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.

High‐efficiency macromolecular intumescent flame retardant (MIFR) is urgently demanded but of great challenge. In this work, a novel N‐alkoxyamine‐containing MIFR‐decorated zirconium phosphate (ZrP) nanosheet (denoted as RQMIFR‐ZrP) was synthesized and combined with ammonium polyphosphate (APP) to endowed polypropylene (PP) with excellent flame retardancy. With the addition of 6.3 wt% RQMIFR‐ZrP and 18.7 wt% APP, PP classed a UL‐94 V‐0 rating with a high LOI value of 39.5%. Moreover, the peak heat release rate, the total heat release, the peak of CO production, and the peak of CO2 production of PP/RQMIFR‐ZrP/APP decreased by 94.0%, 83.2%, 91.3%, and 91.7%, respectively. It revealed that RQMIFR‐ZrP not only generated nitroxyl radicals (NO•) to suppress the chain degradation of PP but also promoted to form high‐quality intumescent char layers with the catalytic carbonization and layered barrier effect of ZrP nanosheet, which effectively prevented PP from burning. This work provides a new approach to preparing high‐performance flame‐retardant polymer.

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Phosphorus‐nitrogen intumescent flame retardant (IFR) is one of the most promising halogen‐free flame retardants in enhancing the fire safety of polypropylene (PP), but its efficiency needs to be further improved. Herein, a novel single‐component polyphosphazene IFR containing pentaerythritol caged phosphate (PEPA) functionalized titanium carbide nanosheet (MXene), named PZS‐MXene, was prepared. When the amount of PZS‐MXene was 25 wt%, PP/PZS‐MXene classed a UL‐94 V‐0 rating with the limiting oxygen index of 32.7%. Compared with PP, its peak of heat release rate, total heat release rate and total smoke production rate were reduced by 74.5%, 33.0%, and 19.8%, respectively. The flame‐retardant mechanism revealed that PZS‐MXene quenched high‐active free radicals to inhibit the degradation of PP during the combustion. MXene rapidly catalyzed the carbonization of PZS to form high‐quality intumescent char layer on its surface. Besides, MXene acted as the supporting skeletons and exerted the layered barrier effect to improve the compactness of the intumescent char layer, thus effectively inhibited the degradation and combustion of PP. This work provided new insights for the efficient halogen‐free flame‐retardant PP.