Recent advances in polymer synthesis have allowed remarkable control over chain microstructure and conformation. Capitalizing on such developments, here we create well-controlled chain folding in sulfonated polyethylene, leading to highly uniform hydrated acid layers of subnanometre thickness with high proton conductivity. The linear polyethylene contains sulfonic acid groups pendant to precisely every twenty-first carbon atom that induce tight chain folds to form the hydrated layers, while the methylene segments crystallize. The proton conductivity is on par with Nafion 117, the benchmark for fuel cell membranes. We demonstrate that well-controlled hairpin chain folding can be utilized for proton conductivity within a crystalline polymer structure, and we project that this structure could be adapted for ion transport. This layered polyethylene-based structure is an innovative and versatile design paradigm for functional polymer membranes, opening doors to efficient and selective transport of other ions and small molecules on appropriate selection of functional groups.

Low temperature fuel cells are clean, effective alternative fuel conversion technology. Oxygen reduction reaction (ORR) at the fuel cell cathode has required Pt as the electrocatalyst for high activity and selectivity of the four-electron reaction pathway. Targeting a less expensive, earth abundant alternative, we have developed the synthesis of cobalt phosphide (Co2P) nanorods for ORR. Characterization techniques that include total X-ray scattering and extended X-ray absorption fine structure revealed a deviation of the nanorods from bulk crystal structure with a contraction along the b orthorhombic lattice parameter. The carbon supported nanorods have comparable activity but are remarkably more stable than conventional Pt catalysts for the oxygen reduction reaction in alkaline environments.

Precise control over polymer architecture unlocks the potential for engineered self-assembled crystal structures with useful features on the nanometer length scale. Here we elucidate the structure of the ordered phase of a semicrystalline, functional polyethylene having a precise linear architecture, namely, pendant carboxylic acid groups precisely every 21st backbone carbon atom. By comparing the results of atomistic molecular dynamics simulations with experimental X-ray scattering and Raman spectroscopy data, we find that the polymer chains are folded in a hairpin manner near each carboxylic acid group, giving rise to multiple embedded layers of functional groups that have an interlayer distance of 2.5 nm. This is in contrast to other precise polyethylenes, where the chains are mostly trans within the crystals. Such layers could act as two-dimensional pathways for ionic or molecular transport given an appropriate choice of functional group.

A series of aliphatic polysulfones is synthesized via ADMET polymerization in which a sulfone group is located precisely after every 8th, 14th, and 20th carbon. Primary structural characterization is accomplished using 1H NMR, 13C NMR, and IR. Polymer morphology is studied by DSC and X‐ray scattering, which reveals layered morphologies comprised of polyethylene crystallites along with sulfone groups arranged in sheets. In contrast to other precision polymers with functional groups synthesized by ADMET, this morphology is found at all spacer lengths. Prior to hydrogenation the sulfone polymers show Tm decreasing with increasing sulfone concentration, a typical phenomenon attributed to the mix of cis and trans configurations producing defects in the crystals. However, following hydrogenation, the melting temperature increases as the sulfone group concentration increased rather than decreased, with the highest Tm being 175 °C. This is an increase of 45 °C relative to linear polyethylene synthesized via ADMET chemistry. The precise location of the sulfone groups, which are not tactic, within these polyethylenes increases crystallinity, promotes secondary bonding and increases Tm.

We report the morphology evolution under tensile deformation for strictly linear polyethylenes with associating functional groups. In situ X-ray scattering measurements during elongation reveal that periodic acid group placement along the backbone is required to form hierarchical layered morphologies that lead to strain hardening. This phenomenon was observed in both semicrystalline and amorphous precise acid polyethylenes with acrylic, geminal acrylic, and phosphonic acids. Polymers with nonperiodic (pseudorandom) acid placement fail to form layered morphologies and instead retain a liquidlike distribution of acid aggregates. Acid chemistry and acid concentration influence morphological evolution in both periodic and nonperiodic polymers predominately through the modification of T g and percent crystallinity, which subsequently impact the mechanical properties. Our results indicate that hierarchical acid-rich layered structures, commensurate with improved mechanical properties, form in polymers with strictly periodic chemical structures and sufficient chain mobility for chain alignment during elongation.