Interfacial Polymerization of TEPA and HMDI: The Role of Water

The interfacial polymerization (IP) between tetraethylenepentamine (TEPA) and 4,4'methylenebis (cyclohexyl isocyanate) (HMDI) at the inorganic-organic solvent interface happens so fast that it is difficult to control the reaction and the morphology of the polymer. Through quantum mechanical (QM) calculations and molecular dynamics (MD) simulations, we clarify the catalytic effect of water on the rapid IP process in the organic phase. QM results reveal that a single water molecule acts as a proton transfer bridge by establishing hydrogen bonds with both TEPA and HMDI, and the hydrogen bonds lower the free energy barriers from 15.1-16.6 kcal·mol^-1 (in the absence of a single water molecule) to 2.3-3.1 kcal·mol^-1 (in the presence of a single water molecule) in implicit hexadecane. The interaction energy analysis, performed via the fine-tuned MACE FF, indicates that HMDI preferentially resides in the hexadecane phase, while TEPA is more likely to diffuse across the interface. The result provides an energy-based perspective for the partition in the IP process, and experimental observations confirm that polymerization occurs toward the organic phase. These findings provide direct evidence that a single water molecule facilitates IP, offering critical insights for the rational design and precise control of polymerization at the interface to enable improved regulation of reaction kinetics and polymer morphology.