Addition polymerisation

In a nutshell

Polymers are large molecules made up of many smaller molecules known as monomers. The monomers are joined together during a reaction known as polymerisation. There are a few ways to dispose polymers and further research is being done to ensure using polymers is sustainable.

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Addition polymerisation

Addition polymers are made up of unsaturated monomers such as alkenes. One of the bonds in the $$C=C$$ bond is broken so the carbon is able to form a bond with the adjacent monomer. Addition polymers are inert hence useful in making durable everyday products such as: plastics, polystyrene cups, resin and nylon.

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Naming polymers

The name of a polymer is formed by putting the name of the monomer in brackets and adding the prefix 'poly.' Some textbooks and online material may not use the brackets.

Example

Let the monomer be propene. The polymer will be named poly(propene).

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Repeat unit

Since polymers are (very) large molecules they are represented using repeat units in the displayed formula.

To draw a repeat unit: 

PROCEDURE

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Plasticisers

Plasticisers are added during polymerisation. Plasticiser molecules go in between the polymer chains, reducing the intermolecular forces between them. This increases the flexibility of polymers allowing them to bend easily.

Example

Rigid PVC is used to make drainpipes. However, plasticised PVC is used to manufacture electrical cable insulation due to its flexibility.

Disposing polymers 

There are a few ways to dispose polymers, although not every method is environmentally friendly.

Landfill

Plastics are dumped in the landfill when the quantity of plastic is not economically viable to separate the plastic out from other waste materials or it is difficult to recycle.

Reuse 

Plastics may be reused usually in one of two ways:

1. Via cracking - the polymers are cracked into smaller monomers or smaller molecules which are then repurposed.
   
2. Via recycling - the polymers are melted then remoulded into a new item.

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​​Burning

Plastics may be burned to generate heat electricity. However, this needs to be moderated as some plastics produce toxic fumes. Scrubbers can be used to neutralise the gases.

Example

PVC contains chlorine which produces hydrogen chloride when burned. When hydrogen chloride is passed through scrubbers it is neutralised by a base.

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Sustainability

Chemists follow a set of principles when designing and manufacturing sustainable polymers. This is to ensure detrimental impacts on humans and the environment are minimised.

Principles

• Use molecules which are safe.
• Ensure waste products are not harmful.
• Use renewable raw materials which are environmentally friendly, wherever possible.
  
• Keep energy consumption to a minimum. Catalysts are usually adopted to keep energy usage low.
• Ensure durable polymers are produced.

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Biodegradable polymers

Biodegradable polymers are a great alternative to traditional polymers, as they can be made from raw renewable materials and can be readily decomposed by micro-organisms. If a plant-based polymer is produced, the impact of the polymer will be carbon neutral because the carbon dioxide released into the atmosphere will be the same carbon dioxide absorbed whilst growing. 

However, there are a few drawbacks. Using biodegradable polymers is more expensive. Further to this, they only decompose under a certain set of conditions. Due to this factor biodegradable polymers are still required to be collected and separated from non-biodegradable plastics.