Soap, Detergents and Polymers: Classification of Polymers: Addition Polymer (For CBSE, ICSE, IAS, NET, NRA 2022)

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Classification of Polymers

Classification of Polymers on the Basis of Method of Polymerization

Addition Polymer

A polymer formed by direct addition of repeated monomers without the elimination of any small molecule is called addition polymer. In this type, the monomers are unsaturated compounds and are generally derivatives of ethene. The addition polymers have the same empirical formula as their monomers. Examples are polyethene, polypropylene and polyvinyl chloride, etc.

Condensation Polymer

A polymer formed by the condensation of two or more than two monomers with the elimination of simple molecules like water, ammonia, hydrogen chloride, alcohol, etc. is called condensation polymer. In this type, each monomer generally contains two functional groups. For example, nylon – 66.

Classification of Polymers on the Basis of Molecular Forces

Elastomers

In case of elastomers the polymer chains are held together by weak van der Waals forces. Due to weak forces, the polymers can be easily stretched on applying small stress and they regain their original shape when the stress is removed. The most important example of elastomer is natural rubber.

Fibres

These are the polymers which have strong intermolecular forces between the chains. These forces are either hydrogen bonds or dipole-dipole interactions. Because of the strong forces, the chains are closely packed, giving them high tensile strength and less elasticity. The common examples are nylon-66, Dacron, silk, etc.

Thermoplastics

These are linear polymers with very few cross linkages or no cross linkages at all. The polymeric chains are held by weak Vander Waal forces and slide over one another. Due to lack of cross linkages these polymers soften on heating and harden or become rigid on cooling. Polythene, PVC, polystyrene are addition type thermoplastics and Perylene, nylon are condensation type thermoplastics.

Plasticizers

Certain plastics do not soften much on heating. These can be easily softened by the addition of some organic compounds which are called plasticizers. For example, polyvinyl chloride (PVC) is very stiff and hard but is made soft by adding di-n-butyl phthalate (a plasticizer) .

Thermosetting Polymers

Thermosetting polymers are produced from relatively low molecular mass semi fluid polymers (called polymers) which on heating develop extensive cross-linkage by themselves or by adding some cross-linking agents and become infusible and insoluble hard mass. Therefore, a thermosetting plastic is cross linked and is permanently rigid. The common example are Bakelite, melamine, formaldehyde resin, etc.

Distinction between Thermoplastic and Thermosetting Polymers

Thermoplastic and Thermosetting Polymers

Poldines

  • These polymers are obtained when an unsaturated hydrocarbon with two double bonds or when a diene (2 double bond compound) is polymerized with a substituted alkene.
  • Consequently, we have natural rubber and synthetic rubber.

Natural Rubber

It is a polymer of unsaturated hydrocarbon, 2-methyl-1,3- butadiene also called isoprene. It is obtained from the latex of rubber trees found in tropical and semi-tropical countries such as India (southern part) , Indonesia, Malaysia, Ceylon, South America, etc. It is a natural polymer and possess remarkable elasticity.

Natural Rubber

Drawbacks of Raw Rubber

  • Rubber is brittle at low temperature and becomes very soft at high temperatures.
  • It is too soft to be used for heavy duty operation.
  • On stretching, it undergoes permanent deformation.
  • Not resistant to mineral oils, organic solvents and even action of water. It has large water absorption capacity.

Vulcanization of Rubber

In 1893, Charles Goodyears discovered that addition of Sulphur to hot rubber cause changes that improve its physical properties in a spectacular manner. This process is called vulcanization.

Vulcanization Depends Upon

  • The amount of Sulphur used: by increasing the amount of Sulphur rubber can be hardened
  • Temperature
  • Duration of heating.

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