Installation of the adamantyl group in polystyrene-block-poly(methyl mathacrylate) via Friedel-Crafts alkylation to modulate the microphase-separated morphology and dimensions

Although polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) is the most widely employed template and scaffold for constructing nanoscale patterns, its relatively small Flory-Huggins interaction parameter makes it challenging to realize microphase-separated structures with a periodicity (or domain spacing) of less than 20 nm. The direct post-polymerization modification of PS-b-PMMA can resolve this issue. In this study, we present the PS block post-polymerization modification of commercially available PS-b-PMMA through a metal-free Friedel-Crafts alkylation reaction with adamantanols to modulate its microphase-separated morphology and dimensions. The adamantyl group can be easily installed on the PS benzene ring, which increases the incompatibility with the PMMA block, enabling ordered microphase-separated structures, including lamellar, gyroid and hexagonally close-packed cylindrical structures, from low-molecular-weight PS-b-PMMA. Notably, a periodicity as low as approximately 16 nm was realized with this strategy, which is much lower than the lowest accessible periodicity of pristine PS-b-PMMA. Furthermore, we observed additional benefits from the installation of the adamantyl group, such as increased thermal stability, glass transition temperature and etching contrast.

Automated summary

By direct post-polymerization modification, commercial PS-b-PMMA can be successfully transformed into ordered microphase-separated structures with a periodicity as low as approximately 16 nm. The installation of adamantyl group not only increases incompatibility with the PMMA block, but also improves thermal stability, glass transition temperature, and etching contrast.