Non-isocyanate polyurethane (NIPU) adhesives: Chemistry to interface engineering and applications

Non-isocyanate polyurethane (NIPU) adhesives have attracted increasing attention as sustainable alternatives to conventional polyurethane adhesives owing to their isocyanate-free synthesis and the availability of renewable feedstocks. Their adhesive performance is governed by complex interactions among molecular structure, reaction kinetics, network architecture, and interfacial phenomena. This review summarizes recent advances in NIPU adhesives with emphasis on the cyclic carbonate-amine polyaddition reaction, discussing the influence of reaction kinetics, β-hydroxy urethane chemistry, hydrogen bonding, and network evolution on adhesion development and mechanical performance. The roles of bio-based precursors, synthetic monomers, hybrid network architectures, and dynamic covalent chemistries are investigated in relation to curing behavior, crosslink density, moisture resistance, thermal stability, and durability. Recent strategies, including epoxy hybridization, siloxane modification, and vitrimer-like network design, are discussed as effective approaches for improving curing efficiency, environmental stability, and mechanical performance while maintaining the sustainability advantages of NIPU systems. The review also highlights current challenges associated with slow curing kinetics, wet durability, processing, and industrial scalability, together with recent developments in cyclic carbonate structural design and alternative synthetic pathways. A comprehensive understanding of the interplay between molecular architecture, network topology, and interfacial interactions is essential for optimizing the performance of NIPU adhesives and advancing the development of sustainable, high-performance adhesive systems.