Visible Light-Induced Living/Controlled Polymerizations

Fossil fuels are non-renewable,which play a vital role in the development of the modern economy and society,but the increasing consumption and the accompanying environmental pollution such as greenhouse gas emissions have become a global problem,currently.Visible light is a unique natural resource,which is not only renewable,pollution-free,accounting for about 50%of the total solar radiation,and is an exceedingly ideal clean energy.Therefore,the conversion and utilization of light energy have become the focus in the field of chemical synthesis since the 1920s.Under the irradiation of visible light,small molecules and macromolecules can be prepared by various ways.It is worth mentioning that photochemical pathway can connect with many high energy intermediates,so as to overcome the huge activation energy barrier in a short time and achieve many reactions that are difficult to be reached by traditional thermal processes.In addition,compared with thermal polymerization,photopolymerization can be carried out at room temperature or even lower temperature,reducing the probability of side reactions,making it great potential and more possibilities in the field of biochemical synthesis and further application.However,the appropriate photocatalysts or photosensitizers are essential to absorb visible light and activate the reaction due to that the common substrates of polymerization can not absorb and utilize visible light directly.In this dissertation,we have developed a new type of organic semiconductor-based photocatalyst,small organic molecule and polymer catalyst,to realize the photopolymerization of various monomers.At the same time,we have successfully constructed a composite visible light catalytic system for controlled polymerization.It includes the following three parts:1.The small organic molecular semiconductors catalyzed living/controlled radical polymerization was studied under the irradiation of visible light.4,7-Di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole(DTBT)can act as an efficient photoredox catalyst for photoinduced electron transfer-reversible addition-fragmentation chain transfer(PET-RAFT)polymerization under irradiation of green light.We studied the living characteristics of the photopolymerization without need of any additional additives by reaction kinetics,chain extension.In addition,we also studied the scope of RAFT agents and monomers of this photopolymerization.2.The conducting polymer nanofibers in induced living/controlled radical polymerization was studied under the irradiation of visible light.Based on the dependence of the bandgap width of conducting polymer-poly(1,4-diphenylbutadiyne)(PDPB)on the degree of polymerization,conducting polymers with different photophysical and chemical properties and different morphologies were synthesized.The PDPB catalyzed polymerization under the irradiation of visible light was carried out in water.We studied the living characteristics of the photopolymerization by reaction kinetics,chain extension,and revealed the catalytic mechanism using fluorescence spectroscopy.Additionally,the nanofibers can be recovered easily by centrifugation,and we also investigated the recycling of the catalyst.3.The photoacid generator under visible light induced living/controlled cationic polymerization was studied.We provided an approach to construct a low-energy activated composite photoacid generators that consist of photocatalyst and onium salts such as diphenyliodonium and triphenylsulfonium salts,which could catalyze living/controlled cationic ring-opening polymerization(CROP)of lactones initiated by alcohol under visible light irradiation.Nuclear magnetic resonance(NMR),gel permeation chromatography(GPC)and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry(MALDI-ToF MS)analyses were invoked to characterize the produced polymers,and the result indicated that the polymerization underwent via activated monomer mechanism.Additionally,owing to the radical species generated concurrently in this system,living/controlled radical polymerization and CROP can be reached on the one propagating chain by utilizing a bifunctional initiator to produce a block polymer easily in one step.