A simple method was developed to realize a self-assembled block copolymer (BCP) lamellar microdomain morphology with a full pitch of 5.4 nm through an acid hydrolysis of poly(solketal methacrylate-b-styrene) (PSM-b-PS), synthesized by a sequential reversible addition-fragmentation chain-transfer (RAFT) polymerization. The acid hydrolysis transforms PSM-b-PS, having two hydrophobic blocks, into poly(glycerol mono-methacrylate-b-styrene) (PGM-b-PS), having one hydrophilic and one hydrophobic block. This transformation markedly increases the segmental interaction parameter such that a phase-mixed PSM-b-PS can be transformed in the solid state into a microphase separated BCP without the use of any additives. With the symmetric BCPs used in this study, the ordered lamellar microdomain pitch was determined by small-angle X-ray scattering (SAXS) as a function of the degree of polymerization (16 ≤ N ≤ 1246). For the lamellar microdomains of PGM-b-PS, the scattering profiles show many higher order reflections with an increase in the domain spacing (L0). Correlation hole scattering of the PSM-b-PS in the phase mixed state yields a segmental interaction parameter (χ) given by χ = 0.0196 + 4.694/T, where T is the absolute temperature. In this analysis, an arbitrary reference volume, 118 Å3, was used to normalize a volume-based degree of polymerization (Nv) because of the difference of homopolymer densities. From the derived linear equation, the χ value between PSM and PS is approximately 0.035 at 25 °C, which is still lower than that for poly(styrene-b-isoprene) (PS-b-PI) and poly(styrene-b-(2-vinylpyridine)) (PS-b-P2VP). After transformation, the massive increase in χ value for PGM-b-PS was found from the lowest molar mass sample (Mn = 2,200 g/mol, N = 16), fitted to linear relation as χ = 0.3144 + 36.914/T, ~0.438 at 25 °C, which is approximately 13 times larger in magnitude than that for PSM and PS and higher than that of poly(styrene-b-dimethylsiloxane) (PS-b-PDMS), poly(styrene-b-lactic acid) (PS-b-PLA), and poly(cyclohexylethylene-b-methyl methacrylate) (PCHE-b-PMMA) at the 118 Å3 reference volume. By this huge increase in χ, multiple higher order reflections were seen for the lowest molar mass sample with sub-3 nm, which is the smallest pitch obtained in this study.

Realizing 5.4 nm full pitch lamellar microdomains by a solid-state transformation

255th National Meeting (2018)

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