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Addition polymerisation joins alkene monomers without producing a small-molecule by-product. The C=C pi bond opens and each monomer forms new sigma bonds to neighbours. Preserve every substituent on its original carbon and draw continuation bonds through the brackets. A repeat unit is a structural pattern, not a separate stable molecule with arbitrary extra hydrogens at each end. To recover the monomer, identify the two backbone carbons of the repeat and restore the double bond.
Video by Eliot Rintoul. The video’s own board label is retained; follow the specification reference and scope notes on this lesson for assessed content.
Viewing focus: Draw repeat units and infer monomers
After watching, attempt these questions before opening the answers. You can also use the written lesson below.
After watching 1: Which polymerisation normally has no small by-product?
Addition polymerisation. All atoms of the alkene monomer remain in the polymer.
After watching 2: Which link occurs in a polyester?
–COO–. Ester links connect the monomer residues.
What you'll be able to do
Addition polymerisation joins alkene monomers without producing a small-molecule by-product. The C=C pi bond opens and each monomer forms new sigma bonds to neighbours. Preserve every substituent on its original carbon and draw continuation bonds through the brackets. A repeat unit is a structural pattern, not a separate stable molecule with arbitrary extra hydrogens at each end. To recover the monomer, identify the two backbone carbons of the repeat and restore the double bond.
A condensation polymer forms when monomers with two or more reactive functional groups join, eliminating small molecules such as water or HCl. A diol and dicarboxylic acid can form a polyester; a diamine and dicarboxylic acid can form a polyamide. A monomer with both complementary groups can polymerise by itself. Show the complete ester or amide link, account for the atoms eliminated, and distinguish the chemical link from a hydrogen bond between neighbouring chains.
Addition-polymer backbones commonly contain strong carbon–carbon bonds that resist hydrolysis. Polyesters and polyamides contain hydrolysable links, though actual biodegradation depends on structure and environmental conditions. Hydrogen bonding between polyamide chains affects strength and melting behaviour. Recycling decisions depend on sorting, contamination, processing energy and polymer degradation. Energy recovery and chemical recycling have different products and trade-offs; the word recyclable alone does not establish a material’s overall environmental advantage.
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: Which two functional-group types can form a polyamide link?
A diamine with a dicarboxylic acid, for example.
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.