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NCERT Class 12 Chemistry Textbook Chapter 15 With Answer PDF Free Download
Chapter 15: Polymers
Do you think that daily life would have been easier and more colorful without the discovery and varied applications of polymers?
The use of polymers in the manufacture of plastic buckets, cups and saucers, children’s toys, packaging bags, synthetic clothing materials, automobile tires, gears and seals, electrical insulating materials, and machine parts has completely revolutionized the daily life as well as the industrial scenario.
Indeed, polymers are the backbone of four major industries viz. plastics, elastomers, fibers, and paints, and varnishes.
The word ‘polymer’ is coined from two Greek words: poly means many and means unit or part. The term polymer is defined as very large molecules having high molecular mass.
These are also referred to as macromolecules, which are formed by the joining repeating structural units on a large scale.
The repeating structural units are derived from some simple and reactive molecules known as monomers and are linked to each other by covalent bonds.
The process of formation of polymers from respective monomers is called polymerization.
There are several ways of classification polymers based on some special considerations.
One of the common classifications of polymers is based on the source from which the polymer is derived. Under this type of classification, there are three subcategories.
- Natural polymers These polymers are found in plants and animals. Examples are proteins, cellulose, starch, some resins and rubber.
What are polymers?
There are two broad types of polymerization reactions, i.e., the addition of chain-growth polymerization and condensation or step-growth polymerization.
In this type of 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.
However, the free radical governed addition or chain-growth polymerization is the most common mode.
(a) Polythene
Polythenes are linear or slightly branched long-chain molecules. These are capable of repeatedly softening on heating and hardening on cooling and are thus thermoplastic polymers. There are two types of polythene as given below:
(i) Low-density polythene: It is obtained by the polymerization of ethene under high pressure of 1000 to 2000 atmospheres at a temperature of 350 K to 570 K in the presence of traces of dioxygen or a peroxide initiator (catalyst).
The low-density polythene (LDP) is obtained through the free radical addition and H-atom obstruction.
It has a highly branched structure. These polymers have a straight-chain structure with some branches as shown below.
| Author | NCERT |
| Language | English |
| No. of Pages | 14 |
| PDF Size | 1483 KB |
| Category | Chemistry |
| Source/Credits | ncert.nic.in |
NCERT Solutions Class 12 Chemistry Chapter 15 Polymers
Q2: What are natural and synthetic polymers? Give two examples of each type.
Solution:
Polymers naturally found are known as Natural Polymers. Natural polymers are formed from animals and plants. Diverse natural polymer examples are protein, starch, cellulose, etc.
Polymers that are human-made are known as Synthetic Polymers. Various examples of synthetic polymer are synthetic rubbers (Buna-5), synthetic fibers (nylon 6, 6), and plastic (polythene).
Q3: Distinguish between the terms homopolymer and copolymer and give an example of each.
Solution:
| HOMO-POLYMER | CO-POLYMER |
| The polymerisation of a single monomer results in the creation of polymers called homo-polymers. Or put it another way, the repeating units of homo-polymers are formed from one monomer. For example, the homopolymer of ethane is polythene. | Co-polymers are polymers whose repeat units are obtained from two-type monomers. Examples: Co-polymer of styrene and 1, 3 – butadiene is Buna – S. |
Q4: How do you explain the functionality of a monomer?
Solution:
The function of a monomer may be defined as the total number of binding sites, which are in this particular monomer.
For example, adipic acid and 1, 3-butadiene is two and that of propene and ethene is one
Q7: Determine the groups where the polymers are graded according to molecular forces?
Solution:
Polymers are classified into groups given below based on the intermolecular magnitude of forces present in polymers:
(a) Fibres
(b) Elastomers
(c) Thermosetting polymers
(d) Thermoplastic polymers
Polymers NCERT Solutions PDF Free Download