Class 12 Chemistry Chapter 15 Polymers

Chapter 15 of Class 12 Chemistry, titled “Polymers,” introduces students to the fascinating world of macromolecules formed through polymerisation. This chapter explains how small molecules (monomers) link together to form long-chain molecules (polymers) that are widely used in our daily lives. From plastic containers to synthetic fibers and rubber, polymers form the backbone of many industrial and household products.

Understanding the types, classification, and mechanisms of polymerisation helps students gain clarity on both the theoretical and practical aspects of organic chemistry and industrial chemistry.

To Help You Excel: NCERT Solutions for Class 12 Chemistry Chapter 15 – Polymers

Our detailed and student-friendly NCERT Solutions for Chapter 15 – Polymers are tailored to the latest syllabus and exam patterns. These solutions help you understand polymer formation, types, and properties with simplified explanations and clear examples.

What You Will Learn in Chapter 15 – Polymers

This chapter provides an in-depth study of polymers — what they are, how they are formed, and their applications in daily life and industry.

Key Topics Covered:

Introduction to Polymers:

  • Definition of monomers and polymers

  • Types of polymerisation reactions

  • Importance of polymers in everyday materials

Classification of Polymers:

  • Based on source: Natural, Synthetic, and Semi-synthetic polymers

  • Based on structure: Linear, Branched, and Cross-linked polymers

  • Based on polymerisation mechanism: Addition and Condensation polymers

Types of Polymerisation:

  • Addition Polymerisation (Chain-Growth): e.g., formation of polyethene, polystyrene

  • Condensation Polymerisation (Step-Growth): e.g., nylon-6,6 and terylene

  • Copolymerisation: Formation of polymers from different monomers (e.g., Buna-S, Buna-N)

Important Commercial Polymers:

  • Synthetic fibers: Nylon-6, Nylon-6,6, Terylene

  • Rubbers: Natural rubber, Vulcanised rubber, Synthetic rubber (Buna-S, Neoprene)

  • Plastic materials: Polyethene, PVC, Bakelite, Melamine-formaldehyde resin

Biodegradable Polymers:

  • Introduction and need for environmentally friendly polymers

  • Examples: PHBV, Nylon-2-Nylon-6

Why Use Our NCERT Solutions for Chapter 15?

Our solutions are prepared with a focus on clarity and accuracy. All NCERT questions are explained in an easy-to-understand manner, helping students build a solid understanding of polymer chemistry and how it applies to both academics and industry.

Highlights of Our Solutions:

  • Step-by-step answers to all NCERT Intext and Exercise Questions

  • Covers mechanisms, structures, and uses of major polymers

  • Clearly labelled diagrams and structures for easy learning

  • Ideal for CBSE board preparation as well as competitive exams like JEE and NEET

  • Written in simple, concise, and student-friendly language

NCERT Solutions for Chapter 15 – Polymers (Intext + Exercise)

Intext Questions

  • Complete solutions to Intext Questions 15.1 to 15.5

  • Each question explained with the underlying concept and relevant examples

Exercise Questions

  • Fully solved Exercise Questions 15.1 to 15.14

  • Covers all aspects including naming polymers, types of polymerisation, synthetic rubbers, and biodegradable polymers

  • Easy-to-remember explanations for polymer names, monomers, and properties

Download Chapter 15 Solutions PDF – Polymers

For convenient access and offline study, download the free PDF of Class 12 Chemistry Chapter 15 – Polymers Solutions.

What’s Inside the PDF:

  • Clean and print-ready format

  • All NCERT questions with structured, easy explanations

  • Useful for quick revisions before exams

  • Perfect for CBSE and entrance exam preparation

Recommended Preparation Tips:

  • Revise definitions and types of polymerisation thoroughly

  • Memorize important monomers and polymers along with their structures

  • Focus on commercial and synthetic applications of polymers

  • Understand differences between addition and condensation polymerisation

  • Practice reaction mechanisms and naming of polymers

Additional Study Resources:

  • Class 12 Chemistry Notes – Chapter 15 Polymers

  • NCERT Exemplar Solutions for Chapter 15

  • Previous Year Questions from CBSE, NEET, and JEE based on Polymers

  • Polymerisation Mechanism Charts and Quick Revision Tables

By mastering the content in this chapter and using our guided solutions, you’ll gain a deeper understanding of how polymers are central to both modern materials and industrial chemistry, ensuring strong performance in your board exams and competitive entrance tests.

Section Name Topic Name
15
Polymers
15.1
Classification of Polymers
15.2
Types of Polymerisation Reactions
15.3
Molecular Mass of Polymers
15.4
Biodegradable Polymers
15.5
Polymers of Commercial Importance

NCERT Solutions for Chemistry Chapter 15 Polymers

 

NCERT Solutions for Class 12 Chemistry Chapter 15 – Polymers
Intext Questions (With Detailed Answers)

Question 15.1:
What are polymers?

