Question

Write short notes on the following:
A. Co-polymers
B. Synthetic rubber
C. Thermoplastic
D. Thermosetting
E. Elastomers
F. Vulcanization of rubber

Answer 1

Hint: Polymers are high molecular mass substances and they always contain a large number of repeating structural units which is connected through a covalent bond. And the reactive molecules which derive repeating structural units are called monomers.

Complete step by step answer:
A. Co-polymer: They are defined as the polymers which are formed by the polymerization of two or more different monomers and the process of their formation is known as copolymerization. Examples of copolymers are nylon-6,6, Buna-s, polyester, and bakelite, etc. A copolymer can be formed not only by chain-growth polymerization but also by step-growth polymerization.
B. Synthetic rubber: They are defined as any vulcanized rubber-like polymer which is capable of getting stretched to twice its length. However, it returns to its original size and shape when the stretching force is withdrawn. Synthetic rubber is either homopolymer of 1,3-butadiene or its derivative or is the copolymer of 1,3-butadiene or its derivative with another unsaturated polymer. Examples of synthetic rubber are Neoprene, Buna-S, Buna-N, and Thiokol.
C. Thermoplastic: These are the polymers in which intermolecular force of attraction is in between those of elastomers and fibers are called thermoplastic. Thermoplastic polymers are linear or slightly branched chain polymers. They are hard at room temperature and on heating, they become soft and viscous and again rigid on cooling. Since in the case of thermoplastic polymers either there is little or no cross-links hence the individual polymer chains can slip past one another on heating. Some examples of thermoplastic polymers are polythene, polyvinyl chloride, and Teflon, etc.
D. Thermosetting: These are the semi-fluid substances with low molecular mass which when heated in a mould, undergo a permanent chain in chemical composition to give hard, infusible, and insoluble mass. This hardening on heating is due to extensive cross-linking between different polymer chains to give a three-dimensional network solid. Examples of thermoplastic polymers are Bakelite,melamine-formaldehyde, etc.
E. Elastomers: Polymers in which the intermolecular force of attraction between the polymer chains are the weakest are known as elastomers. They are amorphous polymers and can stretch out ten times their normal length and return to its original position when force is withdrawn. The weak Vander waal force of attraction between elastomers is responsible for stretching and the cross-linking present helps the polymers to come back. Examples of elastomers are natural rubber, buna-s ,buna-N.
F. Vulcanization of rubber: The process of heating raw rubber with sulphur at 373K-415K to improve their properties is known as vulcanization of rubber. During vulcanization sulphur bridges or cross-links between polymer chains are introduced either at their reactive allylic position or at the site of the double bond. As this process is slow and we add additives like zinc oxide to accelerate the rate of vulcanization. The vulcanized rubber has excellent elasticity, low water absorption tendency.

Note: In case of vulcanized rubber, the extent of hardness or toughness depends upon the amount of sulphur added. Thus, for making tyre rubber about 5% sulphur is used and for making ebonite 20-25% sulphur is used. 30% sulphur is used for making battery case rubber.