Application of Raman Spectroscopy to Determine the α Phase Crystalline Fraction in Poly(vinylidene fluoride) Films

Poly (vinylidene fluoride), PVDF, is a semi-crystalline polymorphic polymer with three stable crystallographic forms. The non-polar alpha phase with TGTḠ chain conformation is the most common crystal form found in PVDF. α phase crystals can be obtained by cooling from the melt at conventional cooing rates of ~10-100 °C/min. We prepared PVDF films by compression molding PVDF (Kynar 301F) at 200ºC and cooling under ambient conditions. Fourier transform infrared spectra (FTIR) spectroscopy confirmed that only α-phase crystals were formed. By application of an annealing heat treatment, the crystalline fraction in the samples was varied from 38% to 65%. The application of Raman spectroscopy to determine the crystalline fraction of α-PVDF is novel. In this study, the degree of crystallinity of α-PVDF determined by Raman spectroscopy is presented and compared to the crystalline fraction found both from thermal analysis of endotherm area and from wide-angle X-ray scattering.