We report combined FTIR–ATR and Raman microscopic studies of the distribution and redistribution of three different silane adhesion promoters in thin (10–20 μm) PVC films deposited on a Si/SiO2/SiOH substrate (a “model” glass surface). It has been shown that the different functionalized silanes diffuse at different rates through the polymer (at 70°C) and therefore have different distributions at the polymer/glass interface. The differences in behavior have been rationalized in terms of their respective abilities to hydrolyze and condense, under the different humidity and temperature conditions used. As the level of humidity rises there is evidence that the diffusion rate (measured using a dual-mode sorption model) decreases as a result of hydrolysis and condensation in the polymer films. The data are of importance as a direct measure of the relation between humidity levels and the adhesive action of a silane promoter at polymer/glass interfaces. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2016–2026, 2001