What is Addition Polymerisation?

S7-SA5-0208

Grade Level:

Class 12

AI/ML, Physics, Biotechnology, FinTech, EVs, Space Technology, Climate Science, Blockchain, Medicine, Engineering, Law, Economics

Definition

What is it?

Addition polymerisation is a type of polymerisation where monomer units (small molecules) add to each other in a chain reaction without the loss of any atoms. This means the polymer formed has the exact same elemental composition as the sum of all the monomers that joined together. It's like joining many small building blocks to make a long wall, but without any part of the blocks breaking off.

Simple Example

Quick Example

Imagine you have many identical small 'Lego' bricks, each representing a monomer. When you snap these bricks together, one after another, to form a long chain, you are doing addition polymerisation. No part of any Lego brick is lost or removed during the joining process; all the material from the small bricks becomes part of the big chain.

Worked Example

Step-by-Step

Let's understand how Polyethene (polythene) is formed from Ethene monomers.

1. Start with many ethene molecules (CH2=CH2). Each ethene molecule is a monomer.
---2. Ethene has a double bond between the two carbon atoms. This double bond is crucial for the reaction.
---3. An initiator (like a free radical) breaks the double bond of one ethene molecule, making it very reactive.
---4. This reactive ethene molecule then attacks another ethene molecule, breaking its double bond and adding to it. This process forms a longer, reactive chain.
---5. This chain reaction continues, with new ethene monomers adding one by one to the growing polymer chain.
---6. Eventually, thousands of ethene units join together to form a long chain of polyethene (–CH2–CH2–)n. No small molecules like water or HCl are removed during this process.
---ANSWER: Polyethene is formed by the repeated addition of ethene monomers without any loss of atoms.

Why It Matters

Addition polymerisation is super important because it creates many plastics we use daily, from water bottles to car parts. Understanding this helps engineers design new materials for EVs and space technology, and even plays a role in making medical equipment. If you want to invent new materials or work in manufacturing, this concept is key!

Common Mistakes

MISTAKE: Thinking that small molecules like water are always removed during polymerisation. | CORRECTION: In addition polymerisation, NO small molecules are removed. All atoms from the monomers are incorporated into the polymer.

MISTAKE: Confusing addition polymerisation with condensation polymerisation. | CORRECTION: Addition polymerisation involves monomers adding directly to each other, often breaking double or triple bonds. Condensation polymerisation involves the joining of monomers with the removal of a small molecule like water.

MISTAKE: Believing that all monomers used in addition polymerisation must have a double bond. | CORRECTION: While many common addition monomers (like ethene) have double bonds, some can have triple bonds or cyclic structures that open up to polymerise. The key is the direct addition without loss of atoms.

Practice Questions

Try It Yourself

QUESTION: Which type of bond is typically broken in monomers during addition polymerisation? | ANSWER: Double bond (or triple bond, or a ring structure)

QUESTION: If 100 ethene (C2H4) molecules undergo addition polymerisation, what is the total number of carbon atoms in the resulting polymer chain? | ANSWER: 200 carbon atoms (100 molecules * 2 carbon atoms/molecule = 200 carbon atoms)

QUESTION: Polypropene is formed from propene (CH2=CH-CH3) monomers. Write the structure of the repeating unit in polypropene. | ANSWER: The repeating unit is (-CH2-CH(CH3)-)n

MCQ

Quick Quiz

Which of the following is a key characteristic of addition polymerisation?

Formation of a small molecule like water

Monomers add directly without losing any atoms

Requires two different types of monomers

Always forms biodegradable polymers

The Correct Answer Is:

Addition polymerisation is defined by monomers adding directly to form a polymer without the loss of any atoms. Options A and C describe condensation polymerisation, and option D is not universally true for addition polymers.

Real World Connection

In the Real World

Think about the plastic 'pani puri' plates or 'chai' cups you see at roadside stalls. These are often made from plastics like polyethylene or polypropylene, which are products of addition polymerisation. Even the PVC pipes used for plumbing in your home are made this way. Scientists and engineers in India, like those at DRDO or ISRO, use this knowledge to create advanced materials for rockets and defence equipment.

Key Vocabulary

Key Terms

MONOMER: A small molecule that can be linked to other identical molecules to form a polymer. | POLYMER: A large molecule made up of many repeating smaller units (monomers). | DOUBLE BOND: A chemical bond between two atoms involving four bonding electrons, often a site of reactivity in monomers. | INITIATOR: A substance that starts the polymerisation reaction, often by forming a free radical. | REPEATING UNIT: The smallest repeating part of a polymer chain.

What's Next

What to Learn Next

Great job understanding addition polymerisation! Next, you should explore 'Condensation Polymerisation'. It's another important way polymers are made, but with a key difference – the loss of small molecules. Comparing both will give you a complete picture of how plastics are formed!