Solid-state additional polycondensation of poly(ethylene terephthalate): Kinetics and development of morphology

The kinetics of the solid-state additional polycondensation of PET in high vacuum (5 x 10(-5) mmHg) was studied. The rate constants of solid-state additional polycondensation in the 230-250 degreesC range were determined. It was shown that, at the degrees of polycondensation P-n < 700, the solid-state additional polycondensation of PET proceeds as a second-order chemical reaction and its apparent activation energy is 205 kJ/mol. It was demonstrated that, at T = 250<degrees>C and annealing times of 10 h and longer, a fourfold reduction in the reaction rate constant is observed. This leads to the deceleration of the molecular mass growth at P-n > 700. The model is advanced to describe a variation in the polymer structure during solid-state additional polycondensation. This model allows one to explain deceleration of the molecular mass growth and a significant rise in the melting temperature T, with increasing molecular mass and provides an opportunity to estimate the ultimate molecular mass that can be achieved by solid-state additional polycondensation.