Cambridge O Level Chemistry · Syllabus 5070 · Organic Chemistry
Polymer
What is Polymer?
A large molecule built up from many smaller molecules called monomers, joined together in a long chain; the repeat unit is the smallest section of that chain which repeats along its length.
This definition is part of the Organic Chemistry chapter in Cambridge O Level Chemistry.
Common mistakes with Polymer
- “All polymerisation reactions release water.” why it fails This over-generalises from condensation polymers to every polymer. correct Addition polymerisation releases nothing at all — the polymer is the only product. Condensation polymerisation releases a small molecule, and you can only say which one by looking at the functional groups actually being joined. Taught in 11.8B.
- 16. “The repeat unit of poly(propene) is –[–CH3–CH2–]n–.” defect A substituent moved onto the wrong backbone carbon. why In propene the CH3 hangs off the second double-bond carbon. Putting it into the backbone gives a carbon with five bonds. repair –[–CH2–CH(CH3)–]n–. Mark the two double-bond carbons before redrawing, and move nothing else. transfer Deduce the repeat unit of the polymer made from CH2=CHF, keeping the F on its own carbon.
- 17. “Nylon is made from ethanoic acid and an amine.” defect Condensation monomers given only one functional group each. why With one reactive end apiece, the two would join once and stop. You would get a small molecule, not a polymer. repair Use a dicarboxylic acid and a diamine: HOOC–□–COOH and H2N–▢–NH2. transfer Explain why an amino acid can build a protein on its own, despite there being only one kind of monomer.
Questions students ask about Polymer
What is the difference between addition polymerisation and condensation polymerisation?
Addition polymerisation joins many unsaturated monomers by opening each C=C double bond, so the polymer is the only product and nothing is released. Condensation polymerisation joins monomers that each carry two functional groups, releasing a small molecule — usually water — at every linkage formed. A polyamide forms a -CO-NH- linkage from a dicarboxylic acid and a diamine; a polyester forms a -CO-O- linkage from a dicarboxylic acid and a diol.