Polymers and their uses:
The forces between the polymers molecules determines the properties of plastics and therefore its use
Strong covalent bonds hold the atoms together in a chain
It is the forces between the chains that determines the properties of the plastic
Long chains that are held together with weak intermolecular are able to move around a lot. This plastic can be stretched easily and has a low melting point because it does not need a lot of energy to break the intermolecular bonds.
Some plastics have strong covalent bonds between chains. They can have cross-linking bridges so that it has a rigid structure. This means that it has a higher melting point as more energy is needed to break the strong covalent bonds. This plastic is very rigid and cannot be stretched unless changed into a molten state.
The properties of the plastic will have an impact on its use:
Strong, rigid plastics - High density polyethene used to make milk bottles