Purification of polymeric dyes by ultrafiltration

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Abstract
Ultrafiltration has been evaluated as a method for the purification of of polymeric dyes. Transport data for solvent and solutes were obtained for several polymer‐impurity mixtures and different membrane types. Relatively low molecular weight impurities were found to be significantly rejected by these membranes. A critical concentration of sodium chloride or sodium hydroxide was found to be necessary to effect efficient transport of these species. Gel permeation chromatography was used to monitor these separations and characterize the purity of the polymeric dyes produced. Impurity concentrations in the final product were typically less than 500 ppm.