In Situ Crosslinking of PEI and Isocyanate for Enhanced Moisture Resistance of Ammonium dinitramide：Computational and Experimental Investigation

Abstract

To address the strong hygroscopicity shortage of Ammonium dinitramide (ADN), a surface coating strategy based on insitu crosslinking of polyethyleneimine (PEI) with isocyanates (MDI/TTI) was developed to enhance moisture resistance via chemical passivation and physical barrier mechanisms. A 3D polyurea network was constructed on ADN particles through a solid-phase reaction. The modified samples were characterized by FTIR, XRD, SEM-EDS, contact angle measurements, and TGA, while Monte Carlo simulations were used to elucidate the inhibition mechanism.Results show that PEI interacts with ADN via its amine groups and crosslinks with isocyanates, forming a uniform and dense coating without altering the crystal structure of ADN. The contact angle increased significantly from 5° (unmodified) to 45° (PEI) and 30° (MDI). At 25 °C and 75% RH, the moisture absorption rate decreased by over 60% within 24 h, with a reduction of up to 70% for the PEI-modified sample. TGA confirmed that thermal stability remained unchanged. Quantum chemical simulations revealed that the average saturated moisture absorption rate of the major exposed crystal faces of ADN was 14.79%, with NH₄⁺ as the key moisture-absorbing site, while that of the ADN-PEI-isocyanate composite dropped significantly to 3.07%-3.87%, in good agreement with experimental results. This in-situ crosslinking strategy offers a simple process, mild reaction conditions, and significant modification effects, providing a feasible technical pathway for the practical application of ADN in high-energy solid propellants and energetic materials.