Making a polyester
4 marks · NormalDescribe what is meant by condensation polymerisation in the formation of polyesters.
Draw the displayed formula for the repeat unit of a polyester made from ethane-1,2-diol and propane-1,3-dioic acid.
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(a) Condensation polymerisation is a reaction in which two different monomers join to form a polymer, with each link releasing a small molecule such as water. · must show Description of two different monomers, Mention of small molecule (e.g. water) lost
(b) — · must show Correct repeat unit with ester linkage, –O–CO– and hydrocarbon chains from both monomers
Common mistakes: Describing addition instead of condensation polymerisation; Incorrect repeat unit structure
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Marking points
B1 (a) · 1 mark · Mentions reaction between two different monomers (e.g. diol and dicarboxylic acid).
B2 (a) · 1 mark · States or implies the loss of a small molecule (e.g., water) each time a bond forms.
B3 (b) · 2 marks · Draws the correct repeat unit for the polyester (from ethane-1,2-diol and propane-1,3-dioic acid) showing the ester linkage and correct connections (allowed: any correct equivalent structure or repeat unit).
Worked solution
a) In condensation polymerisation, two different monomers react together and a small molecule, such as water, is lost each time a new bond forms, resulting in a polymer chain.