DIELECTRIC-RELAXATION OF STYRENE-ISOPRENE DIBLOCK COPOLYMER SOLUTIONS - A COMMON SOLVENT SYSTEM

A dielectric study was carried out on solutions of polystyrene-cis-polyisoprene (SI) diblock copolymers in a common good solvent, toluene (TL). The I-blocks exhibited dielectric relaxation at long time scales due to fluctuation of their end-to-end vectors because of their dipoles along their contour. In concentrated solutions and/or at low temperatures, strong influences of microphase separation prevailed over such relaxations, reflecting the soft and deformable interphase between the S- and I-phases and a rather high mobility of the S-I junctions. These microphase-separated solutions exhibited dielectric loss (epsilon") curves with two broad peaks at high and low frequencies. The former may be attributed to fluctuation of the S-I junctions within the interphase, and the latter, to fluctuation of the free I ends. For homogeneous SI/TL solutions at low SI concentrations and/or at high temperatures, epsilon" curves with a sharp single peak were found. Their epsilon" curves were compared with the prediction of the Stockmayer-Kennedy model for a Rouse chain composed of two chains having a different spring constant and friction factor. A reasonable agreement was found between the data and model prediction.