Adhesive & Conducting Polymers

Chemistry: Cambridge International A Level, topic 3.8.7

Some polymers can act as non-solvent based adhesives. Some are able to conduct electricity.

Many adhesives are dissolved in a solvent. The solvent then evaporates after the adhesive is applied.
This allows the solvent to set.
Polymers can act as non-solvent based adhesives.
Examples include epoxy resins and superglue.

There are lots of different varieties of epoxy resins.
Most epoxy resins work by mixing one species with an acidic -OH group and one species with an epoxy group together.
The structure of an epoxy group is shown on this slide.
Once the two species are mixed together, crosslinks between them form. These crosslinks are strong and form the basis of how epoxy resins function as adhesives.

Superglue often consists of ethyl cyanoacrylate monomers.
When superglue is applied to a surface, water vapour in the air nucleophilically attacks the -CH₂ group of the monomers.
This generates a new nucleophile. The now nucleophilic monomer intermediate can attack neighbouring methyl 2-cyanoprop-2-enate monomers.
So, water vapour triggers a polymerisation event in superglue. This polymerisation sets the glue.

Polyacetylene is a polymer than can conduct electricity. It has the repeating unit (C₂H₂)_n.
This means it is made of alternating single and double carbon bonds.
Double bonds are formed by the overlapping of p-orbitals.
When many double bonds are repeated along a carbon chain, all of the p orbitals can overlap. This forms a delocalised system of electrons along the whole molecule.
This is what happens in polyacetylene. The delocalised system of electrons allows polyacetylene to conduct electricity.

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