Addition Polymers

What are Addition Polymers?

Addition polymers are large molecules formed by joining many small molecules called monomers. These monomers are unsaturated, meaning they contain carbon 6carbon double bonds (C=C). During addition polymerisation, the double bonds open up and link together to form a long polymer chain.

A key feature of addition polymerisation is that no small molecules are released as by-products. The entire monomer molecule becomes part of the polymer chain.

Monomers and Polymerisation

The simplest example of an addition polymer is made from the monomer ethene (C₂H₄), which contains a C=C double bond.

During addition polymerisation, many ethene molecules open their double bonds and join together in a repeating chain:

Monomer: Ethene (C₂H₄)

Polymer: Poly(ethene) (also called polyethylene)

Here, n represents the large number of monomer units joining to form the polymer chain.

The polymer chain consists of repeated -CH₂-CH₂- units linked by strong covalent bonds. The double bonds in the monomers break and become single bonds in the polymer.

For instance, if you start with ethene, the polymer formed is poly(ethene), a common plastic used in bags and bottles.

Example: If 1000 ethene molecules join in addition polymerisation, the polymer chain will have 1000 repeating -CH₂-CH₂- units.

Properties of Addition Polymers

Addition polymers have several important properties:

• Strong covalent bonds: The polymer chains are made of strong covalent bonds between carbon atoms, making the material tough and durable.
• Insoluble in water: Addition polymers do not dissolve in water because their long chains are non-polar and large.
• Thermoplastic behaviour: Most addition polymers are thermoplastics, meaning they soften when heated and harden when cooled. This allows them to be melted and reshaped multiple times.

Common addition polymers and their uses include:

• Poly(ethene) (polyethylene): Used for plastic bags, bottles, and packaging films.
• Poly(propene) (polypropylene): Used for ropes, crates, and food containers.
• Poly(chloroethene) (PVC): Used for pipes, window frames, and waterproof clothing.

Example: Poly(ethene) is widely used because it is cheap, flexible, and resistant to chemicals.

Environmental Issues

Addition polymers pose environmental challenges because they are non-biodegradable. This means they do not break down naturally in the environment.

Problems caused by plastic waste include:

• Pollution of land and oceans harming wildlife.
• Plastic waste accumulating in landfill sites.
• Microplastics entering food chains.

Recycling addition polymers is difficult because:

• Different polymers have different melting points and properties, so they must be separated carefully.
• Contamination with food or other materials reduces recycling quality.
• Recycled plastics often have lower quality and limited uses.

Biodegradable alternatives are being developed to reduce plastic pollution. These break down more easily in the environment but are not yet widely used.