Self-Assembly of Hierarchical Structures Using Cyclotriphosphazene-Containing Poly(substituted methylene) Block Copolymers

The cyclotriphosphazene-substituted diazoacetate homopolymer (polyPNDA′) (PNDA′ = hexaphenoxy-substituted phosphazene-containing methylene) and a novel poly­(substituted methylene) block copolymer, polyPNDA′-<i>block</i>-poly­(hexyloxycarbonylmethylene) (polyPNDA’-<i>b</i>-polyHDA′), were synthesized, and the self-assembly behavior of these polymers was studied in detail. A hexagonally packed aggregated structure was observed in the self-assembled structure of polyPNDA′, whereas a lamellar structure was observed in the microphase-separated nanoassembly of polyPNDA′-<i>b</i>-polyHDA′. These results indicate that a hierarchical structure composed of highly regular polyPNDA′ nanoaggregates and the long-range microphase-separated polyPNDA′ and polyHDA′ domains had formed

Perpendicular Orientation Control without Interfacial Treatment of RAFT-Synthesized High‑χ Block Copolymer Thin Films with Sub-10 nm Features Prepared via Thermal Annealing

In this study, a series of perpendicular lamellae-forming poly­(polyhedral oligomeric silsesquioxane methacrylate-<i>block</i>-2,2,2-trifluoroethyl methacrylate)­s (PMAPOSS-<i>b</i>-PTFEMAs) was developed based on the bottom-up concept of creating a simple yet effective material by tailoring the chemical properties and molecular composition of the material. The use of silicon (Si)-containing hybrid high-χ block copolymers (BCPs) provides easy access to sub-10 nm feature sizes. However, as the surface free energies (SFEs) of Si-containing polymers are typically vastly lower than organic polymers, this tends to result in the selective segregation of the inorganic block onto the air interface and increased difficulty in controlling the BCP orientation in thin films. Therefore, by balancing the SFEs between the organic and inorganic blocks through the use of poly­(2,2,2-trifluoroethyl methacrylate) (PTFEMA) on the organic block, a polymer with an SFE similar to Si-containing polymers, orientation control of the BCP domains in thin films becomes much simpler. Herein, perpendicularly oriented BCP thin films with a χ_eff value of 0.45 were fabricated using simple spin-coating and thermal annealing processes under ambient conditions. The thin films displayed a minimum domain size of <i>L</i>₀ = 11 nm, as observed via atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Furthermore, directed self-assembly (DSA) of the BCP on a topographically prepatterned substrate using the grapho-epitaxy method was used to successfully obtain perpendicularly oriented lamellae with a half pitch size of ca. 8 nm