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Addition Polymerisation

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Addition Polymerisation - Lesson Summary

The process of joining many small molecules or monomers together to form very large molecules (or) polymers is called polymerisation.

Polymers are formed in two ways depending upon on the type of polymerisation mechanism they undergo during formation. They are:

(i) Addition polymerisation (or) chain growth polymerisation

(ii) Condensation polymerisation (or) step growth polymerisation

In addition polymerisation the molecules of a monomer add together to form a polymer. The polymer so formed is called an addition polymer.

Addition polymerisation occurs most frequently by a free-radical mechanism.

Important addition polymers are low density polyethylene, high density polyethylene, Teflon and polyacrylonitrile.

Low density polyethylene (or polythene) is often given the acronym LDPE. It is formed by the polymerisation of ethene under high pressure in a temperature range of 350K - 570 K in the presence of a catalyst.

High density polythene or polyethylene also known as HDPE, is another polymer made from ethene monomers. It is formed by the polymerisation of ethene in the presence of a Ziegler-Natta catalyst at a low temperature of 333K- 343K and a high pressure of 6- 7 atm.

Ziegler-Natta catalyst is a combination of triethyl-aluminium and titanium tetrachloride.

HDPE is tough and hard. It is used to make buckets, dustbins, bottles and pipes...etc

Teflon is another example of an addition polymer. Teflon is the trade name for polytetrafluoroethene.

It is chemically inert and resistant to attack by corrosive substances.

Teflon is used to make oil seals and gaskets. It is extensively used to make non-stick cookware.

Polyacrylonitrile is formed by polymerising acrylonitrile in the presence of a peroxide catalyst.

Polyacrylonitrile produces the commercially important acrylic fibre. Acrylic fibres are soft and flexible and produce lofty yarns.

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