Question

Answer the following.

Write the names of classes of polymers formed according to intermolecular forces and describe briefly their structural characteristics.

Answer 1

1. Polymers are classified into various categories on the basis of intermolecular forces as follows:

• Elastomers
• Fibres
• Thermoplastic polymers
• Thermosetting polymers

2. Their structural characteristics are as follows:

i. Elastomers:

• Elastomers have the property of elasticity in which a substance gets stretched by external force and restores its original shape on the release of that force.
• Elastomers, the elastic polymers, have weak van der Waals type of intermolecular forces that permit the polymer to be stretched.
• A few crosslinks between the chains help the stretched polymer to retract to its original position on removal of applied force.
  e.g. Vulcanized rubber, Buna-S, Buna-N, neoprene, etc.

ii. Fibres:

• Polymeric solids which form threads are called fibres.
• The fibres possess high tensile strength which is a property to have resistance to breaking under tension.
• High tensile strength is due to the strong intermolecular forces like hydrogen bonding and strong dipole-dipole forces. Due to these strong intermolecular forces, the fibres are crystalline in nature.
  e.g. Polyamides (nylon 6,6), polyesters (terylene), etc.

iii. Thermoplastic polymers:

• Thermoplastic polymers have the property of plasticity, that is, these polymers can be easily shaped or moulded.
• They are capable of repeated softening on heating and hardening on cooling.
• These polymers possess moderately strong intermolecular forces that are intermediate between elastomers and fibres.
  e.g. Polythene, polystyrene, polyvinyls, etc.

iv. Thermosetting polymers:

• Thermosetting polymers are rigid polymers.
• During their formation, they have the property of being shaped on heating; but they get hardened while hot. Once hardened, they cannot be softened by heating and therefore cannot be remoulded.
• This characteristic is the result of extensive cross-linking by covalent bonds formed in the moulds during hardening/setting process while hot.
  e.g. Bakelite, urea-formaldehyde resin, etc.