What is Condensation Polymerisation?

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Grade Level:

Class 12

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Definition

What is it?

Condensation polymerisation is a type of polymerisation reaction where two or more different monomer molecules join together to form a larger polymer molecule, while simultaneously releasing a small molecule like water (H2O), ammonia (NH3), or hydrogen chloride (HCl). It's like building a big wall by joining bricks and letting out small bits of cement dust.

Simple Example

Quick Example

Imagine you are making a long garland of flowers. You take one marigold flower and one rose flower, tie them together, and a tiny bit of thread (representing a small molecule like water) is left over from tying. You keep adding more marigolds and roses, tying them, and each time a small bit of thread is 'lost' or released. This continuous process forms a long garland (polymer) from individual flowers (monomers) by releasing small 'thread' molecules.

Worked Example

Step-by-Step

Let's understand how a polyester like PET (used in water bottles) is formed from its monomers, ethylene glycol and terephthalic acid.

STEP 1: Identify the monomers: Ethylene glycol (HO-CH2-CH2-OH) and Terephthalic acid (HOOC-C6H4-COOH).
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STEP 2: Identify the functional groups involved: Ethylene glycol has two -OH (hydroxyl) groups. Terephthalic acid has two -COOH (carboxyl) groups.
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STEP 3: Understand the reaction: One -OH group from ethylene glycol reacts with one -COOH group from terephthalic acid. This reaction is called esterification.
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STEP 4: Formation of water: During esterification, one H atom from the -OH group and one OH group from the -COOH group combine to form a water molecule (H2O), which is released.
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STEP 5: Linkage formation: The remaining parts of the monomers link together to form an ester linkage (-COO-).
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STEP 6: Repetition: This process repeats at both ends of the growing chain, as each monomer has two reactive functional groups, leading to a long polymer chain. This continuous joining and water release forms PET.
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ANSWER: Condensation polymerisation of ethylene glycol and terephthalic acid produces PET polymer and releases water molecules.

Why It Matters

Understanding condensation polymerisation is key to making many useful materials around us, from the clothes we wear (like nylon and polyester) to the plastic bottles we drink from. This knowledge is crucial in fields like Engineering for creating new materials, and even in Medicine for developing biodegradable sutures or drug delivery systems. Imagine designing a new, super-strong plastic for EVs or a smart material for space technology!

Common Mistakes

MISTAKE: Thinking that condensation polymerisation only forms water as a byproduct. | CORRECTION: While water is very common, other small molecules like ammonia (NH3) or hydrogen chloride (HCl) can also be released.

MISTAKE: Confusing condensation polymerisation with addition polymerisation. | CORRECTION: In condensation polymerisation, a small molecule is always released. In addition polymerisation, monomers add to each other without losing any atoms.

MISTAKE: Assuming all monomers in condensation polymerisation must be identical. | CORRECTION: Condensation polymerisation often involves two or more DIFFERENT types of monomers, each with at least two functional groups, reacting alternately.

Practice Questions

Try It Yourself

QUESTION: What small molecule is typically released when a polyester is formed? | ANSWER: Water (H2O)

QUESTION: Name two types of functional groups that commonly react in condensation polymerisation to form a polymer and release water. | ANSWER: Carboxyl (-COOH) and Hydroxyl (-OH) groups, or Amine (-NH2) and Carboxyl (-COOH) groups.

QUESTION: If a polymer chain is formed by condensation polymerisation and releases 100 molecules of water, how many monomer units would have linked together in a linear chain (assuming two different monomers react alternately)? | ANSWER: 201 monomer units (100 water molecules mean 100 linkages, which requires 100 A-B pairs plus one extra monomer to start the chain, so 100 A and 101 B, or vice versa, totalling 201).

MCQ

Quick Quiz

Which of the following polymers is formed by condensation polymerisation?

Polyethylene

Polypropylene

Nylon 6,6

PVC

The Correct Answer Is:

Nylon 6,6 is formed from hexamethylenediamine and adipic acid, releasing water molecules. Polyethylene, polypropylene, and PVC are all formed by addition polymerisation, where no small molecules are released.

Real World Connection

In the Real World

Look at the 'polyester' tag on your school uniform or backpack! Polyester is a common example of a condensation polymer. Similarly, Nylon, another condensation polymer, is used to make ropes, fishing lines, and even some parts of car engines. These materials are crucial for industries ranging from textiles to advanced manufacturing in India, like creating components for ISRO satellites or durable parts for electric vehicles.

Key Vocabulary

Key Terms

POLYMER: A large molecule made of many repeating smaller units | MONOMER: The small, single repeating unit that makes up a polymer | FUNCTIONAL GROUP: A specific group of atoms within a molecule that is responsible for the characteristic chemical reactions of that molecule | BYPRODUCT: A secondary product made during the manufacture of a principal product | ESTER LINKAGE: The chemical bond (-COO-) formed between an alcohol and a carboxylic acid, often seen in polyesters.

What's Next

What to Learn Next

Now that you understand condensation polymerisation, explore 'Addition Polymerisation'. You'll see how it's different and learn about another important way polymers are made. Keep learning; these concepts are building blocks for understanding materials science!