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

The spherulitic crystal structure and thermal transition behavior of poly[b is(phenoxy)phosphazene] have been investigated using differential scanning calorimetry (DSC), polarized microscopy, X-ray diffraction, and thermal mec hanical analysis. polymer films were solution-cast from xylene over relativ ely wide crystallization and annealing ranges. Large-scale spherulites were created at a polymer concentration (in xylene) of 0.50 wt/vol% and a cryst allization temperature of 80 degrees C. One or two endothermic T(1) transit ion 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. In tramolecular 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 t he transitions, however, made the 2-D phase more ordered, with a decrease i n intermolecular spacing. A melting transition was not found in DSC scans, up to the polymer decomposition temperature of 390 degrees C. An annealing treatment of the polymer had a significant effect on the transition behavio r; either one or two T(1) transition peaks were observed in DSC scans, depe nding on the annealing temperature and the Delta H heat how of the transiti ons increased with annealing temperature. X-ray and polarized microscopy re sults showed that a more stable crystal structure was formed after annealin g at a temperature above the T(1) transition(s). (C) 1999 Elsevier Science Ltd. All rights reserved.