Preparation and Properties of Novel Inherent Flame-Retardant Cyclotriphosphazene-Containing Epoxy Resins

A novel flame-retardant cyclotriphosphazene-based epoxy resin (CPEP) was successfully prepared by epoxidation of bis-(4-hydroxyphenylsulfonylphenoxy) tetraphenoxycyclotriphosphazene with epichlorohydrin, and was characterized by 1H nuclear magnetic resonance (NMR), Fourier transform infrared, and gel permeation chromatography (GPC). Then the blends of CPEP and diglycidyl ether of bisphenol A (E51) with different mass ratios were cured using 4,4'-diaminodiphenylmethane as a curing agent. The curing behaviors and the glass transition temperatures of the resulting thermosets were studied by differential scanning calorimetry. The thermal stabilities and flame-retardant properties of the cured resins were studied by thermogravimetric analysis and UL94 tests, respectively. In addition, mechanical, hydrophobic, and electrical properties were also characterized. Compared to the corresponding E51-based thermosets, the cured resins with a mixture of CPEP and E51 showed better thermal stabilities, higher char yields, and greatly improved flame-retardant properties. Furthermore, relatively good mechanical properties, hydrophobicity, and electric resistance were maintained. The cured resins of CPEP/E51 (mass ratio 1:1) achieved UL94 V-0 rating, indicating that the epoxy resin prepared in this study could be used as a flame-retardant coating material.