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Science Class 12 - Polymers Notes

Comprehensive study notes for Class 12 - Polymers olympiad preparation

Polymers

Welcome to the chapter on Polymers for Class 12. In this chapter, you will learn what polymers are, how they are made, their types, properties, and uses. By the end of this chapter, you will understand the importance of polymers in daily life and industry.

Introduction

Polymers are large molecules made by joining many small repeating units called monomers. The process of making polymers is called polymerization. Polymers are found everywhere around us, from plastics and rubbers to proteins and DNA.

Key Concepts

  • Monomer: A small molecule that joins with others to form a polymer.
  • Polymer: A large molecule made up of repeating monomer units.
  • Polymerization: The process of joining monomers to form a polymer.

Types of Polymers

  • Natural Polymers: Found in nature. Examples: cellulose, proteins, rubber, starch.
  • Synthetic Polymers: Made by humans. Examples: polythene, nylon, PVC, bakelite.

Classification Based on Structure

  • Linear Polymers: Long, straight chains (e.g., high-density polythene).
  • Branched Polymers: Chains with side branches (e.g., low-density polythene).
  • Cross-linked Polymers: Chains linked together (e.g., bakelite, vulcanized rubber).

Types of Polymerization

  • Addition Polymerization: Monomers add together without loss of any molecule. Example: polythene from ethene.
  • Condensation Polymerization: Monomers join with the elimination of small molecules like water or HCl. Example: nylon-6,6 from hexamethylenediamine and adipic acid.

Common Polymers and Their Uses

  • Polythene: Used in bags, bottles, and containers.
  • Polyvinyl Chloride (PVC): Used in pipes, cables, and flooring.
  • Nylon: Used in fabrics, ropes, and fishing nets.
  • Bakelite: Used in electrical switches and handles.
  • Rubber: Used in tyres, footwear, and erasers.

Properties of Polymers

  • Lightweight and strong
  • Resistant to chemicals
  • Can be molded into different shapes
  • Some are flexible, some are hard

Environmental Impact

  • Many synthetic polymers are non-biodegradable and cause pollution.
  • Biodegradable polymers are being developed to reduce environmental harm.

Practice Questions

  1. What is a polymer? Give two examples.
  2. Differentiate between addition and condensation polymerization.
  3. Name two natural and two synthetic polymers.
  4. Why are biodegradable polymers important?
  5. What is the monomer of polythene?

Challenge Yourself

  • Draw the structure of polythene and PVC.
  • List three uses of nylon in daily life.

Did You Know?

  • DNA, the genetic material in our cells, is a natural polymer!
  • The word "polymer" comes from Greek, meaning "many parts".

Glossary

  • Monomer: Small molecule that joins to form a polymer.
  • Polymerization: Process of making polymers from monomers.
  • Biodegradable: Can be broken down by natural processes.

Answers to Practice Questions

  1. A polymer is a large molecule made of repeating units called monomers. Examples: polythene, nylon.
  2. Addition polymerization: monomers add without loss of molecules; condensation polymerization: monomers join with elimination of small molecules.
  3. Natural: cellulose, rubber. Synthetic: polythene, PVC.
  4. They help reduce pollution as they can be broken down naturally.
  5. Ethene (ethylene).

Polymers are everywhere! Learn about them to understand the materials you use every day.

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