Condensation Polymerisation: A GCSE Tutorial

Condensation polymerisation is a type of polymerisation where monomers join together to form a polymer, but unlike addition polymerisation, a small molecule (usually water) is also produced as a byproduct. This means the polymer's molecular formula isn't simply a multiple of the monomer's formula.

1. The Monomers:

Condensation polymers are formed from monomers with at least two functional groups capable of reacting with each other. These functional groups are often:

• Alcohols (-OH): Contain a hydroxyl group.
• Carboxylic acids (-COOH): Contain a carboxyl group.
• Amines (-NH2): Contain an amino group.

These groups react together to form an ester linkage (-COO-), an amide linkage (-CONH-), or other linkages, releasing a small molecule like water in the process.

2. The Reaction:

The reaction involves the elimination of a small molecule, typically water, between the functional groups of two monomers. This forms a covalent bond between the monomers, creating a dimer. This process repeats many times, adding more monomers and creating a long chain polymer.

3. Examples:

Let's look at some common examples:

• Polyester formation (from a dicarboxylic acid and a dialcohol):

A dicarboxylic acid (e.g., adipic acid) has two carboxyl groups (-COOH), and a dialcohol (e.g., hexane-1,6-diol) has two hydroxyl groups (-OH). Each -COOH group reacts with a -OH group, releasing a molecule of water and forming an ester linkage (-COO-). This creates a long chain polyester.

HOOC-(CH2)4-COOH  +  HO-(CH2)6-OH  --->  HOOC-(CH2)4-COO-(CH2)6-OH + H2O

(This is a simplified representation; the reaction continues to add more monomers)

• Polyamide formation (from a dicarboxylic acid and a diamine):

A dicarboxylic acid (e.g., adipic acid) reacts with a diamine (e.g., hexane-1,6-diamine). The -COOH group reacts with the -NH2 group, releasing a molecule of water and forming an amide linkage (-CONH-). This process repeats, creating a polyamide like nylon.

HOOC-(CH2)4-COOH + H2N-(CH2)6-NH2 ---> HOOC-(CH2)4-CONH-(CH2)6-NH2 +H2O

(This is a simplified representation; the reaction continues to add more monomers)

4. Properties of Condensation Polymers:

The properties of condensation polymers vary greatly depending on the monomers used. They can be strong, flexible, resistant to heat, or have other desirable characteristics. For example, nylon (a polyamide) is strong and used in clothing, and PET (polyethylene terephthalate, a polyester) is used to make plastic bottles.

5. Key Differences from Addition Polymerisation:

This tutorial provides a basic understanding of condensation polymerisation. Further study will delve into the specifics of different monomers and the resulting polymer properties.