Copolyarylates containing phthalazinone and cardo moieties: An attempt toward the balance between thermal resistance and solubility

Abstract A series of copolyarylates containing phthalazinone and cardo moieties are synthesized by interfacial polymerization of terephthaloyl dichloride with bisphenol monomers including 2,4‐(4‐hydroxyphenyl)‐2,3‐phthalazin‐1‐one, 9,9‐bis(4‐hydroxyphenyl) fluorene, and phenolphthalein. The intrinsic viscosity and number average molecular weight of copolyarylates are in the range of 0.71–1.01 dL g −1 and 16.3–28.4 kDa, respectively, indicating the formation of medium molecular weight copolymers. The effects of phthalazinone and cardo moieties on the solubility and thermal resistance of copolyarylates are discussed in detail. With only phthalazinone moieties, the polyarylate has high thermal resistance with the glass transition temperature ( T g ) of 335 °C, but poor solubility. The introduction of cardo moieties enables the produced copolyarylates readily soluble in chloroform, 1,1,2,2‐tetrachloroethane, and N ‐methyl‐2‐pyrrolidone, for they not only increase the free volume of intermolecular chains but also lead to a fractional reduction in the structural stiffness of copolymers. Although the decrease in structural stiffness is related to a decrease in T g value, fortunately, the rigid cardo and phthalazinone moieties allow the thermal resistance of copolyarylate to reach the leading level among (co)polyarylates. In addition, the resulting copolyarylates have good tensile properties. These copolyarylates have important application prospects in the high thermal‐resistant material industry.