Synthesis and Properties of Novel Aromatic Copolyamides Derived from 2-(4-carboxyphenyl)-4-[3-phenyl-4-(4-carboxyphenoxyl) phenyl]-phthalazinone

A series of four novel aromatic copolyamides were synthesized by the direct polycondensation of 2-(4-carboxyphenyl)-4-[3-phenyl-4-(4-carboxyphenoxyl)phenyl]-phthalazinone (1) and terephthalic acid (TPA) with some commercial diamines. The inherent viscosities of the polyamides were between 0.91 and 2.77 dL g^-1. All the copolyamides showed an amorphous nature as evidenced by wide-angle X-ray diffraction. Introduction of the non-coplanar phthalazinone segments into the polymer main chains remarkably improved the solubility of aromatic copolyamides. Most of the copolymers were soluble in aprotic polar solvents, such as N-methyl-pyrrolidone (NMP), N,N-dimethylacetamide, and dimethylsulfoxide. These aromatic copolyamides showed high thermal properties associated with the glass transition temperatures (T _g) in the range of 261–307°C and 10% weight loss temperatures in N₂ over 481°C. Moreover, the T _g values of the copolyamides increased with the increasing ratio of phthalazinone moiety in the main chain. Some polymer films cast from NMP solution had tensile strengths up to 244.4 MPa, initial moduli up to 5.08 GPa, and elongation at break values up to 9.9%.