Using alkenes to make polymers

Polymerisation- joining lots of small alkene molecules (monomers) to form very large molecules, called polymers.
Eg. many ethene molecules can be joined to produce poly(ethene)/"polythene".
The physical properties of a polymer depend on what it's made from.
A polymers physical properties are also affected by the temperature and pressure of polymerisation.
Poly(ethene) -200*C & 2000 atmospheres pressure=low density + flexible.
-60*C & little atmosphere pressure (with a catalyst)= rigid + dense.
Uses:
*Light, stretchable (low density poly(ethene)) -> plastic bags
*Elastic polymer fibres-> Lycra fibre for tights.
*Dental polymers-> resin tooth fillings
*Waterproof coatings for fabrics
*Polymers that get softer as they get warmer-> memory foam (smart material)
*Hydrogel wound dressings
*Polymers + cornstarch-> biodegradable packaging materials

Most polymers aren't biodegradable.
-> Difficult to dispose since they don't rot.
-> Best to reuse them and recycle if possible.
Products made from polymers are usually cheaper than those made from metal.
-> As crude oil resources are used up, the price of crude oil will rise.
-> Crude oil products like polymers will also be more expensive.
-> In the future, there may not be enough oil for fuel & plastics & all other uses.