Dielectric relaxation spectroscopy in crosslinked polyurethanes based on polymer polyols

This work deals with molecular mobility and microphase separation studies i n blends of crosslinked polyurethanes and styrene-acrylonitrile (SAN), prep ared by reactive blending, by means of differential scanning calorimetry (D SC) and dielectric relaxation spectroscopy (DRS) techniques. The DRS techni ques employed include broadband ac techniques, 10(-2)-10(6) Hz, and thermal ly stimulated depolarization currents (TSDC) techniques, -180 to 30 degrees C. The results suggest, in agreement with each other by the different tech niques, that SAN promotes the microphase separation between hard segment (H S) microdomains and soft segment (SS) microphase due to SAN-MS interactions , whereas SAN-SS interactions are weak. TSDC thermal sampling techniques sh ow that a compensation law holds for the alpha relaxation associated with t he glass transition of the SS microphase, with the compensation temperature being very close to the glass transition temperature. Analysis of the alph a relaxation in terms of fragility indicates that the systems under investi gation are fragile. (C) 2000 Elsevier Science Ltd. All rights reserved.