Crystal structure and thermal transition behavior of poly[bis(phenoxy)phosphazene]

摘要

The spherulitic crystal structure and thermal transition behavior of poly[bis(phenoxy)phosphazene] have been investigated using differential scanning calorimetry (DSC), polarized microscopy, X-ray diffraction, and thermal mechanical analysis. Polymer films were solution-cast from xylene over relatively wide crystallization and annealing ranges. Large-scale spherulites were created at a polymer concentration (in xylene) of 0.50 wt/vol% and a crystallization temperature of 80 deg C. One or two endothermic T(1) transition peaks, involving a change from a three-dimensional (3-D) ordered phase to a two-dimensional (2-D) ordered structure, was observed in DSC scans. Intramolecular X-ray reflections disappeared and the polymer "softened" above the transition(s), due to an increase in the local mobility/flexibility of side chains and some main chains. Further increases in temperature above the transitions, however, made the 2-D phase more ordered, with a decrease in intermolecular spacing. A melting transition was not found in DSC scans, up to the polymer decomposition temperature of 390 deg C. An annealing treatment of the polymer had a significant effect on the transition behavior; either one or two T(1) transition peaks were observed in DSC scans, depending on the annealing temperature and the #DELTA#H heat flow of the transitions increased with annealing temperature. X-ray and polarized microscopy results showed that a more stable crystal structure was formed after annealing at a temperature above the T(1) transition(s).