The kinetics of the polyurethane moisture curing reaction: a combined experimental and DFT mechanistic study†

Abstract

An examination of the temporal dynamics of the moisture curing process of polyurethane (PUR) hot melt adhesives under varied humidity (65–85% RH) and temperature (20–40 °C) was performed via in situ Fourier transform infrared (FTIR) spectroscopy. The commencement of the moisture curing for PUR was substantiated by a reduction in peak intensity at 2271 cm⁻¹. The data revealed that the nascent phase of the moisture curing reaction aligns with the first-order reaction kinetics. Further, there was a noticeable acceleration in the rate of the PUR's moisture curing reaction with an increment in environmental humidity and temperature. Density functional theory (DFT) was harnessed to delve into the effects of additional water clusters on the PUR's moisture curing progression. The theoretical model proposed that these additional water molecules catalyzed the hydrogen transfer, thus bolstering the moisture curing reaction, a finding that corroborated with our empirical observations.