9701 · 35.2

Predicting the type of polymerisation — practice questions

Practice and worked examples for 9701 Predicting the type of polymerisation. Short previews only — attempt the full question in MarkScheme against the official scheme.

Worked example 1

The monomer chloroethene, $CH_2=CHCl$ , is used to make the polymer PVC. Predict the type of polymerisation it undergoes and draw two repeating units of the resulting polymer.

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Analyse the monomer: Chloroethene contains a $C=C$ double bond.
Predict the polymerisation type: The presence of the $C=C$ bond indicates it will undergo addition polymerisation.
Draw the polymer structure: The double bond breaks to form the chain. The H and Cl atoms are attached to the carbon backbone. The repeating unit is $-[CH_2-CHCl]-$ . Two repeating units would be $-[CH_2-CHCl-CH_2-CHCl]-$ .

Worked example 2

A polymer is formed from the monomers hexane-1,6-diamine, $H_2N(CH_2)_6NH_2$ , and decanedioyl dichloride, $ClOC(CH_2)_8COCl$ . (i) Predict the type of polymerisation. (ii) Name the type of polymer formed and the linkage within it. (iii) Identify the small molecule eliminated. (iv) Draw the repeating unit of the polymer.

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(i) Prediction: The monomers are bifunctional (a diamine and a diacyl chloride). Their functional groups will react. This is condensation polymerisation. (ii) Polymer type and linkage: An amine reacts with an acyl chloride to form an amide linkage ( $-CONH-$ ). The polymer is a polyamide. (iii) Small molecule: The H from the amine group ( $-NH_2$ ) and the Cl from the acyl chloride group ( $-COCl$ ) are eliminated as hydrogen chloride ( $HCl$ ). (iv) Repeating unit: The repeating unit consists of one of each monomer, joined by the amide link. $-[NH-(CH_2)_6-NH-CO-(CH_2)_8-CO]-$

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