Thermodynamic and spectroscopic analysis of the conformational transition of poly(vinyl alcohol) by temperature-dependent FTIR

The conformational change of poly(vinyl alcohol) has been studied by Fourier transform infrared spectroscopy at various temperatures in the 4000-400 cm^-1 region. The molecular motion and the trans/gauche content are sensitive to the CH, CC stretching modes. FTIR spectra show that the I₂₉₂₀/I₂₈₄₉ decreases from 1.84 to 1.0 with increasing temperature, companying the decrease in I₁₀₄₇/I₁₀₉₅ from 0.78 to 0.58, implying the conformational transition from trans to gauche in alkyl chain. Based on the van't Hoff relation, the enthalpies and entropies have been calculated in different temperatures, which are 4.61 kJ mol^-1 and 15.23 J mol^-1 K^-1, respectively, in the region of 80-140°C. From the CO stretching mode and OH band, it can be concluded that the intermolecular hydrogen bonds decrease owing to elevating temperature, which leads to more gauche conformers.