Synthesis of a novel phosphorus-containing epoxy curing agent and the thermal, mechanical and flame-retardant properties of the cured products

A novel a, to-dicarboxyl aromatic polyphosphonate (HP-1001-COOH) was synthesized and characterized. It was used as a reactive flame retardant for diglycidyl ether of bisphenol A (DGEBA)/methyl tetrahydrophthalic anhydride (MeTHPA) cured system. The thermal, mechanical and flame retardant properties of the cured epoxy resins were examined. The glass transition temperature (T-g) of the cured epoxy resins decrease with the increasing of the HP-1001-COOH content. The mechanical properties of cured films were slightly affected, although the crosslinking density decreases with the incorporation of HP-1001-COOH. The onset decomposition temperatures and the maximum-rate decomposition temperatures decrease, while the char yields increase with the increase of the phosphorus content. When the mass fraction of HP-1001-COOH is 30 wt%, the epoxy thermosets reaches a LOI value of 32.4% and successfully pass UL-94 V-0 rating. The heat release rate (HRR), peak heat release rate (P-HRR), total heat release (THR), average of effective heat of combustion (AvEHC) and total smoke production (TSP) of the flame retardant epoxy resins decrease significantly compared with neat epoxy resin. The macro-morphology and micro-morphology of the residues after cone calorimeter tests show that the flame retardant epoxy thermosets compact char layers are formed to prevent the transmission of heat and gases during combustion process, and the main structure in the char residues of the phosphorus-containing epoxy resins are polyaromatic carbons and phosphate esters. (C) 2016 Elsevier Ltd. All rights reserved.