The thermal, thermomechanical and thermal-dielectric properties of polyurethane blends based on branched polymer polyol (PUR) and styrene-acrylonitrile (SAN) copolymer were studied by differential scanning calorimetry (DSC), thermomechanical analysis (TMA), thermally stimulated depolarization currents (TSDC) techniques and dielectric relaxation spectroscopy (DRS). Several molecular mobility mechanisms associated with secondary local relaxations, primary (main) relaxations due to the dynamic glass transition and conductivity effects were observed and studied in detail. The use of several molecular mobility techniques, characterized by various spatial and time scales, allowed for several intercomparisons, in particular with respect to the determination of glass transition temperatures and of the temperature dependence of relaxation times which indicate the advantages and the limits of each particular technique. The results by the different techniques suggests in agreement to each other, that on addition of SAN the microphase separation between hard segment (HS) microdomains and soft segment (SS) microphase of PUR is improved.