Interaction of polyurethane model compounds with metal oxides

The chemical interaction of ester and urethane compounds as models for polyurethanes with chromium dioxides and aluminum oxides was investigated. The pigment was coated by suspending it in a solution of the model compound and evaporating the solvent. The amount of the compound remaining after contact with a pigment was determined by gas chromatography. The ester and urethane compounds can be extracted from the pigments in yields of 95–100% with dioxane. They decompose in contact with the pigments by a hydrolytic process. The oxidative potential of the unstabilized chromium dioxide causes an oxidation of the products of hydrolysis. The rate of decomposition is influenced by the temperature, by the water content in the system, by a structural modification of the model compound, and by surface modification of the pigment. The kinetics of decomposition follows a pseudo-first-order process in systems with a water surplus. In the presence of acidic aluminum oxide, adipic acid-di-n-butylester (ADnBE) will decompose faster than will phenylcarbamide acid-n-butylester (PCnBE), whereas the rate of decomposition in contact with basic aluminum oxide is much faster and without any difference between the ester and urethane compound. The surface modification of the pigment has the best effect on the reduction of the decomposition rate as shown with the stabilized chromium dioxide. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2449–2455, 1997