Study On Interchain Transfer Reaction In Acrylate Polymerization Based On RAFT Polymerization And GEPC

The chain transfer reaction in the process of acrylate radical polymerization has a significant effect on the properties and structure of polymers,especially the formation of long branched chain or even gel phenomenon generated by interchain transfer.In this study,an effective method for direct determination of the interchain transfer constant(C_tr)was established.The RAFT polymerization of the second monomer was carried out in the presence of the first monomer polymer using benzyl N-carbazole dithiocarbamate（BCBD）as RAFT reagent and subsequent separation using polymer chromatography.The C_tr of benzyl acrylate（Bz A）and butyl acrylate（BA）to poly（ethyl acrylate）（PEA）was studied.This method does not depend on more kinetic parameters.Using dichloromethane and acetonitrile as eluents,the suitable separation conditions were selected on a normal phase silica column to separate the RAFT homopolymer of Bz A（RPBz A）and its interchain transfer product RPBz A-b-PEA,and the RAFT homopolymer of BA（RPBA）and its interchain transfer product RPBA-b-PEA.Based on the characteristic UV absorption of BCBD terminal group,the rate of interchain transfer（ β ）of growth chain free radical of Bz A or BA to PEA was measured,and the detection accuracy was investigated.The minimum effective detection accuracy of β is 0.3%,and the order of magnitude of the lowest measurable C_tr is 10^-6.In view of the interchain transfer reaction process of Bz A to PEA,the variation of β with the conversion（x）was investigated,and the effects of the amount of BCBD,monomer and solvent in the polymerization formula on the determination of C_tr were investigated.The results show that β increases with the increase of x,and there is no consistent linear relationship between β and-ln（1-x）in the range of total conversion.In the early stage of polymerization,the short chain radical effect is obvious,and the growth rate of β is faster,and this phenomenon is independent of the polymerization system.The experimental formula has little effect on determination of C_tr,although it affects β value.Using the β values in the conversion range of 20%-70%,the C_trs values of Bz A growth chain radical to PEA at 90,100,110 and 120^oC were obtained as 0.39×10^-4,0.80×10^-4,1.25×10^-4 and 1.61×10^-4 respectively,and the activation energy of C_tr was47.8 k J·mol^-1.The C_trs of BA growth chain radical to PEA were 0.56×10^-4,0.67×10^-4,0.82×10^-4and 1.06×10^-4 respectively,and the activation energy was 30.4 k J·mol^-1.The C_trs of short chain radicals of BA to PEA at 80,90,100,110 and 120^oCwere obtained as 2.76×10^-4,3.056×10^-4,4.06×10^-4,5.51×10^-4and 6.63×10^-4 respectively by using the β values in conversion range of 0%-20%,and the activation energy was33.24 k J·mol^-1.The short chain radical has significantly high interchain transfer activity,but its activation energy was has little change.