STRUCTURE AND DEFORMATION-BEHAVIOR OF A VINYLIDENE FLUORIDE-TETRAFLUOROETHYLENE-HEXAFLUOROPROPYLENE TERPOLYMER

The statistical terpolymer composed of 52 mol% vinylidene fluoride (VD F), 36 mol% tetrafluoroethylene (TFE) and 12 mol% hexafluoropropylene (HFP) is a ductile material that can be highly deformed in uniaxial te nsile tests. Wide-angle and small-angle X-ray scattering (WAXS, SAXS) techniques have been used to study the structure of uniaxially oriente d samples. WAXS shows that the terpolymer exhibits a low degree of cry stallinity (x(c) approximate to 0.1). The crystalline structure combin es features of both VDF and TFE, in agreement with previous studies on VDF/TFE copolymers. Concentration fluctuations do not contribute sign ificantly to SAXS of the VDF/TFE/HFP melt. Melt-crystallized samples e xhibit a lamellar morphology with a long period of L = 12 nm and a vol ume fraction of crystallites of Phi(c) = 0.26. Deformation of the terp olymer at T = 50 degrees C results in a four-point SAXS pattern, which gradually changes to a two-point pattern when the drawing temperature increases. The mean-square fluctuation of the electron density strong ly decreases at low drawing temperatures. It is assumed that vacancies introduced near the grain boundaries reduce the density of the crysta lline layers.