The liquid chromatography of aromatic diamines: analytical and preparative
Liquid chromatographic methods were developed for determining the purity, reactivity, and preparative separation of aromatic diamine isomers used in the synthesis of aromatic polyimides. Approximately 50 diamine isomers were separated on various silica gels using chloroform and/or cyclohexane mobile phases. A linear relationship between pKb, and log of the capacity factor was discovered for four series of simple aromatic amines. This suggested that the relative basicities of more complex diamine isomers might be established from chromatographic retention data. A chromatographic basicity index for two series of isomers was then proposed and correlated with polymer viscosity measurements.
Several parameters which can affect the efficiency of preparative separations of diamine monomers were also evaluated. These parameters included the effect of the column packing technique, flow rate, column diameter and length, adsorbent surface area and particle size, and column capacity. The results of this evaluation indicate that preparative liquid chromatography can be used to prepare highly purified milligram quantities of monomers for polymer synthesis.