Elution behaviour of polyamic acid and polyamide—imide in size-exclusion chromatography

Abstract

The causes of the peculiarities of the elution behaviour of thermoresistant resins, when N,N-dimethylformamide (DMF) is used as the mobile phase were investigated. In order to establish whether the peculiarities are caused by the properties of DMF, by the interactions between the stationary phase and DMF, or by the generation of specific properties of the solutes in DMF, tetrahydrofuran (THF)-soluble polyamic and polyamide—imide resins were prepared. Two stationary phases, hydrophobic polystyrene gel and hydrophilic polymer gel, were used and DMF, THF and a mixture of DMF and THF with or without H 3PO 4 and LiBr were used as the mobile phases. The peculiarities are discussed from the point of dissociation of carboxylic groups of the solutes and of the hydrophilic stationary phase. Adsorption of the resins on the columns or early elution from the columns were prevented by the addition of H 3PO 4 and early elution of the neutral polyamide—imide from the column was prevented by the addition of LiBr. The early elution of the resins was not due to the intramolecular chain expansion of the resins in DMF, but to the interactions between carboxylic groups of the resins and of the hydrophilic polymer gels. The addition of H 3PO 4 suppressed the dissociation of carboxylic groups of the resins. DMF partially controls the dissociation of the carboxylic groups.