"Living" Radical Polymerization Of Methyl Methacrylate And Acrylonitrile Under LED Irradiation

It is well know that robust reversible deactivation radical polymerization（RDRP）methods possess strong ability on precision synthesis and topologies design for macromolecules.The most widely used methods among them are atom transfer radical polymerization（ATRP）and reversible addition-fragmentation transfer（RAFT）polymerization.Photocatalytic chemistry is indeed unique in its powerful ability to meet the energetic requirements for conducting processes that would not be accomplished with other counterparts,such as thermal.Furthermore,the utilization of economic and efficient visible light meet the demand of the sustainable development strategy in chemical industry.Combining the advantages of visible light catalysis strategy and RDRP methods,more efficient“living”radical polymerization systems would be established in preparing various macromolecules with precise structure and controlled molecular weight and molecular weight distribution.On the other hand,the electron-rich carbazole moiety paired with an electron-deficient group,forms a series of carbazole-based derivatives with donor-acceptor pair.It has widely applied in fields of organic electrons（OEs）,organic photovoltaics（OPVs）and organic light-emitting diodes（OLEDs）due to charge transfer feature.1,2,3,5-Tetrakis（carbazol-9-yl）-4,6-dicyanobenzene（4CzIPN）exhibits effect of thermally induced delayed fluorescence for efficient OLED application and can be served as photoredox catalyst in small molecule synthesis for formation of C-C bonds.Additionally,it attracts our significant attention that 4Cz IPN was applied to“living”radical polymerization for this work,due to the inherent properties of a long visible region absorbance,reversible cyclic voltammetry curve and high excited state reduction potential.System Ⅰ:Construction of metal-free ATRP of methyl methacrylate（MMA）system under blue LED irradiation.Traditional transition metal-based catalyzed ATRPs have been trapped in transition metal residue in polymers and failed to apply to electronic materials fields.Although lots of low transition metal loading and highly active ATRP systems and efficient catalyst removal and recycling ATRP systems have been developed,it is still inevitable tiny amounts of metal catalyst retained in the resultant polymers.The most promising way to eliminate completely the metal catalyst residue is metal-free ATRP catalyzed by organic catalysts.In this work,we have established a visible light induced metal-free ATRP system with ppm range of organic catalyst using MMA as the model monomer and ethylα-bromophenylacetate（EBPA）as the typical ATRP initiator.Herein,4CzIPN was used as an organic catalyst candidate due to its strong excited state reduction potential for photoredox catalysis,and 1,3-dimethyl-2-imidazolidinone（DMI）was used as the“green”solvent.The results of polymerization kinetics,chain extension and light“ON/OFF”experiments can prove the“living”feature of this system.Moreover,it has been found that even the amount of 4Cz IPN was reduced to 15 ppm,the resultant PMMA remained well-designed molecular weights close to their corresponding theoretical ones.System Ⅱ:Construction of RAFT polymerization of acrylonitrile（AN）system under blue LED irradiation.It is generally known that PAN-based carbon fibers are a kind of important material for development of advanced technology.Therefore,high quality PAN precursor with low molecular weight distribution is essential to prepare PAN-based carbon fibers.On the other hand,compared to unhealthful UV orγ-ray and high energy consumption thermal external stimulus,the promising LED external stimulus with virtues of narrow wavelength distribution,low energy consumption,no pollution,efficient and harmless to human beings etc.have been considered as an ideal external stimulus for RDRPs.Based on our previous work about 4Cz IPN,we developed a RAFT polymerization of AN system under irradiation of blue LED light at room temperature,using 4Cz IPN as a novel radical initiator and 2-cyanoprop-2-yl-1-dithionaphthalate（CPDN）as the typical chain transfer agent.Well-defined PAN with controlled molecular weight and narrow molecular weight distribution was successfully synthesized.This strategy may provide another effective method for scientific researchers or industrial community to synthesize PAN-based precursor of carbon fibers.System Ⅲ:Construction of surface initiated metal-free ATRP of MMA system under blue LED irradiation.Based on our previous work about metal-free ATRP in system I,an organic/inorganic hybrid nanoparticle was prepared by surface initiated metal-free ATRP in this work.Silica（SiO₂）nanoparticles were synthesized by St?ber method.And Then the moieties of EBPA was immobilized on the surface of SiO₂nanoparticles by functional group post-modification.Subsequently,surface initiated metal-free ATRP of MMA was carried out on the surface of SiO₂ nanoparticles.This work extended applications of metal-free ATRP and methods for preparation of organic/inorganic hybrid nanoparticles.