Producing a copolyester from two lower dialkyl esters of dicarboxylic acid and a glycol

A process for producing a copolyester by copolymerizing the monomers from the ester interchange of at least two lower dialkyl esters of dicarboxylic acid and glycol using a novel catalyst system. The novel catalyst composition includes from about 20 ppm to about 150 ppm manganese; from about 50 ppm to about 350 ppm lithium; preferably from about 10 ppm to about 70 ppm cobalt; and from about 200 ppm to about 400 ppm antimony, all amounts being based upon the expected yield of the copolyester. The novel process to make copolyester includes the step of employing an effective catalytic amount of manganese and lithium in an ester interchange reaction where the lower dialkyl esters and glycol produce a monomer mixture; and using an effective catalytic amount antimony in a copolycondensation reaction of the monomers.