Dynamics of poly(vinyl butyral) studied using dielectric spectroscopy and 1 H NMR relaxometry.

Dielectric Spectroscopy (DS) and H-1 Fast Field-Cycling (FFC) NMR relaxometry were applied for understanding the dynamic behavior of the amorphous ter-polymer poly(vinyl butyral) (PVB) across the glass transition temperature (T-g = 70 degrees C by Differential Scanning Calorimetry). Above T-g, main chain segmental motions (alpha relaxation) were detected and characterized using both DS and FFC NMR relaxometry. The correlation times extracted by the analysis of DS and FFC NMR relaxometry data agreed within a factor of three and showed a Vogel-Fulcher-Tammann temperature dependence, with an associated T-g of 69 degrees C and a fragility of 155 for PVB glass. Below T-g, a secondary process (beta relaxation) was revealed by DS, and was ascribed to reorientations of the vinyl alcohol dipoles due to local twisting motions with an associated activation barrier of 11 kcal mol(-1). The beta process was also found to contribute to H-1 NMR relaxation above T-g.