What is polymerisation? Write the example and uses of that reaction.

(N/A) Definition: Polymerisation is a process in which a large number of small monomer molecules combine together under high temperature,high pressure,and in the presence of a catalyst to form a large molecule called a polymer.
$(b)$ Examples:
$(i)$ Polymerisation of ethene $(nCH_2=CH_2)$ at $473-673 \ K$ under high pressure and catalyst forms polyethene $(-(CH_2-CH_2)-_n)$.
$(ii)$ Polymerisation of propene $(nCH_3-CH=CH_2)$ under high temperature and pressure yields polypropene $(-(CH(CH_3)-CH_2)-_n)$.
$(c)$ Uses: Polymers are used for the manufacture of plastic bags,squeeze bottles,refrigerator dishes,toys,pipes,radio and $T$.$V$. cabinets,etc. Polypropene is used for the manufacture of milk crates,plastic buckets,and other moulded articles.
Limitations: Though these materials have now become common,excessive use of polythene and polypropylene is a matter of great environmental concern.