X-Ray photoelectron spectroscopy investigations of acid–base interactions in adhesion. Part 1.—Estimation of polymer properties by a solvent swelling technique

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Abstract
The acid–base properties have been studied for two polymers: a homopolymer, poly(methyl methacrylate), and a commercial aromatic moisture-cured poly(urethane). The method is based on the swelling of polymer films by solvent vapours having a range of Gutmann's donor and acceptor numbers (DN and AN). The solvent concentration in the swollen polymer is determined by XPS and then related to the AN of the acidic solvents or to DN when the solvent is basic (pyridine). The plot is S-shaped and the inflection point is referred to as the ‘acceptor number equivalent’, ANE. This parameter should describe the Lewis base strength of the candidate polymer.The binding energies of Cl 2p and F 1s from the acidic solvents are shifted to low values because of the electrophilic properties of the acidic solvents, and this phenomenon is related to the formation of the solvent–polymer adduct. By contrast, the N 1s chemical shift of pyridine following interaction with PMMA is positive relative to that in pure pyridine suggesting the formation of a PMMA–pyridine adduct where pyridine is the Lewis base and PMMA is the Lewis acid species. This suggests that PMMA has both electrophilic and nucleophilic properties.