L'uso combinato della spettroscopia dielettrica (DS) e della rilassometria 1H NMR Fast-Field Cycling ha permesso di comprendere il comportamento dinamico del ter-polimero amorfo polivinil butirrale (PVB) in un intervallo di temperatura che includeva la transizione vetrosa (Tg). Sopra la Tg, moti segmentali della catena principale sono osservati e caratterizzati con entrambe le tecniche. Sotto Tg, la spettroscopia dielettrica ha rivelato un rilassamento beta ascritto a riorientazioni dei dipoli sulle unita' di vinil alcool associate con moti locali di twisting. I dati di rilassometria NMR hanno supportato la presenza di questo moto.
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.
DYNAMICS OF POLY(VINYL BUTYRAL) STUDIED BY DIELECTRIC SPECTROSCOPY AND 1H NMR RELAXOMETRY
Silvia Pizzanelli;Daniele Prevosto;Massimiliano Labardi;Tommaso Guazzini;Simona Bronco;Claudia Forte;Lucia Calucci
2017
Abstract
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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
