Making a polyester
4 marks · NormalWrite a balanced chemical equation using structural formulae for the reaction between ethane-1,2-diol (HOCH2CH2OH) and butane-1,4-dioic acid (HOOCCH2CH2CH2COOH) to form a polyester and water.
Explain why the product formed is called a polyester.
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(a) n HOCH2CH2OH + n HOOCCH2CH2CH2COOH → [–OCH2CH2O–COCH2CH2CH2CO–]n + 2n H2O
(b) The product is called a polyester because it contains many (poly-) ester functional groups linking the monomer units in the polymer chain.
Common mistakes: Fails to show repeat unit or water among products; Repeats the stem without explanation
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Marking points
B1 (a) · 1 mark · Writes correct reactants using full/structural formulae.
B2 (a) · 1 mark · Gives correct product formulae, including correct repeat unit and water.
B3 (b) · 1 mark · Explains that there are multiple ester groups in the polymer chain.
B4 (b) · 1 mark · Refers to bonding/linkage between the monomers.
Worked solution
The product is called a polyester because its structure contains many ester bonds joining the monomer units together in a long chain.