Ionomer

An ionomer is a polymer that contains ionic groups in its structure, often as pendant groups on the backbone or as part of side chains. The ionic groups, such as sulfonate, carboxylate, or phosphate, are typically associated with counterions (H+, Na+, or metal ions). In many commercial ionomer resins, a portion of the polymer contains ionic domains that form microphase-separated clusters, giving rise to distinctive transport and mechanical properties.

These ionic clusters interact with water and other molecules to enable ionic conduction and improve toughness relative to nonionic polymers. Processing often involves neutralizing acid groups with metal salts, which can tune conductivity and stiffness. The resulting materials can be dry or hydrated, with conductivity increasing upon hydration in proton-conducting variants.

Well-known ionomers include Nafion, a perfluorinated sulfonic acid ionomer used as a proton-exchange membrane in fuel cells and electrolyzers. Other ionomers include sulfonated poly(ether ether ketone) (SPEEK) and various copolymers used as membranes or sealants. In dentistry, glass ionomer cements are a distinct class of ionomer materials formed from polyacrylic acid and fluoroaluminosilicate glass that release fluoride and bond to tooth structure.

Applications span energy conversion and storage, chemical separations, and dentistry. In energy devices, ionomers serve as solid electrolytes or components of composite membranes, enabling selective ion transport. In general, the term covers a broad family of polymers engineered to combine organic polymer backbones with ionic functionality.