ANNEALED SAMPLES OF SOME TETRAFLUOROETHYLENE PERFLUORINATED COPOLYMERS STUDIED BY SMALL-AND WIDE-ANGLE X-RAY-SCATTERING AND DIFFERENTIAL SCANNING CALORIMETRY

Some quenched and annealed samples of tetrafluoroethylene copolymers c ontaining perfluoropropyl vinyl ether, perfluoromethyl vinyl ether, an d hexafluoropropene were studied by small-angle X-ray scattering and d ifferential scanning calorimetry. Small-angle X-ray scattering experim ental spectra were analyzed by a fitting method with the profiles calc ulated from some theoretical distribution models of the lamellar thick ness. The mathematical evaluation of small-angle X-ray scattering patt erns has provided crystallinity values which were compared with those obtained by wide-angle X-ray scattering in order to obtain information on the organization of the lamellar stacks. The experimental results allow one to conclude that, during the annealing of the quenched fluor inated copolymers, at increasing temperatures, the melting of the thin lamellae takes place together with the appearance and the growth of n onlamellar crystallites.