Photoinduced Controlled Radical Polymerization With Aromatic Aldehyde Derivative As Photocatalyst

The light irradiation as an ideal condition used in controlled radical polymerization to prepare polymers with specific structure have many unique advantages,such as environment friendly,low energy consumption,suitable for heat sensitive monomers and so on.It is also consistent with the national sustainable development strategies.On the other hand,metal complexes are commonly used as catalysts for ATRP and PET-RAFT system.While containing metals in the polymerization system will cause the polymer degradation,and also astrict the application of them in the field of biomedical and electronic materials.Thus,develop a new type of metal-free organic photoredox catalysts used in ATRP and PET-RAFT system is the key point of this paper.The following two systems were studied by using aromatic aldehyde derivatives as photoinduced metal-free catalysts:System 1 used 6-methoxy-2-naphthaldehyde(6Nap)as photoinduced metal-free catalyst in ATRP system.Ethyl(α-bromophenyl)acetate(EBPA)as initiator and Pentamethyldiethylenetri amine(PMDETA)as the reducing agent.According to a series of experiments about the blank contract of each components,different catalyst concentration,solvents,light sources and different substituents of naphthaldehyde as catalyst.It was demonstrated that metal-free catalysts containing with electron-donating groups in higher polarity solvent such as DMSO by using the ratio of[MMA]:[EBPA]:[6Nap]:[PMDETA]was 100:2:3:5 could greatly speed up the polymerization rate.System 2 used carbazolyl benzaldehyde as photoinduced metal-free catalyst in PET-RAFT system.Carbazolyl benzaldehyde compared to methoxy naphthaldehyde has a longer fluorescence lifetime to provide electronic transfer,a wider range of UV-vis absorption and a stronger reduction potential.So this system used 4-(9H-carbazol-9yl)benzaldehyde(4CzA)as the metel-free catalyst,4-cyano-4-(Thionobenzoyl)pentanoic acid(CTP)as RAFT reagent.Achieved the controlled radical polymerization of MMA and St as monomer irradiated by 23 W CFL bulb.According to the chain extension reaction could also prove the controlled radical polymerization characteristics.For example,PMMA(Mn=5100 g/mol,PDI=1.27)is used as a macroinitiator,and after chain extension reaction,a higher molecular weight(Mn=8800 g/mol,PDI=1.24)polymer is obtained.In addition,when the monomer conversion of St increased from 22.8%to 50.5%,the molecular weight of the corresponding polymer increased from 2100 g/mol to 17200 g/mol,PDI<1.42.In this research,with the experiments of different solvents,the ratio of components,temperature,light sources and light "on/off".It could proved that this system is controlled by light irradiation.At the same time,the temperature also plays an important role to jointly promote the reaction rate in the photoinduced metal-free RAFT system.