Synthesis of phosphorodiamidates as crosslinking agent for epoxy resin

Abstract

Two phosphorodiamidates including phenyl phosphonic ethylene diamine diamide (PPEDD) and phenyl phosphonic p-phenylene diamine diamide (PPPDD) have been synthesized and used as crosslinking agents for the preparation of phosphorus-nitrogen-containing epoxy polymers. The investigation of kinetics revealed that activation energy for crosslinking reaction of epoxy resins cured with phosphorodiamidates were higher than crosslinking reaction of epoxy resins cured with ethylenediamine and cured with p-phenylenediamine which were employed as references. The results from TGA experiments indicated that the onset temperature of thermal degradation decreased but char yield increased when epoxy resins were cured with phosphorodiamidates. Limiting Oxygen Index (LOI) results demonstrated that flame resistances of phosphorus-containing polymers are higher than those of ethylenediamine-cured and p-phenylenediamine-cured epoxy resins. Smoke evolution is also reduced. The results obtained from the UL-94 tests show that phosphorus-containing polymers passed flame retarding class V according to the UL-94 standard. The investigations of mechanical properties were that epoxy resins cured with phosphorodiamidates give lower tensile strength, but better elongation at break than epoxy resins cured with ethylenediamine and cured with p-phenylenediamine where no phosphorus were present.