Evaluation of the Interaction Parameter for Poly(solketal methacrylate)-block-polystyrene Copolymers*

A series of symmetric poly(solketal methacrylate-b-styrene) (PSM-b-PS) copolymers that can transform a hydrophobic PSM block to a hydrophilic poly(glycerol mono-methacrylate) (PGM) block through an acid hydrolysis was investigated. This simple method significantly enhances the segmental interaction parameter (χ), enabling a phase-mixed block copolymer (BCP) to microphase separate without any additives. Temperature-dependent small-angle X-ray scattering (SAXS) measurements as a function of the degree of polymerization (16 ≤ N ≤ 316) and PSM hydrolysis conversion were conducted to characterize the order-to-disorder transition (ODT) behavior, as well as the lamellar microdomain features. Using a mean-field correlation-hole analysis of the scattering, the χ value for PSM and PS was determined as a function of the conversion of PSM to PGM. For 100% conversion of PSM to PGM, the χ with PS was found to be given by χ = 0.3144 + 36.91/T, with χ = 0.438 at 25 °C, which is ~13 times larger in magnitude than χ parameter for PSM-b-PS copolymer (~0.035 at 25 °C). With this large increase in χ, full pitch lamellar microdomains of sub-3 nm were achieved by the lowest molar mass sample.