Phase-transition behavior of a crystalline polymer near the melting point: case studies of the ferroelectric phase transition of poly(vinylidene fluoride) and the β-to-α transition of trans-1,4-polyisoprene

Abstract

Many crystalline polymers exhibit phase transitions between the low-and high-temperature phases during the heating process. Sometimes, however, the temperature-dependent measurement of the X-ray diffraction peaks and vibrational spectra leads us to the incorrect conclusion that these two phases transform in a direct solid-to-solid transition mode instead of the melt and recrystallization process. As a reliable method to confirm the transition behavior just below the melting region, we have developed a temperature-jump cell system, with which a time-dependent measurement of the X-ray diffraction peaks (and Fourier-transform infrared spectra) is performed in the rapidly changing temperature process from the low-to the hightemperature phase. This method was applied to two types of polymers and revealed that (i) the high-temperature phase transition of poly(vinylidene fluoride) is not a direct ferroelectric transition between the ferroelectric and paraelectric phases, as proposed in our previous studies (Polymer (1983), Polym. Bull. (1983)), but a melt of the ferroelectric phase (form I) followed by the recrystallization into the nonpolar crystalline phase (form III or V) and (ii) the b-to-a phase transition of trans-1,4-polyisoprene had been also controversial for many years but it was revealed to occur via a melt-recrystallization mechanism.

Structural Evolution Mechanism of Crystalline Polymers in the Isothermal Melt-Crystallization Process: A Proposition Based on Simultaneous WAXD/SAXS/FTIR Measurements

“…The appearance of an intermediate phase can be detected clearly for this polymer [36,37]. As shown in Figure 7, where the temperature-dependent intensity change was plotted for the various IR bands in the continuous cooling process, the band at 1205 cm −1 appeared when the molten sample was cooled to about 45 °C.…”

Ferroelectric PVDF nanofiber membrane for high-efficiency PM0.3 air filtration with low air flow resistance

“…This leads to a re-ordering of dipole moments, thereby sharpening the crystalline peak of the β phase and subsequent intense ferroelectricity at higher annealing temperatures [39] , [62] . Prolonged heating treatment at high temperature might result in the filtration performance degradation due to the slight deterioration of PVDF crystalline phases consisting of β phase [63] , which is clearly depicted by XRD patterns in Fig. S6 .…”

Micropatterning of the Ferroelectric Phase in a Poly(vinylidene difluoride) Film by Plasmonic Heating with Gold Nanocages

“…The thermally induced ferroelectric to paraelectric phase transition of PVDF has been reported to occur near its melting point (ca. 170 °C) through an intermediate amorphous or liquid‐crystalline phase . When the laser energy added into the AuNC/PVDF film reached 800 J cm −3 , the corresponding temperature could be over 170 °C (see Figure b).…”