Case Study Questions for Class 12 Chemistry Chapter 15 Polymers
Case Study
Question 1:
There are two broad types of polymerization reactions, i.e., the addition or chain growth polymerization and condensation or step growth polymerization. In the addition polymerization, the molecules of the same monomer or different monomers add together on a large scale to form a polymer. The monomers used are unsaturated compounds, e.g., alkenes, alkadienes and their derivatives. This mode of polymerization leads to an increase in chain length and chain growth can take place through the formation of either free radicals or ionic species while condensation polymerization generally involves a repetitive condensation reaction between two bi-functional or trifunctional monomeric units. These polycondensation reactions may result in the loss of some simple molecules as water, alcohol, hydrogen chloride, etc. and lead to the formation of high molecular mass condensation polymers.
In these reactions, the product of each step is again a bi-functional species and the sequence of condensation goes on. Since, each step produces a distinct functionalized species and is independent of each other, this process is also called step growth polymerization.
(i) Give one example of chain growth polymer.
Answer
Answer: PVC (Poly vinyl chloride).(ii) Write the monomer units of bakelite.
Answer
Answer: Phenol and formaldehyde(iii) Why are rubbers called elastomers?
Answer
Answer: Rubbers are stretched on application of force and regain original state after the force is removed. Therefore, these are called elastomers.(iv) What do you understand by addition polymers?
Answer
Answer: Polymers which are formed by repeated addition of monomer molecules containing double and triple bonds are called addition polymers. Examples are polythene, PVC, PAN, PMMA, etc.(v) Mention which of the following are addition polymers:
(a) Terylene (b) Nylon-6, 6 (c) Neoprene (d) Teflon.
