Segmental Relaxation of Hydrophilic Poly(vinylpyrrolidone) in Chloroform Studied by Broadband Dielectric Spectroscopy

Dielectric relaxation caused by the segmental motion of poly(vinylpyrrolidone) (PVP) was studied in chloroform solutions with 5−40 wt % PVP at temperatures between 298 and 210 K above the melting temperature of chloroform (210 K) to obtain information on the dynamics of hydrophilic polymer. The asymmetric broadening of the loss peak and the fragility, i.e., the degree of deviation from the Arrhenius temperature dependence of relaxation time, increase with increasing PVP concentration. Both are due to increase in cooperativity of the segmental motion of PVP. The temperature-independent shape of the loss peak at a fixed concentration satisfies the time−temperature superposition and can be interpreted to be due to the small concentration fluctuation in the PVP/chloroform solutions. The repulsive force between PVP chains is expected to make the mixture homogeneous in chloroform, which is a good solvent of PVP.