🟣 This is Higher Level (HL) content.
📘 Key Principle
Condensation polymers form when monomers with two functional groups react with each other, releasing a small molecule (usually H₂O) at each linkage.
Two Types
| Polyester | Polyamide (Nylon) | |
|---|---|---|
| Monomers | Diol (–OH at each end) + Dicarboxylic acid (–COOH at each end) | Diamine (–NH₂ at each end) + Dicarboxylic acid (–COOH at each end) |
| Linkage formed | Ester bond (–COO–) | Amide bond (–CONH–) |
| Small molecule lost | H₂O | H₂O |
| Example | PET (polyethylene terephthalate) – plastic bottles | Nylon-6,6 – textiles, rope, parachutes |
Key Differences from Addition
Addition
- One type of monomer (with C=C)
- No atoms lost
- Non-biodegradable
Condensation
- Two types of monomer (bifunctional)
- H₂O lost per linkage
- Hydrolysable → potentially biodegradable
🔑 Mark-Scoring Note
The small molecule lost is usually H₂O, but can also be HCl (e.g. When acyl chlorides are used). Always identify the specific small molecule in your answer – don't assume it's always water.
⚠️ Examiner Trap
Each monomer must be bifunctional (functional group at BOTH ends). If a monomer only has one functional group, the chain terminates immediately. No polymer can form.
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