Polymers

Polymers

1. Forces between molecules determine the properties of plastics

   • Covalent bonds hold the atoms together in long chains
   • But it’s the bonds between the different molecules chains that determine the properties of the plastic

2. Weak Forces:

   • Individual tangled chains of polymers, held together by weak intermolecular forces
     • Are free to slide over each other

3. Thermosoftening polymers

   • Don’t have cross-linking between chains. The forces between the chains are really easy to overcome
   • So it dead easy to melt the plastic
     • When it cools, the polymer hardens into a new shape
   • You can melt thes plastics and remould them as many times as you like.

4. Strong Forces

   • Some plastic have stronger intermolecular forces between the polymer chains, called crosslinks, that holds the chains firmly together

5. Thermosetting polymers

   • Have crosslinks
   • These hold the chain together in a solid structures
   • The polymer doesn’t soften when it’s heated
   • Thermosetting polymers are the tough guys of the plastic world as they’re strong, hard and rigid

6. Two types of polythene can be made using different condition:

   • Low density (LD)
     • Polythene is made by heating ethane to about 200 oC 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 catalyst)
     • Its more rigid and is used for water tanks and drainpipes.

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