Phosphate-containing catalysts composition for the preparation of polyesters, and related processes

Polyesters having relatively low melt viscosities and without excessive level of undesirable reaction byproducts in short reaction times are prepd. from a dicarboxylic acid/ester/ester-forming deriv. and a dihydroxy compd. in the presence of a catalyst compn. comprising a Ti-based compd., a Zr-based compd. and a phosphate. Thus, poly(butylene terephthalate) was prepd. from 705 g di-Me terephthalate and 458 g 1,4-butanediol, using tetra-Bu titanate, Zr tetrakis(2,4-pentanedionate), and sodium dihydrogen phosphate at 0.8 mmol Ti and Zr compds. per mmol di-Me terephthalate and 245°.