Abstract: Glycol solutions of a bis glycol ester of a difunctional aromatic compound possessing one or more metallo sulfonate groups suitable for use in continuous or non-continuous preparation of fiber-forming cationic dyeable copolyesters by copolymerization with a low molecular weight glycol-dicarboxylic acid prepolymer are prepared by reacting the dimethyl ester of a metallo sulfo dicarboxylic acid with glycol at a mole ratio of about 4-30 of the glycol to 1 of the dimethyl ester, under ester interchange conditions so as to provide a solution of the bis glycol ester of the metallo sulfo dicarboxylic acid in glycol containing about 20-75% of the bis glycol ester having a carboxyl plus carboxylate content of not more than about 200.mu.eq/g of bis glycol ester, and no more than about 10 weight percent of glycol ether based on bis glycol ester. A conventional ester interchange catalyst and glycol ether suppressant may be employed.