Polymers - Chapter 15 - chemistry notes for class 12

Polymers - Chapter 15 - chemistry notes for class 12

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Polymers are created via polymerization of many small molecules, known as monomers.

Polymers can be classified in number of ways

• Classification based upon source

1. Natural polymers:– These polymers are the naturally occurring polymers such as starch, cellulose, nucleic acids and natural rubber.
2. Synthetic polymers:- These polymers are man-made polymers, such as polyvinyl chloride (PVC), Bakelite, nylon, polystyrene, etc

• Classification based on synthesis

1. Addition polymers: These types of polymers are formed by the repeated additions of monomeric unit; the monomers involved are unsaturated compounds and are usually the derivatives of ethane.e.g.:-polypropylene, PVC,polythene,etc.
2. Condensation polymers:-These types of polymers are formed by a series of a condensation reaction between two monomers, each monomer having two functional groups. During condensation simple molecule like H2O, HCl, NH3 are eliminated.The reaction is called condensation polymerization reaction. e.g. nylone66.

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• Classification based on inter molecular forces

1. Elastomers:-These polymers have elasticity like rubber is an elastomer. The polymer chain in elastomers is held together by the weakest intermolecular forces. They have the ability to be elongated under stress and regain their former shapes when the stress is removed.
2. Fibbers: These are thread-like polymers which can be woven into the fabric. They have the high tensile strength and high modulus. This is due to strong intermolecular forces like hydrogen bonding.e.g.:- cotton, wool, silk, nylon, and Dacron etc.
3. Thermoplastic: The molecular forces of attraction in the thermoplastics polymers are intermediate between those of elastomers and fibers. As a result, thermoplastic polymers, when heated melt and can be moulded again in different forms. Example:- polyethylene, polypropylene, and polystyrene.
4. Thermosetting plastic:- These polymers are prepared from low molecular mass semifluid They cannot be reshaped on heating because the polymer chain undergoes extensive cross-linking resulting in the formation of a three-dimensional network of the interconnected polymer chain. e.g.:- Bakelite, melamine etc.

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