Synthesis of high-χ PTFEMA-b-P2VP block copolymers and perpendicular lamellar orientation control via neutral underlayer design

Controlling molecular architecture and interfacial interactions is critical for realizing well-defined microphase-separated structures in block copolymer systems. Here, we investigate poly(2,2,2-trifluoroethyl methacrylate)-block-poly(2-vinylpyridine) (PTFEMA- b -P2VP) as a high-χ platform enabled by strong repulsive interactions between fluorinated and polar blocks. A series of low-degree-of-polymerization PTFEMA- b -P2VP diblock copolymers was synthesized via reversible addition–fragmentation chain-transfer (RAFT) polymerization. Molecular dynamics simulations indicate a high Flory-Huggins interaction parameter (χ ≈ 0.3 at 150 °C), leading to rapid microphase separation into ordered lamellar morphologies within 15 min at 100 °C. Small-angle X-ray scattering measurements reveal lamellar spacings of 17.9 - 32.7 nm, corresponding to feature sizes down to approximately 9 nm, demonstrating the suitability of this system for sub-10 nm directed self-assembly (DSA). Despite the strong segregation strength, the large surface-energy contrast between the two blocks induces a pronounced preference for parallel lamellar orientation at solid interfaces, which limits perpendicular alignment. To address this interfacial constraint, we introduce a matched neutral underlayer strategy using random copolymer brushes chemically analogous to the constituent blocks of PTFEMA -b- P2VP, incorporating glycidyl methacrylate (GMA) as a cross-linkable third monomer. These underlayers effectively balance interfacial interactions, enabling robust perpendicular lamellar orientation during solvent-thermal annealing. Furthermore, combining the neutral underlayers with grapho-epitaxial templates enables directed self-assembly of well-ordered line patterns with linewidths of ∼10–12 nm. This work thus establishes a practical and materials-efficient route for achieving perpendicular lamellar orientation in fluorinated block copolymers and other high-χ systems, providing a general and transferable strategy for DSA and related nanofabrication technologies that demand precise nanoscale morphology control.