- They are formed from alkenes and substituted alkenes (where 1 H atom swapped for another atom or group, e.g. swapping 1 H in ethane for Cl atom you get chloroethene when polymerised you get poly(chloroethene)).
- Long chain formed by several monomers joined.
- Can be natural or synthetic.
- Double bonds in alkenes can open up and join together, make long chain called polymer and this is called addition polymerisation.
- Take repeating unit and remove unnecessary side bonds and add double bonds.
- Once found monomer used to form addition polymer you know they form poly(X) where X is the name of the monomer.
- Alkene monomers are unsaturated, once polymers they are saturated.
- Main C chain of polyalkenes is usually non-polar which means polyalkenes are very unreactive.
- The monomers in polymer chain have strong covalent bonds but weak intermolecular forces.
- Long chains, fewer branches have strong intermolecular forces so the polymers are strong and rigid.
Examples of Polymers
- Polyethene – They do not have branches so packed close together. Chains attracted by Van der Waals force, making it so strong and rigid.
- Polystyrene (poly(phenylethene)) – Benzene ring coming off main C chain is large branch so difficult for chains to pack closely. So only form weak Van der Waals force, making it more flexible.
- Polychlorethene (polyvinyl chloride/PVC) – Covalent bonds between Cl and C are polar, Cl more electronegative. Slightly –ve charge on Cl and slightly + on C means permanent dipole – dipole forces between polymer chains. So PVC is hard but brittle, used for drainpipes and window frames.
- Plasticisers – Can add these chemicals to polymers to modify properties. It makes polymers bendier. Chemicals get between chains and push apart which reduces strength of intermolecular forces so chains can slide and move more so more flexible.
- Plasticised PVC used to make electrical cable insulation, floor tiling and clothing.
Thats's the end of the topic!
Drafted by Bonnie (Chemistry)