Polymerisation - This is the process of making long chains of plastic (polymer) molecules from lots of single unit alkene molecules (monomers).
For example, many ethene molecules can be joined together to make polyethene or 'polythene'.
The physical properties of a polymer depends on what it's made of and the temperature and pressure of polymerisation.
For example, polyethene is made at 200oC and 2000 atmospheres pressure and it's flexible with a low density. But polyethene made at 60oC and a few atmospheres pressure with a catalyst is…