biostudies-literatureUnknown11(5)Takashima INext-generation polymer electrolyte fuel cells (PEFCs) require polymer electrolyte membranes (PEMs) capable of operating at temperatures above the boiling point of water (100 °C) and under low-humidity below 40% RH. In this study, we synthesized poly-(8-(<i>p</i>-styryl)-1-octanephosphonic acid) (soPA), a polymer bearing phosphonic acid groups on the side chains connected via eight-carbon alkylene spacers. soPA was insoluble in water and formed a highly oriented lamellar phase-separated nanostructure with a 2.9 nm domain spacing, consisting of a hydrophobic phase formed by the alkylene spacers and the polystyrene backbone, and a hydrophilic phase containing the phosphonic acid groups. Despite its lower acid group density compared with poly-(4-(<i>p</i>-styryl)-1-butanephosphonic acid) (sbPACS omega8272-8282https://www.ebi.ac.uk/biostudies/studies/S-EPMC12902858biostudies-literatureLong Alkylene Spacers Promote Structural Ordering and Proton Transport in Phosphonic Acid-Based Polymer Electrolyte Membranes.PMC12902858Kajita TTanaka HTakashima INakayama TNishimoto MNoro AfalseLong Alkylene Spacers Promote Structural Ordering and Proton Transport in Phosphonic Acid-Based Polymer Electrolyte Membranes.Next-generation polymer electrolyte fuel cells (PEFCs) require polymer electrolyte membranes (PEMs) capable of operating at temperatures above the boiling point of water (100 °C) and under low-humidity below 40% RH. In this study, we synthesized poly-(8-(<i>p</i>-styryl)-1-octanephosphonic acid) (soPA), a polymer bearing phosphonic acid groups on the side chains connected via eight-carbon alkylene spacers. soPA was insoluble in water and formed a highly oriented lamellar phase-separated nanostructure with a 2.9 nm domain spacing, consisting of a hydrophobic phase formed by the alkylene spacers and the polystyrene backbone, and a hydrophilic phase containing the phosphonic acid groups. Despite its lower acid group density compared with poly-(4-(<i>p</i>-styryl)-1-butanephosphonic acid) (sbP2026-01-01T00:00:00Z2026 Feb2026-07-15T15:39:36.043Z2026-07-06T03:11:32.958ZS-EPMC129028584169634610.1021/acsomega.5c10883