Influence of Hydrocarbon Oils on the Physical Gelation of Poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) Triblock Copolymers

The physical gelation of triblock copolymer poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) in different hydrocarbon oils with different concentrations is studied in this article. The linear viscoelastic behavior, thermal transitions, swelling behavior, and gel properties on physical gelation are presented. The linear viscoelastic behavior is highly dependent on the copolymer concentration and type of oils. The degree of moduli responses of SEBS gels increase with higher gelation temperature, thereby indicating the longer lifetime of gel junctions. Small amounts of aromatic content in the hydrocarbon oil decreases the thermal stability of micelle formation of the gel and increases the compatibility of the solvent with copolymer, thereby resulting in low gelation temperature, lower moduli, as well as gel strength. With an increase in paraffinic content and molecular weight of hydrocarbon oil, the gelation temperature, moduli, and gel properties show improvement. Differential scanning calorimetric results show phase separation of soft segment and hard segment. The glass transition temperature (Tg) of soft ethylene—butylene (EB) midblock is not dependent on the triblock copolymer concentration nor on the type of oil, whereas the Tg of hard segment styrene endblock is highly dependent on triblock copolymer concentration and type of oil. The molecular weight and paraffinic hydrocarbon content of the oils are found to contribute to the stability of micelles and the incompatibility of hydrocarbon oil in SEBS triblock copolymer.