Fracture surface morphology of poly[bis(trifluoroethoxy)phosphazene]

Poly[bis(trifluoroethoxy)phosphazene] (PBFP) films were prepared from tetrahydrofuran solution. Fracture surface morphology was studied by scanning electron microscopy. Two morphologies associated with heat treatment have been established: (a) cospherically grown aggregates are obtained in solution-cast films and films heated through the T(1) transition; (b) aggregates of irregular shaped crystalline platelets obtained after melting and crystallization. Ion etching was also applied to the fracture surface in order to clarify the morphological and structural features. The striations originally associated with the [c] axis direction of PBFP crystals can be accentuated on the fracture surface of original as-cast spherulitic films by employing this technique. The texture of the fracture surface after etching is compared with that obtained for an oriented fibre made from this polymer. From this comparison it can be concluded that the [c] axis direction is perpendicular to the spherulite radius. Furthermore the morphology is analogous in many respects to that of Kevlar.