Well-defined precision ethylene/vinyl fluoride polymers: Synthesis and crystalline properties

Here we report the synthesis and crystalline structure of a family of three precision ethylene/vinyl fluoride (EVF) polymers with fluorine atoms on each and every 9th, 15th, and 21st carbon via ADMET polymerization, followed by exhaustive hydrogenation. The primary structure of the polymers is confirmed by NMR, TGA, IR, and elemental analysis. The crystallization pattern of these systems is analogous to that of homopolymers as evidenced by the equivalent halogen content in amorphous and crystalline regions, as obtained by solid-state NMR. This is supported by SAXS periodicities that conform with layered crystalline-amorphous structures of folded chains. While the thickness of the amorphous layer is small (similar to 45 angstrom) and constant within the series, the crystallite thicknesses (similar to 200-100 angstrom) decrease with. increasing fluorine. The latter, and the depression of crystallinity, equilibrium melting, and heat of fusion with increasing content of F attest to the restrictions of this halogen, although of a small volume, as a defect to the crystallization of these systems. Nonetheless, strain from the inclusion of the fluorine atom in the crystal lattice of the three precision EVF polymers investigated is small, such that the orthorhombic packing of the polyethylene chain is maintained in these new polymers.