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Classification

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Classification - Lesson Summary

Origin of the term "polymer":

"Mer" is derived from the Greek word for 'unit (or) part' and "Poly" comes from the Greek word 'many'.

A polymer is formed when many monomers are linked together in a chain. Thus, a monomer is the building block or repeating structural unit of a polymer.

Monomers are simple, reactive molecules. They join by covalent bonds to form polymers in a process called polymerisation.

Polymers are extremely large molecules, with high molecular masses. For this reason, they are also called "macromolecules".

Applications of Polymers:

Polymers are used in the manufacture of

(a) plastic buckets, plastic cups and saucers, children's toys, and synthetic clothing material.

(b) Automobile tyres, packaging bags, gears, seals and electrical insulation.

Polymers are the basis for four major industries: plastics, elastomers, fibres, and paints and varnishes.

Classification of Polymers:

Polymers can be classified in a variety of ways.

Depending upon the source, polymers are categorised into three types - natural polymers, semi-synthetic polymers and synthetic polymers.

Natural polymers are found in plants and animals. They provide much of our food, clothing and shelter.

Semi-synthetic polymers are derivatives of natural polymers. These are obtained from the chemical treatment of natural polymers.

Synthetic polymers are prepared in the laboratory.

Ex: polythene,

On the basis of their structure, polymers are classified into three types - linear, branched chain and cross-linked polymers.

Linear polymers are made from long, straight chains. Branched chain polymers contain linear chains that have some branches.

Cross-linked or network polymers have connections between chains. These connections are strong covalent bonds that link various linear polymer chains.

Polymers are classified into two categories based on type of addition. They are addition polymers and condensation polymers.

Addition polymers form by the repeated addition of monomers containing double or triple bonds. The reaction involves breaking of pi bonds.

Ex:

Condensation polymers (or) step-growth polymers are the result of repeated condensation reactions between two different bi-functional monomers.

Ex: PET (or) Dacron, nylon 6, 6, and nylon 6

The condensation reactions involve the elimination of small molecules such as water, alcohol and hydrogen chloride.

Based on the molecular forces present in them, polymers are classified into four types. They are elastomers, fibres, thermoplastic polymers and thermosetting polymers.

The polymer chains in elastomers are held together by very weak intermolecular forces. There may be a few cross-links between chains.

Fibres are thread-forming solids as; these polymers can be elongated into long, thin threads.

Plastics that soften on heating and regain their original properties on cooling are called thermoplastic polymers.

Plastics that change into hard and rigid materials upon heating are called thermosetting polymers.

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