We have combined attenuated total reflectance/Fourier transform infrared (ART/FT-IR) and Raman microscopy to examine the diffusion rates and redistribution profiles of three different silane adhesion coupling agents into plasticized and unplasticized PVC. Below the glass transition temperature ( T_g) of the polymer, little or no diffusion occurs, and above the T_g (for pure PVC at about 70 °C) the three silanes behave differently, reflecting their different propensities to hydrolysis and subsequent condensation. For plasticized PVC, the fitted diffusion coefficients (obtained via the dual mode model) increase rapidly with increasing (adipate) plasticizer content and decreasing T_g. Correlation of this behavior is with chain “mobility” and not with silane size nor shape. The infrared data for unplasticized PVC laminates were confirmed by using Raman microscopy. Redistribution within the polymer film is shown to be induced by heating to 70 °C. However, the Raman data give a more accurate picture of the silane distribution throughout the film. Although no direct adhesion mechanistic information has been obtained, it has been shown that there are detailed differences in silane diffusion behavior which must be associated with reactivity differences, both within the polymer and at the Si/SiO₂/SiOH interface.