Synthesis of novel poly(aminophosphonate ester)s flame retardants and their applications in EVA copolymer

Novel oligomeric intumescent flame retardants, poly(amino phosphonate ester)s (PAPEs), containing both phosphorous and nitrogen, were synthesized by reacting diethyl phosphite with two different polyschiff bases obtained from the reaction of diamines with dialdehyde. The target PAPEs (designated as PAPE-d and PAPE-e, respectively) were characterized by 1H NMR, 31P NMR, Fourier Transform infrared spectroscopy, elemental analysis, gel permeation chromatography and thermogravimetric analysis (TGA) techniques. Thermal stability and flammability of ethylene-vinyl acetate copolymer (EVA)/PAPE blends with various PAPE content were investigated by TGA, limited oxygen index (LOI), vertical burning test (UL-94) and microscale combustion colorimeter (MCC). The results indicate that PAPEs effectively improve the flame retardancy of EVA. The EVA/30%PAPE-e blend has a LOI value of 28, and its peak heat release rate (PHRR) value in MCC measurement is reduced by 36%. At the same time, the EVA/PAPE blends also have high yield of residual char, indicating that PAPEs are effective charring agents. Scanning electron microscopy observations of the residues of the EVA/PAPE blends show the existence of compact char layer on the surface of the residues, which is responsible for the improvement of the flame retardancy of EVA. Copyright (c) 2012 John Wiley & Sons, Ltd.