What is a polymer?
A polymer is a very large molecule made by joining many small repeating units. Each small unit is called a monomer, and the process of joining them is polymerisation. A single polymer chain may contain thousands of monomer units, giving materials that are strong, light and easy to shape.
Natural and synthetic polymers
- Natural polymers occur in living things, for example starch and cellulose (from glucose), protein (from amino acids) and natural rubber.
- Synthetic polymers are made in factories from petroleum products, for example polythene, polyvinyl chloride (PVC), polystyrene, Perspex and nylon.
Key idea / 要点
In addition polymerisation, unsaturated monomers with C=C double bonds join together without losing any atoms. Example: n CH2=CH2 → −(CH2−CH2)n− (ethene → polythene).
Worked example / 例题
Vinyl chloride, CH2=CHCl, is the monomer of PVC. During polymerisation the C=C double bond opens and many molecules link into a long chain: n CH2=CHCl → −(CH2−CHCl)n−. PVC is used for pipes, cable insulation and floor tiles.
Uses and impact
| Polymer | Everyday use |
|---|---|
| Polythene | plastic bags, bottles |
| PVC | pipes, insulation |
| Polystyrene | packaging, cups |
Synthetic polymers are cheap, durable and resistant to chemicals, but most are non-biodegradable. Burning them can release toxic gases, so recycling and careful disposal are important.
Remember / 记住
- Monomer = the small unit; polymer = the giant chain.
- Addition polymers form from monomers containing C=C.
- Most synthetic polymers do not rot, causing plastic pollution.