X-RAY PHOTOELECTRON-SPECTROSCOPY INVESTIGATIONS OF ACID-BASE INTERACTIONS IN ADHESION .2. THE DETERMINATION OF A SCALE OF POLYMER BASICITY BY A SOLID-STATE ACID-BASE TITRATION METHOD

A qualitative scale of polymer basicity has been obtained using X-ray photoelectron spectroscopy (XPS). The method is based on the uptake of sodium cations (Na+) by polymeric films cast onto glass slides containing sodium oxide. The diffusion of Na+ from the glass substrate to the polymers is interpreted in terms of acid-base interactions between Na+ (Lewis acid) and a series of basic polymers; poly(styrene) (PS), poly(methylmethacrylate) (PMMA), and poly(ethylene oxide) (PEO), and a series of acidic polymers; poly(vinyl butyral) (PVB), poly(vinyl chloride) (PVC), and poly(vinylidene fluoride) (PVdF). The Na+ concentration determined by XPS is consistently higher in the basic polymers. By comparing the Na+ uptake by different polymers we have determined the following decreasing order of basicity: PS>PMMA>PEO>PVB>PVC>PVdF. An extension of this approach, to relate the relative uptakes of Na+ to the hardness or softness of the polymers, is also considered.