Normal-mode analysis of infrared and Raman spectra of polyhinyl fluoride)

Infrared and Raman spectra of samples of poly(vinyl fluoride) (PVF) have been recorded. The vibrational spectra have been analyzed by means of normal-mode calculations. A force field was derived by using Zfluorobutane as a model compound. Crowder’s force field for hydrofluorocarbons was employed as a starting point and subsequently refined in application to secondaty fluorides. A planar zigzag, syndiotactic single-chain model of crystalline PVF was submitted to be analyzed by this scheme. A comparison of observed infrared and Raman bands with frequencies calculated for syndiotactic PVF shows that PVF produced by conventional free radical polymerization has an atactic structure, supporting the “F-NMR results and conclusions reached by Koenig and Boerio. Band assignments in terms of atactic structure are proposed. Keyworda: Infrared spectrometry; Raman spectrometry; ZFluorobutane; Normal-mode analysis; Poly(viny1 fluoride) Several researchers have reported infrared and Raman spectra of poly(viny1 fluoride) (PVF), and tentative band assignments have been made. The infrared spectra of PVF were used by Koenig and Mannion [l] as a basis for analyzing enchainment, conformational and configurational defects in the material. The Raman spectrum subsequently obtained by Koenig and Boerio [2] led to the interpretation of the stereochemical configuration of the polymer. The polarized infrared spectrum of PVF has also been interpreted by Zerbi and Cortelli [3]. However, there are still many aspects of the vibrational spectrum that are not completely understood. The stereoregularity of PVF, in particular, has been the subject of controversy. Both the x-ray work of Natta et al. [4] and Koenig’s Raman spectra [2] subsequently obtained have led to the conclusion that the polymer is atactic. In addition, the tacticity of PVF has been recently studied by 19F solution NMR, and has been shown to be atactic [5-71. Zerbi and Cortelli [3], on the other hand, have suggested a syndiotactic structure for PVF. In the general case, the straightforward nature of interpreting NMR data would favor the atactic structural assignment. However, in the case of PVF, like PVC, the differential solubility of alternative chain configurations may play an important role. It is suspected that highly syndiotactic PVF, like highly syndiotactic crystalline PVC [8], is marginally soluble even in good solvents. This would imply that NMR analysis of syndiotactic PVF chain segments, localized in insoluble crystallites, would suffer a negative bias due to spin0924~2031/92/$05.00