Metallopolymer-block-oligosaccharide for sub-10 nm microphase separation

High-chi (where chi is the Flory-Huggins interaction parameter) block copolymers (BCPs) have great potential to achieve ultra-small microphase-separated structures with domain spacings (d) of <10 nm, which in turn are promising for nanofabrication applications. However, when considering their practical application in next generation lithographic processes, sufficient heat resistance and high etching selectivity are also required to attain high-chi BCPs for precise pattern transfer to the substrate. Herein, we report novel high-chi BCPs comprising poly(vinyl ferrocene) (PVFc) and an oligosaccharide (maltotriose and maltohexaose), which simultaneously accomplish small d values, sufficient thermal stability, and high etching selectivity. These novel BCPs, which displayed different architectures and saccharide volume fractions, were synthesized by combining living anionic polymerization and the click reaction. Small angle X-ray scattering measurements revealed that PVFc-b-maltohexaose and PVFc-b-(maltotriose)(2) formed hexagonal cylinder morphology with d values of similar to 8 nm. Furthermore, a lamellar morphology with d values of 9.3 nm was realized by mixing PVFc-b-(maltotriose)(2) and glucose. The thermal properties and etching resistance of PVFc and the oligosaccharides were also investigated. As expected, PVFc displayed a high thermal stability (PVFc: T-g, similar to 140 degrees C and decomposition temperature, similar to 350 degrees C) and higher etching resistance than the oligosaccharides.