Question

Explain the classification of polymers on the basis of structures.

How are polymers classified on the basis of structure? Mention the important characteristics of each type.

Answer 1

Depending upon how the monomers are linked together, that is, the chain configuration, polymers are classified into three types:

1. Linear or straight chain polymers: When the monomer molecules are joined together in a linear arrangement, the resulting polymer is a straight chain polymer. It is obtained from bifunctional monomers or alkenes.
   Example: PVC, high-density polythene.
2. Branched chain polymers: Monomers having 3 functional groups or already having side chains give rise to branched chain polymers.
   Example: Low-density polythene.
3. Three-dimensional cross-linked polymers: The third type of arrangement is said to be cross-linked or network polymers, where cross-links are produced between linear chains. Cross-linking results from polyfunctional monomers.
   Example: Bakelite, melamine.

Answer 2

1. Linear polymers: The polymers in which the constituent monomeric units are joined together to form long straight chains are called linear polymers or straight-chain polymers. The polymeric chains of a linear polymer typically stack on top of one another to create a densely packed structure. Linear polymers have high densities, high tensile strengths, and high melting temperatures because of the tight packing of polymeric chains. One significant illustration of a linear polymer is high-density polythene.
2. Branched chain polymers: The polymers that consist of side chains (made of monomer units) attached to the main chain (linear chain) are called branched chain polymers. Branching in polymer chains prevents them from packing compactly. They are typically irregularly packed. Branched-chain polymers have lower densities, melting temperatures, and tensile strength than linear polymers. Low-density polythene is a prime example of this class of polymers.
3. Cross-linked polymers: The polymers in which the adjacent polymeric chains link together through side chains to form a three-dimensional network structure are called cross-linked polymers. The additional term for these polymers is network polymers. Cross-linked polymers are stiff, rigid, and brittle because of the cross-links. Bakelite, urea-formaldehyde resins, and melamine formaldehyde resins are a few significant examples of cross-linked polymers.