Self-Nucleation Ability and Intermolecular Interactions Mechanism in Fluoropolyolefins

Self-nucleation behavior is a critical phenomenon in polymer crystallization, and the impact of the chemical structure on this behavior has been extensively investigated. However, the underlying mechanism has not been fully elucidated. In this study, the self-nucleation behavior of a series of polyolefins with varying degrees of fluorine substitutions is comprehensively surveyed. Incorporation of fluorine atoms, which increase the polarity of polyolefin chains, considerably improves the self-nucleation ability, resulting in an apparent expansion of the temperature widths of Domain II for poly(vinyl fluoride) and poly(vinylidene fluoride) in comparison with polyethylene. However, further fluorine substitution diminishes the self-nucleation ability of fluoropolyolefins. Then, the correlation between the self-nucleation ability and dielectric constant is studied. It is found that the width of Domain IIb increases monotonously with respect to dielectric constant, expect for poly(vinylidene fluoride) which exhibits a slightly narrow Domain IIb than poly(vinyl fluoride). However, a rather wide Domain IIa appears in poly(vinylidene fluoride). Based on the intermolecular interactions, a correlation between the width of Domain II and the dielectric constant is reasonably established. Further, Fourier transformation infrared spectroscopy directly reveals that the hydrogen-bonding interactions between C–F and C–H are the essential reason for the self-nucleation behavior of fluoropolyolefins. However, in combination with the intriguing disappearance of self-nucleation behavior for the ethylene–tetrafluoroethylene alternating copolymer, the isomer of poly(vinylidene fluoride), and ethylene–chlorotrifluoroethylene alternating copolymer, it is unveiled that the possible scattering, isolated F···H–C hydrogen bonds in fluoropolyolefin are not a sufficient condition for endowing self-nucleation behavior. Thus, an interacting mechanism of long-range continuous structure of hydrogen bond is speculated for the display of the self-nucleation ability of fluoropolyolefins. This work deepens the understanding of self-nucleation crystallization in fluoropolyolefins and provides guidance for the melt processing.