Polymers

Polymers

1. Forces between molecules determine the properties of plastics

   • Strong covalent bonds hold the atoms together in long chains. But it's the bonds between the different molecule chains that determine the properties of the plastic
     • Weak forces
       • Individual tangled chains of polymers, held together by weak intermolecular forces are free to slide over each other
     • Strong forces
       • Some plastics have stronger intermolecular forces between the polymer chains called crosslinks, that hold the chains firmly together

2. Thermosoftening polymers don't have cross-linking between chains are really easy to overcome,so it's dead easy to melt the plastic. When it cools, the polymer hardens into a new shape. You can melt these plastics and remould them as many times as you like

3. Thermosetting polymers have crosslinks. These hold the chains together in a solid structure. The polymer doesn't soften when it's heated. They're strong, hard and rigid

4. Different monomers

   • The polymer chains in nylon are made from two different monomers. One monomer has acidic groups at each end. The other has basic groups at each end. The polymer they make is very different from the polymer chains made from hydrocarbon monomers, such as ethene. So the monomers used make a big difference to the properties of the polymer made

5. Different reaction conditions

   • There are two types of poly(ethene). One is called high density (HD) and the other low density (LD) poly(ethene). Both are made from ethene monomers but they are formed under different conditions

6. How you make a polymer affects its properties

   • The starting materials and reaction conditions will both affect the properties of a polymer
     • Two types of polythene can be made using different conditions:
       • Low density (LD) polyethene is made by heating ethene to about 200C under high pressure. It's flexible and is used for bags and bottles
         • High density (HD) polythene is made at a lower temperature and pressure (with a catalyst). It's more rigid and is used for water tanks and drainpipes

7. Monomers affect the properties of the polymers that they produce

8. Changing reaction conditions can also change the properties of the polymer that is produced

9. Thermosoftening polymers will soften or melt easily when heated. Thermosetting polymers will not soften but will eventually char if heated very strong