Effect of the organophosphate structure on the physical and flame-retardant properties of an epoxy resin

Abstract

2-(6-Oxido-6H-dibenzo <1,2>oxa-phosphorin-6-yl)1,4-benze nediol (ODOPB) and bis(3-dihydroxyphenyl) phenyl phosphate (BHPP) were successfully synthesized and used as reactive flame retardants in o-cresol formaldehyde novolac epoxy resin. Because of the rigid, cyclic, side-chain structure of ODOPB, the resultant phosphorus-containing epoxy resin exhibited a higher glass-transition temperature, better flame retardancy, higher modulus, and greater thermal stability than the regular bromine-containing tetrabromobisphenol A epoxy resin and the linear, main-chain, phosphorus-containing BHPP epoxy resin. A UL-94VO rating was achieved with a phosphorus content as low as 1.1% with ODOPB (comparable to a bromine content of 12% and a phosphorus content of 2.2% with BHPP) in the cured resins, and no fumes or toxic gas emissions were observed.