Based On Molecular Force

Based on molecular forces

Elastomers: The rubber-like elastic polymer that is held together by the weakest intermolecular forces are called Elastomers. Elastomers are the polymer in which the intermolecular force of attraction between the polymer chains are the weakest. They are amorphous polymers that have high degree of elasticity that is they are able to stretch out even more than ten times of their normal length and return to original whenever force is deformed. Elasticity of polymer can be increased by vulcanization. Elastomers become soft on heating and can be moulded to any desired shape.

Examples: Buna-S, Buna-N, neoprene, etc.

Fibers: Fibres are the thread forming solid that has high tensile strength developed by the strong intermolecular forces are called fibers. The strongest intermolecular force in fibres are due to hydrogen bonding (nylon) or dipole-dipole interactions (terylene, orlon, etc.). Due to strong molecular force of attraction, fibres have high tensile strength, least elasticity, high modulus, crystalline nature and sharp melting point.

Example: nylon 6,6, polyesters, etc.

Thermoplastic polymers: The polymers that are capable of repeatedly softening on heating and hardening on cooling and have intermolecular forces less than fibers and more than elastomers are called thermoplastic polymers. These are the polymers with no cross-links. They are generally soluble in organic solvent. They softens on heating and hardens on cooling, it can be moulded in heating. To enhance the work ability of thermoplastics at relatively lower temperature, certain compound called plasticizers are added during processing.

Example: polythene, polystyrene, polyvinyl, Teflon, Perspex etc.

Thermosetting polymers: The cross-linked densely branched molecules that undergo cross-linking when heating and become infusible and cannot be reused are called thermosetting polymers. They are semi-fluid substance with lower molecular mass which on heating undergo permanent change in chemical composition to give a hard, infusible and insoluble mass. This hardening on heating is due to extensive cross linking between different polyer chains to give a three-dimensional network solids.

Example: Bakelite, Urea-formaldehyde, resins, etc.