Ambient Temperature Photoinduced RAFT Polymerization With Benzaldehyde Derivatives As Photoredox Catalysts

Photoinduced living radical polymerization has drawn wide attention in recent years due to its advantages of low energy consumption,high efficiency,environmental friendly and economical.So far,many metal-based photosensitizers or photocatalysts were successfully used for the photoinduced RAFT polymerization of a variety of monomers.However,the residual metal catalysts are difficult to be removed completely from the produced polymers,it may cause aging failure of the product.Thus,the use of metal catalysts can potentially limit the application of the RAFT polymerization in commerce or even increase the cost of product.Therefore,the development of low-cost,simple-structure metal-free organic photoredox catalysts is still of great significance.1.In this dissertation,The benzaldehyde derivatives,such as 2,4-dimethoxy benzaldehyde and 4-methoxy benzaldehyde,were successfully used as photoredox catalyst in combination with typical RAFT agent 4-cyano-4-(phenylcarbonothioylthio)-pentanoic acid(CTP)for the controlled RAFT polymerization of methyl methacrylate(MMA)and benzyl methacrylate(BnMA)at room temperature.The reaction was carried out under 23 W compact fluorescent lamps.At the same time,the living features of polymerizations have also been further supported by chain extension and synthesis of PMMA-b-PBnMA diblock copolymer.For instance,the well-defined block copolymer of PMMA-b-PBnMA(Mn,GPCc=18900 g·mol-1;PDI=1.42)were prepared using PMMA(Mn,GPC=8200 g·mol-1;PDI=1.20)as a macroinitiator and 4-methoxy benzaldehyde as the photoredox catalyst.2.The polymerization of styrenic monomers and its applications get a lot of attention in recent years.However,the retardation effect of styrenic-based monomers during RAFT polymerization led to few reports about the rapid and controlled RAFT polymerization of styrenic monomers at ambient.In this treatise,the photoinduced RAFT polymerization of styrene(St)and p-methylstyrene(p-MS)with benzaldehyde derivatives as photoredox catalysts,including 4-cyanobenzaldehyde,2,4-dimethoxy benzaldehyde and 4-methoxy benzaldehyde and 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid(DMP)as a RAFT agent was demonstrated by using 23 W compact fluorescent lamps as the light source at ambient.Specifically,the polymerization of p-MS showed good controllability with 4-cyanobenzaldehyde(when the molar ratio of[p-MS]:[4-cyanobenzaldehyde]was 3:1 and the monomer concentration was 45%)as the photoredox catalyst and tetrahydrofuran(THF)as the solvent.