Synthesis Of Thioxanthone-based Visible Light Photobase Generators And Their Applications In Hybrid Photopolymerization

Photopolymerization induced by photobase generators(PBGs)features low shrinkage,free of oxygen inhibition and no corrosion to the substrates.Highly active PBGs,which directly determine the rate and extent of photopolymerization,are the key component of the photosensitive formulation.Traditional PBGs suffer from short wavelength absorption and weak basicity of the released active species as well as low initiation activity.Based on photodecarboxylation mechanism,a series of efficient unimolecular visible light PBGs were successfully designed and synthesized in the present project and their applications in hybrid photopolymerization were explored.The first part of the thesis reported the synthesis of thioxanthone-based PBGs and systematically studied the the structure-property relationship.Several novel unimolecular thioxanthone derivatives were prepared in two steps using thiosalicylic acid,(phenylthio)acetic acid derivatives and 1,5,7-triazabicyclo[4.4.0]dec-5-ene(TBD)as starting materials.The structures of the PBGs were characterized by 1H NMR,13 C NMR and high-resolution mass spectrometer.The PBGs showed a strong absorption at around 400 nm,indicating that the PBGs are able to initiate polymerization under visible light.The introduction of electron-donating groups not only induced red-shift absorption,but also increased the quatum yields of the fluorescence emission.The photolysis mechanism was systematically studied via steady photolysis and electron spin resonance tests.The results showed that under 405 nm LED irradiation,the PBGs undergo decarboxylation to generated free radicals and strong base simultaneously and the later active species can efficiently induce thiol-epoxy photopolymerization.Taking advantage of the simultaneously formed two active species which can induce the thiol-yne and thiol-epoxy polymerization,respectively,the second part of the thesis focused on the preparation of thiol-yne-epoxy hybrid material.The effect of the type of photoinitiators and the compositional ratio on the initiation efficiency and material properties were studied.Real time FT-IR results indicated that the proposed unimolecular photoinitiators are more efficient than the bimolecular initiation system from the literature.Increased thiol-epoxy amount in the hybrid resin had marginally impact on the thiol-yne photopolymerization kinetics,but increase the total amounts of consumed functionalities of thiol-yne polymerization.The photocured materials using unimolecular photoinitiators exhibited superior thermal and mechanical properties compared to those prepared using bimolecular initiation system.Additionaly,both pendulum hardness and pencil hardness of the hybrid cured films increased along with the increase of the proportion of thiol-epoxy in the hybrid resin.The third part of the thesis studied the preparation of organic-inorganic hybrid material obtained via thiol-epoxy polymerization and hydrolysis/condensation reaction of siloxane,which were triggered by PBGs under visible LED light irradiation.Real-time FTIR were employed to study the hybrid photocuring process.The results demonstrated that increased siloxane amount in the hybrid resin induced slower thiol-epoxy polymerization rate and lower funcitionality conversion due to the competition between thiol-epoxy reaction and sol-gel process.TEM and XRD were performed to characterize the formation and structures of the hybrid coatings.The results of property study indicated that the obtained hybrid coatings possessed good thermal stability(? 223.8?)and high surface hardness(? 5H).