The polycondensation of bis(ethylene glycol) terephthalate to poly(ethylene terephthalate) was investigated by thermogravimetric measurements at 260-300 Deg. A model is developed which enables to ext. the apparent kinetic parameters from the measured mass loss curves. Changing the height of the polymer layer from 0.03-2.10 mm shows an influence of mass transfer on the reaction rate. The efficiency of a Sb(III) catalyst was examd. [on SciFinder (R)]