Synthesis and characterization of novel aromatic poly(imide-benzoxazole) copolymers

New poly(imide-benzoxazole) copolymers were prepared directly from a dianhydride, a diacid chloride, and a bis(o-diaminophenol) monomer in a two-step method. In the first step, poly(amic acid-hydroxyamide) precursors were synthesized by low-temperature solution polymerization in an organic solvent. Subsequently, the thermal cyclodehydration of the poly(amic acid-hydroxyamide) precursors at 350 °C produced the corresponding poly(imide-benzoxazole) copolymers. The inherent viscosities of the precursor polymers were around 0.19-0.33 dL/g. The cyclized poly(imide-benzoxazole) copolymers had glass-transition temperatures in the range of 331-377 °C. The 5% weight loss temperatures ranged from 524 to 535 °C in nitrogen and from 500 to 514 °C in air. The poly(imide-benzoxazole) copolymers were amorphous, as evidenced by the wide-angle X-ray diffraction measurements. The structures of the precursor copolymers and the fully cyclized copolymers were characterized by Fourier transform infrared, ¹H NMR, and elemental analysis.