| Abstract
| - The phase behaviors of polystyrene-block-poly(n-butyl methacrylate) (P(S-b-nBMA)) andpolystyrene-block-polyisoprene (P(S-b-I)) copolymers were studied in the presence of methane, ethane,propane, butane, and tetradecane. Sorption of the light alkanes induces phase segregation in P(S-b-nBMA), depressing the lower disorder-to-order transition (LDOT). The chain length of the solvent dictatesthe severity of the depression. At equivalent volume fractions, methane induces the most substantialshift of the LDOT, and as the length of the alkane chain is increased, the degree of the depression isdiminished. In contrast to the influence of expanded solvents, dilution of the P(S-b-nBMA) melt withtetradecane slightly increases the miscibility of the segments. In all P(S-b-I)/alkane systems studied,solvent sorption increases the region of miscibility and depresses the upper order-to-disorder transition(UODT). This effect is independent of alkane chain length and depends only on the volume fraction ofalkane sorbed into the copolymer. The difference in behaviors between the copolymers is due to the natureof microphase separation. In the P(S-b-I) system, the UODT is enthalpically driven and solvent sorptionscreens unfavorable contacts. In the P(S-b-nBMA) system, the LDOT arises due to disparities incompressibility between the segments that are exacerbated by the selective sorption of compressiblesolvents.
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