Synthesis of a novel <i>N</i>‐alkoxyamine containing macromolecular intumescent flame retardant and its synergism in flame‐retarding polypropylene

Abstract

Abstract Endowing intumescent flame retardant (IFR) with free‐radical quenching capability is a promising method to improve its efficiency. Herein, a novel N ‐alkoxyamine containing macromolecular intumescent flame retardant (RQMIFR) was synthesized via nucleophilic substitution reaction and combined with ammonium polyphosphate (APP) to improve the thermostability and fire resistance of polypropylene (PP). The results showed that there was a good synergism between RQMIFR and APP, which effectively enhanced the thermostability and flame retardancy of PP. When the content of RQMIFR was 8.33 wt% and APP was 16.67 wt%, the limiting oxygen index of PP increased from 19.0% to 39.5% and achieved a UL‐94 V‐0 rating. Besides, the peak heat release rate, total heat release, carbon monoxide production, and carbon dioxide production were remarkably reduced. It was revealed that during combustion, RQMIFR generated nitroxyl free‐radicals and quenched the active free radicals produced by PP both in gas and condensed phase. Simultaneously, RQMIFR and APP worked synergistically to form a compact intumescent char layer through the esterification, cross‐linking, cyclization, and foaming reactions, thus effectively improved the thermostability and flame retardancy of PP.