Process for the preparation of sulfo-modified polyesters

Claim 1

A process for the preparation of a sulfo-modified polyester comprising (a) reacting under polyester forming conditions (1) a 100 mole % dicarboxylic acid component comprising at least about 85 mole % terephthalic acid or an ester-forming derivative thereof and about 0.1 to about 5.0 mole % of a difunctional sulfo-monomer containing at least one metal sulfonate group attached to an aromatic nucleus, the functional groups being hydroxyalkoxy, carboxy or amine, and (2) a 100 mole % glycol component comprising at least about 85 mole % ethylene glycol, the reaction being conducted in the presence of a catalyst system comprising a titanium compound and an organic salt of an alkali metal, the titanium being present in the amount of at least about 10 to about 60 ppm based on the acid component of the polyester and the organic salt being present in the amount, based on a sulfo-monomer content of 0.5 mole % or less, of at least 0.025 mole per mole of polymer with the amount of organic salt increasing proportionately from 0.025 mole to at least 0.250 mole per mole of polymer as the sulfo-monomer content increases from 0.5 mole % to 5.0 mole %, said sulfo-monomer content being based on a 100 mole % acid fraction, (b) polycondensing the reaction product of step (a) in the presence of about 13 to about 240 ppm, based on the acid component of the polyester, of a phosphate ester to obtain a polymer having an inherent viscosity of about 0.3 to about 0.9 and characterized by an improved critical planar stretch ratio relative to a given inherent viscosity and an improved rate of acetaldehyde generation relative to a given planar stretch ratio.