Synthesis of a novel azaphosphorine flame retardant and its application in epoxy resins

A novel P-C-N bond containing azaphosphorine, 5-(4-hydroxy)anilinomethyl-1,3-di(4-hydroxy)phenyl-1,3,5-diazaphosphorinane (ADDPP-OH), which could be used as both a cocuring agent and a flame-retarding agent for epoxy resins (EPs), was synthesized from tetrakis(hydroxymethyl) phosphonium sulfate and characterized by FTIR, H-1-NMR, C-13-NMR, P-31-NMR, and so on. Compared with the pure EP, the ADDPP-OH-EP composites showed increased decomposition temperatures and char yields. When the content of ADDPP-OH was 10 wt %, the cured EP composite possessed a limiting oxygen index value of 33.7% and passed the V-0 rating of the UL-94 test. The mechanical properties of the ADDPP-OH-EP composites was improved because of the increased crosslinking density. In addition, the morphology of the residual char indicated an intumescent and multiporous structure in the inner space and a compact and continual appearance in the outer layer; this was important in preventing the materials from burning further. (C) 2017 Wiley Periodicals, Inc.