Vapour-phase chemical derivatisation for the determination of surface functional groups by X-ray photoelectron spectroscopy

Abstract

A vacuum adsorption apparatus has been used for vapour-phase chemical derivatisation of standard polymers, to identify specific reactions for carboxylic acid and carbonyl functional groups. The reactivity and selectivity of trifluoroethanol (TFE)–pyridine-di-tert-butylcarbodiimide and 3-(trifluoromethyl)phenylhydrazine for these respective groups were studied. Depths of reaction were also investigated using F 1s/F 2s peak intensity ratios determined by X-ray photoelectron spectroscopy (XPS). The TFE–/pyridine-/di-tert-butylcarbodiimide system was found to be suitable for the selective derivatisation of carboxylic acid groups, achieving ca. 75% conversion of carboxylic acid groups. The depths of fluorine incorporation for both the TFE and TFAA reactions were found to be invariant with reaction time over the XPS sampling depth for the range of conditions studied. Derivatisation of carbonyl groups using 3-(trifluoromethyl)phenylhydrazine was not sufficiently selective, reactions being observed with hydroxy and carboxylic acid groups. Flame treatment of polyethylene produced oxidised surfaces with a variety of functional groups. Using the methods described above and previously reported the hydroxy and carboxylic acid group concentrations were found to be invariant with flame intensity, with the latter having the consistently lower concentration.