Polyesters are prepared by the reaction of a dicarboxylic acid, preferably
an aromatic acid such as terephthalic acid, or an ester or ester-forming
derivative thereof with a dihydroxy compound such as 1,4-butanediol in the
presence of a catalyst composition comprising the combination of a
titanium-based compound such as tetra-n-butyl titanate, a zirconium-based
compound such as zirconium tetrakis(2,4-pentanedionate) and a
phosphate-forming compound such as sodium dihydrogen phosphate. This
catalyst composition affords polyesters having relatively low melt
viscosities in short reaction times and does not produce an excessive
level of undesirable reaction by-products.