Condensation Polymers
Polymers formed with the release of a small molecule.
The Mechanism
Unlike addition polymerization, condensation requires monomers with two functional groups. A reaction occurs between group ends, linking the monomers and releasing a small molecule (usually H₂O or HCl) for every link formed.
Atom Economy: <100% (due to loss of small molecule).
Key Polymer Types
| Type | Reactants | Linkage | Example |
|---|---|---|---|
| Polyester | Dicarboxylic Acid + Diol | Ester (–COO–) | PET (Terylene) |
| Polyamide | Dicarboxylic Acid + Diamine | Amide (–CONH–) | Nylon, Kevlar |
Biodegradability
Addition Polymers
Contain a strong, non-polar C–C backbone. They are chemically inert and therefore non-biodegradable.
Condensation Polymers
Contain polar linkages (Ester/Amide). These bonds are susceptible to hydrolysis (breakdown by water), making them biodegradable.
Think About It
Proteins are natural polyamides and DNA is built from condensation reactions. Given that condensation polymers are biodegradable through hydrolysis, why don't our proteins constantly break apart inside us?
Proteins are kinetically stable — the amide bonds are strong enough to resist spontaneous hydrolysis at body temperature. Breaking them requires enzymes (biological catalysts) that specifically lower the activation energy. Without the right enzyme, the hydrolysis reaction is far too slow. This is why digestion requires proteases — our body controls when and where proteins are broken down.