THERMAL-PROPERTIES OF A TOUGH, NEW SEMICRYSTALLINE POLYIMIDE

Thermal properties of a new semicrystalline polyimide synthesized from 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and 2,2-dimethyl-1,3(4-aminophenoxy)propane (DMDA) have been studied. Heat capacities in the solid and liquid states of BTDA-DMDA have been measured. The heat capacity increase at the glass transition temperature (T(g) = 230-degrees-C) is 145 J/degrees-C mol for amorphous BTDA-DMDA. The equilibrium heat of fusion of the BTDA-DMDA crystals has been obtained using wide-angle X-ray diffraction and differential scanning calorimetry measurements, and is 75.8 kJ/mol. Based on the information on crystallinity and the heat capacity increase at T(g), a rigid amorphous fraction is identified in semicrystalline BTDA-DMDA samples, which represents an interfacial region between the crystalline and amorphous states. In particular, this fraction increases with the crystallinity of the sample, which should be associated with crystal sizes, and therefore with crystal morphology. It has also been found that this polymer has a high-temperature crystal phase upon annealing above its original melting temperature. The thermal degradation activation energies of BTDA-DMDA in nitrogen and air are determined to be 154 and 150 kJ/mol, respectively.