Flame-retardant epoxy resins with high glass-transition temperatures from a novel trifunctional curing agent: Dopotriol

A novel phosphorus-containing trifunctional novolac (dopotriol) was synthesized through the addition reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide and rosolic acid. The structure of dopotriol was confirmed with NMR spectroscopy and elemental analyses. The dopotriol was blended with phenol novolac in the ratios of 10/0, 8/2, 6/4, 4/6, 2/8, and 0/10 to serve as a curing agent for diglycidyl ether of bisphenol A. Thermal properties, such as the glass-transition temperature, thermal decomposition temperature, and flame retardancy, moisture absorption, and dielectric properties of the cured epoxy resins were evaluated. The activity and activation energy of curing were studied with the methods of Kissinger and Ozawa by dynamic differential scanning calorimetry scans. The glass-transition temperatures of the cured epoxy resins were 138-159 degrees C, increasing with the phosphorus content. This is rarely seen in the literature after the addition of a flame-retardant element. The flame retardancy increased with the phosphorus content, and a UL-94 V-0 grade was achieved with a phosphorus content of 1.87%. Similar dielectric properties and moisture absorption were observed for these phosphorus-containing epoxy resins, and this implied that the addition of phosphorus to epoxy did not affect the dielectric properties and moisture absorption. (c) 2005 Wiley Periodicals, Inc.