Highly phase-separated alternating copolymer of alkyl vinyl ether and sulfonic acid group-containing trifluoro vinyl ether

Abstract

This study explores the development of novel cation exchange membranes (CEMs) by synthesizing alternating copolymers of perfluorosulfonic acid monomers and alkyl vinyl ethers with varying chain lengths. Unlike traditional Nafion-based CEMs, which form cluster-channel morphologies, the newly synthesized copolymers exhibit well-defined lamellar structures. Small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) analyses revealed that increasing the alkyl chain length enhances the area of these structures. Moreover, self-diffusion coefficient measurements by PFG-NMR showed that water diffusivity increased with longer side chains, despite a decrease in ion exchange capacity (IEC). This inverse relationship highlights the importance of morphological control in optimizing membrane transport properties. The findings demonstrate that integrating hydrocarbon and fluorocarbon components enables the design of distinct phase-separated structures, expanding the landscape of structure–property relationships in ion-conducting materials. These insights offer new strategies for engineering high-performance membranes for energy and water-related applications.