Bottlebrush Copolymer as Surface Neutralizer for Perpendicular Orientation of Block Copolymer Nanodomains in Thin Films
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Bottlebrush copolymers (BTBs) were designed for use as a neutral additive to block copolymer (BCP) thin films, in which, they are segregated to the interfaces via architectural effects and produce neutral interfaces to induce perpendicular orientation of BCP microdomains. Two BCP systems were employed, a conventional poly(styrene-b-methyl methacrylate) with relatively low χ and similar surface energies between blocks, and a high χ poly(styrene-b-methacrylic acid) with distinct surface energies. The BTBs, with either short side-chains of PS-r-PMMA or PS-r-PMAA, were synthesized via ROMP. Top and bottom interfaces of both BCP films were enriched with BTBs and vertically oriented microdomains were achieved for both BCP systems. This can be attributed to the screening of polymer interactions by a good solvent during the spin casting process, allowing architectural effects to play a role in surface segregation of BTBs, as confirmed by contact angle measurements and TOF-SIMS.