Kinetics of the polymerization of methylhydroquinone diacetate, terephthalic acid and poly(ethylene-terephthalate)

Poly(ethylene terephthalate) (PET) was modified using methyl hydroquinone diacetate (MHQDA) and terephthalic acid (TA) to develop copolyester membranes for pervaporation separation. These membranes are expected to have improved thermomechanical properties. Two different polymer compositions (PET 70/30 (MHQDA+TA) and PET 50/50 (MHQDA+TA)) were synthesized using the melt polymerization route. The melt polymerization kinetics of these systems are reported. Two different polyesterification catalysts sodium acetate and potassium acetate were tried at 280°C, 290°C and 300°C. The polycondensations were found to obey second order kinetics irrespective of whether the reaction was catalyzed or uncatalyzed. No breaks were observed in the kinetic plots suggesting the absence of different kinetic regime during the course of the reaction. An elaborate kinetic model that presupposes a steady state approach to the reaction fits the experimental data accurately. Activation energy values for the first rate constant (k1) for uncatalyzed PET 70/30 (MHQDA+TA) and PET 50/50 (MHQDA+TA) lie between 100 and 150 kJ mol−1 while for reactions catalyzed using sodium acetate and potassium acetate the values were between 25 and 40 kJ mol−1. Differential scanning analysis of the copolyester reveals that PET 70/30 (MHQDA+TA) and PET 50/50 (MHQDA+TA) are liquid crystalline in nature.