Confirmation of Crystal Structure of Poly(vinylidene fluoride) through the Detailed Structure Analysis of Vinylidene Fluoride Oligomers Separated by Supercritical Fluid Chromatography

Abstract

Vinylidene fluoride (VDF) oligomers with uniform molecular weights were separated successfully by using supercritical fluid chromatography, and the crystal structures were determined by X-ray analysis of the single crystals. Although the chemical formulas of these oligomer components had not been known clearly, the X-ray structure analysis gave us the following results: CF(CF3)2−(CH2CF2)n−I with n = 6−12. The oligomer chains were found to form a layer structure, in which the chains are tilted slightly from the normal to the layer plane. The chain conformation of the oligomers, when crystallized from ethanol solutions, was a repetition of TGTḠ, essentially the same with that of poly(vinylidene fluoride) crystal form II. The packing structure of central VDF sequence parts was also found to be the same with that of form II: the chains are packed in an antiparallel mode with respect to the chain direction as well as the direction of CF2 dipoles. A series of oligomers were found to show a variety of crystal modifications depending on the sample preparation conditions, as seen from the infrared spectral patterns.