A polymer is classified as a condensation polymer primarily because of the specific type of chemical reaction used to create it.
The Defining Process: Condensation Polymerization
What exactly makes a polymer a condensation polymer? It's the process of polymerization itself. As defined in polymer chemistry, condensation polymers are characterized by their formation process:
- In polymer chemistry, condensation polymers are any kind of polymers whose process of polymerization involves a condensation reaction (i.e. a small molecule, such as water or methanol, is produced as a byproduct).
This means that during the formation of the long polymer chain from smaller molecules (monomers), a small molecule is eliminated or "condensed" out at each step where two monomers join together.
What is a Condensation Reaction in this Context?
In organic chemistry, a condensation reaction typically involves two molecules joining to form a larger molecule, with the simultaneous loss of a small molecule like:
- Water (H₂O)
- Methanol (CH₃OH)
- Hydrogen chloride (HCl)
- Ammonia (NH₃)
When this type of reaction repeats continuously between many monomers, linking them end-to-end to form a polymer chain, the result is a condensation polymer.
Key Characteristics
The defining feature differentiating condensation polymers from other polymer types (like addition polymers) is the production of a byproduct during their synthesis.
Here's a simple way to look at it:
| Polymer Type | Formation Process | Byproduct Produced? |
|---|---|---|
| Condensation Polymer | Involves a condensation reaction | Yes (e.g., water, methanol) |
| Addition Polymer | Monomers add together directly | No |
Examples of Condensation Polymers
Many common and important polymers are formed through condensation polymerization. Some well-known examples include:
- Polyamides: Like Nylon. These are formed by the reaction between a diamine and a dicarboxylic acid, with water being eliminated.
- Polyesters: Like PET (Polyethylene terephthalate) used in bottles and fibers. Formed from the reaction of a diol and a dicarboxylic acid, also typically eliminating water.
- Proteins: Naturally occurring condensation polymers formed from amino acids, with water eliminated at each peptide bond formation.
- Polysaccharides: Like cellulose and starch, formed from monosaccharides with the elimination of water.
Why is This Distinction Important?
Understanding whether a polymer is formed by condensation helps predict:
- The monomers used: Condensation polymerization usually requires monomers with at least two functional groups that can react with each other (e.g., -OH, -COOH, -NH₂, -Cl).
- The reaction mechanism: It involves step-growth polymerization where monomers react with each other, oligomers, and polymers at any stage, rather than chain-growth where monomers add sequentially to a growing chain end.
- The properties: The presence of polar functional groups and often the step-growth mechanism can influence the polymer's properties like melting point, strength, and susceptibility to hydrolysis.
In summary, a polymer is a condensation polymer because its creation involves a chemical reaction where monomers link together while simultaneously releasing a small molecule byproduct like water or methanol.
