Effect of the third monomer unit on the phase transition of oriented ethylene-tetrafluoroethylene copolymer studied by the temperature-dependent measurements of 2D X-ray scattering and polarized infrared spectroscopy

Abstract

The influence of third monomer units with different chain lengths on the phase-transition behavior of the uniaxially oriented ethylene tetrafluoroethylene (ETFE)-alternating copolymer has been investigated through the use of temperature-dependent measurements of X-ray fiber diagrams, small-angle X-ray scattering patterns and polarized infrared spectra. (i) The phase transition between the low-and high-temperature phases occurs discontinuously; (ii) in the transition, the conformational disordering and radical thermal motion of the chains occur drastically as known from the increment of the half-width of the X-ray 004 reflection profile in the high-temperature region, which is associated with the trans-gauche conformational disordering; (iii) the phase-transition temperature decreases with an increase in the third monomer unit content, and the decreasing rate is overwhelmingly higher for the terpolymer with short CF 3 groups than for the terpolymer with longer C 4 F 9 groups. The CF 3 groups are included in the crystal lattice and affect the phase-transition point significantly, whereas the C 4 F 9 groups are expelled from the lattice and affect the transition behavior to a small degree; and (iv) The temperature-dependent two-dimensional small-angle X-ray scattering pattern measurements of the oriented samples revealed that the long period of the stacked lamellar structure did not change in the transition between the low-and high-temperature phases.

Characteristic Features of Crystalline Poly(1,2-difluoroethylene): Revisiting the Old-but-Totally-Unknown Fluorine Polymer

“…As a result, even random arrays of the H and F atoms as the side groups of skeletal chains may not disturb the crystallization, with relatively regular chain packing in the crystal lattice. This type of example can also be seen for other kinds of fluorine polymers such as the ethylene–tetrafluoroethylene random copolymer − and so on. In this way, we do not have any positive reason why PVLF had been told to be totally amorphous.…”

“…As listed in Table , we know the various industrially and scientifically important fluorine polymers. Depending on the number of fluorine and hydrogen atoms in the monomeric unit, the structure and physicochemical properties change remarkably. − The copolymerization between the various kinds of fluorine monomeric units also gives us unique and practically useful copolymers. − In Table , we focus on one characteristic fluorine homopolymer having two fluorine atoms in one monomeric unit, that is, poly­(1,2-difluoroethylene) (PVLF, −[CHFCHF] n −), which was also called poly­(vinylene fluoride) …”