Flame-retardant epoxy resins from novel phosphorus-containing novolac

A novel phosphorus-containing novolac (DOPO-PN) from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 4-hydroxyl benzoaldehyde was obtained via simple addition reactions. The chemical structure of the obtained DOPO-PN was characterized with FTIR, H-1 and P-31 NMR and elemental analysis. The DOPO-PN novolac, with multi-phenol groups in the molecular chain, was used as a polyfunctional curing agent for epoxies. The activity and activation energies of the DOPO-PN curing reactions with epoxies were investigated with differential scanning calorimetry (DSC). The thermal properties and thermal degradation behaviors of the DOPO-PN-cured epoxy resins were also studied with DSC and thermogravimetric analysis. High glass transition temperatures (above 160 degreesC) and extremely high thermal stability (above 300 degreesC) were observed for the DOPO-PN/CNE200 (o-cresol novolac epoxy)-based resins. High char yields and high limited oxygen index (LOI) values were also found to demonstrate the good flame retardancy of the DOPO-PN-cured epoxy resins. The LOI values of the epoxy resins were proportional to the phosphorus contents of the epoxy resins. A least phosphorus content of 2 wt% is detected for the DOPO-PN-cured epoxy resins to exhibit a LOI value of 26 and to pass the UL 94V-0 test. (C) 2001 Elsevier Science Ltd. All rights reserved.