Condensation Polymers and Rubber: Class 12 Chemistry Notes
Updated 18 October 2026 · Fact-checked
Condensation (step growth) polymers form when bi- or tri-functional monomers react repeatedly, losing small molecules like water. Examples: nylon 6,6, nylon 6, terylene, bakelite and melamine-formaldehyde polymer. Natural rubber is cis-1,4-polyisoprene, an elastomer whose cross-links restore shape; Buna-S is a synthetic copolymer substitute.
Understand Condensation Polymers and Rubber
Condensation polymerisation. Bi-functional or tri-functional monomers react repeatedly, often losing small molecules such as water, alcohol or HCl. Each step gives a new bi-functional product and each step is independent, hence step growth.
Polyamides (nylons). Contain amide links; made from diamines and dicarboxylic acids, or from amino acids or lactams.
- Nylon 6,6: hexamethylenediamine and adipic acid at high pressure and temperature. A fibre-forming solid with high tensile strength because hydrogen bonding between chains packs them closely. Used for sheets, brush bristles and textiles.
- Nylon 6: caprolactam heated with water at a high temperature. Used for tyre cords, fabrics and ropes.
Polyesters. From dicarboxylic acids and diols. Terylene (dacron): ethylene glycol and terephthalic acid heated at 420 to 460 K with a zinc acetate-antimony trioxide catalyst. Crease-resistant; used in blends with cotton and wool and as glass reinforcing material in safety helmets.
Phenol-formaldehyde polymers. The oldest synthetic polymers. Phenol and formaldehyde with an acid or base catalyst give o- and/or p-hydroxymethylphenols, which join through -CH2- groups. The linear product novolac is used in paints. Heating novolac with more formaldehyde cross-links the chains into bakelite, a thermosetting polymer that cannot be remoulded. Uses: combs, phonograph records, electrical switches, handles of utensils.
Melamine-formaldehyde polymer. From melamine and formaldehyde; used for unbreakable crockery.
Rubber. Natural rubber is a natural polymer with elastic properties: an elastomer. Its chains are held by weak intermolecular forces, which let it stretch; a few cross-links pull it back to its shape when the force is removed. It is made from latex, a colloidal dispersion of rubber in water from the rubber tree (grown in India, Sri Lanka, Indonesia, Malaysia and South America). Natural rubber is a linear polymer of isoprene (2-methyl-1,3-butadiene), called cis-1,4-polyisoprene. Buna-S, a copolymer of buta-1,3-diene and styrene, is a tough synthetic substitute.
Condensation Polymers and Rubber: formulas and key facts
- Monomers of condensation polymers
Nylon 6,6 hexamethylenediamine + adipic acid Nylon 6 caprolactam Terylene ethylene glycol + terephthalic acid Bakelite phenol + formaldehyde Melamine polymer melamine + formaldehyde - Small molecules like water are lost.
- Thermoplastic versus thermosetting
- Thermoplastic: softens on heating, remouldable | Thermosetting: cross-linked, cannot be remoulded (bakelite)
- Novolac is linear; bakelite is cross-linked.
- Rubber
Natural cis-1,4-polyisoprene from isoprene Synthetic Buna-S from buta-1,3-diene + styrene Elastomer weak forces + few cross-links - Latex is a colloid.
How to solve Condensation Polymers and Rubber questions
Formative (school) assessment only in 2026-27. Questions ask for monomers, by-products, classification and a small mass balance.
- 1Identify the functional groups on the monomers and the small molecule lost.
- 2Count the small molecules lost for a given chain length: for n diamine and n diacid units, (2n - 1) molecules of water.
- 3Subtract the mass of water lost from the sum of monomer masses.
- 4For thermoplastic or thermosetting, check for cross-links.
- 5State the use after the structure.
Condensation Polymers and Rubber in real life
Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.
Why bakelite handles
Suppose a manufacturer makes pan handles that must not soften on a hot stove.
Why is a thermosetting polymer like bakelite suitable?
Try it first, then show the solutionSolution
- Bakelite is cross-linked.
- It cannot be remoulded on heating.
Answer: Bakelite is a cross-linked thermosetting polymer that does not soften or remould on heating, so it is suitable for handles of utensils.
Memory hook: Cross-linked, so it keeps its shape.
