Degradation reactions in the ethylene glycol terephthalate polycondensation process.

In the catalyzed polycondensation reaction of ethylene glycol terephthalate (EGT), the reaction rateconstant of the main reaction, 2(-_??__??_-COOC2H4OH)_??_k1k1'-_??_-COOC2H4OCO-_??_-+CH2OH-CH2OH (1)is given by the following equationk1=84.5•Cx•108e-18, 500/RT+4.0×1016e-40, 000/RT (2)The degradation reactions which are defined by-_??_-COOC2H4OCO-_??_-→k3-_??_-COOH+-_??_-COOCH=CH2 (3)-_??_-COOC2H4OH→k4-_??_-COOH+CH3CHO (4)always occur simultaneously with the main reaction.In order to study the degradation reaction rate in the presence of antimony trioxide under industrial conditions, the number-average degree of polymerization (DP) and the acid value of the carboxyl end-groups in 106g of polymer (AV) were investigated. The activation energies of reactions (3) and (4) were found to be 37.8kcal/mol and 29.8kcal/mol, respectively. Reaction (4) is significant only in the very early stages of the polycondensation reaction, so the greater part of degradation is due to reaction (3) whose rate constant is given by the following equation.k3=4.5•Cx•1013e-37, 800/RTwhere, Cx is the concentration of antimony trioxide.