Polar Properties of PVDF Copolymers with Tetrafluoropropene: A First-Principles Based Study*

Polyvinylidene fluoride (PVDF, -CH₂-CF₂-) is a well-known organic electroactive compound — not only because of its respectable polar, piezoelectric and pyroelectric properties, but also as a convenient template for obtaining detailed insights into the nature of polymer ferroelectricity. In this investigation, we predictively evaluate the polar properties of β-PVDF copolymerized with 2,3,3,3-tetrafluoropropene (TFP, -CH₂-CF(CF₃)-) by utilizing a plane-wave-based density functional theory (DFT) approach. Contributions of individual VDF and TFP monomer dipole moments to the total polarization of the polymer crystal are identified from calculated maximally localized Wannier function (MLWF) charge centers. A number of different structural arrangements, involving combinations of β-PVDF chains with isotactic and syndiotactic TFP chains is explored, and the influence of these geometries on magnitudes of monomer dipole moments and total crystal polarization are elucidated.