Answer:
Polymers are large molecules composed of repeating structural units called monomers, connected by covalent bonds. These macromolecules generally possess high molecular masses ranging from 10³ to 10⁷ u. Common examples include polythene, nylon-6,6, bakelite, and natural rubber.

Question 15.2:
How are polymers classified on the basis of structure?

Answer:
On the basis of structure, polymers are classified into three types:

  1. Linear Polymers:
    These have monomer units joined in long, straight chains. The close packing leads to high density and tensile strength.
    Examples: High-density polythene (HDPE), PVC, nylon, and polyesters.

  2. Branched-Chain Polymers:
    These contain side chains of varying lengths attached to the main chain. They are loosely packed, resulting in lower density and melting points.
    Examples: Low-density polythene (LDPE), glycogen, and starch.

  3. Cross-Linked (Network) Polymers:
    These consist of monomers forming a three-dimensional network through strong covalent bonds. They are hard, rigid, and brittle.
    Examples: Bakelite, melamine-formaldehyde resin, glyptal.

Question 15.3:
Write the names of the monomers of the following polymers:
(i) Nylon-6,6
(ii) Nylon-6
(iii) Teflon

Answer:
(i) Nylon-6,6 → Hexamethylene diamine and adipic acid
(NH₂-(CH₂)₆-NH₂ and HOOC-(CH₂)₄-COOH)

(ii) Nylon-6 → Caprolactam

(iii) Teflon (PTFE) → Tetrafluoroethene (CF₂=CF₂)

Question 15.4:
Classify the following as addition or condensation polymers:
Terylene, Bakelite, Polyvinyl chloride (PVC), Polythene

Answer:

  • Addition Polymers: Polyvinyl chloride (PVC), Polythene

  • Condensation Polymers: Terylene, Bakelite

Question 15.5:
Explain the difference between Buna-N and Buna-S.

Answer:
Both Buna-N and Buna-S are synthetic rubber copolymers but differ in composition:

  • Buna-S (Styrene Butadiene Rubber):
    Formed by polymerizing buta-1,3-diene with styrene in the presence of sodium.
    Monomers: Buta-1,3-diene + Styrene
    Properties: Used in tyres, footwear, etc.

  • Buna-N (Nitrile Rubber):
    Formed by polymerizing buta-1,3-diene with acrylonitrile.
    Monomers: Buta-1,3-diene + Acrylonitrile
    Properties: Resistant to oil, used in fuel hoses, gaskets, etc.

Question 15.6:
Arrange the following polymers in increasing order of intermolecular forces:
(i) Nylon-6,6, Buna-S, Polythene
(ii) Nylon-6, Neoprene, Polyvinyl chloride

Answer:
The order of intermolecular forces is generally:
Elastomers < Plastics < Fibres

(i) Buna-S < Polythene < Nylon-6,6
(ii) Neoprene < Polyvinyl chloride < Nylon-6

NCERT Solutions for Class 12 Chemistry
Chapter 15 – Polymers
Exercise Questions

Question 15.1
Explain the terms polymer and monomer.

Answer:
A polymer is a large molecule with a high molecular mass formed by the chemical combination of a large number of repeating structural units (monomers).
A monomer is a simple molecule that can undergo polymerisation, joining with other similar or different molecules to form a polymer.
Example: In polythene, ethene (C₂H₄) is the monomer.

Question 15.2
What are natural and synthetic polymers? Give two examples of each type.

Answer:

  • Natural polymers: These occur naturally and are formed in plants or animals.
    Examples: Proteins, cellulose, natural rubber.

  • Synthetic polymers: These are man-made and are prepared in laboratories.
    Examples: Nylon-6,6, Bakelite.

Question 15.3
Distinguish between the terms homopolymer and copolymer. Give one example of each.

Answer:

  • Homopolymer: A polymer made from only one type of monomer unit.
    Example: Polyethene (from ethene).

  • Copolymer: A polymer made from two or more different types of monomers.
    Example: Buna-S (from butadiene and styrene).

Question 15.4
How do you explain the functionality of a monomer?

Answer:
Functionality refers to the number of bonding sites a monomer has for forming covalent bonds during polymerisation.

  • Monomers with two functional groups (like HO–CH₂–CH₂–OH) have functionality 2 and can form linear polymers.

  • Monomers with three or more functional groups can form cross-linked or network polymers.

Question 15.5
Define the term polymerisation.

Answer:
Polymerisation is the process of converting small molecules (monomers) into large chain-like molecules (polymers) through chemical reactions involving covalent bonding.

