Characterization of two precursor polyblends: Polyhydroxyamide and poly(amic acid)

Blends of two precursor polymers, polyhydroxy amide (PHA) and poly(amic acid) (PAA), were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The presence of PHA enhanced thermal and mechanical properties of the polyblends. All of the polyblended films showed large endothermic peaks that decreased monotonically with increasing heat treatment temperature. The cyclization onset temperature (T-1), initial decomposition temperature (T-2), and weight residue at 900 degrees C of the polyblends were shown to be in the ranges of 144-146 degrees C, 532-540 degrees C, and 44-45%, respectively. Also, the thermal stabilities were enhanced consistently with increasing annealing temperature from 25 to 250 degrees C. The ultimate strength and initial modulus of the polyblends increased from 84 to 136 MPa and from 2.93 to 5.34 GPa, respectively, with increasing PHA content. Similar to the trend of thermal stability, increasing the annealing temperature of the polyblends increased the tensile properties of the films. The observed tensile properties are discussed in terms of the morphology of the fractured films as studied by scanning electron microscopy (SEM). The degree of crystallinity of the polyblends was characterized as a function of heat treatment temperatures by wide angle X-ray diffractometry (WAXD).