Microdomain expansion and transition behavior of PS-b-PMMA/PS homopolymers by SAXS analysis

We present the microdomain expansion and transition behavior of binary blends of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA)/PS homopolymers using small-angle X-ray scattering (SAXS) analysis, where the PS molecular weight (or chain length) was varied with chain length ratios (α) of 0.3, 1, and 2 with respect to the PS block length of the PS-b-PMMA. The d-spacing and order-to-disorder transition (ODT) by addition of PS homopolymers were significantly influenced by the PS molecular weight. In contrast to the typical decrease in d-spacing with increasing temperature in PS-b-PMMA, the d-spacing for PS-b-PMMA/PS homopolymers showed unusual behavior; specifically, it increased for shorter PS chains of α ≤ 1, but was independent of temperature for PS chains of α = 2. This variation can be attributed to a competing interaction between the thermal expansion effects of the microdomains with homopolymers and the decrease in the chain stretching between the two block components.