Supramolecular Nanoconfinement-Accelerated Synthesis of Two-Dimensional Styrenic Polymers Boosting Proton Conductivity in Nafion-doped Membranes.

Two-dimensional (2D) covalent polymers offer environmental stability, surface area, and mechanical resilience, but preparation of functional, freestanding 2D polymers remains challenging. Inspired by phospholipid bilayers, we developed a bilayer self-assembly strategy for 2D covalent polymer synthesis with tailored functionalized surface. Ionic amphiphilic styrene monomers employ intramolecular face-to-face stacking, inducing a folded monomer conformation that achieves a critical packing parameter near unity. This drives 2D nanosheet formation in basic aqueous solution. Concurrent electrostatic repulsion enabled spontaneous exfoliation. In situ radical polymerization within preorganized framework, accelerated by nanoconfinement effect, converted supramolecular assemblies into covalent bilayer polymers with 95% monomer conversion. Incorporating sulfonic acid-functionalized 2D polymers (0.66 wt%) into Nafion D2020 membrane enhanced mechanical strength and proton conductivity at room temperature. Fuel cell testing (70°C, 100% RH) demonstrated increased open-circuit voltage (1.00 V vs. 0.96 V), suppressed hydrogen permeation, elevated peak power density (678.9 vs. 454.6 mW·cm-2), and reduced ohmic resistance (25.2 vs. 55.1 mΩ).