36. 1 Definitions and Nomenclature
Polymer: Polymers are large chain molecules having a high molecular weight in the range of 103 to 107.These are made up of a single unit or a molecule, which is repeated several times within the chained structure.
Monomer : A monomer is the single unit or the molecule which is repeated in the polymer chain. It is the basic unit which makes up the polymer.
Thermosetting Polymer : There are some polymers which, when heated, decompose, and hence, cannot be reshaped. Such polymers have a complex 3-D network (cross-linked or branched) and are called Thermosetting Polymers. They are generally insoluble in solvents and have good heat resistance quality. Thermosetting polymers include phenol-formaldehyde, urea-aldehyde, silicones and allyls.
Thermoplastic Polymer : The polymers in this category are composed of monomers which are linear or have moderate branching. They can be melted repeatedly and casted into various shapes and structures. They are soluble in solvents, but do not have appreciable thermal resistance properties. Vinyls, cellulose derivatives, polythene and polypropylene fall into the category of thermoplastic polymers.
36.2 Polymer Classification
Polymers are generally classified on the basis of –
- i. Physical and chemical structures.
ii. Preparation methods.
iii. Physical properties.
iv. Applications.
36.3 Classification According To Physical And Chemical Structures :
1. On the basis of functionality or degree of polymerization :
The functionality of a monomer or its degree of polymerization determines the final polymer that will be formed due to the combination of the monomers. The number of reactive bonds or groups that are available for coupling will determine whether the monomer will be mono-, bi-, tri-, or polyfunctional.