Study On Photoinduced “Living”/Controlled Radical Polymerization System At Room Temperature

For more than 30 years, photo-induced polymerization has been widely used in coatings, inks, adhesives, printing plates and micro-electronics. Compared to thermally based polymerization, photo-induced polymerization has some particular advantages. For instance, it can be performed at mild condition without released volatile organic compounds. And the photo-induced polymerization is usually fast, efficient, environmental and low energy consumption and it can be controlled via turn-off transfer. Because of the advantages of photochemistry, the photochemical also has been widely used in the "living" /controlled radical polymerization(LRP). In this paper, we successfully built two types of photo-initiated LRP at mild temperature. Firstly, a facile and universal photo-induced living radical polymerization system suitable for various types of monomers, such as oil-soluble methyl methacrylate(MMA), n-butyl acrylate(n-BA) and styrene(St) as well as water-soluble poly(ethylene glycol) monomethyl ether methacrylate(PEGMA) and 2-(dimethylamino) ethyl methacrylate(DMAEMA), was successfully developed with iniferter agent 1-cyano-1-methylethyl diethyldithiocarbamate(MANDC) and organic catalyst copper(II) acetate(Cu(OAc)2) under UV irradiation at ambient temperature. The polymerization system showed typical “living”/controlled radical polymerization feature, and a possible polymerization mechanism was discussed in this work. Secondly, we built a RAFT system which used organic phosphorus compounds as the initiator, such as diethyl phosphite, diphenyl phosphine oxide, triphenylphosphine, tetraphenyl diphosphine and trithiocarbonate(DDMAT) as chain transfer agent, to synthesize poly(methyl acrylate) under the green LED light at 25 oC. The main contents and conclusions are summarized as follows:(1) We achieved the living radical polymerization of many types of monomers, such as MMA, n-BA,VAc, St, PEGMA, DMAEMA and so on, which using MANDC as the chain transfer agent(or initiator) and Cu(OAc)2 as the catalyst under UV irradiation at room temperature. We investigated the polymerization behaviors at different amounts of Cu(OAc)2. With the reduction of Cu(OAc)2 from 2000 to 1 ppm, the polymerization reaction rate was accelerated; however, the actual molecular weights somewhat deviated to the theoretical ones. The polymerization system showed typical “living”/controlled radical polymerization features, indicating by a linear increase of molecular weights with monomer conversion while keeping relatively narrow molecular weight distributions(Mw /Mn = 1.19-1.45). The polymer with a molecular weight of 90000 and narrow molecular weight distribution can be prepared by changing the ratio between the monomers and MANDC. The living features of the obtained polymers were further confirmed by a successful chain-extension experiment. In addition, a possible polymerization mechanism was discussed in this work.(2) Well-controlled poly(methyl methacrylate) was synthesized by the mediating of organic phosphorus compounds(diethyl phosphite, diphenyl phosphine oxide, triphenylphosphine, and tetraphenyl diphosphine) and DDMAT under the green LED light(λmax = 565 nm) at 25 oC. We studied in detail the RAFT polymerization kinetics of MA using diethyl phosphite as the initiator to obtain polymers with a narrow MWD(Mw /Mn = 1.19-1.45) and the polymerization showed a living feature.