| Tougheness and reinforcement, heat-resistance and solvent-free of epoxy resins(EPs) are main development trend in the research field of epoxy resin. At present, most of the reported synthetic methods of epoxy resins are tedious and serious pollution to the environment, and the products carrying a lot of hydroxyl groups affect the stability of one-component epoxy resins. Facing to these challenges, we used thiol-ene click reaction, which has advantages of fast speed, high yield and controllable product speed, characteristics of reaction quantitation and localization, to design and synthesize heat-resistant epoxy resins and thiol-ended hyperbranched polymers. Detailed research results have been followed:(1) Preparation of multivariate mercaptan and sulfur-containing epoxy resins. A series of mercaptopropionates, including 1,3,5-tris(2-hydroxyethyl)isocyanurate-tris(3-mercaptopropionate)(THMP), diethylene glycol dimercaptopropanoate(DEMP), and 1,4-butanediol dimercaptopropanoate(BDMP), were prepared by esterifications between diols(or triols) and 3-mercaptopropionic acid(MPA). The mercaptopropionates reacted with glycidyl methacrylate(GMA) through a thiol–ene click process to produce three types of EPs(THEP, DEEP and BDEP). Chemical structures of EPs were characterized by FT-IR, 1H-NMR and TOF-MASS. Purity of EPs are above 99.9%. Epoxy values of THEP, DEEP and BDEP are 0.305, 0.323 and 0.347 mol/100 g by using titration method, respectively, being very close to their theoretical values. Methyl nadic anhydride as cross linker was used to cure THEP, DEEP and BDEP, and the resultant materials show excellent heat-resistance due to the absence of hydroxyl groups. Cured THEP, DEEP and BDEP have high thermal decomposition temperatures, demonstrated by thermal decomposition temperatures of 277.3, 281.3 and 290.4oC about weight loss of 5% and no dehydration decomposition at 260 oC, indicating that they are suitable for applications as solvent-free resins.(2) Preparation of thiol-terminated linear polymers(TTP-n, n=1, 2, 3, 4 and 5) were also researched as well as their thermal performance. TTP-n with molecular weights from 2000~6000 g/mol were synthesized by thiol-ene click reactions between DEMP and 1,4-butanediolacrylate(BDDA). Chemical structures of TTP-n were characterized by FT-IR and 1H-NMR. Molecular weights of TTP-1, TTP-2, TTP-3, TTP-4 and TTP-5 about 2565, 3563, 4908, 5790 and 8437g/mol were determined through the thiol titration method, respectively. TTP-n as cross linker was used to cure diglycidyl ether of bisphenol-A(DGEBA), and TGA analysis was used to study the thermal properties of cured TTP/DGEBA, and apparent thermal decomposition temperatures of cured samples are 331.1, 322.7, 323.7, 329.6 and 328.1oC, respectively.(3) Preparation of thiol-terminated hyperbranched polymers(HBTP-n,n=0, 03, 05, 07, 1) were studied as well as their thermal performance. A series of HBTP with different branch degrees(BD) were synthesized by thiol-ene click reactions, basing THMP, DEMP and BDDA as the main raw materials. Chemical structure of HBTP was characterized by FT-IR and 1H-NMR. HBTP as cross linker was used to cure DGEBA, and then the thermal property of cured HBTP-DGEBA samples were characterized by DSC and TGA technologies. Glass transition temperatures of cured(HBTP-n,n=0, 03, 05, 07, 1)are 16.1,-1.6,-6.3,-15.5oC and below-40 oC, indicating that they decreases with decrease in their BD, but their apparent thermal decomposition temperatures remain about 310 oC. |
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