Morphology and rheology of SIS and SEPS triblock copolymers in the presence of a midblock-selective solvent

While numerous fundamental studies have sought to elucidate the effect of a parent homopolymer on the morphological characteristics and mechanical pro perties of microphase-ordered block copolymer blends, few comparable effort s have extended such studies to concentrated copolymer solutions in the pre sence of a low-molar-mass block-selective solvent. In this work, we investi gate the microstructures that form in blends of a poly(styrene-block-isopre ne-block-styrene) (SIS) triblock copolymer with a midblock-selective alipha tic mineral oil. To discern the influence of midblock/oil compatibility on blend morphology and properties, identical blends with a poly[styrene-block -(ethylene-alt-propylene)-block-styrene] (SEPS) copolymer, the hydrogenated variant of the SIS copolymer, have likewise been examined. The saturated m idblock of the SEPS copolymer is responsible for the observed shifts in mor phology stability limits and higher dynamic elastic sheer moduli relative t o the SIS analogue. These results reveal that the morphologies and properti es of such triblock copolymer/oil blends are sensitive to the chemical/stat istical nature of the copolymer midblock and may be judiciously tailored to satisfy application-specific requirements.