Chromatography of polycarbamoyl sulphonates (anionic polyurethane derivatives)

Abstract

The composition of some polyurethanes used to shrink-resist wool with a poly(propylene oxide) backbone and terminal −NHCOSO 3 −Na + groups, i.e. polycarbamoyl sulphonates (PCSs), have been investigated by chromatographic methods. The molecular weight distribution at different stages in the preparation of PCSs was examined by gel permeation chromatography (GPC) using detection methods appropriate to either the total polymer concentration or the number of terminal groups. Low-molecular-weight impurities in PCS preparations were investigated by GPC and reversed-phase liquid chromatography. Problems in assigning PCS molecular weights on aqueous GPC on a surface modified silica column were resolved by the use of polystyrene gel columns and tetrahydrofuran eluent with either: (i) the conversion of the PCS to a urea derivative by reaction with di- n-butylamine, or (ii) changing the PCS counter ion from sodium to methyltrioctylammonium. The principle of the second method was also applied to some cationic polyurethane derivatives. Reaction with 1-(2-pyridyl)piperazine converts carbamoyl sulphonates and isocyanates into derivatives with strong ultraviolet absorption at 300 nm. This derivatization reaction gives an estimate of the number of terminal carbamoyl sulphonate groups in the GPC fractions of a PCS, or terminal isocyanates in polyisocyanates. This method was the most sensitive way to estimate the bisulphite adduct of hexamethylene diisocyanate in PCS preparations.