BISHYDROXYETHYL TEREPHTHALATE

PET) is produced by esterification of terephthahc acid [100-21 -0] (1) to form bishydroxyethyl terephthalate [959-26-2] (BHET) (2). BHET polymerizes in a transesterification reaction catalyzed by antimony oxide to form PET (3). 

Chen, J.-W. and Chen, L.-W., The kinetics of diethylene glycol formation from bishydroxyethyl terephthalate with antimony catalyst in the preparation of PET, J. Polym. Sci., Polym. Chem. Ed., 37, 1797-1803 (1999). 

Kamatani, H. and Kuze, K., Formation of aromatic compounds as side reactions in the polycondensation of bishydroxyethyl terephthalate, Polym. J 11, 787-793 (1979). 

Step-growth condensation polymers, such as polyesters and polyamides, are formed by reversible reactions. In the case of PET, the commercial synthesis is essentially carried out by two reactions. The first is the formation of bishydroxyethyl terephthalate by esterification of a diacid with a glycol or by transesterification of a diester with a glycol. The second is the formation of the polymer by a polycondensation reaction. 

Bishydroxyethyl terephthalate (BHET) is the monomer used to make the PET polymer. BHET can be made either by the esterification of terephthalic acid (TPA) with ethylene glycol (EG) ... 

An initial esterification reaction occurs between an excess of ethylene glycol with dimethylterephthalate under basic catalysis at 150 °C. Removal of methanol by distillation drives the formation of bishydroxyethyl terephthalate, which can be considered an monomer. A secondary transesterification step performed at 280 °C drives polymer formation via ester exchange, which is pushed toward high molecular weight by removal of ethylene glycol via distillation. 

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