Exploring the Phase Behavior of Poly(styrene)-block-Poly(dimethylsiloxane) Brush Block Copolymers

We report the experimental phase behavior of a family of poly(styrene)-block-poly(dimethylsiloxane) (PS-b-PDMS) bottlebrush block copolymers (BBCPs). The BBCPs rapidly self-assemble into microphase separated morphologies after mild thermal annealing. By systematically tuning architectural parameters such as volume fraction (f_PS), side chain length (N_sc), and overall backbone length (N_bb), a diverse array of morphologies were resolved and a phase map was constructed. We identify ordered lamellar, cylindrical, and deformed spherical morphologies. The lamellar window spans a wide range of f_PS from 0.40 – 0.75 when N_bb is short and N_sc of PS and PDMS are equal. However, order-order transitions to cylindrical and spherical morphology are observed as N_bb increases and N_sc becomes asymmetric. The self-assembly and phase transitions are described by a contrast between both the backbone and side chain flexibility of the PDMS and PS blocks. These findings provide an insight into the rich phase behavior of this architecturally complex class of macromolecules and provide direction towards the future fabrication and design of BBCP templated functional materials.