",monomers(MAMs)(e.g.,methyl acrylate(MA),butyl acrylate(BA)and styrene(St))and "less-activated”monomers(LAMs)such as vinyl acetate(VAc)and N-vinyl pyrrolidone(NVP).On the one hand,the molecular structures of MAMs and LAMs are much different,so the polymerization methods applicable to MAMs are usually not suitable for LAMs.LAMs are non-conjugated monomers and their corresponding radicals are very active,and therefore some side reactions are prone to occur during the polymerization process so that the polymerization is usually retarded or completely terminated.On the other hand,the reported methods for preparing P(MAM)-b-P(LAM)block copolymers have still been some disadvantages,such as poor control over molecular weight distribution,low block efficiency,complicated synthesis steps or high catalyst residue,etc.Based on the discussion above,the main purpose of this thesis is to develop efficient methods for the controlled synthesis of P(MAM)-b-P(LAM)block copolymers by desigjning special structure mediators according to different RDRPs.The main research contents and conclusions are as follows:1.Controlled synthesis of P(MAM)-b-P(LAM)block copolymers based on single RAFT polymerization.Compared with other RDRP methods,RAFT polymerization is considered to be the most effective way to mediate the polymerization of LAMS,due to its simple polymerization system,wide range of monomers,and strong designability of mediators.Herein,a novel RAFT agent S-[1-(methyl)-4-(hydroxyphenylacetate)]-O-ethyl dithiocarbonate(CTA-OH),was designed to mediate the polymerization of different MAMs(including MA,BA and St)and VAc.Firstly,PMA homopolymers with narrow molecular weigt distributions ?1.21)were synthesized at 60?,using CTA-OH as the mediator and 2,2'-azobisisobutyronitrile(AIBN)as the initiator.After characterizing its end-group functionality by 1H NMR,PMA was directly used as a macro-RAFT agent to mediate the polymerization of VAc,and finally well-defined PMA-b-PVAc block copolymers were obtained(Mw/Mn?1.12-1.21).Chain extension kinetics also demonstrated the "living" characteristics of the polymerization system.This method is also suitable for polymerization of BA and St,and well-defined PBA-b-PVAc and PS-b-PVAc block copolymers were obtained.In addition,another xanthate O-phenyl-S-[1-(phenylethyl)]dithiocarbonate(PXPE)was also utilized as the RAFT agent synthesized by our group before.Subsequently,various block copolymers,such as PMA-b-PVAc,PS-b-PVAc,PBA-b-PVAc,PMA-b-PNVP,and PS-b-PNVP,were successfully synthesized by successive single RAFT polymerization method under irradiation with purple LED light(?max=391 nm,0.6 mW/cm2)at room temperature.2.Controlled synthesis of P(MAM)-b-P(LAM)block copolymers by combination RAFT polymerization and SET-LRP.By comparison to traditional ATRP,SET-LRP has its special advantages such as with zero-valent metal as the catalyst,low metalresidue and good controllability over acrylates.Although well-defined P(MAM)-b-P(LAM)block copolymers could be synthesized in the above system,the controllability over the molecular weights of P(MAM)homopolymers was not ideal.However,the RAFT agent CTA-OH could mediate the polymerization of LAMs(including NVP and VAc)well and result in well-controlled P(LAM)homopolymers(Mw/Mn?1.48)with hydroxyl terminal groups.Then the resultant P(LAM)homopolymer was reacted with 2-chloropropionyl chloride to be converted into a macroinitiator(P(LAM)-Cl)for the SET-LRP method.Finally,by combination the advantages of SET-LRP,a series of block copolymers with controlled molecular weights and narrow molecular weight distributions(Mw/Mn?1.39),such as PNVP-b-PBA,PNVP-b-PMA and PVAc-b-PMA,were successfully prepared with P(LAM)-Cl as the macroinitiator,BA and MA as monomers,copper wires as the catalyst,tris(2-dimethylaminoethyl)amine(Me6TREN)as the ligand and DMSO as the solvent.