Multiscale Mechanical Performance Analysis of Polyurethane Adhesives Based on Molecular Dynamics Simulations

ABSTRACT Moisture‐curable one‐component polyurethane (1K‐PU) adhesives are widely used in bonding and sealing applications due to their excellent flexibility and sealing properties. Under the condition that the adhesive is not fully cured before entering the service phase, insufficient interface adhesion and reduced load‐bearing capacity may lead to joint loosening, posing safety risks. Although the mechanical properties of polyurethane adhesives have been widely studied, the quantitative characterization of mechanical‐property evolution during the curing process remains limited. This study proposes a multiscale‐coupling method for mapping the curing time to mechanical properties. In situ Fourier‐transform infrared (FTIR) monitoring tracks the real‐time conversion of isocyanate groups, enabling the identification of parameters for the curing reaction kinetics model, which predicts the degree of cure (DOC) over time as a constraint introduced in molecular dynamics (MD) simulations. Based on the principles of moisture curing, MD simulations model gradual crosslinking and generate crosslinked network structures at different curing degrees. The mechanical parameters of adhesives are computed under boundary conditions, establishing a quantitative, cross‐scale mapping relationship between curing time and mechanical performance. The proposed method addresses the challenge of obtaining mechanical properties of the adhesive during the curing process and elucidates the modulus growth mechanism driven by crosslinking densification and reduction in free volume. It provides a practical basis for evaluating the mechanical properties of low‐elastic‐modulus adhesives throughout the curing phase and for optimizing assembly processes.