Effect of steric constraints on the physico‐electrochemical properties of sulfonated polyaromatic copolymers

Abstract

The impact of incorporating additional steric restrictions into highly sterically encumbered sulfonated polyaromatic polymers was investigated. Copolymers possessing between 0 and 10% nonlinear ortho or meta biphenyl units in an otherwise linear para biphenyl-containing sulfo-phenylated poly(phenylene) were synthesized in yields >80% and evaluated on the basis of their physical and electrochemical properties. When incorporated into sulfonated copolymers in ≤5 mol%, ortho and meta linked biphenyl moieties reduced membrane swelling in water by up to 23 and 19 vol%, respectively, compared to strictly para biphenyl-linked copolymers. Despite this, copolymers possessing nonlinear, biphenyl-linked monomers displayed a decrease in proton conductivity and mechanical strength. This study reinforces the importance of considering restricted rotation, backbone flexibility, and chain entanglement in the design of polymers aimed at improving their physical and electrochemical properties.

On the evolution of sulfonated polyphenylenes as proton exchange membranes for fuel cells

“…Timeline for evolution of sulfonated polyphenylenes. 28,29,30,36,[71][72][73][74][75][76][77][78][79] Corresponding authors from each publication are named.…”

“…Open 31,66,67,69,72,73,212,213 This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.…”

“…Similar negative trends in physical and electrochemical properties were reported in copolymers possessing mixtures of ortho and para, or meta and para-substituted biphenyl moieties, when compared to sPPB-H + . 73 The dramatic differences in membrane characteristics with changes in polymer regiomeric connectivity from ortho (water soluble membranes) to meta (fragile) to para (robust) were attributed to a lack of macroscopic chain entanglement caused by sterically encumbered, rotationally-restricted polymer backbones, reinforcing the importance of chain flexibility and entanglement in PEM materials. 72,73 That is, the para-substituted biphenyls…”

“…The synthetic versatility of pre-sulfonated phenylated polyphenylenes opens doors to macromolecular sequence control and the introduction of macroscopic chain entanglement caused by sterically encumbered, rotationally restricted polymer backbones, molecular branching, acid-base interactions, and other controlled cross-linking strategies. 70,72,73,213 Synthetic versatility also facilitates up-scaled syntheses using traditional thermal methods, as well as microwave-assisted techniques. 71 Of note, the synthetic versatility of pre-sulfonated phenylated polyphenylenes is being adopted by Ionomr Innovations, Inc., who have taken a step to commercialize hydrocarbon membranes based on reinforcements and roll-to-roll manufacturing.…”

Linking Perfluorosulfonic Acid Ionomer Chemistry and High-Current Density Performance in Fuel-Cell Electrodes

“…These suggest that developing ionomers with bulky groups and large free volume to enhance transport and impede the interactions of side chains with the catalyst surface is a possible means for improving PEFC performance. [58][59][60]…”