Photo-induced RDRP Catalyzed By 4-(N,N-diphenylamino) Benzaldehyde

The photo-induced reversible deactivation radical polymerization(photo-RDRP)catalyzed by metal-free photo catalyst(PC)has been witnessed a fast growth in the past few years.However,so far,the PCs that have been disclosed in literature are relatively complicated and uncompetitive.It is of great importance for both academic and industrial communities to develop highly efficient metal-free PCs of commercial available and affordable for photo-RDRP.In this paper,a novel organic photoredox catalyst with a reducing tertiary amino group,4-(N,N-diphenylamino)benzaldehyde(DPAB),has been exploited as a metal-free catalyst for photo-ATRP and photo-RAFT systems.The effects of UV-Vis and fluorescence spectra of DPAB,the concentrations of DPAB and the temperature on polymerization of methacrylate monomers have been investigated in detail.The livingness of the photo-RAFT has been demonstrated by the linear increasing of Mn with monomer conversion,chain extension reaction and block copolymerization.Follows are the main results:1.DPAB shows UV-Vis absorption band in the range of 270 nm to 435 nm.Excited with 354 nm incident light,the fluorescence emission i-at about 515 nm.The fluorescence quantum yield of DPAB is about 26%,and the fluorescence lifetime is about 5.54 ns.When added the 4-cyano-4-(phenylcarbonothioylthio)-pentanoic acid(CTP)to DPAB solution,the emission intensity decreases with respect to the ratios of CTP(or diethyl 2-bromo-2-methylmalonate(DBMM)or ethyl alpha-bromophenylacetate(EBPA))/DPAB while the fluorescence emission peak is neither blue shift nor red shift.E0(PC·?PC*)is-1.61 V,shows that excited state of PC has high reducing property.The optical/electrical physicochemical properties of DPAB indicate that it can be used as photoredox catalyst.2.With DPAB as a catalyst for photo-ATRP,the effects of reaction temperature,DPAB concentrations and light resources on the polymerization of methacrylate monomers are systematically studied.The experimental results show that the polymer dispersity index(PDI)is higher as the monomer conversions increase without significant increasing of Mn.When 365 nm UV light is applied,the Mn has a tendency to increase slightly with the monomer conversions,but the GPC curve is asymmetrical and the PDI increases gradually.Photo-ATRP catalyzed by DPAB is a typical conventional radical polymerization.3.The photo-RAFT polymerization of methacrylate monomers with DPAB as PC and CTP as RAFT regent has been systematically studied.The experimental results show that the apparent rate constants(knapp)of the polymerization at 33?,40? and 50? are 0.019 h-1,0.056 h-1 and 0.102 h-l respectively.Control run(dark reaction)and light on/off tests demonstrate that the polymerization is activated by light and characterized by living polymerization.At 50? and[MMA]:[CTP]:[DPAB]?100:0.5:5,the Mn of the polymer is close to Mn,theo,PDI?1.2,and kappp is as high as 0.102 h-1.The above experimental results show that the polymerization temperature has a positive synergistic effect on photo-RAFT polymerization.4.With PMMA-CTP as macromolecular RAFT reagent(Macro-RAFT),chain extension and block polymerization are successfully achieved.For example,Mn,GPC(18500 g/mol)and Mn,NMR(18300 g/mol)of PMMA-b-PBnMA are obtained by using PMMA-CTP(Mn=6000 g/mol,PDI=1.21)as Macro-RAFT.5.With DPAB as PC,the polymerization of styrene,propargyl methacrylate and polyethylene glycol methacrylate is also investigated.The Mn of polymer increases with the monomer conversion.However,polymerizations of these monomers are slightly less controllable than that of MMA.