CBSE Class 12 Polymers-Definition, Types, Structures, Examples Of Polymers

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What are Polymers?

Polymers are high molecular mass compounds whose structures are composed of a large number of simple repeating units. The simple repeating units are obtained from simple low molecular mass compounds which are called monomers. The process of joining together a large number of monomers to form a polymer is called Polymerization.

Depending upon the number of the repeating units, Polymers are of two types-

1. Homo-Polymers

2.Co-Polymers

HOMO-POLYMERS

These are the polymers which are derived from only one type of monomers. For Example- Polythene which is derived from Ethene.

CO-POLYMERS

Polymers are derived from more than one type of polymer. For Example- Bakelite is obtained from phenol and formaldehyde.

CLASSIFICATION OF POLYMERS ON THE BASIS OF SOURCE OF ORIGIN

1. Natural Polymers

2.Synthetic Polymers

3.Semi-Sythetic Polymers

1.Natural Polymers

They are of natural origin and found in nature in plants and animals. For Example- Proteins, Carbohydrates, Silk, Natural rubber, wool, starch, etc.

2.Synthetic Polymers

These are man-made polymers that are synthesized in labs or industries. For Example- Bakelite, PVC (Polyvinylchloride), Teflon, Nylon, Polythene.

3.Semi-Synthetic Polymers

These are derived from natural Polymers by artificial modification. For Example- nitrocellulose, Vulcanized rubber, cellulose acetate.

CLASSIFICATION OF POLYMERS BASED ON SYNTHESIS

1.Addition Polymers

2.Condensation Polymers

1.Addition Polymers

The monomers join together to form a polymer by simple addition without the loss of any small molecule. For Example- vinyl chloride combines to form Polyvinylchloride.

These polymers are formed by chain growth polymerization.

2.Condensation Polymers

They are obtained from combination of polymers by the loss of smaller molecules CO2, NH3, H2O etc. For Example- Tere-pthalic acid and ethylene glycol combines step-by-step and forms Terylene (Dacron).

These polymers are formed by step growth polymerization.

CLASSIFICATION OF POLYMERS BASED ON STRUCTURE

1.Linear Polymers

2.Branched Chain Polymers

3.Cross Linked 3-D Polymers

1.Linear Polymers

These are the polymers in which monomers are joined to form long straight chains and there are no side branches. They may be called one 1-D Polymers. The polymer chains are then packed parallel to each other and this results in a very close packing, therefore, they have high melting point, high density and high tensile strength. For Example- Nylon, PVC, Polythene.

2.Branched Chain Polymers

The monomers joined together to form long chains with side branches, i.e why they are called 2-Dimensional but because of side branching, the packing is not very close but it is irregular packing. Therefore, they have lower melting point, lower density and lower tensile strength. For Example- Glycogen, Amylopectin.

amylopectin

3.Cross Linked Polymers

Initially, linear polymer chains are formed then they develop number of cross links to form a crossed linked 3-D network structure due to which they become hard, rigid and brittle. For Example- Bakelite, Melamine, Formaldehyde Resin.

CLASSIFICATION OF POLYMERS BASED ON MOLECULAR FORCES

1.Elastomers

2.Fibres

3.Thermoplastics

4.Thermosetting Polymers

1.Elastomers

These are the polymers having very weak inter-molecular forces of attraction between the chain, i.e why they can be stretched upon ten times their original length. But there are a few cross links due to which the polymer comes to its original length after the force is released. Therefore, they posses high degree of elastic character.

For Example- natural rubber, vulcanized rubber.

2.Fibres

These are the polymers which have very strong intermolecular forces like Hydrogen Bonding or dipole-dipole interactions, therefore, they have less elasticity but high tensile strength with high melting point.

For Example- Nylon, Terylene, Orlon.

Orlon

3.Thermoplastics

These are the polymers in which intermolecular forces of attraction are less than Fibres but more than elastomers. There are no crosslinks. When they are heated, they become soft and liquify and when they are cool, they again become hard. Therefore, they can be easily moulded into desired shapes by heating.

For Example- Polythene, Polypropylene, PVC.

4.Thermosetting Polymers

These are the polymers which become hard in fusible and insoluble mass upon heating. In the first step long chains of polymers are torned. In the next step there’s an application of heat which results in the formation of a complex cross linked structure which is hard and infusible.

For Example- Bakelite

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