Verfahren zur Herstellung von Polyaethylenterephthalat

In a process for making polyethylene terephthalate by esterifying free terephthalic acid with the ethylene glycol and polycondensing the product, there is added as a catalyst, prior to the completion of the esterification reaction, a quaternary ammonium compound of formula wherein X is a chlorine or bromine atom or a hydroxy group, and R1, R2, R3 and R4 are (a) a group A-B- where B is an alkylene group of 1-10 carbon atoms, an arylene or alkylarylene group of 6-16 carbon atoms, a cycloalkylene group of 6-16 carbon atoms or an arylalilylene group of 6-16 carbon atoms; and A is hydrogen or hydroxyl; (b) a group H-B-O- where B is as defined above; (c) a lower alkyl group having a lower alkoxy substituent; or (d) a lower alkyl group having lower acyl substituent. The quarternary ammonium compounds may be used in combination with other catalysts, e.g. cobalt chloride, cobalt acetate, manganese acetate, calcium acetate, lead acetate or antimony oxide or with colour inhibitors, e.g. phosphoric acid, phosphorous acid, triphenyl phosphite, triphenyl phosphate or trihexyl phosphite. The reaction mixture may also include other esterifiable components, e.g. isophthalic acid, adipic acid, sebacic acid, sodium sulphoisophthalic acid, p-hydroxybenzoic acid or pentaerythritol or inert ingredients, e.g. carbon black, titanium dioxide, phthalocyanine pigments or Indanthrene pigments.