Effect of heat treatment on the thermal and mechanical properties of polyhydroxyamic acid presursor films

Summary

Polyhydroxyamic acid (PHAA) with an inherent viscosity of 0.45 dL/g was prepared from 3, 3'-dihydroxybenzidine and pyromellitic dianhydride. The mechanical and thermal properties of PHAA films and powders before and after annealing were investigated on the basis of their potential use as fire-safe polymers. Cyclization of PHAA to the corresponding hydroxy-containing polyimide is an endothermic reaction. During annealing of PHAA, water was released at 180 °C and carbon dioxide at over 400 °C. The weight residue of PHAA at 900 °C was about 38 %. After annealing at 500 °C, this value increased to 75 %. After annealing at 450 °C, the ultimate stress and initial modulus of the PHAA precursor films increased from 133.8 MPa and 5.86 GPa to 306.2 MPa and 11.0 GPa, respectively.