Synthesis of a novel dimethylglyoxime-bridged phosphinate and its application in flame-retardant epoxy resins

Considering the need for flame retardancy in epoxy resin (EP), a novel dimethylglyoxime-bridged phosphinate (DMG-DC) has been suggested and applied for the purpose of flame-retardant modification of epoxy resin. As a result of the substitution reaction between dimethylglyoxime (DMG) and diphenylphosphoryl chloride (DPPC), DMG-DC was successfully characterized chemically. The research has demonstrated a notable enhancement in the flame-retardant characteristics of EP/DMG-DC. Especially, with the addition of 15 wt.% DMG-DC, the EP composite passed the UL-94 test with a V-0 rating and achieved a limiting oxygen index (LOI) value of 28.4 %. In addition, cone calorimetry test (CCT) results showed that the peak heat release rate (PHRR), total heat release rate (THR), and carbon dioxide production (CO2P) of EP/DMG-DC-15 were reduced by 54.1 %, 35.2 %, and 64.4 %, respectively, compared to EP. Not merely, the activities of DMG-DC in the gas and condensed phases also enhanced the flame retardancy of EP. That was the decomposition of DMG-DC not only released phosphorus-containing radicals to trap reactive radicals and nitrogen-containing inert gases to dilute flammable materials but also promoted the epoxy matrix to form more char residues. Generally, this work develops a novel dimethylglyoxime-bridged phosphinate with the potential in the application of flame-retardant polymers.