Raman and IR spectroscopy were used to examine polyvinyl alcohol (PVA) thermally treated in air or vacuum. It was found that after several hours of treatment in air at 470 K bands in Raman spectrum disappear. After vacuum treatment some bands disappear and other become stronger, and slightly change their positions. Such a phenomenon is attributed to the increase of molecular polarizability along polymer chain caused by conjugation.
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Prosanov et al. (2010) studied this question.
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