Phosphorus‐Bromine Synergistic Preparation of High‐Performance Polyphenylene Ether/Polystyrene Flame‐Retardant Foams

ABSTRACT This work tackles the challenge of flame‐retarding high‐porosity (porosity > 70%) polyphenylene oxide‐polystyrene (PPO/PS) composite foams with traditional condensed‐phase flame retardants. A synergistic system of phosphate ester (PX220) and brominated compound (BPS) was developed, relying on gas‐phase flame retardancy (primary) and condensed‐phase barrier/smoke suppression (supplementary). Their complementary decomposition temperatures enable timely gas‐phase product release to suppress PPO/PS thermo‐oxidative degradation, while PX220's plasticization improves BPS dispersion. For unfoamed samples, the system achieved a maximum LOI of 36.4%, with HRR reduced by up to 17 MJ/m 2 (4.8% higher than single systems). It also lowers smoke release via intumescent char. For 85% porosity foams, LOI reached 25.4% (HF‐1 pass), and even at > 90% porosity, HRR and melt dripping were suppressed. Moreover, PX220 and BPS refine cell morphology (via viscosity reduction and heterogeneous nucleation), increasing compressive strength by 0.67 MPa at 85% porosity. This study provides a novel flame‐retardant approach and strategy for lightweight, high‐performance PPO/PS composite foams.