Structural models for crystallographic disorder in poly(tetrafluoroethylene)

Abstract

Some structurally disordered models for poly(tetrafluoroethy1ene) were elaborated and the corresponding calculated X-ray diffraction patterns compared with experimental patterns. This and differential scanning calorimetry results suggest some differences between the virgin powder and a sintered polycrystalline plate of poly(tetrafluoroethy1ene). These differences may be related to the crystal phase transitions that occur in a range of temperatures close to room temperature.

Effect of the initial matrix material on the structure of radiation‐grafted ion‐exchange membranes: Wide‐angle and small‐angle X‐ray scattering studies

“…The crystal structure of PTFE depends on the pressure and temperature. The transition temperatures of different crystal phases of PTFE are low; that is, phase IV of PTFE is stable in the range from 19 to 30 °C, phase II is stable below 19 °C, and phase I is stable in temperatures higher than 30 °C 19. Figure 2 shows the positions of the reflections of PTFE taken from a PDF file (number 47‐2217).…”

Spherulitic structures of poly [tetrafluoroethylene‐co‐(perfluoroalkyl vinyl ether)]

“…In addition, since tetrafluoroethylene copolymers obtained by incorporation of several comonomers exhibit extremely fast crystallization rates,6 their spherulites generally cannot be observed until they are sufficiently large. Therefore, PTFE exhibit a high degree of crystallinity of over 90% 7–9. Although there are a few reports that assume the formation of the spherulites of PTFE and their copolymers,10 it is hard to entirely believe them.…”

Phase behavior at low temperature of poly(tetrafluoroethylene) by temperature-modulated calorimetry

“…2b c b for the native sample, shows, according to what reported in the literature [1,2], the two endothermic transitions at about 22 and 31 8C, corresponding to the triclinic-hexagonal and to the hexagonal-pseudohexagonal transitions, respectively, with a total heat of transition of 15.3 J/g. Moreover, a shoulder of the first peak, studied by us extensively using DSC and WAXS [8][9][10][11][12], at about 18 8C, is observed. We interpreted it as the triclinic-hexagonal transition of morphologically disordered PTFE crystals.…”

“…a crystal characterized by dynamic conformational disorder and long-range positional and orientational order, common in liquid crystalline polymers. The native (never-melted) polymer, when obtained from aqueous dispersion polymerization, shows in the differential scanning calorimetry (DSC) pattern at low temperature, another small peak at about 17 8C [8,9], which has been interpreted by us, also through the support of wide angle X-ray scattering (WAXS) [10][11][12], by admitting the coexistence in the never-melted samples, of two phases with different order status, according to the folded ribbon model proposed by Suwa et al [13]. Native PTFE morphology has been extensively studied.…”