GCSE · Chemistry · Edexcel · Spec 1CH0

Condensation polymers: polyesters

Picture a chain where, each time two links click together, a tiny bit pops off and drops on the floor. Some polymers are made exactly like that.

Chemistry · Polymers

Addition, condensation, or both?

Six features, two types of polymerisation. For each feature, tick addition, condensation, or both. Then check and see what the overlap turns out to be.

A Addition polymerisation
B Condensation polymerisation

Monomers join into a long chain
Each monomer has a C=C double bond
The polymer is the only product
A small molecule such as water forms too
Each monomer has two functional groups
A polyester, with ester bonds

Polyester formation · block diagram

Tap each chip. The [ ] is a block standing in for the rest of each monomer, because only the ends matter here.

Tap a molecule to see what it does in the reaction.

Chemistry · Polymers

Which of these could build a chain?

Look at what each molecule has, then place it. Pick a molecule, then pick a box, and read why.

Still to sort

Can make an addition polymer (0)

Its molecules have a C=C double bond.

Where the line is: C=C is the clue here, not the number of functional groups.

Can be one of the two monomers of a polyester (0)

Two carboxylic acid groups, or two alcohol groups.

Where the line is: A polyester needs one monomer of each kind, so each of these is one half of a pair.

Cannot make a polymer chain on its own (0)

No C=C, and fewer than two functional groups.

Where the line is: With one functional group a molecule can join at only one end, so the chain stops there.

5 of 5 still to sort.

Chemistry · Polymers

Which one sounds right to you?

You've met addition polymerisation first, so some habits from it are sticking. Which of these ideas is closest to what you think right now?

Pick the idea you agree with most, say how sure you are, then check.

Every polymer is built from just one kind of monomer, repeated over and over.Polymerisation always gives you the polymer and nothing else.In condensation polymerisation you get the polymer, and a small molecule such as water as well.A monomer with just one functional group is enough to build a condensation polymer.

How sure are you?

I'm sureI think soI'm guessing

Every polymer is built from just one kind of monomer, repeated over and over.

This is a common misconception

It's an easy idea to pick up, because addition polymerisation can look that way. But condensation polymers can be made from two different monomers. A polyester uses one monomer with two carboxylic acid groups and one with two alcohol groups. So 'one kind of monomer' isn't a rule for every polymer.

Polymerisation always gives you the polymer and nothing else.

This is a common misconception

This is true of addition polymerisation: the polymer is the only product. It isn't true of condensation polymerisation, which forms a small molecule such as water as well. 'Always' is the trap word.

In condensation polymerisation you get the polymer, and a small molecule such as water as well.

This matches the evidence

Yes. The polymer is one product and the small molecule, usually water, is the other. That second product is exactly what addition polymerisation doesn't have.

A monomer with just one functional group is enough to build a condensation polymer.

This is a common misconception

One functional group means one end that can join, and then the chain stops. Condensation polymerisation requires monomers with two functional groups, so each one can join at both ends and the chain keeps growing.

Don't carry addition's habits into condensation. Two different monomers are allowed, each needs two functional groups, and the polymer isn't the only product.

Chemistry · Polymers

Write the comparison

Compare addition polymerisation and condensation polymerisation. Refer to the monomers needed and the products formed. [4 marks]

Your answer

0 words · your answer stays on this page and is not sent anywhere.

The mark scheme

Addition polymerisation uses monomers that have a C=C double bond. (1 mark)
Addition polymerisation forms only one product, the polymer. (1 mark)
Condensation polymerisation uses monomers that each have two functional groups. (1 mark)
Condensation polymerisation forms a small molecule such as water as well as the polymer. (1 mark)

Model answer

In addition polymerisation the monomers have a C=C double bond, and the polymer is the only product. In condensation polymerisation each monomer has two functional groups, and as well as the polymer a small molecule such as water is formed.

Cover both sides for each type: the monomers and the products. A comparison needs both halves.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

What you need to know

Polymerisation joins lots of small monomers together to make one long polymer.
In addition polymerisation, monomers with a C=C double bond join and the polymer is the only product.
Alongside the polymer, condensation polymerisation also forms a small molecule, usually water.
Have a goDetective time: the flask holds the polymer and absolutely nothing else. No water, no sneaky extras. Which type of polymerisation made it?
Addition polymerisation.
Condensation polymerisation also forms a small molecule, usually water, so a polymer-only flask points to addition.
Each monomer in condensation polymerisation needs two functional groups, so it can join at both ends.
Have a goA monomer has two functional groups, one at each end. Predict: how many other monomers can it join to at the same time?
Two, one at each end.
Each functional group is an end that can join, so two groups means two joins, and that is what lets the chain keep growing.
Condensation polymers can be made from two different monomers, so not every polymer comes from just one.
A polyester forms when a monomer with two carboxylic acid groups reacts with a monomer with two alcohol groups.
Polyesters contain ester bonds, the links that join the two kinds of monomer.
Have a goFinish the sentence: an ester bond is the link that forms where a ______ group on one monomer joins an ______ group on the other.
Carboxylic acid group; alcohol group.
The ester bond is not one of the starting groups. It is the new link made when an acid group and an alcohol group join.
To tell the types apart, check the monomers and the products: C=C and one product, or two functional groups and a small molecule.

The big picture

Condensation polymerisation joins monomers that each have two functional groups into a polymer, and a small molecule such as water forms as well. A polyester is made from a monomer with two carboxylic acid groups and a monomer with two alcohol groups, joined by ester bonds. Addition polymerisation is different: C=C monomers join and the polymer is the only product.

Key points

1Condensation polymerisation forms a polymer and a small molecule such as water; addition polymerisation forms only the polymer.

2Condensation polymerisation needs monomers with two functional groups, and it can use two different monomers.

3A polyester forms from a monomer with two carboxylic acid groups and a monomer with two alcohol groups, joined by ester bonds.

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Worked example

Problem

A chemist makes a polymer from a monomer with two carboxylic acid groups and a monomer with two alcohol groups. At the end, the flask holds the polymer and water. Say what type of polymerisation it is, what type of polymer, and what links the monomers.

⚠ Watch out

Treating all polymerisation like addition: one kind of monomer, and the polymer as the only product. Condensation polymers can be made from two different monomers, and a small molecule such as water forms as well.

🧠

Memory hook

Addition: one product, the polymer. Condensation: two-ended monomers, and the polymer comes with a drip of water.

✓

Check yourself

Close the page and answer in your own words: what two things must be true of the monomers for a polyester to form, and what is formed besides the polyester?

Flashcards

(10)

What is condensation polymerisation?

A type of polymerisation where monomers join to form a polymer and a small molecule such as water.

What must each monomer in addition polymerisation contain?

A C=C double bond.

How many products does addition polymerisation make?

Only one: the polymer.

What forms as well as the polymer in condensation polymerisation?

A small molecule, usually water.

What does each monomer need for condensation polymerisation?

Two functional groups.

Why do monomers need two functional groups?

So each monomer can join at both ends and the chain can keep growing.

Can a condensation polymer be made from two different monomers?

Yes. So not every polymer is made from only one kind of monomer.

Which two monomers react to form a polyester?

A monomer with two carboxylic acid groups and a monomer with two alcohol groups.

Which bond do polyesters contain?

Ester bonds.

What feature do addition and condensation polymerisation share?

In both, monomers join together into a long chain, a polymer.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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Addition, condensation, or both?

Which of these could build a chain?

Which one sounds right to you?

Write the comparison

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