Question 15.6
Is (-CH₂-CH=CH₂-)n a homopolymer or copolymer?

Answer:
The given polymer is a homopolymer because it is formed from the repeated units of only one type of monomer—propylene (CH₂=CH–CH₃).

Question 15.7
In which classes, the polymers are classified on the basis of molecular forces?

Answer:
On the basis of molecular forces, polymers are classified into:

  1. Elastomers – weak intermolecular forces (e.g., rubber).

  2. Fibres – strong hydrogen bonding, high tensile strength (e.g., nylon).

  3. Thermoplastics – intermediate forces, soften on heating (e.g., polythene).

  4. Thermosetting polymers – hard, infusible, cross-linked (e.g., bakelite).

Question 15.8
How can you differentiate between addition and condensation polymerisation?

Answer:

  • Addition polymerisation: Involves joining of monomers without the elimination of any small molecules. Monomers usually have double or triple bonds.
    Example: Formation of polythene from ethene.

  • Condensation polymerisation: Involves joining of monomers with the elimination of small molecules like water or HCl.
    Example: Formation of nylon-6,6 from hexamethylene diamine and adipic acid.

Question 15.9
Explain the term copolymerisation and give two examples.

Answer:
Copolymerisation is a process in which two or more different types of monomers combine to form a polymer.
Examples:

  1. Buna-S (from buta-1,3-diene and styrene)

  2. Buna-N (from buta-1,3-diene and acrylonitrile)

Question 15.10
Write the free radical mechanism for the polymerisation of ethene.

Answer:
Step 1: Initiation
A free radical (R•) is formed by a peroxide initiator:
R–O–O–R → 2R• (free radicals)

Step 2: Chain Initiation
R• + CH₂=CH₂ → R–CH₂–CH₂•

Step 3: Chain Propagation
R–CH₂–CH₂• + CH₂=CH₂ → R–CH₂–CH₂–CH₂–CH₂•
…and so on.

Step 4: Chain Termination
R–(CH₂–CH₂)n• + •CH₂–CH₂–R → R–(CH₂–CH₂)n–CH₂–CH₂–R

Question 15.11
Define thermoplastics and thermosetting polymers with two examples of each.

Answer:

  • Thermoplastics: Soften on heating and can be reshaped.
    Examples: Polythene, PVC.

  • Thermosetting polymers: Harden permanently on heating; cannot be reshaped.
    Examples: Bakelite, melamine-formaldehyde resin.

Question 15.12
Write the monomers used for the preparation of Buna-S and Buna-N.

Answer:

  • Buna-S: Buta-1,3-diene and styrene.

  • Buna-N: Buta-1,3-diene and acrylonitrile.

Question 15.13
Write the name and structure of one of the common initiators used in free radical addition polymerisation.

Answer:
Benzoyl peroxide is a common initiator.
Structure:
(C₆H₅CO–O)₂
It decomposes to form phenyl radicals that initiate the polymerisation.

Question 15.14
How does the presence of double bonds in rubber molecules influence their structure and reactivity?

Answer:
The double bonds in rubber molecules:

  • Provide elasticity due to flexible coiled structure.

  • Allow chemical modifications like vulcanisation with sulfur.

  • Make the rubber reactive towards oxidising agents and ozone.

Question 15.15
Discuss the main purpose of vulcanisation of rubber.

Answer:
Vulcanisation involves heating raw rubber with sulfur to form cross-links.
It improves the elasticity, strength, and resistance to heat and oxidation, making rubber more durable and useful.

Question 15.16
What are the monomeric repeating units of Nylon-6 and Nylon-6,6?

Answer:

  • Nylon-6: Repeating unit from caprolactam (a single monomer).

  • Nylon-6,6: Repeating unit from hexamethylene diamine and adipic acid.

Question 15.17
Write the names and structures of monomers of the following polymers:
(i) Buna-N, (ii) Teflon, (iii) PVC, (iv) Bakelite.

Answer:
(i) Buna-N: Buta-1,3-diene and acrylonitrile
(ii) Teflon: Tetrafluoroethene (CF₂=CF₂)
(iii) PVC: Vinyl chloride (CH₂=CHCl)
(iv) Bakelite: Phenol and formaldehyde

Question 15.18
Identify the monomer in the following polymeric structures:

(i) –[–NH–(CH₂)₆–NH–CO–(CH₂)₄–CO–]n–
(ii) –[–CO–CH=CH–CO–O–CH₂–CH₂–O–]n–

Answer:
(i) Monomers: Hexamethylene diamine and adipic acid (Nylon-6,6)
(ii) Monomers: Maleic anhydride and ethylene glycol (Glyptal or a polyester)