Polymer & Polymerization

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Monomer:

A monomer is a molecule that forms the basic unit for a polymer.

Polymer:

A polymer is defined as the repeating unit of a chemical. (or) It is a substance or material consisting of very large molecules, composed of many repeating subunits (or) Polymers are high molecular weight compounds, fashioned by the aggregation of many smaller molecules called monomers. The term Polymer is a Greek word Poly means many and Mer means part.

The performance properties of a textile fiber are determined by the structure of the fibers, which ultimately depends upon the processing technique, physical properties, and chemical structure of a polymer (ex. Molecular weight/ molecular weight distribution, side reactions, thermal stability, chemical nature etc.,)



The properties of polymers which influence fiber formation and fiber properties are:

  1. Thermal stability.

  2. Defects in linear chain structure.

  3. Impurities or side reaction products.

  4. Chemical structure and properties.

  5. Molecular weight and Distribution.

Polymerization:

It is the process through which large number of monomers react together to form a polymer.

Types of Polymerizations:

  1. Step growth polymerization / condensation polymerization.

  2. Chain growth polymerization / addition polymerization.



Step growth polymerization:

Step growth polymerizations is proceeded by condensation reaction between the functional groups of reactant molecules and elimination of small molecular weight molecules like water. In condensation reactions each of the two reactants can react at one point. Therefore, in monofunctional reactants, once this reaction has taken place the product is incapable of taking part in any further reactions as shown in equation [1-3]. Now, if the reactants capable of reacting at two sites are used the linear polymers suitable for fiber forming can form. In synthesis of polymers a minimum functionality of two is essential.





Chain growth polymerization:

In chain growth polymerization the situation is quite different; the reactive double bond of the monomer is activated and opened up to form new bonds as shown below. The chain polymerization is characterized by three steps: the initiation, the growth reaction and the termination reaction.









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