Engineering High-Performance Reactive Hot-Melt Polyurethanes: The Role of Chain Extenders in Modulating Polyester Polyols Properties

This study introduces a novel targeted synthesis and comprehensive evaluation for optimizing the composition of hot-melt polyurethane reactive adhesives (HMPUR) by methodically varying the soft segment of the polyester polyol (PSPO) and carefully choosing the chain extender. Three PSPOs (synthesized from succinic, adipic, and dodecanedioic acid) were formulated with either ethylenediamine (EDA) or 1,4-butanediol (BDO), due to the fundamental differences in their chemical reactivity. Characterization using DSC, FT-IR, GPC, 1H NMR, viscosity, lap shear analysis, and titration revealed critical structure-property relationships. EDA-based adhesives have consistently demonstrated superior crosslinking efficiency, resulting in significantly enhanced mechanical performance and faster cure kinetics. The PSPO-1_EDA formulation exhibits a cure time of 8.5 hours. In contrast, BDO formulations offered greater flexibility and lower processing viscosity. The longest-chain polyol, PSPO-3, was found to be the most high-performing, achieving the highest lap shear strength of 2.0 MPa when coupled with EDA, a result attributed to its ability to form highly ordered hard domains (ΔHm = 31 mJ/mg). This research highlights the critical importance of polyol chain length and chain extender chemistry in decoupling mechanical strength from processing characteristics, providing a clear pathway for tailoring HMPUR formulations to meet diverse industrial demands.