Structural Variations As A Function of Temperature and Dynamic-mechanical Relaxations For Ethylene-tetrafluoroethylene and Ethylene-chlorotrifluoroethylene Alternating Copolymers

The X-ray diffraction patterns at different temperatures of alternating ethylene-tetrafluoroethylene (ETFE) and of alternating ethylene-chlorotrifluoroethylene (ECTFE) copolymer samples are compared. For ECTFE, a reversible variation with temperature of the half-width of the diffraction peaks, analogous to but much smaller than that one which corresponds to the topotactic crystal-to-crystal transition of ETFE, was found. A comparison of the dynamic mechanical spectra of the two copolymers seems to confirm the different nature of the two high-temperature relaxation peaks. In particular, the so called alpha and beta relaxations of ECTFE occur in the amorphous phase while the so called alpha and alpha' relaxations of ETFE occur in the amorphous and crystalline phase, respectively.