Polymers - Addition vs. Condensation Polymerisation

This document outlines the key differences between addition and condensation polymerisation, a crucial topic in organic chemistry for the IGCSE Chemistry 0620 exam.

Addition Polymerisation

Addition polymerisation involves the joining together of many small molecules (monomers) to form a large molecule (polymer) without the loss of any atoms. The monomers simply add to each other.

Mechanism

1. The process usually requires an initiation step, involving a free radical, ion or catalyst.
2. The initiated monomer then adds to another monomer, creating a growing polymer chain.
3. This process repeats, with monomers adding to the chain end, until the chain is terminated.

Examples

• Polyethylene (plastic bags, bottles)
• Polypropylene (containers, fibres)
• Polystyrene (packaging, insulation)
• Polyvinyl chloride (PVC - pipes, flooring)

Key Characteristics

• No atoms are lost during the polymerisation process.
• Monomers are typically unsaturated (contain double or triple bonds).
• Often requires a catalyst.
• Polymer chains are generally long and linear.

Condensation Polymerisation

Condensation polymerisation involves the joining together of monomers to form a polymer, with the loss of a small molecule, such as water.

Mechanism

1. Monomers react with each other, forming a new bond.
2. A small molecule (e.g., water, HCl) is eliminated for each bond formed.
3. This process continues, building up the polymer chain.

Examples

• Polyesters (clothing, bottles)
• Polyamides (Nylon - clothing, ropes)
• Polyurethanes (foam, coatings)
• Proteins (amino acids)
• Starch (glucose)

Key Characteristics

• A small molecule is lost during the polymerisation process.
• Monomers typically contain functional groups that can react with each other (e.g., -COOH, -OH, -NH2).
• No catalyst is usually required.
• Polymer chains can be linear or branched.

Comparison Table

Feature	Addition Polymerisation	Condensation Polymerisation
Monomer Requirement	Typically unsaturated (double/triple bonds)	Functional groups (e.g., -COOH, -OH, -NH2)
Atom Loss	No atoms lost	Small molecule (e.g., water) is lost
Catalyst	Often required	Usually not required
Polymer Chain Structure	Generally linear	Linear or branched
Examples	Polyethylene, Polyvinyl chloride, Polystyrene	Polyesters, Polyamides, Polyurethanes

Understanding the differences between addition and condensation polymerisation is essential for comprehending the properties and uses of various polymers. The type of polymerisation determines the structure, properties, and applications of the resulting polymer.