Abstract
Byproducts are formed at various times or positions within the PET process. During esterification, the conversion rate of terephthalic acid and ethylene glycol is the highest, and the largest changes are observed in prepolymer carboxyl end group and diethylene glycol concentration. During the polycondensation stage, under full vacuum, when the reaction temperature is highest, molecular weight increases at the fastest rate. Color changes dramatically during this period. The product becomes grayer and greener as a result of the reduction of the Sb 3+ polycondensation catalyst to antimony metal and more yellow because of the formation of colored, high molecular weight byproducts via polymer degradation reactions. A previously unidentified byproduct, trans-4,4'-dicarboxystilbene, formed in this stage, is fluorescent and could contribute to the fluorescence of PET. This compound is also significant because it indicates that the redox chemistry which produces high molecular weight byproducts during polycondensation may result in the reduction of Sb 3+ to Sb 0 .
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