• End groups guide polymer self-assembly into complex 3D nanostructures. • Linker design tunes end–end binding and expands phase space of morphologies. • New end groups enable thermodynamically stable double primitive and double diamond network phases. • End-functionalization offers a compelling pathway for the development of advanced polymer electrolytes and mechanical metamaterials. • End-functionalized block copolymers enable bottom-up optical metamaterials. End-group functionalization has emerged as a powerful and versatile strategy in polymer science, offering precise control over physical properties, nanoscale self-assembly, and interfacial functionality without altering the polymer backbone. This review summarizes recent progress in the chemistry and applications of end-functionalized polymers across three thematic domains. First, we examine how tailored end groups influence intrinsic polymer properties, including thermal transitions, solubility, crystallization behaviors, and interfacial adhesion. Second, we explore the role of end-group interactions in directing polymer self-assembly, emphasizing their ability to modulate chain packing, interfacial curvature, and phase behavior in block copolymer systems, particularly in the formation of complex network morphologies. Third, we highlight the growing technological relevance of end-functionalized polymers with network morphologies in emerging applications such as solid-state battery electrolytes, mechanical metamaterials, and optical metamaterials. In polymer electrolytes, ion–dipole interactions localized at the chain termini decouple ion transport from segmental motion, yielding high ionic conductivity and low activation energy at low salt concentrations. In mechanical metamaterials, end-group-directed 3D networks enhance structural resilience and tunable deformation behavior. In optical metamaterials, metal-end-functionalized block copolymers could serve as nanoscale templates for the bottom-up fabrication of high-refractive-index architectures via metal–ligand coordination, tackling the resolution limits of top-down lithography. Collectively, these advances underscore the transformative potential of end-group chemistry for next-generation polymer materials.

Superionic Disulfonic Acid Polymers In article number 2501998, through controlled polymerizations of precisely engineered disulfonic acid monomers with well-defined functional group arrangements, Moon Jeong Park and co-workers simultaneously enhance the mechanical strength and ion transport properties of acid-functionalized polymers. This precise molecular design enables superionic conduction in elastic states, revealing unexpected hydrophobic behavior, and enabling the decoupling of ion relaxation from polymer chain dynamics.