Proton Transport through a Crystalline Polymer: Lamellar Water Channels in Chain-Folded Precisely Sulfonated Polyethylene

Recent advances in polymer synthesis have allowed precise control over polymer architectures and microstructures, opening the door for the design of highly controlled nanoscale morphologies with previously inaccessible properties. Our previous work has shown that precisely periodic placement (every 21^st carbon) of carboxylic acid groups along linear polyethylene gives rise to regular chain folding at the location of each acid group, and concurrent crystallization of the alkyl segments. Here we demonstrate that sulfonic acid groups along linear polyethylene give rise to similar chain folding, and that the resulting acid layers become hydrated upon exposure to humidity, providing high proton conductivity. This is the first time, to our knowledge, that controlled polymer folding has been utilized for proton or ion transport, and that high proton conductivity has been reported within a crystalline polymer. To supplement the experimental methods, atomistic molecular dynamics simulations were performed. These simulations confirm our characterization of the structure, and show that the ordered hydrated layers improve proton diffusion relative to tortuous channels of the same chemical composition.