| Epoxy resin is widely used in coatings and adhesives for its excellent mechanical properties,heat resistance and bonding properties.Thiol-epoxy “click” reaction has become one of the hotspots in the field of photocuring due to its mild and efficient reaction conditions.As a latent photoinitiator,the photobase generator improves the storage stability of the formulation when it catalyzes the thiol-epoxy reaction.However,due to the low quantum efficiency and poor solubility of the photobase generator,thiol-epoxy reaction rate is slow under light conditions.This thesis focused on the thiol-epoxy system catalyzed by the photobase generator.Through the optimization of epoxy resin and thiol monomers,a thiol-epoxy UVthermal curing system with both high stability and performance was prepared.Further established a thiol-epoxy curing system radiated by near-infrared light.The specific work is as follows:(1)Five types of epoxy resins curing systems including aliphatic epoxy resin,ester ring epoxy resin,glycidyl ether,glycidyl ester and glycidyl amine were designed and the curing behavior was studied.The apparent activation energy of each epoxy resin and thiol under base catalyzed conditions were tested by a non-isothermal differential scanning calorimeter(DSC),the curing kinetics were monitored by real-time infrared,and stabilities of each formulation were tested by a rotary rheometer.In the end,the curing conditions of the formula and the thermal properties of the cured material were tested by DSC.The study found that the five types of epoxy resins and thiols catalyzed by photobase generator have good storage stability,among which hydantoin epoxy resin(GDH)with nitrogen structure and pentaerythritol tetra(3-mercaptobutyrate)(PE-1)exhibited high reactivity,and the coating could be completely cured after light exposure and drying at 120 °C for 30 minutes.(2)In order to improve the thermomechanical properties of thiol-epoxy coatings catalyzed by photobase generator,a series of thiol-epoxy coatings were prepared by adjusting the ratio of 2,4,6-trimercapto-s-triazine(TTCA)and PE-1.The conversion of thiol and epoxy groups in each coating system were monitored by real-time infrared.The mechanical properties of the cured films were tested through dynamic mechanical analysis(DMA)while tensile tests,and the thermal stability,glass transition temperature and basic properties of the coatings were evaluated.The results showed that with the increase of TTCA content,the glass transition temperature and mechanical properties of the cured film were significantly improved,and the surface hardness of the coating increased from 2H to 6H,while the photo curing rate decreased slightly.(3)In order to further improve the thiol-epoxy curing rate catalyzed by photobase generator,based on the up-conversion material assisted near-infrared photopolymerization technology,a thiol-epoxy catalyzed by photobase generator under near-infrared light curing system was established,and the effect of the photo-thermal synergistic effect of near-infrared light on the thiol-epoxy reaction catalyzed by the photobase generator was explored.The molecular weight of the polymer was measured by gel chromatography,the kinetics of nearinfrared photopolymerization were monitored by real-time infrared,the temperature change during polymerization was monitored by infrared thermal imager,and the relationship between polyfunctional thiol and epoxy resin was investigated by real-time infrared.The research results showed that the use of the light-heat synergistic effect of near-infrared light realized the complete curing of the thiol-epoxy catalyzed by photobase generator in one step. |
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