Catalyst composition for the preparation of polyesters

Polyesters are prepd. by the reaction of a dicarboxylic acid, preferably an arom. acid such as terephthalic acid, or an ester or ester-forming deriv. with a dihydroxy compd. such as 1,4-butanediol in the presence of a catalyst compn. comprising the combination of a Ti-based compd. such as tetra-Bu titanate, a Zr-based compd. such as Zr tetrakis(2,4-pentanedionate) and a phosphate-forming compd. such as Na dihydrogen phosphate. This catalyst compn. gives polyesters having relatively low melt viscosities in short reaction times and does not produce an excessive level of undesirable reaction byproducts. Thus, poly(butylene terephthalate) was prepd. from 705 g di-Me terephthalate and 458 g 1,4-butanediol, using tetra-Bu titanate, Zr tetrakis(acetylacetonate), and sodium dihydrogen phosphate at 0.8 mmol Ti and Zr compds./mmol di-Me terephthalate and 245°.