CIE A Level Chemistry (9701) 2019-2021

Revision Notes

7.7.9 Applications of Polymers

Applications of Polymers

Polymers as non-solvent based adhesives

  • Many adhesive products contain a soft polymer with a solvent
  • When applied to a surface, the solvent evaporates leaving the polymer residue on the surface
  • Adhesives without the solvent has become a widely used alternative
  • Epoxy resin and superglue are 2 examples of a non-solvent based adhesive

Epoxy resin

  • Epoxy resin is used as an adhesive for metal surfaces, electronic circuit boards and filling gaps on concrete surfaces amongst other applications
  • Before applying to the desired surface, epoxy resin exists as 2 parts (often in 2 tubes)
  • These two parts have to be mixed together then applied to the surface
  • One of the parts consists of substance made up of small polymer molecules
  • Each polymer is capped by an epoxy group at either end
  • The other part is a diamine
  • When epoxy polymer and diamine are combined, the diamine assists in forming cross links between the polymer molecule
  • So, rather than forming a long linear polymer molecule, the cross linking allows the epoxy adhesive to form into a large molecule
  • The cross-links harden the adhesive over the applied surface
  • The resulting material is hard and cannot be moulded
  • This chemical reaction between the two components of epoxy resin avoids the need for a solvent to set the polymer

Exam Tip

  • You won’t need to remember the structure of the epoxy polymer or the cross linked molecule
  • It is important for you to remember that mixing these two molecules, then the subsequent cross-linking reaction, creates a large molecule that sets in the shape it was applied
  • Once the epoxy resin sets, you can’t mould it to take another shape

Super glue

  • The monomer involved in superglue is methyl 2-cyanoprop-2-enate
  • Also known as methyl 2-cyanoacrylate
  • When superglue is purchased in a tube, the material inside consists of just the monomer molecules
  • Once the glue like substance is apple to a surface, a polymerisation reaction begins
  • Water molecules in the atmosphere (or on the applied surface) acts as a nucleophiles to turn molecules of methyl 2-cyanoacrylate into nucleophiles
  • Each of the newly formed methyl 2-cyanoacrylate nucleophiles then attack another of its kind
  • This polymerisation mechanism essentially forms (poly)methyl 2-cyanoacrylate and hardens onto the applied surface
  • The ability of methyl 2-cyanoacrylate to react with water vapour in the air avoids the need for solvents in this type of adhesive

Conducting polymers

  • For any material to conduct electricity, delocalised electrons must be present
  • These delocalised electrons can carry charge through the structure of a material
    • For example, copper wire is able to conduct electricity
    • It’s metallic structure has positive metal centres neatly arranged in a ‘sea’ of delocalised electrons
  • There are polymeric materials that have the ability to conduct electricity
  • Polyacetylene is a conducting polymer
    • It’s monomer is an alkyne – Ethyne
    • Alkynes contain a C-C triple bond
    • A covalent bond is formed by sharing 3 pairs of electrons
  • When ethyne is polymerised, it forms a polymer chain with alternating single and double C-C bonds
  • A C-C double bond consists of one sigma bond and one pi bond
  • The pi bond is formed through the sideways overlap of carbon’s p orbitals
    • These overlapping p orbitals are at right angles to the plane of the polymer molecule
  • All carbon atoms in (poly)acetylene are able to have sideways overlapping p orbitals, allowing a system of delocalisation to be set up
  • The delocalisation over the length of polymer chain enables carrying of charge and therefore conduction of electricity

Exam Tip

  • When identifying polymer molecules capable of conducting electricity, it is important to note that the molecule has to be planar
  • So the atoms/bonds/groups of the molecule has to lie in the same plane
  • This is in addition to the delocalisation effect from alternating double and single bonds

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
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