Wednesday, January 23, 2008

Polymers and Polymerisation Process - Revision Points

A polymer is a large molecule built by repetitive binding together of many small units called monomers.

Homopolymer: A polymer derived from a single repeating monomer. Only one type of monomer will have repetitive binding and a large molecule appears.

Copolymer: When two or more different monomers bind together in a repetitive manner and give rise to a large polymer, it is called copolymer.

Classification of Polymers

Classification based on source:

Natural and synthetic

Classification based on structure:

1. Linear polymers
2. Branched chain polymers
3. Cross linked polymers

Classification based on molecular forces and physical properties

1. Elastomers
2. Fibres
3. Thermoplastics
4. Thermosetting polymers

Classification based on mode of synthesis:

1. Addition polymers
2. Condensation polymers

Methods of Polymerisation

Synthetic polymerisation processes are categorised as Chain growth and step growth polymerisation.

Chain growth polymerisation: Also called addition polymerisation.

In this process, the combination of monomers does not result in elimination of some by product molecules. The process is initiated by by a free radical, a cation or an anion and once initiated, the process gets repeated as a chain reaction as the process produces bigger and bigger active molecules.

Many vinyl polymers (Vinyl indicates compounds having double bonds) are formed by chain growth polymerisation (chain reaction polymerisation).

Step Growth polymerisation: Also called as condensation polymerisation

In condensation polymerisation, two or more different monomers combine together and in this process of combination elimination of simple molecules like water, ammonia, hydrogen chloride etc. takes place.

In this polymerisation generally the monomers contain two functional monomers (difunctional monomers).
Illustratitive model

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