Types of polymerisation
Unsaturated alkenes are added together to form saturated alkane chains with no double bonds. Individual alkenes are called monomers.
E.g. poly(ethene) is made by adding ethene monomers to make straight chains.
With no double bonds, polymers are unreactive.
A small molecule like H2O or Hydrogen is expelled to form polyester or polyamide linkages
Properties of polymers vary depending on their structure .
- Low density polyethene is soft and flexible and can make plastic bags.
- This is due to short side chains pushing individual chains apart.
- High density polyethene is more dense because it has no side chains, and the polymer chains fit closer together.
- It is stronger and can be made into plastic bottles,
- HDPE is not transparent, but can become translucent when stretched into a film.
Polymers are generally un reactive due to saturated bonds, there are no double bonds.
polymers can dissolve in water by hydrogen bonding with it.
Halogeno alkane polymers
Alkenes with halogens like chlorine or fluorine can make special polymers with extra properties such as non stick or durability and flexibility.
Thermo plastic polymers have no crosslinks between chains, and weak inter molecular forces hold them together, they can be melted and reformed again and again.
Thermo setting polymers have cross links that hold the chains together in a giant covalent structure, they don't melt and will burn. They are strong, hard and insoluble.
Synthetic polymers are designed to be unreactive and store food safely etc, so they are hard to dispose of.
Landfill is used when;
- Plastics difficult to separate from other waste
- Not enough quantity of plastics to make recylcing financially viable
- Too difficult to recycle
Recycling of polymers must be increased to reduce landfill as much as possible, as use of polymers is increasing rapidly.
An alternative would be to make biodegradable polymers which can decompose in landfil within 2 weeks.
Burning polymers can release toxic gasses into the atmosphere, but can be beneficial by generating electricity. Toxic gasses released can be HCL from PVC.
To remove harmful gasses from the combustion; scrubbers are used, which can neutralise HCL by reacting it with a base.
Plastics are made from non renewable sources, which makes recycling a good idea.
Some plastics can me melted down and remoulded as something else.
Some can be cracked into monomers that can be used to make new compounds.