Direct Photolysis RAFT Polymerization Of (Metha) Acrylate With TTP As Mediator

In the direct photolysis RAFT polymerization,which requires no external photoinitiator or photosensitizer,the RAFT agent is directly photolyzed into active free radicals and stable free radicals under light irradiation.Here,RAFT agent plays the dual role as a photoinitiator and a chain transfer agent.In this study,a photolysis RAFT polymerization of methacrylate and acrylate monomers was developed with 2-cyano-2-propyldodecyl trithiocarbonate(TTP)as the RAFT agent,under blue light irradiation.The polymerization of methacrylate monomers presents some characteristics of controlled free radical polymerization,but the molecular weight distribution of the polymer product is relatively broad(PDI=1.1-1.8).The polymerization of acrylate monomers meets the features of controlled radical polymerization with PDI<1.2.On the basis of realizing controlled free radical polymerization,the effect of temperature on photolysis RAFT polymerization was further studied,and it was found that the apparent reaction rate of polymerization increased significantly with the elevating reaction temperature.The main results of this study are as follows:1.In N,N-dimethylformamide(DMF),the ultraviolet-visible(UV-vis)spectrum of TTP has absorption bands in the range of 326 nm and 445 nm,where the former is the absorption of spin-allowed ?-?*electronic transition,the latter is the absorption of spin-forbidden n??*electronic transition.From the UV-vis spectrum,TTP can absorb blue light,so it possible to regulate blue light-activated polymerization.2.With TTP as the RAFT agent,effect of solvents on blue light-regulated methyl methacrylate(MMA)photolysis RAFT polymerization was first studied.The polymerization of MMA presents some features of living polymerization.For example,the first-order kinetic curve is approximately a straight line,and the molecular weight increases linearly with monomer conversion.However,the PDI of the polymer product is broad(1.1-1.8).Under dark conditions,the monomer conversion was 0%for 48 h at 60? in the presence of TTP,indicating that the polymerization reaction was not activated by heat.The "start-stop" experiment confirmed that the polymerization was light-activated.In a certain range of reaction temperature,heat has no significant effect on the decomposition of TTP.The experimental results show that increasing the temperature can significantly accelerate the rate of the photolysis RAFT polymerization of MMA.The apparent rate constant is 0.0987 h-1 at 32?,0.113 h-1 at 40?,and 0.230 h-1 at 50?respectively.In addition,increasing the MMA concentration can also accelerate the rate of polymerization.Although the PDI of PMMA product is broad,the macromolecular chain transfer agent obtained by polymerization can be used for chain extension and block copolymerization.The PMMA-TTP(Mn=6700 g/mol,PDI=1.29)was used for chain extension to prepare high molecular weight PMMA(Mn=14600 g/mol,PDI=1.67).No obvious tailing was observed in the GPC traces.PMMA-TTP was also used to initiate block copolymerization of glycidyl methacrylate(GMA),tert-butyl methacrylate(tBuMA)and benzyl methacrylate(BnMA)respectively.As a result,PMMA-b-PGMA(Mn=14400 g/mol,PDI=1.48),PMMA-b-PtBuMA(Mn=17100 g/mol,PDI=1.71),and PMMA-b-PBnMA(Mn=14200 g/mol,PDI=1.54)block polymers were obtained.The molecular weight of PMMA-b-PBnMA block copolymer measured by NMR is Mn,NMR=14900 g/mol which is very close to Mn,GPC=1 4200 g/mol.3.With TTP as the RAFT agent,effect of solvents on blue light-regulated methyl acrylate(MA)photolysis RAFT polymerization was first studied.The polymerization of MMA presents some features of living polymerization.For example,the theoretical molecular weight is more consistent with the experimental molecular weight,and the polymerization molecular weight distribution is kept below 1.2.Under dark conditions,the monomer conversion was 0%for 36 h at 50? in the presence of TTP,indicating that the polymerization reaction was not activated by heat.The apparent rate constant is 0.080 h-1 at 32?,0.086 h-1 at 40?,and 0.115 h-1 at 50? respectively.The macromolecular chain transfer agent obtained by polymerization can be used for chain extension and block copolymerization.The PMMA-TTP(Mn=6700 g/mol,PDI=1.29)was used for chain extension to prepare high molecular weight PMA(Mn=23500 g/mol,PDI=1.28).PMMA-TTP was also used to initiate block copolymerization of benzyl acrylate(BnA).As a result,PMA-b-PBnA(Mn=26500 g/mol,PDI=1.19)block polymers were obtained.