Chapter 18 · Organic Chemistry
18.17Polymers
9 min · two checks
Predict
What is a polymer, and what is polyethylene made from?
The idea
- Distinguish addition and condensation polymers.
- Name the monomer of a simple addition polymer.
Polymers are large molecules made of repeating monomer units. Addition polymers form when monomers with double bonds add to a growing chain: ethene makes polyethylene, propene makes polypropylene, vinyl chloride makes PVC, and styrene makes polystyrene. The backbone is a saturated carbon chain, and the side group is whatever the monomer carried. Chain length and branching decide whether the plastic is flexible or rigid.
Condensation polymers form when monomers join and a small molecule, often water, is released. Nylon joins a diamine and a diacid (or a related pair) through amide links. PET, a polyester used in bottles, joins a diacid and a diol through ester links. Proteins and starch, in the next chapter, are biological condensation polymers. Recycling codes and fabric labels are polymer chemistry written in abbreviations. The reaction type — addition or condensation — tells you whether a small molecule was split out.
Keep these
- Polymers are long chains of monomer units.
- Addition polymers come from alkenes. No small molecule is lost.
- Condensation polymers, such as nylon and PET, release a small molecule as links form.