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  Home > JCE Print > Journal of Chemical Education > Issues > 1999  > February  >
In the Laboratory
An Undergraduate Experiment in Polyester (PET) Synthesis
Andrew N. Cammidge
University of East Anglia, School of Chemical Science, Norwich NR4 7TJ, England
Cover
February 1999
Vol. 76 No. 2
p. 236
Abstract
The most important polyester manufactured industrially is PET (polyethyleneterephthalate). We describe an experiment that conveniently mimics the industrial synthesis in the undergraduate laboratory. The first step of the reaction is a base-catalyzed transesterification between ethane diol and dimethylterephthalate. Methanol is distilled off to drive the reaction to completion. Excess ethane diol is employed to suppress formation of higher oligomers. The intermediate (bis-(2-hydroxyethyl)terephthalate) is isolated by crystallization and filtration and characterized by 1H NMR spectroscopy. In the second step the monomer is heated (with and without acid catalyst) to form polymer. Samples are removed at intervals and their physical properties are recorded as they cool. These properties are used to qualitatively monitor polymerization. This experiment reinforces some fundamental chemical concepts and introduces the students to new laboratory procedures. The students perform a distillation and apply their knowledge of the reaction equilibrium to calculate the volume of distillate (methanol) expected. The reversible nature of esterification reactions is emphasized during the polymerization step (acid-catalyzed), where the process is driven towards polymer formation by the removal (evaporation) of ethane diol.
More Information
*  Citation
 Cammidge, Andrew N. J. Chem. Educ. 1999 76 236.
*  Keywords
 Polymer Chemistry; Synthesis; Equilibrium; Stoichiometry; Laboratory Instruction; Organic Synthesis
*  History
 Created:
Last Updated:		 June 15, 1999
June 22, 2005
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