Aryl phosphinate anhydride curing for flame retardant epoxy networks

An aryl phosphinate anhydride (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide)-methyl succinic anhydride (DMSA), with a pendent phosphorus group was synthesized and used as a reactive type flame retardant. The structure of DMSA was confirmed by FTIR, mass, elemental analysis, 1H and 31P NMR spectroscopies. The aryl phosphinate anhydride was successfully used to cure some commercial epoxides, such as bisphenol A diglycidyl ether (DGEBA) and epoxy-novolac. The epoxy networks obtained were characterized by dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and the limiting oxygen index (LOI) test. Epoxy resins cured with DMSA exhibit higher LOI values and char yields compared with those cured by commercial anhydrides, such as phthalic anhydride (PA) and hexahydrophthalic anhydride (HHPA). Furthermore, the LOI value and the char yield of the epoxy-resin composites increase with increasing phosphorus content. The flame retardancies of the epoxy-resin composites were significantly improved by using aryl phosphinate anhydride.