Preparation and performance study of aspartic acid ester modified moisture-curing polyurethane hot melt adhesive

Moisture-curable polyurethane hot-melt adhesives （PUR） generally exhibited low initial adhesion strength prior to curing, which easily caused slippage or misalignment during bonding, limiting their application in high-speed assembly processes. To address these limitations, poly（butylene adipate） （PBA） was employed as the soft segment and 4,4′-diphenylmethane diisocyanate （MDI） as the hard segment, while an aspartate ester （PAE） with secondary amine functionality was introduced as a chain extender to construct a PAE-modified moisture-curable PUR system. The effects of PAE content on hydrogen-bonding interactions, crystallization behavior, adhesion performance, and mechanical properties were systematically investigated. The results showed that the secondary amine in PAE reacted with isocyanate groups to form substituted uretidione carbamate, enhancing hydrogen-bonding interactions between hard segments and increasing aggregation. Simultaneously, the flexible segments of PAE regulated molecular mobility and suppressed soft-segment crystallization, thereby improving adhesion strength and mechanical performance while maintaining low melt viscosity. When the PAE content was 6 wt.%, the PUR system exhibited optimal comprehensive performance, with a melt viscosity of only 3325 mPa·s, an initial adhesion strength of 3 N/25 mm （150% higher than that of the un-chain-extended system）, a final adhesion strength of 198 N/25 mm （100% increase）, an elongation at break of 808.25% （170% increase）, and a tensile strength of 14.97 MPa （56% increase）. In addition, the thermal resistance and curing rate were superior to those of the un-chain-extended system. These findings demonstrate that PAE-based chain extension provides an effective strategy for developing low-viscosity PUR with high initial adhesion and enhanced overall.