Rubber band returns
Suppose you stretch a rubber band and release it.
Explain why it returns to its shape.
Try it first, then show the solutionSolution
- Chains held by weak forces can stretch.
- A few cross-links pull the chains back.
Answer: Natural rubber chains are held by weak intermolecular forces, so they stretch. A few cross-links between the chains pull them back to the original shape when the force is removed.
Memory hook: Weak forces stretch; cross-links restore.
Tricks to remember Condensation Polymers and Rubber
Short memory aids. Say each one aloud once, then use it on a question the same day.
6,6 = six carbons each
Nylon 6,6 from a six-carbon diamine and a six-carbon diacid.
Use it when: Name origin.
Novolac linear, bakelite net
Add more formaldehyde to cross-link.
Use it when: Bakelite formation.
Natural rubber = cis
cis-1,4-polyisoprene.
Use it when: Structure.
Condensation Polymers and Rubber: solved examples
Ordered from board level to HOTS. Try each one before you open the solution.
Example 1: Monomers of nylon 6,6 · 1 mark · MCQBoard level
Nylon 6,6 is made from:
(a) caprolactam
(b) hexamethylenediamine and adipic acid
(c) ethylene glycol and terephthalic acid
(d) phenol and formaldehyde
Try it first, then show the solutionSolution
- Nylon 6,6 is a polyamide of a diamine and a dicarboxylic acid (1 mark).
Answer: (b) hexamethylenediamine and adipic acid
Example 2: Bakelite (2 marks) · 2 marks · Very short answerBoard level
How is bakelite formed from novolac, and why can it not be remoulded? (2 marks)
Try it first, then show the solutionSolution
- Novolac is heated with more formaldehyde to cross-link the chains (1 mark).
- The cross-linked thermosetting polymer cannot be remoulded (1 mark).
Answer: Heating novolac with more formaldehyde cross-links the chains to form bakelite, a thermosetting polymer, so it cannot be softened and remoulded.
Example 3: Mass balance in nylon 6,6 (4 marks) · 4 marks · Short answerHarder board level
1 mol of hexamethylenediamine (116 g/mol) reacts with 1 mol of adipic acid (146 g/mol) to form one amide link and one molecule of water (18 g/mol). Find the mass of the product, and the mass of water lost when 100 molecules of each monomer form one chain (end groups unchanged). (4 marks)
Try it first, then show the solutionSolution
- Product mass = 116 + 146 - 18 = 244 g/mol (1 mark).
- For n diamine and n diacid units, links = 2n - 1 (1 mark).
- n = 100 gives 199 links, 199 water molecules (1 mark).
- Water lost per mole of chain = 199 x 18 = 3582 g (1 mark).
Answer: The one-link product has mass 116 + 146 - 18 = 244 g/mol. For 100 units of each monomer there are 2 x 100 - 1 = 199 links, so 199 water molecules are lost, 199 x 18 = 3582 g per mole of chain.
Example 4: Thermoplastic vs thermosetting (5 marks) · 5 marks · Long answerHarder board level
Distinguish thermoplastic and thermosetting polymers with one example each from this chapter, and explain how cross-linking changes properties. (5 marks)
Try it first, then show the solutionSolution
- Thermoplastics soften on heating and harden on cooling repeatedly; example polythene (1 mark).
- Thermosetting polymers are cross-linked and cannot be remoulded; example bakelite (1 mark).
- Cross-links bind chains into a network (1 mark).
- Novolac is linear and used in paints; further formaldehyde cross-links it into bakelite (1 mark).
- Uses: bakelite for switches and handles; polythene for pipes (1 mark).
Answer: Thermoplastics such as polythene soften on heating and harden on cooling again and again. Thermosetting polymers such as bakelite are cross-linked into a network and cannot be remoulded. Linear novolac, used in paints, becomes bakelite when heated with more formaldehyde. Bakelite suits electrical switches and handles; polythene suits pipes and bottles.
Example 5: Rubber reasoning · 4 marks · Case-basedHOTS / competency
(i) Name the monomer of natural rubber and its structure type. (1) (ii) Explain why latex is called a colloid. (1) (iii) Why is Buna-S used in tyres? (2)
Try it first, then show the solutionSolution
- (i) Isoprene (2-methyl-1,3-butadiene); cis-1,4-polyisoprene (1 mark).
