Although there are various forms of energy available for conducting surface and interfacial reactions, microwave plasma energy is an attractive means for surface modifications because it is fast and it usually does not alter bulk properties. In this study, a closed-system microwave plasma reactor was used to react imidazole molecules to poly(vinyl chloride) (PVC) surfaces. Newly created surfaces were analyzed using attenuated total reflectance (ATR) Fourier-transformed infrared (FTIR) spectroscopy. These studies show that surface reactions on PVC are heavily dependent upon a prior thermal history of the PVC substrate. It appears that the plasma reactions on hotpressed PVC not only result in the development of CH 2 linkages, but a significant increase of crystallinity in the hot-pressed PVC inhibits the reactivity of imidazole to the PVC surface. On the other hand, for a solvent-cast PVC with a significantly lower surface crystalline phase content, imidazole reacts to the PVC surface through CAC bond opening. The amount of imidazole reacted to the PVC surface changes with the depth from the surface. Using quantitative ATR FTIR spectroscopy, imidazole content can be quantified, and its concentrations are in the 10 ฯช6 mol/cm 2 range at about 0.8 -1.2 m for the PVC surface. A mechanism of the PVC-imidazole reactions is also proposed.