Dielectric relaxation spectroscopy in crosslinked polyurethanes based on polymer polyols

This work deals with molecular mobility and microphase separation studies in blends of crosslinked polyurethanes and styrene-acrylonitrile (SAN), prepared by reactive blending, by means of differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DRS) techniques. The DRS techniques employed include broadband ac techniques, 10(-2)-10(6) Hz, and thermally stimulated depolarization currents (TSDC) techniques, -180 to 30 degrees C. The results suggest, in agreement with each other by the different techniques, that SAN promotes the microphase separation between hard segment (HS) microdomains and soft segment (SS) microphase due to SAN-MS interactions, whereas SAN-SS interactions are weak. TSDC thermal sampling techniques show that a compensation law holds for the alpha relaxation associated with the glass transition of the SS microphase, with the compensation temperature being very close to the glass transition temperature. Analysis of the alpha relaxation in terms of fragility indicates that the systems under investigation are fragile. (C) 2000 Elsevier Science Ltd. All rights reserved.