Phase transformations of some poly(vinyl alcohol)–NiCl2 composites

Abstract

AbstractSamples of poly(vinyl alcohol)–NiCl2 composites containing up to 30 wt% NiCl2 were prepared by casting in order to study phase transformation–structural change relationships of these samples before and after heat treatment. Differential thermal analysis (DTA) thermograms were recorded at 10, 15, 20 and 30 °C min−1. For untreated samples four endotherms were assigned as: rotation of hydroxyl groups in the glassy state, glass transition, structural transition in the rubber‐like state, and melting transition. Ultrasonic attenuation measurements were carried out to confirm these transitions in the glassy and rubber‐like states. In the glassy state, the effect of NiCl2 addition is explained in terms of chain stiffness due to the creation of local crosslinked regions in amorphous parts of the polymer. Average values of activation energies for glass transition were calculated using both methods of Kissinger and Ozawa. However, addition of NiCl2 had an opposite effect on the heating rate independent crystallization melting temperature (Tm), relative to that on Tg. The DTA thermograms of heat‐treated samples indicated that square planar NiCl2 molecules were embedded in the polymer matrix with no local crosslinking role due to the formation of conjugated polyenes along the polymer chains by thermal treatment. Copyright © 2003 Society of Chemical Industry