Guided lesson

Condensation Polymers

4CH1-4.48C4CH1-4.49C4CH1-4.50C

3 guided lessons · 27 checks · 4. Organic Chemistry → Synthetic polymers

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Lesson 1 of 3

Condensation versus addition

Addition polymers form from one monomer alone; condensation polymers are built by two different monomers that release a small molecule, usually water, every time they link. This lesson sets the two mechanisms side by side and shows where the water comes from.

What you know already

From Esters you already know the -COO- link that forms when an acid meets an alcohol. This note scales that single link up to industrial size: two-ended monomers joining into polyesters, water leaving at every bond, and a green branch of the family that the soil can reclaim.

Key points of understanding

Condensation polymers form when two different monomers link with the removal of a small molecule.
The small molecule released is usually water.
Each monomer carries two functional groups, one at each end.
One water molecule forms for every ester linkage made.
Addition polymerisation forms the polymer molecule only, with no other product.

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1.Condensation versus addition

4CH1-4.48C

Key points

Condensation polymers form when two different monomers link with the removal of a small molecule.
The small molecule released is usually water.
Each monomer carries two functional groups, one at each end.
One water molecule forms for every ester linkage made.
Addition polymerisation forms the polymer molecule only, with no other product.

First pass

Two different monomers join to build a condensation polymer, releasing a small molecule, usually water, at every link. Addition polymers make the chain alone, with no second product.

Analogy — Addition polymer formation is a solo handshake; the condensation kind is two people shaking hands while dropping a water bottle each time their hands meet.

Exam pointer — State the difference as products: polymer only versus polymer plus water.

Going deeper

Condensation polymers arise when two different monomers, each carrying functional groups at both ends, link in long alternating chains and release one small molecule per bond, usually water. Addition polymers instead consume one monomer type and leave no second product.

Analogy — Watch a zip closing: addition is one tape zipping onto itself, while condensation is two different tapes zipping together and shedding a droplet at every tooth.

Exam pointer — Quote the per-linkage water count: one molecule of water for every ester linkage formed.

Checks

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1.How many different monomers build a condensation polymer?
2.Which small molecule is released as the monomers link?
3.How many functional groups does each monomer carry?
4.Which extra product distinguishes condensation from addition polymer formation?
5.What joins the monomers in a polyester chain?
6.In most condensation polymerisations, what is the formula of the small molecule that is released?
Written response · recall
Your answer
7.State the difference between the product lists of addition and condensation polymerisation.
Written response · recall
Your answer
8.Explain why each condensation monomer must carry a functional group at both ends of its molecule.
Written response · explain why
Your answer
9.State how many water molecules form for each ester linkage made, and hence how many were released for a chain with 150 ester linkages.
Written response · application
Your answer

2.Polyesters: terylene and deducing the monomers

4CH1-4.48C4CH1-4.49C

A dicarboxylic acid with -COOH at both ends meets a diol with -OH at both ends, and the chain that results is a polyester such as terylene. This lesson also runs the film backwards: adding water across the ester links, known as hydrolysis, recovers the monomers.

Condensation polymerisation — The condensation reaction in which the polyester terylene is produced

The repeat unit terylene — Diagram showing a section of the polyester terylene

deducing-monomers-from-a-polyester-image-1-2 — Diagram showing a section of the polyester polybutylene terephthalate, PBT

deducing-monomers-from-a-polyester-image-3-2

deducing-monomers-from-a-polyester-image-4-2 — A diagram to show the two monomers used to form the polyester*** ***polybutylene terephthalate, PBT

Key points

A dicarboxylic acid carries a -COOH group at either end.
A diol carries an -OH group at either end.
Terylene is a polyester made from a dicarboxylic acid and a diol.
Each -COOH group reacts with an -OH group, forming an ester link and losing one water molecule.
Hydrolysis adds water back to break the polyester into its monomers.

First pass

A dicarboxylic acid has -COOH at both ends and a diol has -OH at both ends; joined together they make a polyester such as terylene. Adding water back across the ester links, called hydrolysis, recovers the monomers.

