DYNAMICS OF POLY(VINYL BUTYRAL) STUDIED BY DIELECTRIC SPECTROSCOPY AND 1H NMR RELAXOMETRY

The combined use of Dielectric Spectroscopy (DS) and 1H Fast Field-Cycling (FFC) NMR relaxometry allowed a detailed understanding of the dynamic behavior of the amorphous ter-polymer poly(vinyl butyral) (PVB) to be achieved across the glass transition temperature (Tg=70 °C by Differential Scanning Calorimetry). Above Tg, main chain segmental motions (alpha relaxation) were detected and characterized by both DS and FFC NMR relaxometry. The alpha process showed a Vogel Fulcher Tammann temperature dependence, with an associated Tg of 69 °C and a fragility of 155 for PVB glass. Below Tg, DS revealed a beta relaxation ascribed to reorientations of the vinyl alcohol dipoles due to local twisting motions and allowed an activation barrier of 11 kcal/mol to be determined. NMR relaxometry data supported the occurrence of this motion, although 1H relaxation could also be affected by reorientations of propyl side chains.