Realizing Sub-3 nm Feature Size in Thin Films by an In-Situ Hydrolysis of PSM-b-P4VBP

We synthesized linear diblock copolymers of poly(solketal methacrylate-block-4-vinyl biphenyl) (PSM-b-P4VBP) that can form sub-3 nm lamellar microdomains in thin films after in situ acid catalyzed hydrolysis, the smallest reported value to date for synthetic block copolymers where the orientation of the microdomains in thin films can be controlled. Acid hydrolysis with trifluoracetic acid (TFA) vapor converts the hydrophobic PSM block into hydrophilic poly(glycerol monomethacrylate) (PGM), increasing immiscibility with P4VBP and driving microphase separation in the resulting PGM-b-P4VBP. In the bulk, small-angle X-ray scattering (SAXS) confirms lamellae with a 5.7 nm full-pitch, while thin films exhibit vertical and parallel lamellae with a 5.4 nm full-pitch, as verified by grazing-incidence SAXS (GISAXS) and atomic force microscopy (AFM). The effective interaction parameter χ for both PSM-b-P4VBP (χ = 0.1035 + 6.340/T, =0.238 at 25 °C) and PGM-b-P4VBP (χ = 0.2165 + 40.43/T, =0.352 at 25 °C) are determined by temperature-dependent SAXS.