Application Of Dithiocarbonate Compounds In Visble Light Induced Controlled Polymerization

The usage of polymeric materials has revolutionized the development of modern society.Scientists have paid much attention to the structures of polymers,which determine the properties of the materials.Various living/controlled polymerization techniques have been developed to satisfy different requirements in synthesis of polymers with controlled structure.In other hand,visible light has attracted more and more attention as a mild external stimulus and been widely used in living/controlled polymerization techniques,which has advantage of temporal and spatial control.Vinyl monomers can be divided into more-activated monomer(MAM)and less-activated monomer(LAM)according to the connecting group to double bond.It is still a challenge to develop a method to control the polymerization of both MAM and LAM.This thesis was aimed to expand monomer range,improve polymerization rate,simplify the polymerization procedure based on visible light induced reversible addition-fragmentation transfer(RAFT)polymerization under the fundamental understanding of the mechanism.In addition,visible light induced controlled cationic polymerization of vinyl ethers,which belong to LAMs,was built on the basis of halide ion reaction between manganese carbonyl and organic halide for the first time.Furthermore,transformation between radical and cationic polymerization was realized by combining RAFT polymerization and the halide abstraction reaction,which brought new strategies for preparing copolymers with novelty structures.The specific research contents are as follows:(1)Two xanthates,e.g.2-((phenoxycarbonothioyl)thio)ethyl propanoate)(PXEP)and 2-((4-fluorophenoxycarbonothioyl)thio)ethyl propanoate(FPXEP),were synthesized and used as initiator-regulator dual-functional agent in visible light induced polymerization.Controlled polymerization were obtained for various monomers including both more-activated monomers(methyl acrylate,butyl acrylate,and N-isopropylacrylamide)and less-activated monomer(vinyl acetate).The controlled characteristics of the polymerization were demonstrated by the linearly increasing molar mass with conversion and first order kinetics.Polyacrylates with well-regulated molecular weight and relatively narrow molecular weight distribution(D<1.30)were successfully synthesized.High conversion(>95%)can be achieved within several minutes.Polymerization shows oxygen tolerance,owing to the comsuption of dissolved oxygen by the photolysis of RAFT agent.Furthermore,the block copolymer of poly(methyl acrylate)-b-poly(vinyl acetate)was successfully synthesized through chain-extension using poly(methyl acrylate)prepared with FPXEP as the macroRAFT agent and vinyl acetate as the second monomer.(2)Visible light induced RAFT polymerization of acrylonitrile was performed in a two-component system using 2-cyano-2-propyl dodecyl trithiocarbonate(CPDT)as the initiator-regulator dual-functional agent.The polymerization was carried out under mild conditions,e.g.under irradiation of blue light-emitting diode(LED)light at ambient temperature,which reduced the side reactions in traditional thermal induced RAFT polymerization.Well-controlled polymers with high molecular weight and narrow molecular weight distribution were obtained.The light on and off experiments showed photosensitivity of this polymerization system.The structure of the obtained polymers was characterized by nuclear magnetic resonance(NMR),size exclusion chromatography(SEC)and matrix-assisted laser desorption/ionization time-of-flight mass spectra(MALDI-ToF MS).Polymers with molecular weight as high as Mn=286300 g/mol could be obtained in optimized condition.(3)The direct photolysis of RAFT agents under visible light was demonstrated by electron spin resonance(ESR)using 5,5-dimethyl-1-pyrroline N-oxide(DMPO)as a typical spin trap.The hyperfine coupling lines obtained by ESR spectroscopy showed the successful capture of the carbon-centered and the sulfur-centered radical.Photo-polymerization of vinyl acetate under different wavelengths was performed to verify the effects of wavelength on the process.The effect of the R group of RAFT agents on the photolysis was investigated by spin-trapping experiments using poly(butyl acrylate)and poly(vinyl acetate)as macroRAFT agents.The quantitative experiment showed the yield of photolysis of a xanthate to be only 0.023%under ?>440 nm.(4)A robust method for preparing controlled poly(vinyl ethers)utilizing commercially available reagents under visible light was built.Pentacarbonylbromomanganese(Mn(CO)5Br),generated from the conventional photolysis of manganese carbonyl and halide abstraction.is considered as a catalyst to oxidize carbon radical to carbeniumion in this polymerization.Polymerization behavior including the effects of solvents,temperature and monomers have been investigated.Polystyrene-b-poly(isobutyl vinyl ether)was prepared combining atom transfer radical polymerization(ATRP)and this method.Poly(butyl vinyl ether)-b-poly(methyl methacrylate)was prepared by end-capping with RAFT agent and chain extension employing visible light induced RAFT polymerization.(5)The manganese carbonyl induced cationic reversible addition-fragmentation chain transfer(C-RAFT)polymerization under mild conditions such as visible light,room temperature and even in the presence of small quantities of water was developed.In this method,halide abstraction reaction between organic halide and manganese carbonyl is used to generate the oxidant and initiate radicals.The C-RAFT agents are generated in-situ from radical transfer reactions between vinyl ethers and three traditional RAFT agents including xanthate,trithiocarbonate and dithiocarbamate species.Poly(vinyl ether)s with controlled molecular weight and narrow molecular weight distribution(<1.2)can be obtained when using dithiocarbomate.Poly(vinyl ether)s with RAFT agent terminated chain ends have been successfully obtained and used as macroRAFT agents for preparation of block copolymers combining RAFT radical polymerization.Poly(isobutyl vinyl ether)-b-poly(vinyl acetate)and poly(isobutyl vinyl ether)-b-poly(methyl acrylate)are successfully prepared.In addition,poly(butyl acrylate)-b-poly(isobutyl vinyl ether)have also been obtained using poly(butyl acrylate)prepared by RAFT radical polymerization as macroRAFT agent.Furthermore,Mn(CO)5Br was used as dual thermally and photo-responsive catalyst for C-RAFT polymerization.Well-defined poly(vinyl ether)s with high chain end fidelity were obtained.