Identify the repeat units and/or linkages in addition polymers and in condensation polymers
Organic Chemistry – Polymers
Objective
Identify the repeat units and/or linkages in addition polymers and in condensation polymers 🧪.
Addition Polymers (Chain‑Growth)
In addition polymerisation, the double bond of the monomer opens and the monomers link together without losing any atoms. Think of it as a line of dominoes falling one after another – each domino (monomer) adds to the chain, but nothing is removed. 🔄
- Initiation – a radical or cation starts the chain.
- Propagation – the active end adds new monomers one by one.
- Termination – the chain stops growing (two radicals combine, for example).
| Polymer | Monomer | Repeat Unit | Linkage |
|---|---|---|---|
| Polyethylene (PE) | $C_{2}H_{4}$ (Ethylene) | $-CH_{2}-CH_{2}-$ | C–C single bonds |
| Polystyrene (PS) | $C_{8}H_{8}$ (Styrene) | $-CH_{2}-CH(C_{6}H_{5})-$ | C–C single bonds |
| Polyvinyl chloride (PVC) | $C_{4}H_{6}Cl_{2}$ (Vinyl chloride) | $-CH_{2}-CH(Cl)-$ | C–C single bonds |
Condensation Polymers (Step‑Growth)
Condensation polymerisation involves the removal of a small molecule (usually water or methanol) each time two monomers join. Imagine two Lego blocks snapping together and a tiny piece of plastic (the by‑product) falling off. 🧩
- Monomers with two reactive ends (e.g., –OH and –COOH) react.
- Each step releases a small molecule (H₂O, CH₃OH).
- Chain grows until all reactive ends are consumed.
| Polymer | Monomers | Repeat Unit | Linkage |
|---|---|---|---|
| Nylon‑6,6 | Hexamethylenediamine + Adipic acid | $-NH-(CH_{2})_{6}-NH-CO-(CH_{2})_{4}-CO-$ | –NH–CO– linkages (amide bonds) |
| Polyester (PET) | Ethylene glycol + Terephthalic acid | $-O-CH_{2}-CH_{2}-O-CO-(C_{6}H_{4})-CO-$ | –O–CO– linkages (ester bonds) |
| Polyurethane | Polyol + Isocyanate | $-O-CO-NH-CH_{2}-CH_{2}-O-$ | –O–CO–NH– linkages (urethane bonds) |
Exam Tips 📚
- Remember: addition polymers keep all atoms; condensation polymers lose a small molecule.
- Draw the repeat unit – this is the key to answering structure questions.
- Use the linkage name (amide, ester, urethane) to show the type of bond.
- Practice matching monomers to polymers – flashcards help! 🔄
- When given a polymer name, write the repeat unit and identify the linkage.
Revision
Log in to practice.
14 views
0 suggestions