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Morphological Evolution of Poly(solketal methacrylate)-block-polystyrene Copolymers in Thin Films

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journal contribution
posted on 06.05.2019, 00:00 by Duk Man Yu, Darren M. Smith, Hyeyoung Kim, Jose Kenneth D. Mapas, Javid Rzayev, Thomas P. Russell
The morphological evolution of the lamellar microdomains in the thin films of symmetric poly­(solketal methacrylate-b-styrene) (PSM-b-PS) copolymers that can be converted into poly­(glycerol monomethacrylate-b-styrene) (PGM-b-PS) copolymers through acid hydrolysis reaction was investigated. This simple chemical transformation was performed in the solid state using trifluoroacetic acid vapor, markedly increasing the segmental interaction parameter (χ) from 0.035 to 0.438 at 25 °C and a 118 Å3 reference volume by changing the hydrophobic PSM block to the hydrophilic PGM block. To control the orientation of the lamellar microdomains using this responsive block copolymer (BCP), a protected random copolymer (PSM-r-PS) with 31 mol % SM, which was concurrently transformed into PGM-r-PS with the BCP, was used to tune the interfacial energies at the substrate. Atomic force microscopy and grazing-incidence small-angle X-ray scattering measurements as a function of exposure time to an acid vapor were performed to characterize the transition from the disordered state into the ordered state and to assess the orientation of the microdomains. As a result, a 9.4 nm full pitch lamellar microdomain morphology in the thin films was achieved after full conversion and thermal annealing, indicating that the modified substrate exhibited the surface neutrality toward the two blocks and successfully induced vertical orientation without any additional layers.