Rheological Properties and Mixed Structures of SEBS Block Copolymer/Polystyrene Blend System

In order to obtain a fundamental knowledge of polymer blends, the rheological and thermal properties of two model blend-systems, (i) styrene-ethylene·butylene-styrene block copolymer (SEBS) and polystyrene (PS) and (ii) SEBS and polyethylene (PE), were investigated. And the effects of the interactions between the common segments of the component polymers on these properties and the mixed structures were discussed.(1) The molten blends of SEBS and PS showed abnormal increases in the viscosities and the moduli and the remarkable decrease in the activation energy of flow at some mixed compositions. The flow curves of these blends exhibited remarkable yielding behaviors at low strain rate region. In these cases, the shear viscosity-shear rate curves of the blends did not coincide with the complex viscosity-angular velocity curves, and this result suggested, from the Cox-Merz rule, the existence of some heterogenous mixed structures in the molten state. Furthermore, these blends kept the high moduli even at low angular velocity region, suggesting the longer relaxation time due to the formation of some heterogeneous high order-structures. (2) In the SEBS/PE blends, such abnormal rheological behaviors could not be recognized but the approximately additive relations with the blend compositions were observed. (3) From the thermal analysis, the partial compatibilities between the component polymers through the common segment-units were recognized in both of the SEBS/PS and the SEBS/PE blend-systems. (4) From these results of the rheological behaviors and the thermal analysis, the complicated mixed structures of the SEBS/PS blends, due to the partial solubility of the PS chains into the St-domains of the SEBS and the consequent enlargement of the domain structures, were proposed.