Surface (XPS, SIMS) chemical investigation on poly(pyrrole-3-acetic acid) films electrosynthesized on Ti and TiAlV substrates for the development of new bioactive substrates

Electropolymerization of pyrrole-3-acetic acid was performed by cyclic voltammetry on titanium and Ti90Al6V4 substrates with the aim of developing a multilayer structure for applications in advanced biomaterials. The polymeric films obtained were characterized by both XPS and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Information on the poly(pyrrole-3-acetic acid) (PPy-3-acetic) surface structure was achieved by a detailed XPS analysis of C 1s and N 1s signals. The number of COOH groups was quantified by XPS coupled to a chemical derivatization reaction in which esterification with trifluoroethanol was exploited so that the presence of fluorine (or the CF3 component in C 1s spectra) could be used as a marker for COOH groups. As a result, it was found that more than 90% of the monomer units along PPy-3-acetic chains bear carboxylic functionalities, of which 60% are protonated and 40% are present as carboxylate groups. Some decarboxylation occurs with film ageing. The PPy-3-acetic films were also investigated by ToF-SIMS in the negative ion mode, thus obtaining, for the first time, interesting information on the structure of the top surface layers of a polymer belonging to the polypyrrole family. In particular, clusters of peaks related to PPy-3-acetic oligomers were detected and the decarboxylation phenomenon on top of the polymer surface was confirmed. Copyright © 2005 John Wiley & Sons, Ltd.