Synthesis And Characterization Of Non-Shrinkage Flame Retardant Epoxy Resin And Its Curing Agent

Epoxy resins (EP) are widely used in various industrial fields such as adhesive, coating, laminate, semiconductor encapsulation, and insulating material due to their advantageous properties of adhesion, excellent characteristics of solvent, chemical and moisture resistance, and superior electrical and mechanical properties. However, volume shrinkage is ubiquitous in the curing process. After gelation, further shrinkage would cause a residual stress inside the material. This shrinkage stress would cause the properties of the material to become worse, and the mechanical strengths to go down. These materials are rather brittle and exhibit poor toughness.Moreover, conventional epoxy resins are very flammable and cannot satisfy some applications which require high flame retardancy, especially the application in the electronic and electrical industry, and so epoxy resins need imparted flame retardance either by adding flame retardants or by introducing reactive flame retardants before used.In this paper, a series of DOPO-based spiro orthocarbonate (DSOC) was synthesized through molecular design to be used as anti-shrinkage additives and flame retardants in epoxy curing. A novel DOPO-based double hexatomic ring spiro orthocarbonate named DSOC 1, a novel DOPO-based double five-membered ring spiro orthocarbonate named DSOC 2 and a novel phosphorus-nitrogen double hexatomic ring spiro orthocarbonate named DTSOC, were synthesized. The structure of DOPO-based spiro orthocarbonates were characterized by 1H NMR, FT-IR spectra and Elemental Analysis (EA). The volume change of their ring-opening polymerization products were measured by dilatometer. The intrinsic flame retardancy and thermal stability of their ring-opening polymerization products were evaluated by limiting oxygen index (LOI), UL-94 test and thermogravimetric analysis (TG). The results show all the DOPO-based spiro orthocarbonates have good expansion performance, excellent flame retardancy and thermal stability.The bisphenol-A epoxy resin (E-51) was cured with the DOPO-based spiro orthocarbonates used as curing agents and boron trifluoride ethylamine used as curing catalyst. The curing processes were studied by the non-isothermal DSC method to determine the curing conditions. The effect of the DOPO-based spiro orthocarbonates on the conversion ratio of epoxy group was discussed by FT-IR spectra, and given the indirect evidence of the copolymerization of spiro orthocarbonates and epoxy resins. The volume shrinkage ratio of cured epoxy resins were investigated by density method. And their anti-shrinkage performances were evaluated. The results show the shrinkage of modified epoxy resins are greatly improved and even induce volume expansion. The flame retardancy of modified epoxy resin was studied by LOI and UL-94 test. The results show that the DOPO-based spiro orthocarbonates can effectively improve the flame retardancy of epoxy resins. The mechanical properties of modified epoxy resin were studied. The results show the tensile strength decreased with increased concentration of the DOPO-based spiro orthocarbonates, while the adhesive strength and the impact strength increased with the increasing content of the DOPO-based spiro orthocarbonates. The toughness of the material had an obvious improvement and it is crucial to improve the application of epoxy resin.