Thermo-oxidative stabilization and degradation pathway regulation of polyarylates by main-chain incorporation of DOPO-HQ

To address the limited solution processability and insufficient thermo-oxidative char stability of conventional polyarylates, a molecular structure regulation strategy was proposed in this work. A series of DOPO-HQ-containing copolyarylates were synthesized by incorporating 10 - (2,5 - dihydroxyphenyl) - 10H - 9- oxa-10-phosphaphenanthrene-10-oxide (DOPO-HQ) into the polyarylate backbone through solution copolycondensation. The chemical structures and copolymer compositions were confirmed by 1 H NMR, HSQC NMR, quantitative 1 H NMR, and FT-IR analyses, while GPC and XRD were used to characterize the molar-mass parameters and amorphous structures, respectively. Thermal analysis showed that DOBA-20, prepared with 20 mol% DOPO-HQ in the total bisphenol feed, exhibited a glass transition temperature of 194.9 °C and a char yield of 38.3% at 800 °C under nitrogen. More importantly, DOBA-20 retained a char yield of 32.7% at 800 °C under air atmosphere, far exceeding that of the DOPO-HQ-free polyarylate, DOBA-0 (0.04%), indicating significantly enhanced char stability under oxidative conditions. TG-FTIR and Py-GC/MS analyses, together with XPS and SEM analyses of char residues, demonstrated that DOPO-HQ mainly promoted the retention of phosphorus species in the condensed phase, facilitating the formation of a continuous and compact phosphorus-rich char layer containing phosphate/pyrophosphate structures. This stable char layer could suppress heat transfer and oxygen diffusion, possibly accompanied by limited gas-phase inhibition. This work provides a molecular design strategy for regulating the thermal degradation pathway of polyarylates and improving their solution processability and thermo-oxidative stability.