Question

How do the thermoplastic polymers differ from the thermosetting polymers in their mode of formation? Give an example of each.

Answer 1

Thermoplastic polymers: The polymers in which the intermolecular forces of attraction are intermediate to those of elastomers and fibres are called thermoplastics.

There is no cross-linking between polymeric chains in thermoplastics, which are linear polymers. Thermoplastics soften when heated because of the presence of moderate (not very strong) intermolecular forces of attraction. They are rather firm at ambient temperature but mushy and gooey when heated. But when they cool, they solidify once more. They are easily molded by heating since heating does not result in cross-linking. Heat softening, molding, and cooling can be repeated as many times as needed without changing the polymer’s mechanical characteristics. Polythene, polypropylene, polyvinyl chloride (PVC), polystyrene, Teflon, and other common materials are examples of thermoplastics.

Thermosetting polymers: The polymers that, on heating, change irreversibly into hard, rigid, and infusible materials are called thermosetting polymers.

Semi-fluid polymers with a relatively low molecular mass are typically heated in a mold to create thermosetting polymers. They become infusible and solidify into an intractable substance when heated. When heated, the hardening results in the creation of substantial cross-linking between different polymeric chains. As a result, a three-dimensional network of linkages joining the polymer chains is created. The thermosetting polymers cannot be reprocessed because the three-dimensional network structure is inflexible and does not soften when heated. Melamine-formaldehyde resins, urea-formaldehyde resins, phenol-formaldehyde (bakelite) resins, and others are significant instances of thermosetting polymers.