PRODUCING A COPOLYESTER FROM A LOWER DIALKYL ESTER OF TEREPHTHALIC ACID, A GLYCOL AND A DICARBOXYLIC ACID

PRODUCING A COPOLYESTER FROM A LOWER DIALKYL ESTER OF TEREPHTHALIC ACID, A GLYCOL AND A DICARBOXYLIC ACID of the Invention A process for producing a copolyester by copolymerizing the monomers from the ester interchange of a lower dialkyl ester of terephthalic acid and glycol and the direct esterification of a 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 ester and glycol produce a first monomer; to the monomer adding a slurry of dicarboxylic acid and glycol and employing an effective catalytic amount of lithium and cobalt in a direct esterification reaction where the dicarboxylic acid and glycol produce a second monomer; and using an effective catalytic amount antimony in a copolycondensation reaction of the monomers. Using the catalyst system allows for the combination of the ester interchange reaction with the direct esterification reaction to produce a copolyester.