Kinetics and Modeling of PCTG Final Polycondensation

The reaction kinetics of the final polycondensation stage of poly（cyclohexylene dimethylene terephthalate-co-ethylene terephthalate） （PCTG） was studied using a static thin-film experimental apparatus under conditions of 250–290℃ and 40–1000 Pa. A polycondensation kinetic model featuring four reaction pathways was developed to elucidate the mass transfer behavior of volatiles and the dynamic evolution of composition in high-viscosity PCTG melts. By integrating ¹H NMR measurements of average molecular weights with a coupled mass-transfer and reaction scheme for ethylene glycol and cyclohexanedimethanol, the model quantitatively predicts the time-dependent profiles of end-group concentrations and molecular weights.Twenty-two model parameters were obtained by least-squares fitting of experimental data, with a coefficient of determination R²; of 0.968. The results showed that increasing temperature and decreasing pressure promoted the forward polycondensation reaction, leading to higher average molecular weights. Reducing film thickness facilitated volatile removal and accelerated the reaction. The rate constants followed the order k₁>k₂>k₃>k₄ with similar apparent activation energies. An application example for a disc reactor demonstrated that the model can guide the optimization of operating conditions for industrial PCTG production.