Investigation On Photolysis RAFT Polymerization In The Absence Of Photocatalyst

The strategy of combining photochemical reactions and the“living”/controlled radical polymerization opened up a new avenue for designing and preparation of polymers,which made a substantial contribution to the polymer science community.Photo-induced free radical polymerization has gradually become one of the research hotpots in the field of polymer chemistry owing to its brilliant merits,such as switchable polymerization process,environmentally-friendly reaction system,inexpensive light source and mild reaction conditions.Photo-induced free radical polymerization not only provides a facile and efficient method for preparation of novel functionalized polymers and macromolecules with complex structure,but also has broad application prospects in the field of biomedicine,intelligent material synthesis,electronic circuits and ink printing.In this paper,we firstly synthesized a special trithiocarbonate RAFT agent and explored the photopolymerization behavior of methyl methacrylate?MMA?and progargyl methacrylate?PgMA?at room temperature without any photocatalyst in the presence of visible light.Moreover,by combing the ambient visible light-induced RAFT polymerization and click chemistry,the side-chain functionalized polymer was prepared in a one-pot/one-step method.Secondly,the successful sunlight-photolyzed RAFT polymerization was achieved using a range of monomers and corresponding RAFT agents in the absence of photocatalyst.More importantly,the sunlight-photolyzed RAFT polymerization can be successfully carried out in a fully open-to-air atmosphere in the presence of the recyclable magnetic semiconductor nanoparticles.The main contents of this paper are divided into the following two parts:?1?The visible light-induced RAFT polymerizations of methyl methacrylate and progargyl methacrylate were successfully carried out using the white LED light as light source in the presence of trithiocarbonate agent?MPPA?without any photocatalyst.The photopolymerization behaviors for each monomer were investigated.The obtained results showed that the molecular weight of PMMA and PPgMA almost increased linearly with the monomer conversion at relatively low monomer conversion?<40%?,while maintaining a relatively low polydispersity index?M_w/M_n<1.29?.However,the molecular weight increased slowly at higher monomer conversion?>40%?and the kinetics deviated from the linear relationship.Moreover,a one-pot/one-step reaction combing the ambient visible light-induced LRP and click chemistry can be successfully employed to prepare the side-chain functionalized polymer using CuBr₂/PMDETA as catalyst system.The Cu?I?generated in situ can be used to catalyze the Cu AAC click reaction.Finally,the plausible reaction mechanism was proposed.?2?The sunlight-photolyzed RAFT polymerizations for different monomers?methyl methacrylate?methyl acrylate?vinyl acetate?N-isopropyl acrylamide?were successfully conducted in the absence of photocatalyst using simulated sunlight as light source.The results showed that thiocarbonylthio compounds?dithiobenzoate,trithiocarbonate,and xanthate?can all be employed to realize the sunlight-photolyzed RAFT polymerization.The living feature of the polymerization was verified by the linear kinetic plots,controlled molecular weight and narrow molecular weight distributions.The sunlight-photolyzed RAFT polymerization can be temporally stopped and restarted by adjusting the“ON”/”OFF”state of the light source.Most importantly,the sunlight-photolyzed RAFT polymerization can be successfully carried out in a fully open-to-air condition in the presence of the magnetic semiconductor nanoparticles and the polymerization had obvious living feature?M_w/M_n<1.50?.In addition,the nanoparticles can be easily recycled and reused in further photopolymerization.