Elucidating Ortho-Methyl Positioning Effects on Decomposition Pathways in Soluble Copolyarylates: A Synergistic Optimization of Solubility and Thermal Property Regulation

Optically transparent amorphous copolyarylates based on tetramethylbisphenol A (TMBPA) and bisphenol B (BPB) were synthesized via low-temperature interfacial polymerization. These copolyarylates exhibited high solubility, with number average molecular weight ( M n ) of 1.48 × 10 4 –1.92 × 10 4 g/mol, weight average molecular weight ( M w ) of 6.64 × 10 4 –9.13 × 10 4 g/mol, polydispersity index (PDI) of 3.45–5.89, and intrinsic viscosity of 0.62–0.83 dL/g. Incorporation of TMBPA alters the thermal properties of the copolyarylates, decreasing thermal stability ( T 5% ) from 473.4°C to 444.4°C and char yield from 34.6% to 19.7%, but increasing the glass transition temperature ( T g ) from 202.9°C to 234.1°C. TG/FTIR and Py-GC/MS analysis revealed that methyl groups adjacent to the phenolic hydroxyl group promoted chain breakage and accelerated thermal decomposition. The main gaseous products included H 2 O, CO 2 , CO, CH 4 , and phenolic compounds. Tensile strength, tensile modulus, and elongation at break of copolyarylates ranged from 51.83 to 60.21 MPa, 1023.28 to 1283.14 MPa, and 32.9% to 53.6%, respectively. This study highlighted the solubility-thermal property balance, providing insights for designing processable high-performance polyarylates.