Process for the preparation of polyester, a polyester and its use

Process for making a polyethylene terephthalate polyester, said process comprising the steps of:

• a) performing a transesterification of dimethyl terephthalate with ethylene glycol in a reaction mixture in the presence of an antimony-free transesterification catalyst consisting of a manganese salt at temperatures from 160.degree. to 230.degree. C. to form methanol and an ester product, wherein said manganese salt present in said reaction mixture provides 10 to 100 ppm of manganese based on a total weight of said terephthalic acid ester present in said reaction mixture prior to the transesterification;
• b) removing the methanol from the reaction mixture by distilling;
• c) then heating the reaction mixture to temperatures from 230.degree. to 245.degree. C.;
• d) when the temperature of the reaction mixture reaches 230.degree. C., adding a sufficient amount of an inorganic phosphorous compound to the reaction mixture to provide a molar ratio of P/Mn in the reaction mixture of from 0.66 to 0.89 and to form a blocked portion of the manganese salt and a free portion of the manganese salt;
• and
• e) after adding of the inorganic phosphorus compound to the reaction mixture, adding 10 to 100 ppm of germanium by adding a germanium compound to the reaction mixture to provide a germanium-containing antimony-free polycondensation catalyst consisting of the free portion of the manganese salt and the germanium compound, wherein said 10 to 100 ppm of said germanium is based on a total weight of said terephthalic acid ester present in said reaction mixture initially prior to the transesterification;
• and
• f) performing a polycondensation of the ester product formed in step a) in the reaction mixture in the presence of the germanium-containing antimony-free polycondensation catalyst at temperatures from 245.degree. to 285.degree. C. to form the polyethylene terephthalate polyester;
• wherein antimony-containing compounds are not present in the reaction mixture during the transesterification and the polycondensation.