The effect of humidity during storage on the crosslinking reactions of isocyanate groups was investigated with attenuated total reflectance Fourier transform infrared spectroscopy with pressure-sensitive adhesives composed of poly[ethyl acrylate-co-(2-ethylhexyl acrylate)-co-(2-hydroxyethyl methacrylate)] as a base resin and polyisocyanate as a crosslinker. A peak-resolving analysis of the amide II region revealed four bands. According to an analysis of the Fourier transform infrared spectra of the model compounds, these four bands were assigned to free urethane linkages, hydrogen-bonded urethane linkages, free urea linkages, and hydrogen-bonded urea linkages. As expected, storage under humid conditions led to the formation of free and hydrogen-bonded urea linkages corresponding to the promotion of isocyanate consumption. Peak resolution of the amide II region was found to be a reasonable way of monitoring urethane and urea linkages during crosslinking reactions. (C) 2003 Wiley Periodicals, Inc.