Structure of a Ring-Containing Fluoropolymer

Abstract

The structure of a ring-containing fluoropolymer poly(1,2-difluoromethylene-1,2,3,3-tetrafluoro-4,4-dihydrofuran) has been investigated by X-ray methods. Pressed films are more than 60% crystalline, and small-angle X-ray data show that these contain lamellae oriented with their long axes parallel to the surface. The wide-angle X-ray data show that the chains are perpendicular to the film surface and have an axial repeat of 9.62 Å, probably containing two monomers (an axial advance of 4.81 Å per monomer). Molecular mechanics modeling indicates that the most likely structure contains syndiotactic chains in which the monomers have the threo configuration: such chains are ribbonlike, with an axial advance of ∼4.8 Å, in good agreement with the observed repeat. In contrast, the preferred conformation for the isotactic chain of threo monomers is a nonintegral helix with close to five monomers per turn and an axial advance of ∼4.1 Å/monomer, which is not compatible with the X-ray data. Chains of monomers in the higher energy erythro configuration have monomer repeats in the region of 3.9−4.2 Å and appear unlikely. Thus, the results suggest that the high degree of crystallinity is due to a highly syndiotactic, probably blocky microstructure for the polymer.