Let's have a look at Polyoxymethylene (POM), how to modify plastics and some related questions in A-Level Chemistry!
1. Explain each of these differences in properties. Use ideas of intermolecular bonding between polymer chains in your answer. You should clearly link the property of water absorption to the type of intermolecular bonding.
Water absorption is greater in nylon because
- It can form hydrogen bonds with water
- Because it has both –NH and C=O groups whereas POM has only an –O group
- Because it has more electronegative atoms to form hydrogen bonds
- It can form more hydrogen bonds with water than POM can
POM has a lower melting point because
- Weaker intermolecular bonds between polymer chains
- Less energy needed to separate chains
POM is more rigid because:
- Polymer chains can not slide over each other so easily
- Chains are aligned more closely
- Crystallinity is greater
2. What type of additive could be mixed with the POM to make it more flexible?
- Plasticiser
Longer chains make stronger polymers
• Longer chains are more tangled together –this make it difficult for the chains to slide over each other, so reducing flexibility
• When chains are longer they have more points of contact with chains of neighbouring polymer molecules therefore there are more intermolecular bonds to hold the chains together
• An increase in the number of intermolecular bonds means that the chains are attracted to each other more strongly
• This means its difficult for the chains to slide over each other –the polymer is less flexible
Modifying Polymer Properties
Copolymerisation
Introducing monomers with larger side groups pushes the polymer chains further apart, weakening the bonds between them
Plasticisers
Molecules that sit between the polymer chains, allowing them to slide more freely, lowering the Tg
Cold Drawing
Cold drawing stretches the polymer so that the polymer chains become aligned giving more opportunities for intermolecular bonding
Drafted by Eunice (Chemistry)