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Define the following terms : (i) Elastomers (ii) Fibres (iii) Thermoplastics (iv) Thermosetting polymers |
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Answer» Solution :The CLASSIFICATION of polymers on the basis of inter-molecular forces of atraction such as van der Waal.s forces and hydrogen bonding etc. can be done in the following way : (i) ELASTOMERS . Such of polymers have weakest inter-molecular forces between the polymer chains. As a RESULT of this stretching of chains can take place . However , there are a few cross-links also between the chains due to which the chains regain their original position when the stretching force is withdrawn. (ii) Fibres . Such of polymers have the strongest inter-molecular forces such as hydrogen bonds and dipole-dipole interactions. As a result of this, fibres have high tensile strength and elasticity.  The molecules of fibres are long, thin and thread-like and can be woven into fabrics. Nylon-66 and terylene are examples the magnitude of inter-molecular forces is intermediate between those in elastomers and fibres. These are no cross links between the polymer chains. As a result , thermoplastics are not very rigit and can be moulded into different shapes. POLYTHENE , polypropylene and polystyrene are some examples of thermoplastics. (iv) Thermosetting polymers . Such polymers have RELATIVELY low molecular masses which get highly cross-linked on heating . This gives rise to a hard, infusible nad insoluble three dimensional network soild. Bakelite and melamine are examples of thermosetting polymers. |
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