Linear Viscoelasticity of Lamellae-Forming Brush Block Copolymers

We report the linear viscoelastic behavior of symmetric volume fraction poly(styrene)-block-poly(ethylene oxide) (PS-b-PEO) brush block copolymers (BBCP) with side chain lengths below the entanglement molecular weights over a range of overall backbone degree of polymerizations. The BBCPs readily self-assemble into microphase separated lamellar morphologies upon thermal annealing. The increasing backbone length results in a direct increase of the lamellar spacing from 29 to 90 nm. BBCPs are thermorheologically simple and maintain liquid-like rheological response even up to large molecular weights (~500 kg/mol). Scaling relationships in the dynamic master curves show power law behavior analogous to un-entangled Gaussian chain dynamics across all measured backbone lengths. The sequence of relaxations from the side chains and backbone are correlated to the overall molecular weight. This study expands upon the understanding of the unique “liquid-like” response of microphase separated BBCPs and their potential processing advantages over conventional LBCP materials.