Self‐assembled structures in d8‐polystyrene‐block‐polyisoprene/polystyrene blends in the weak segregation regime: SAXS and TEM study

Abstract

AbstractBACKGROUND: This paper reports an investigation of the microphase‐separated morphology and phase behaviour in blends of d‐polystyrene‐block‐polyisoprene with homopolystyrene in the weak segregation regime, using small‐angle X‐ray scattering and transmission electron microscopy, as a function of composition, weight‐average molecular weight and temperature. The chain length ratio parameter rM = MH/MC (where MH and MC are the weight‐average molecular weights of the homopolymer and corresponding block copolymer chain) was selected to encompass all possible types of mutual homopolymer/block copolymer sizes.RESULTS: In the weak segregation regime the polystyrene block chains behave as a ‘wet brush’ for rM < 1 similarly to the intermediate and strong segregation regimes. For rM > 1 a macroscopic phase separation occurs. The domain spacing D increases systematically in the range 0 < rM ≤ 1 with increasing concentration of homopolymer wP and increasing rM regardless of the implemented specific morphology, but the slope of the periodicity D versus wP relation is smaller than in the intermediate and strong segregation regimes.CONCLUSION: The criterion for ‘wet and dry brush’ morphologies has been applied to explain the changes in microdomain morphology during the self‐assembly process. It has been shown that the parameters rM and χ3/2N (where χ is the Flory–Huggins parameter and N the number of segments per chain) characterize the slope of the D versus wP relation in the weak and intermediate segregation regimes. Copyright © 2009 Society of Chemical Industry