In simple terms
A friendly intro before the formal notes — no formulas yet.
Building Chains, Losing Molecules
Monomers with two functional groups join end-to-end to form a long polymer chain. Each time a link is made, a small molecule like water is eliminated.
Imagine making a long chain of pop-beads. However, to connect two beads, you must first snap off a small connector tab from each one. The final chain is made of the main parts of the beads, and you're left with a small pile of discarded tabs. In chemistry, these 'tabs' are small molecules like water.
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A small molecule, such as water (H₂O) or hydrogen chloride (HCl), is eliminated every time two monomers join.
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Polyesters form when a dicarboxylic acid and a diol monomer react, creating a repeating ester linkage (–COO–).
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Polyamides form from a diamine and a dicarboxylic acid (like Nylon), or from self-reacting amino acids (like proteins), creating a repeating amide linkage (–CONH–).
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To draw the polymer, identify the repeating unit formed after the small molecule is removed, and place it in square brackets with continuation bonds.
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Full topic notes
Formal explanation with the rigour you need for the exam.
Polyesters: The Ester Linkage
Polyesters are polymers characterised by the presence of repeating ester functional groups () in their main chain. They are typically formed by the reaction between a dicarboxylic acid (a monomer with two carboxylic acid groups) and a diol (a monomer with two alcohol groups). The reaction is an esterification, repeated thousands of times to build the polymer chain. For each ester link formed, one molecule of water is eliminated.
Polyamides: The Amide Linkage
Polyamides are polymers containing repeating amide functional groups (). This is the same linkage found in proteins, where it is called a peptide bond. Synthetic polyamides, such as Nylon and Kevlar, are known for their exceptional strength and durability. They are typically formed from the reaction between a dicarboxylic acid and a diamine (a monomer with two amine groups). Similar to polyester formation, a molecule of water is eliminated for each amide bond created.
Polyamides contain the repeating amide linkage: .
They are formed from monomers containing amine () and carboxylic acid () groups.
The polymer chains are held together by strong intermolecular hydrogen bonds between the polar and groups.
This extensive hydrogen bonding gives polyamides high melting points and high tensile strength, making them suitable for fibres and ropes.
Identifying Monomers and Polymerisation Type
In an exam, you may be asked to identify the type of polymerisation from a given monomer or polymer structure. A simple rule is to look at the functional groups. If the monomer has a double bond, it will undergo addition polymerisation. If the monomer (or monomers) has two functional groups at its ends that can react together (e.g., –OH, –COOH, –NH₂, –COCl), it will undergo condensation polymerisation. If you are given the polymer, look for an ester () or amide () link in the main chain; their presence is a clear indicator of a condensation polymer.
When drawing a repeating unit, a foolproof method is to first draw the two monomers side-by-side. Use a pencil to circle the atoms that will be eliminated (e.g., H from an –OH group and OH from a –COOH group to make H₂O). Then, redraw the remaining fragments, connecting them with a new bond. Finally, place the unit in square brackets, ensuring the bonds at each end pass through the brackets to indicate the chain continues.
Worked examples
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Terylene (also known as PET) is a common polyester formed from the monomers ethane-1,2-diol and benzene-1,4-dicarboxylic acid. Draw the structure of the repeating unit of Terylene.
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Identify and draw the monomers:
Nylon 6,6 is a polyamide formed from hexanedioic acid () and 1,6-diaminohexane (). Draw a section of the polymer chain showing two repeating units.
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Identify the monomers:
How it all connects
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Glossary
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Quick check
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Revision flashcards
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What is condensation polymerisation?
A polymerisation reaction where monomers join together with the elimination of a small molecule (e.g., H₂O or HCl) for each link formed.
Key takeaways
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Polyamides contain the repeating amide linkage: .
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They are formed from monomers containing amine () and carboxylic acid () groups.
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The polymer chains are held together by strong intermolecular hydrogen bonds between the polar and groups.
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This extensive hydrogen bonding gives polyamides high melting points and high tensile strength, making them suitable for fibres and ropes.
Practice — then mark it
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Practice Questions: Condensation Polymerisation
Practice Questions: Condensation Polymerisation
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