Analogy — The ester link is a staple joining two sheets; hydrolysis is a staple remover that returns each sheet to its original desk.

Exam pointer — Remember which monomer loses what: the acid loses OH, the diol loses H, and reversing that rebuilds them.

Going deeper

Terylene forms as each -COOH of the dicarboxylic acid meets an -OH of the diol, creating an ester link with one water lost per link, its chain drawn with boxes for the carbon sections. Hydrolysis reverses the process: water is added, the C-O single bond of each ester link breaks, OH returns to the acid end and H returns to the alcohol end.

Analogy — Deducing monomers is unwrapping a parcel you once taped shut: cut the tape, the C-O bond, and the two original sheets fall apart, ready to be re-wetted into their old shapes.

Exam pointer — Break the C-O single bond only, never the C=O; the added water then completes both halves.

Checks

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1.What is terylene?
2.When an ester link forms, from where does the -OH of the released water come?
3.And from where does the -H of the released water come?
4.What is hydrolysis?
5.Which bond is broken first when deducing the monomers from a polyester?
6.State the functional group carried at both ends of a dicarboxylic acid monomer.
Written response · recall
Your answer
7.What name is given to a monomer that carries an OH group at both of its ends?
Written response · recall
Your answer
8.Explain why making a polyester from a dicarboxylic acid and a diol releases exactly one water molecule per ester link formed.
Written response · explain why
Your answer
9.A polyester is boiled with water and breaks back into its two monomers. State the name of this reverse process and the small molecule it consumes.
Written response · application
Your answer

3.Biopolyesters

4CH1-4.50C

Not every polyester outlives the planet that made it. Biopolyesters are synthesised from sugars and plant oils with the help of micro-organisms, and their ester, amide and ether groups let them biodegrade once their job is done. This lesson closes the corpus with the greenest member of the family.

Diagram of biopolysters — The biodegradation of a bottle made of biopolyesters

Key points

Biopolyesters are synthesised from sugars and plant oils using micro-organisms.
They biodegrade naturally in the environment once their job is done.
Their chains contain ester, amide and ether functional groups.
Those groups give the polymers their biodegradable character.
Biopolyesters are still synthetically made, not harvested directly from nature.

First pass

Biopolyesters are made from sugars and plant oils with the help of micro-organisms. Their ester, amide and ether groups let them biodegrade naturally once their purpose is served.

Analogy — Where ordinary plastic is a stone, a biopolyester is a leaf: engineered by people, yet built to be reclaimed by the soil.

Exam pointer — Name the green closing point of the topic: some polyesters, the biopolyesters, are biodegradable.

Going deeper

These polymers are synthesised industrially from sugars and plant oils using micro-organisms, and their chains mix ester, amide and ether functional groups. That mix of groups is what grants their biodegradable character, letting them break down naturally after their intended purpose ends.

Analogy — A biopolyester bottle is written in two languages at once: synthetic enough to be manufactured, natural enough for microbes to read and dismantle it.

Exam pointer — Contrast with the previous note: addition polymers resist biodegrading, while biopolyesters are the designed exception.

Checks

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1.Which raw materials are biopolyesters synthesised from?
2.Which agents assemble biopolyesters from their feedstocks?
3.Which functional groups do biopolyester chains contain?
4.Which property separates biopolyesters from ordinary polyesters?
5.Which statement matches the specification exactly?
6.Name the two feedstocks from which micro-organisms build biopolyesters.
Written response · recall
Your answer
7.List the three functional group types found along a biopolyester chain.
Written response · recall
Your answer
8.Explain why a biopolyester breaks down in the environment while an ordinary addition polymer does not.
Written response · explain why
Your answer
9.A supermarket wants packaging that composts after use. State which family of polymers meets this requirement and what happens to it in the ground.
Written response · application
Your answer

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2.Polyesters: terylene and deducing the monomers

4CH1-4.48C4CH1-4.49C

3.Biopolyesters

4CH1-4.50C