Relaxational study of poly(vinylpyrrolidone-co-butyl acrylate) membrane by dielectric and dynamic mechanical spectroscopy

A poly(vinylpyrrolidone-co-butyl acrylate) (60VP-40BA) membrane is synthesized as a tractable and hydrophilic material, obtaining a water-swelling percentage around 60%. An investigation of molecular mobility by means of differential scanning calorimetry, dynamic mechanical analysis and broadband dielectric relaxation spectroscopy (DRS) is fulfilled in the dry membrane. Dielectric and viscoelastic relaxation measurements are carried out on the 60VP-40BA sample at several frequencies between −150 and 150 °C. The dielectric spectrum shows several relaxation processes labelled γ, β and α in increasing order of temperature, whereas in the mechanical spectrum only the β and α relaxation processes are completely defined. In the dielectric measurements, conductive contributions overlap the α-relaxation. The apparent activation energies have similar values for the β-relaxation in both, the mechanical and the dielectric measurements. The β process is a Johari–Golstein secondary relaxation and it is related to the local motions of the pyrrolidone group accompanied by the motion of the segments of the polymer backbone. The γ process is connected with the butyl unit's motions, both located in the side chains of the polymer.