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Addition polymerisation opens carbon–carbon double bonds and joins many monomers into a chain. A repeat-unit drawing retains all substituents, changes the double bond to a single bond and shows continuation bonds crossing the brackets. Poly(ethene) contains repeated CH2–CH2 units. Molecular size and interactions influence properties, so polymers can behave very differently from their small monomers.
Video by Cognito. The video’s own board label is retained; follow the specification reference and scope notes on this lesson for assessed content.
Viewing focus: Draw an addition-polymer repeat unit
After watching, attempt these questions before opening the answers. You can also use the written lesson below.
After watching 1: What forms in addition polymerisation?
A chain with no small-molecule by-product. The alkene atoms are retained.
After watching 2: Which link joins amino acids in proteins?
Peptide link. Amino acids condense to form peptide bonds.
What you'll be able to do
Addition polymerisation opens carbon–carbon double bonds and joins many monomers into a chain. A repeat-unit drawing retains all substituents, changes the double bond to a single bond and shows continuation bonds crossing the brackets. Poly(ethene) contains repeated CH2–CH2 units. Molecular size and interactions influence properties, so polymers can behave very differently from their small monomers.
Condensation polymerisation joins molecules with suitable reactive groups and eliminates a small molecule such as water. Polyesters contain ester links; proteins contain peptide links joining amino acids. DNA and carbohydrates are also large molecules built from repeating small units, but their link types and sequences differ. A polymer is not defined solely by being man-made or plastic. Trace the atoms through formation of the link rather than relying only on a material’s familiar name.
Metals, alloys, ceramics, polymers and composites offer different combinations of strength, flexibility, thermal behaviour and density. A composite combines materials to obtain useful properties. A lifecycle comparison includes raw materials, manufacture, use and disposal. Recycling needs collection and separation and may affect material quality. Some hydrolysable polymers degrade under suitable conditions, but biodegradability does not mean immediate disappearance in every environment. Tie conclusions to evidence and the service required.
Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.
Common mistakes to avoid
Key takeaways
Question 1: Why can a composite be preferable to one material for a specific use?
A justified combination can suit the use better; there is no universal best material.
Check the assessed scope and practical or mathematical requirements.
An external explanation or interactive activity to use alongside the lesson. It may include extension material.
Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.