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

Silvia Pizzanelli,Simona Bronco,Tommaso Guazzini,Claudia Forte,Lucia Calucci,Massimiliano Labardi,Daniele Prevosto

doi:10.1039/c7cp02595e

Abstract

Dielectric Spectroscopy (DS) and 1H 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 (Tg = 70 °C by Differential Scanning Calorimetry). Above Tg, main chain segmental motions (α 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 Tg of 69 °C and a fragility of 155 for PVB glass. Below Tg, a secondary process (β 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 β process was also found to contribute to 1H NMR relaxation above Tg.

Highlights

Poly(vinyl butyral) (PVB) is a random ter-polymer of vinyl butyral, vinyl alcohol and vinyl acetate (Fig. 1)
Dielectric Spectroscopy (DS) data were reported only at a few temperatures above the PVB glass transition in comparative studies of pristine PVB and PVB either UV irradiated[14] or loaded with alumina particles.15 13C solid state NMR spectroscopy experiments highlighted the formation of regions with different polymer mobility in plasticized PVB and the dynamics of some functional groups could be qualitatively investigated at room temperature as a function of the plasticizer content.[16,17,18]
Local dynamics, which is related to the glass transition phenomenon, usually dominates 1H NMR longitudinal relaxation at low temperature and high frequency, while polymer chain dynamics prevails at high temperature and low frequency.[20,21]

Summary

Introduction

Poly(vinyl butyral) (PVB) is a random ter-polymer of vinyl butyral, vinyl alcohol and vinyl acetate (Fig. 1). The random structure of PVB results in an amorphous polymer showing excellent optical clarity, adhesive properties, toughness, and flexibility Thanks to these properties, PVB is widely employed as an interlayer material in the manufacture of safety glass laminates, in automotive and architectural glass. Dynamics of melt-like polymer chains can be depicted as a hierarchy of processes starting from very fast and local conformational rearrangements (i.e. isomeric motions in side chains and local reorientations of the chains within the so-called Kuhn segment) and extending to slow, diffusive and collective motions of the polymer chains.[23,24,25] Local dynamics ( referred to as glassy dynamics), which is related to the glass transition phenomenon, usually dominates 1H NMR longitudinal relaxation at low temperature and high frequency, while polymer chain dynamics prevails at high temperature and low frequency.[20,21] In recent papers, it was shown that the combination of DS and 1H FFC NMR relaxometry can give detailed information on the dynamics of melt polymers, not attainable when a single method is used.[21,26,27]. Contributions to 1H T1’s may arise from reorientations of both main chain segments and side groups, in particular propyl chains of butyral monomers

Sample preparation

Molecular weight determination

Differential scanning calorimetry

Dielectric spectroscopy