Spectroscopic behavior of poly(vinyl alcohol) films with different molecular weights

Pure poly(vinyl alcohol) (PVA) films with molecular weights 5000, 17,000, 72,000, 125,000 g/mol, respectively were prepared by a casting technique. The thickness of the prepared samples was 0.21 mm. Optical absorption and transmission measurements were performed on these samples. The UV-Visible absorption spectra gave the same band positions but the absorption intensity varies in a reverse trend with increase of the molecular weight, which may be due to decrease in the concentration of C=C, C=O groups. Identification of the structure and assignments of energy bands were also studied by using FTIR and NMR. The refractive indices of the samples were measured and it was found the refractive index decreases with increasing molecular weight. (C) 2002 Elsevier Science Ltd. All rights reserved.