- (ii) Latex is a colloidal dispersion of rubber in water (1 mark).
- (iii) Buna-S is a tough copolymer and a good substitute for natural rubber (2 marks).
Answer: (i) Isoprene; the polymer is cis-1,4-polyisoprene. (ii) Latex is a colloidal dispersion of rubber in water. (iii) Buna-S, a copolymer of buta-1,3-diene and styrene, is tough and a good substitute for natural rubber, so it is used for auto tyres.
Where students lose marks in Condensation Polymers and Rubber
The slips examiners see most often, and what to write instead.
Mistake: Counting links incorrectly
Assuming each monomer loses one water.
Wrong working
100 monomers lose 100 water molecules.
Right working
n diamine plus n diacid: 2n - 1 links, so 199 water molecules for n = 100.
Do this: Links = monomer units - 1.
Usually costs: 2 marks.
Mistake: Naming wrong monomers for terylene
Confused with nylon.
Wrong working
Terylene is made from a diamine and adipic acid.
Right working
Terylene: ethylene glycol and terephthalic acid.
Do this: Polyester: diol plus diacid.
Usually costs: 1 mark.
Mistake: Calling bakelite thermoplastic
Heating polymers confuses the classes.
Wrong working
Bakelite softens on heating.
Right working
Bakelite is cross-linked thermosetting.
Do this: Cross-linked, so set.
Usually costs: 1 mark.
Exam tips
- Polymers is formative (school) assessment only in 2026-27.
- Write 'loss of water' for condensation polymers.
- Pair each polymer with its monomers and one use.
Practice questions on Condensation Polymers and Rubber
Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.
Q1 · 1 mark · MCQBoard level
Terylene is prepared from ethylene glycol and:
(a) adipic acid
(b) terephthalic acid
(c) caprolactam
(d) styreneHint
Polyester.
Answer
(b) terephthalic acid
Q2 · 2 marks · Very short answerBoard level
Name the monomer of nylon 6 and one use. (2 marks)
Hint
Lactam.
Answer
Caprolactam; used for tyre cords, fabrics and ropes.
Q3 · 3 marks · Short answerHarder board level
A chain forms from 50 molecules of diamine and 50 molecules of diacid. How many water molecules are lost, and what is the total mass of water for 1 mol of chains? (3 marks)
Hint
2n - 1 links.
Answer
Links = 2 x 50 - 1 = 99, so 99 water molecules. Mass = 99 x 18 = 1782 g per mole of chains.
Q4 · 5 marks · Long answerHarder board level
Explain the structure and elastic behaviour of natural rubber, naming the monomer, and why Buna-S is a copolymer. (5 marks)
Hint
Isoprene, weak forces, cross-links.
Answer
Natural rubber is cis-1,4-polyisoprene, a linear polymer of isoprene (2-methyl-1,3-butadiene) obtained from latex. Its chains are held by weak intermolecular forces, so it stretches, and a few cross-links pull the chains back to the original shape, making it an elastomer. Buna-S is a copolymer because it is formed from two monomers, buta-1,3-diene and styrene, and it is a tough substitute for natural rubber.
Q5 · 1 mark · Assertion-reasonHOTS / competency
Assertion (A): Bakelite cannot be remoulded after heating.
Reason (R): Its chains are cross-linked into a network.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.Hint
Network structure.
Answer
(a) Both A and R are true, and R is the correct explanation of A.
Test your recall
Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.
1.Which polymer is the oldest synthetic polymer?Show answer
The phenol-formaldehyde polymer (bakelite).
2.What is latex?Show answer
A colloidal dispersion of rubber in water.
3.Name a use of terylene.Show answer
Blends with cotton and wool; glass reinforcing material in safety helmets.
4.What is the monomer of natural rubber?Show answer
Isoprene (2-methyl-1,3-butadiene).
Condensation Polymers and Rubber: frequently asked questions
What is condensation polymerisation?
Repeated reaction of bi- or tri-functional monomers with loss of small molecules such as water.
What is novolac?
The linear phenol-formaldehyde product used in paints.
What makes rubber elastic?
Weak forces allow stretching and a few cross-links restore the shape.