Study On Visible Light Induced RAFT Polymerization Of Alternating Copolymerization System

Light-induced controllable/"living" free radical polymerization(photo-CLRP)has received widespread attention because of its mild polymerization conditions and the ease of the spatial and temporal control of polymerization.A large number of researchers have done research on photo-CLRP,but there is no relevant report on the RAFT polymerization of the alternating copolymerization system under visible light.This paper aims to explore the visible light-induced RAFT polymerization behavior of the alternating copolymerization system.In this thesis,the mechanism of activation and photodegradation of RAFT chain transfer agent CDCTP under visible light are first studied,and the photodegradation under different light sources and other conditions are explored.Then,the RAFT polymerization behavior of the visible light-induced St-MAH alternating copolymerization system was systematically studied.The effects of temperature,monomer concentration,light source wavelength and power on polymerization are compared.When CDCTP is irradiated under visible light,the carbon-sulfur double bond n??*in the thiocarbonyl group transitions to generate R· and thiyl radicals.In addition to trapping R· to form dormant species,thiyl radicals also produce photodegradation.The degradation rate is closely related to the wavelength and intensity of the irradiated light,and the degradation is fastest under blue light irradiation.Reducing the light intensity can significantly delay the photodegradation of CDCTP.In the polymerization system with monomers,the thiyl radicals move more towards the dormant species,so the degradation of CDCTP is slower.In the visible light-induced RAFT polymerization process of the St-MAH alternating copolymerization system,it was found that the system can be controlled by "on/off" lamp to control the polymerization to proceed/stop,showing obvious light controllability.Moreover,choosing a suitable light source can place the polymerization under better control.The irradiation wavelength of blue light and CDCTP have the highest degree of light absorption in the light region,so the polymerization rate is fastest under blue light conditions,and the kpapp reaches 0.122 h-1 with PDI?1.2.Properly increasing the monomer mass concentration can not only increase the polymerization rate,but also reduce the PDI to a certain extent.Although increasing the temperature can also increase the conversion rate of monomers,at the same time,the accelerated photodegradation rate of CDCTP reduces the chain end fidelity of the polymerization product and broadens the PDI.Through the study of different M/CDCTP molar ratios,it is found that when the designed molecular weight is 10k-20k,the polymerization under all experimental conditions of this thesis is the best,the actual molecular weight is close to the theoretical molecular weight and PDI?1.2.Using the prepared PSM as a macroinitiator,PMA and PBzMA block copolymers were prepared by reinitiation.Finally,the polymerization method was successfully extended to other alternate copolymerization systems such as vinyl ethers and maleimides.In summary,this topic has successfully applied visible light-induced RAFT polymerization to the St-MAH alternating copolymerization system,enriched and developed the visible light-induced RAFT polymerization method,and provided a new method for synthesizing polymers with specific composition and structure.