Recent developments in P(O/S)-N containing flame retardants

Synthesis of organophosphorus compounds containing nitrogen as heteroatom and its application as a flame retardant (FR) have attracted much attention in the academic and industrial communities over the past decade. Such compounds are relatively easy to synthesize and offer advantages such as high thermal stability, which is useful for high temperature processing, improved char stability, density, and yield during the thermal decomposition of polymer, and release phosphorus species active in the flame inhibition process. Though a variety of phosphorus-nitrogen (P-N) compounds can be found in the literature, this review mostly summarizes the recent (since 2013) development in phosphorus (O)-nitrogen containing flame retardants which have been published in peer-reviewed journals. General strategies of synthesizing P(O)-N compounds as FRs from various phosphorus-based starting materials are highlighted in this review. Some of the most common classes of researched P(O)-N containing compounds as FRs include the phosphinamides, phosphonamides, phosphoramides, phosphoramidates, phosphorodiamidates, phosphonamidates and their thio counterparts which are usually obtained via a one- or two-step synthetic strategy. Incorporation of these compounds as FRs in various polymer systems such as polyurethane, epoxy resins, polyamides, cellulose, polylactide, poly(butylene terephthalate), polycarbonates, and acrylonitrile-butadiene-styrene are discussed in detail in this review. Special emphasis on the various fire and thermal performances of the new materials are also summarized. The mechanical performance of new materials and the influence of these additives on polymer processing are also briefly discussed. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 47910.