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 (alpha) 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 alpha <= 1, but was independent of temperature for PS chains of alpha = 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. (C) 2012 Elsevier Ltd. All rights reserved.