(286e) A Molecularly Impermeable Polymer from Two-Dimensional Polyaramids

All polymers exhibit gas permeability through the free volume of entangled polymer chains. By contrast, two-dimensional (2D) materials including graphene stack densely and can exhibit molecular impermeability. Solution-synthesized 2D polymers that exhibit the latter by poly-condensation have been a longstanding goal. Herein, we demonstrate self-supporting, spin-coated 2D polyaramid nanofilms pressurized over silicon oxide (SiO₂) microwells that exhibit nitrogen (N₂) permeability below 3.1×10^-9 Barrer, nearly four orders of magnitude lower than every class of existing polymers, and similar for other gases tested (argon, oxygen, methane, and sulfur hexafluoride). A 60-nm coating of air-sensitive perovskites reduces the lattice degradation rate 14-fold with an oxygen (O₂) permeability of 3.3×10^-8 Barrer. The remarkable transport resistance imposed by the 2D polyaramid film necessitates a lamellar framework absent of free volume and transmembrane defects. Molecularly impermeable polymers promise the next generation of barriers that are synthetically processable, chemically amenable, and maximize chemical rejection with minimal material, ultimately advancing sustainability goals