Abstract: A continuous direct esterification and polycondensation process is disclosed in view of the production of polyester comprising units of ethylene terephthalate as the major repeating units, said polyester being substantially improved in particular in respect of its electroconductive properties. Said process comprises supplying terephtalic acid and ethylene glycol to bis(betahydroxy ethyl) terephthalate or its oligomer so as to carry out esterification, followed by polycondensing the resulting oligomer under increasingly reduced pressure, and wherein a solution in ethylene glycol of an electroconductivity enhancing additive, preferably a metallic salt, such as e.g. magnesium acetate, is added to the oligomer reaction mixture when the esterification rate has reached at least 80% and characterized in that said ethylene glycol solution is added to the oligomer reaction mixture in such manner that escape of the added ethylene glycol out of the said oligomer reaction mixture is prohibited.

Abstract: A continuous direct esterification and polycondensation process is disclosed for the production of polyester comprising units of ethylene terephthalate as the major repeating units by supplying a slurry of mainly terephthalic acid and ethylene glycol to bis(betahydroxyethyl) terephthalate or its oligomer so as to carry out esterification, followed by polycondensation whereby the resulting oligomer is kept under increasingly reduced pressure, characterized in that a stabilizing solution of an aliphatic diol containing a diethyl or tributhyl phosphite and a hindered phenolic phosphonate is added to the reaction mixture before the start of the polycondensation.