Phase behavior and molecular mobility in polyurethane/styrene-acrylonitrile blends

Differential scanning calorimetry (DSC), thermally stimulated depolarizatio n currents (TSDC) techniques, dielectric relaxation spectroscopy (DRS), and dynamic mechanical thermal analysis (DMTA), covering together a wide range of temperatures and frequencies, were employed to investigate molecular mo bility and microphase separation in blends of crosslinked polyurethane (PUR ) and styrene-acrylonitrile (SAN) copolymer, prepared by reactive blending with polymer polyols. The results by each technique indicate that the degre e of microphase separation of PUR into hard-segment (HS) microdomains and s oft-segment (SS) microphase increases on addition of SAN. The various techn iques were critically compared to each other, with respect to their charact eristic time and length scales, on the basis of activation diagrams (Arrhen ius plots). The results show that for the dynamic glass transition of the P UR SS microphase the characteristic time scales at the same temperature are similar for DMTA, DSC, and TSDC and shorter for DRS. In terms of fragility , the PUR/SAN blends are classified as fragile systems. (C) 2001 John Wiley & Sons, Inc.