Temperature transitions and orientational order in surface layers of poly-bis-trifluoroethoxyphosphazene

Poly[bis(trifluoroethoxyphosphazene)] films were studied using mechanical and dielectric loss spectroscopies, and photoelasticity and birefringence measurements. Glass transition temperature (-70 degrees C), temperature of the transition to mesomorphic state and spontaneous disordering in surface layers (70 degrees C), temperature of the transition of mesophase to a new modification (120 degrees C), and the temperature of isotropization and transition of the polymer to amorphous state (225 degrees C) were determined. It was demonstrated that the segmental optical anisotropy of poly[bis(trifluoroethoxyphosphazene)] in bulk is two times higher than that in solution. On this basis, a conclusion was made that strong orientational interaction exists between the molecules of polymer; this interaction accounts for the higher thermodynamic rigidity of poly[bis(trifluoroethoxyphosphazene)] chains in bulk polymer than in solution. It was found that the chain fragments of the polymer are predominantly oriented parallel to the film surface. Optically anisotropic surface layers are approximately 110 mu m thick, that is, their thickness is about 2-3 times larger than that in amorphous carbochain polymers; this indicates that the molecules of poly[bis(trifluoroethoxyphosphazene)] show a marked tendency to orientational ordering.