Synthesis, characterization and properties of novel crystalline epoxy resin with good melt flowability and flame retardancy based on an asymmetrical biphenyl unit

Abstract

A novel crystalline epoxy resin—4-(p-glycidyloxyphenoxy)-4′-glycidyloxybiphenyl (DGEBP) was synthesized via a four-step procedure on base 4,4′-biphenol as the starting material. The obtained epoxy exhibited good crystallinity with a melting point of 165.7°C. A monoclinic crystal phase was elucidated by a single crystal X-ray diffraction measurement. The curing behavior of DGEBP with a commercial phenol-4,4′-dimethylbiphenylene novolac resin (trade name GPH65) as the hardener was investigated. For comparison, another two epoxy systems based on the same hardener and two commercially-available biphenyl-containing epoxy resins, including a crystalline epoxy compound, 3,3′,5,5′-tetramethyl-4,4′-dihydroxybiphenyl diglycidyl ether (trade name: YX4000H) and an amorphous 4,4′-dimethylbiphenylene type epoxy resin (trade name NC3000H) were also prepared. It was found that the DGEBP/GPH65 formulation exhibited a superior melt flow behavior to those of YX4000H/GPH65 and NC3000/GPH65 systems. DGEBP/GPH65 epoxy formulation exhibited a minimum melt viscosity of 0.12 Pa s at 150°C. This value is obviously lower than those of YX4000H/GPH65 (0.27 Pa s) and NC3000H/GPH65 (0.59 Pa s) systems. The cured DGEBP/GPH65 thermoset exhibited good thermal stability with a glass transition temperature of 123°C and a 5% weight loss temperature of 415°C. In addition, the DGEBP/GPH65 thermoset possessed good tensile and flexural properties, low water uptake, good dielectric properties and flame retardancy.