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AS/A-level Chemistry - Polymer

Organic Chemistry, Polymer, Addition Polymerisation 

July 7, 2021

A polymer is a long chain molecule made up of small units called monomers. 

Addition polymerisation

  • Process of turning lots of monomer into a long polymer chain.
  • The process by which alkenes monomers form long polymers, which are technically alkanes but are named with alkene names, such as poly(ethene). 
  • The polymer structure can be represented more simply by drawing the repeating unit. 

In AS/A-level chemistry exam, you will be asked to identify the repeating unit of a polymer! 👩‍🏫

Co-polymerisation

When 2 different monomers become incorporated into the polymer chain. 

Characteristics of polymers✍🏻

Chain length:

  • The longer the chain, the stronger the polymer.
  • Tensile strength is a measure of how much force needs to be applied before a polymer snaps.
  • Tensile strength increases with chain length because longer chains become more entangled and they have stronger intermolecular bonds and therefore are more difficult to pull apart.

Side groups:

  • The more polar a side group, the stronger the bonds between the polymer chains, therefore the stronger the polymer.

Branching:

  • Straight chain polymers can pack closer together allowing stronger bonds between the chains.

Chain flexibility:

  • The more rigid the chain the stronger the polymer.
  • Hydrocarbon chains are flexible.
  • Incorporating benzene rings makes the polymer chain stiffer.

Cross linking:

  • More extensive cross linking makes the polymer harder to melt.

Stereoregularity:

  • The more regular the orientation of the side groups and the closer the packing, the stronger the polymer.

Elastomers:

  • soft and springy
  • they can be stretched but will return to their original shape.

Plastics: 

  • Not so springy
  • When deformed, it tends to stay out of shape
  • Undergoes permanent or plastic deformation 

Fibers:

  • Strong polymers
  • Do not deform easily
  • can be made into strong, thing threads
  • Eg: Nylon
  • Used for making clothing materials

Thermoplastics:

  • No cross-links.
  • Intermolecular bonds are weak.
  • Attractive forces can be overcome by warming.
  • Chains can slide over each other.
  • Can be deformed.
  • On cooling the weak bonds reform and it will hold its new shape.
  • Poly(ethene) and nylon are examples.

Thermosets:

  • Extensive cross-linking.
  • Strong bonds.
  • Covalent bonds cannot be broken by warming.
  • Chains cannot move relative to one another.
  • Cannot change shape.
  • Continued heating leads to chars and burns.
  • Bakelite is an example.

Uses and properties of polymers:

LDPE

  • Low density, flexible
  • eg. Carrier bags
HDPE
  • Higher density, less flexible
  • eg. Buckets, food storage, car petrol tanks
PEX (HDPE with cross-linking)
  • Can withstand higher temperatures than HDPE; good chemical resistance
  • eg. Water and gas pipes
PTFE
  • Hydrophobic; slippery non-stick surface; resistant to chemical attack.
  • eg. ‘Gore-tex’ clothing, ‘Teflon’ non-stick pans
ETFE (ethene/PTFE co-polymer)
  • Highly transparent; low density; shatterproof; resistant to stains and UV radiation.
  • eg. Structural roofing material, such as used on the Eden project biomes.
Neoprene
  • Elastomer; non-porous; very tough; resistant to heat, light and chemical attack.
  • eg. Wetsuits, cases for MP3 players and mobile phones.

Reference:

https://getrevising.co.uk/resources/polymers8

This is the end of the topic! Good job!

Drafted by Cherry (Chemistry)

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