Poly(vinyl alcohol) (PVA) can be dissolved in a nonaqueous medium in the presence of catalytic concentration of ethyl nitrate dimethyl sulfoxide, C2H5ONO2 DMSO (EN DMSO). From the PVA solution, poly(vinyl butyral) (PVBu) was prepared by acid-catalyzed homogeneous acetalization of PVA with butyraldehyde. The formation of PVBu was confirmed by IR and H-1-NMR spectra. The degree of acetalization of PVBu was found to be 95 mol %, which was verified by H-1-NMR data and acetylation method. The molecular mass of the polymer was determined by GPC method. The glass transition temperature, T-g, was measured from differential scanning calorimetric (DSC) thermograms. Thermal stabilities were checked by thermogravimetric analysis (TGA) and differential thermogravimetry (DTG). The acetal decomposed in three stages. The corresponding initial decomposition temperatures were found to be 285, 390, and above 500 degreesC.