Synthesis and Self-Assembly of PS-b-PDMS Bottle Brush Block Copolymers

Recently, brush block copolymers (BBCPs) have attracted significant interest due to their ability to rapidly self-assemble into phase separated nanoscale morphologies. The precise control over side chain chemistry/length and backbone M_w has opened many new opportunities for designing a diverse library of nanostructures. Here, we report the successful synthesis of Poly(styrene)-block-Poly(dimethyl siloxane) (PS-b-PDMS) BBCPs by ring opening metathesis polymerization (ROMP) of norbornene functionalized macromonomers of variable side chain length (PS M_n = 2.9 and 4.7 kg/mol, PDMS M_n = 4.8 kg/mol). BBCPs synthesized over a wide range of M_w (M_w = 195 to 982 kg/mol) at symmetric volume fraction microphase separate into ordered lamellar morphologies via rapid self-assembly after thermal annealing. The lamellar spacing (d) was determined by small angle X-ray scattering and scales with the overall degree of polymerization (d ~ DP^a). The scaling exponents of a = 0.70 and 0.82 for the two series of side chains indicate an extended backbone conformation when compared to linear BCPs in the strong phase segregation limit. The PDMS side chains appear to impart additional flexibility when compared to previously reported BBCP systems, and this is directly influenced by the side chain length.