Preparation And Performance Of Epoxy Resins And UV Cured Film By UV Initiation Thiol–ene Click Reaction

Epoxy resins have a broad range of applications,including electronics,construction and other fields due to their excellent physical and mechanical properties.But the conventional synthesis of epoxy resins has some disadvantages of the complex process and environmental pollution.Scientists and engineers are interesting in studying simple,efficient and pollution-free synthesis technology of epoxy resins.Thiol–ene click reaction is a highly efficient method for synthesizing organic monomers and polymeric materials with desirable properties.In this work,we have synthesized a series of glycidyl ether epoxy resins,hyperbranched epoxy resins and phosphorous-nitrogen-containing UV-curable film via thiol-ene click reaction,and studied the performance of hyperbranched epoxy resins/diglycidyl ether of bisphenol-A(DGEBA)composites and modification function and mechanism of hyperbranched epoxy resins.Detailed research results have been followed:(1)Epoxy resins with various functional degrees were prepared and characterized by UV-initiated thiol-ene reaction.Several kinds of thiols were synthesized by the main materials of mono-alcohol(phenylcarbinol),di-alcohols(ethylene glycol,diethylene glycol,butanediol),tri-alcohols(THEIC,trimethylolpropane)with a yield of above 95%.Then thiols reacted with allyl glycidyl ether(AGE)by UV initiation and produced several kinds of epoxy resins with a yield of above 99%,including phenylcarbinol-glycidyl ether(PMEP),ethylene glycol-di-glycidyl ether(EGEP),diethylene glycol-di-glycidyl ether(DGEP),butanediol-di-glycidyl ether(BGEP),THEIC-tri-glycidyl ether(THGEP),trimethylolpropane-tri-glycidyl ether(TMGEP).The epoxy equivalent weight of very epoxy resin is very close to its theoretical value.Their chemical structures and molecular weights were characterized by FT-IR,1H-NMR and electrospray ionization mass spectrometry(ESI-MS).(2)We have synthesized three kinds of epoxy-ended hyperbranched polyesters(EHBP)and studied the performance of EHBP/DGEBA composites.Three kinds of thiol-ended hyperbranched polyesters were synthesized by esterification between hydroxyl-ended hyperbranched polyesters and mercapto propionic acid.Three kinds of EHBP were obtained by the reaction between thiols and AGE under UV irradiation.Their chemical structures and molecular weights were characterized by FT-IR,1H-NMR and GPC spectra.The results showed that the epoxy equivalent weight of the resultant EHBP is very close to its theoretical value,and every EHBP has a narrow molecular weight distribution.The performance of EHBP/DGEBA composites showed that mechanical performances of the composites increase first and then decrease with the increase of molecular weight and content of EHBP.Their excellent performances of the composites with 9wt% EHBP-12 content were obtained.Compared with the performances of DGEBA,tensile strength,flexural strength and impact strength of the composites would be increased about 27.82%,39.84% and 132.40%,respectively,and the heat resistance decreased a little.The toughness and strength improvement function of EHBP can be explained by an in situ reinforcing and toughening mechanism.(3)UV-curable polymeric coatings were prepared by thiol–ene click reaction.One nitrogen-containing trithiol monomer(DAMP)and two kinds of phosphorous-containing diene monomers were synthesized by the main materials of diethanolamine,mercapto propionic acid,diphenyl phosphine acid chloride,methyl acrylic glycidyl ester and AGE.The one diene(DPDA)contains two different groups of allyl ether and acrylate,and the other diene(DPMA)contains two same methacrylate groups.FT-IR and NMR spectra were used to characterize the structure of the monomers.UV-cured films were prepared by the click reaction between trithiol and two diene.The UV-cured reaction kinetics of the different ene groups(allyl ether,acrylate,and methacrylate)and the thiol group were studied using real-time FT-IR technology.The results showed that thiol could increase cross-linking density,conversion of double bond,gel content of the coating.The incorporation of phosphorous and nitrogen to the system also improved the flame retardancy of the cured film due to a phosphorous–nitrogen synergistic action.