Dielectric investigations of microphase separation in polyurethane-styrene/acrylonitrile blends

This work deals with dielectric studies of microphase separation in blends of thermoplastic polyurethanes (TPUs) styrene/acrylonitrile (SAN) copolymers. The dielectric techniques used include broadband ac dielectric relaxation spectroscopy (DRS)-in frequency range of 10² to 10⁶ Hz and temperature range of 200 to 450 K and thermally stimulated depolarization currents (TSDC) techniques. TSDC techniques were mainly employed to investigate the sub-glass local relaxations in TPU, SAN and their blends. DRS allowed to follow the dynamics of the glass transition in the pure components and and their blends. The α-relaxation due to the glass-rubber transition of the TPU phase becomes faster with increasing SAN content. On the other hand, the α-relaxation due to the glass-rubber transition in SAN becomes slower with increasing TPU content. These results are in agreement with glass transition measurements by calorimetry (DSC). The shape of dielectric loss peak for the primary α-relaxation of SAN does not change significantly with temperature and blend composition