Chemical Modification, Thermal Characterization and Dielectric Spectroscopy of Polystyrene-block-Polyisoprene Diblock Copolymers

In this work, synthesis and chemical modification of a polystyrene-block-polyisoprene (PS-b-PI) diblock copolymer is presented. The modification reactions result in hydroxyl, amine, and carboxyl end-functional groups, respectively. Thermal analysis reveals a shift of the glass transition temperature of the polystyrene block to lower temperatures with respect to the polystyrene precursor because of the partial miscibility of the PS and the PI blocks. Comparing the glass transition temperature of the PS block of the three different end-functionalized diblock copolymers, the analysis in this work shows that a large end-group (i.e., the amine end-group) yields a lower glass transition temperature of the polystyrene block. The modified diblock copolymers were characterized by means of broadband dielectric spectroscopy in order to compare the results of thermal analysis and to monitor the dielectric relaxation behavior which is associated with the different end-functional groups. Comparing the dielectric loss of the pristine and the functionalized diblock copolymers, the segmental relaxation of the PS microphase is significantly influenced by the presence of these polar end-functional groups.