Hyperbranched Phosphorus‐Containing Polyamide Enables Balanced Flame Retardant and Mechanical Performance in Polypropylene

ABSTRACT A novel hyperbranched phosphorus‐containing polyamide (HPA‐NP) was synthesized and incorporated into a polypropylene (PP) matrix to achieve a superior balance between flame retardancy and mechanical performance. The distinctive three‐dimensional hyperbranched architecture, in which 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) and phenolic moieties were grafted as functional “fruits,” improved the interfacial compatibility between HPA‐NP and the PP matrix, thereby promoting effective stress transfer. The combined introduction of phosphorus‐ and hydroxyl‐containing groups imparted HPA‐NP with flame‐retardant functions in both the condensed and gas phases, thereby promoting the development of a compact intumescent char upon combustion. Consequently, the composite with only 2.4 wt% HPA‐NP achieved a high limiting oxygen index (LOI) of 28%, a UL‐94 V‐0 rating, and an 80% reduction in peak heat release rate (PHRR, from 780.4 to 155.5 kW m −2 ). Importantly, these improvements in fire safety were achieved without compromising mechanical integrity, as evidenced by a tensile strength of 18.2 MPa and a notched impact strength of 6.6 kJ·m −2 . These results demonstrated an effective approach for simultaneously enhancing flame retardancy and mechanical reinforcement in polyolefin composites.