There are two types of Polymerization:

•   Addition Polymerization
•   Condensation Polymerization

Addition Polymerization

Addition Polymerization is the process where small unsaturated monomer (alkene ) molecules join together to form a large saturated molecule. 

Only alkenes undergo addition Polymerization.

 Addition polymers are named from the alkene/monomer making the polymer and adding the prefix “poly” before the name of the monomer to form a Polyalkene.

During addition Polymerization

(i) The double bond in alkenes break.

(ii) Free radicals are formed.

(iii) The free radicals collide with each other and join to form a larger molecule.

The more the collisions the larger the molecule.

Condensation Polymerization is where two or more small monomers join together to form a larger molecule by elimination of a simple molecule (usually water OR  ammonia).

Condensation polymers acquire a different name from the monomers as the two monomers are two different compounds

Formation of Polyethene

Polyethene is an addition polymer formed when ethene molecule/monomer join together to form a large molecule/Polymer at high temperatures and pressure.

During Polymerization:

(i) Many molecules are brought nearer to each other by the high pressure(reduce distance between reacting paticles).

The commercial name of polyethene is polythene. It is an elastic, tough, transparent and durable plastic. Polythene is used:

• In making plastic bags.
• Bowls and plastic bags.
• Packaging materials.