Polymers Flashcards
Monomers
Small identical molecules used to make polymers. Always alkenes.
Mono means…
one.
Poly means…
many.
Polymers have…
a single bond.
Poly(ethene)
Ethene molecule turned to a polymer. It is very useful plastic as it is easy to shape, strong and transparent. Used for plastic bags, some drink bottles…
Polymers are used to make…
plastics.
Ethene
Is the smallest unsaturated hydrocarbon molecule.
C2H4
Poly(propene)
Forms very tough plastic. Used to make carpets, milk crates and ropes.
Propene formula
C3H6
Polymerisation
A reaction of monomers to make a polymer. The double bond opens.
How to draw a repeating unit of polymer?
- Pick up two carbon atoms next to each other
- Draw the unit of two carbons
- Put it inside a bracket
- Extend the bonds from carbon to left and write, outside the bracket
- Put n indicating a large number
The properties of polymers depend on:
- the monomers used to make it
- the conditions are chosen to carry out the reaction
Two types of poly(ethene)
-High density (HD) or HDPE
-Low density (LD) or LDPE
Both are formed from same monomers but made under different conditions.
LD polyethene
Using very high pressure and a trace of oxygen. This causes that polymer chains are randomly branched and they cannot pack closely, so it has a lower density.
HD polyethene
Using a catalyst at 50 degrees and slightly raised pressure. This produces straighter chains, which can pack more closely together, so it has a higher density. It has also a higher softening temperature and it is stronger than LD.
Thermosoftening
Made up of individual polymer chains that are tangled together. These will soften very easily because the intermolecular forces between polymer chains are weak.
When thermosoftening polymer cools down…
the intermolecular forces bring the polymer molecule back together and the polymer hardens.
A thermosoftening polymer can be…
remoulded.
Thermosetting polymers
These have strong covalent bonds forming cross-links between their polymer chains. It does not melt when heated.
In thermosetting, the covalent bonds between polymer chains are made…
when they are first heated in order to shape them. These bonds are strong, stopping the polymer from softening. If heated strongly, the polymer will not soften but char.
Development of polymers to:
- new softer linings for denatures (false teeth)
- new packaging materials
- implants that can slowly release drugs into a patient
Light sensitive plasters
Uses light-sensitive polymer. If it is exposed to light, it will become less sticky and easily removable.
Hydrogels
Polymers with a few cross-linking units between chains. This makes a matrix that can trap a water. These gels can be used as a wound dressing, allowing the body to heal in moist and sterile conditions.
Smart polymer
Changes in a response to changes in its surroundings. E.g. light, temperature or other changes.
Shape memory polymer
Makes stitching in difficult places easier. The temperature of the body makes the thread tighten and close the wound, applying the right amount of force.
The PET from…
plastic bottles are used to make polyester fibres for clothing.
PET
Very light and strong at the same time. Can be made transparent. Therefore, it is suitable for plastic bottles.
