In Situ Study of Buried Interfacial Bonding Mechanisms of Carboxylic Polymers on Zn Surfaces

This study investigates the buried interfacial bonding properties of carboxylic polymers on Zn by means of ATR-FTIR in a Kretschmann geometry and X-ray photoelectron spectroscopy (XPS). Poly(methyl vinyl ether-alt-maleic acid monobutyl ester) and cured propoxylated bisphenol A fumarate unsaturated polyester were applied on a set of differently treated Zn samples. In the Kretschmann geometry, a thin Zn layer and subsequently the polymer were applied on an internal reflection element (IRE). The buried metal-polymer interface was studied in situ by passing infrared beams through the metal layer and reaching the metal-polymer interface in the attenuated total reflection (ATR) setting. Moreover, the metal-polymer interfacial bonding density was evaluated by application of the polymer on a Zn foil and XPS analysis of the Zn layer and the top polymer coating. Furthermore, the interfacial bondings were mimicked by adsorption of succinic acid molecules as the representative model compounds. The differently treated Zn layers were found to be capable of adsorption of the carboxylic groups, resulting in the formation of carboxylates. A comparison of the interfacial bondings of the polymers with those formed by the molecular adsorption showed a resembling interfacial mechanism. Additionally, it was found that the deprotonation kinetics depend on the polymer-weight, while the polymer metal interfacial bonding density mainly depends on the Zn surface hydroxyl fraction as well as initial molecular weight.