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Polymers used to be a full chapter in NCERT Class 12. If you are using an older guide, you may be unsure whether you still need it. This post sorts that out first, then explains the one distinction most polymer questions turn on, addition versus condensation, with the standard examples and two calculations.
Do you still need polymers?
The current NCERT Class 12 Chemistry Part II (reprint 2026–27) has five units, from haloalkanes to biomolecules, with no polymers unit. The JEE (Main) 2026 syllabus and the NEET (UG) 2026 syllabus have no polymers unit either; they mention polymerisation only as a reaction of alkenes and alkynes. The JEE (Advanced) 2026 brochure is different. It lists a Polymers topic: "Types of polymerization (addition, condensation); Homo and copolymers; Natural rubber; Cellulose; Nylon; Teflon; Bakelite; PVC; Bio-degradable polymers; Applications of polymers."
So: JEE Advanced aspirants need this topic. JEE Main and NEET students need the alkene polymerisation line and the biomolecule links below. State board students should check their own syllabus.
What is a polymer?
A polymer is a very large molecule built from many small repeating units. The idea that such giant molecules are real, held together by ordinary covalent bonds, was not always accepted. Hermann Staudinger won the 1953 Nobel Prize in Chemistry "for his discoveries in the field of macromolecular chemistry". In 1929, Wallace Carothers published an introduction to the general theory of condensation polymers in the Journal of the American Chemical Society.
What makes a polymer "addition"?
In addition polymerisation, monomers with a carbon–carbon double bond join end to end. The double bond opens, and no atoms are lost. The repeat unit has exactly the same formula as the monomer.
Polythene: from ethene, CH₂=CH₂. Repeat unit –CH₂–CH₂–.
PVC: from vinyl chloride (chloroethene), CH₂=CHCl.
Teflon: from tetrafluoroethene, CF₂=CF₂.
Natural rubber: a polymer of isoprene (2-methylbuta-1,3-diene).
This is the "polymerization" that the JEE Main and NEET syllabi list under alkenes.
What makes a polymer "condensation"?
In condensation polymerisation, each monomer has two reactive groups, such as –COOH, –NH₂ or –OH. Every time two monomers link, a small molecule, usually water, is lost.
Nylon-6,6: from hexamethylenediamine, H₂N(CH₂)₆NH₂, and adipic acid, HOOC(CH₂)₄COOH. Each link is an amide, –CO–NH–.
PET (terylene): from ethylene glycol and terephthalic acid. Each link is an ester.
Bakelite: from phenol and formaldehyde, with water lost as the rings are joined by –CH₂– bridges.
You already know two natural condensation polymers. Unit 10 of NCERT Class 12 Chemistry Part II says proteins are polymers of α-amino acids joined by peptide bonds, with a water molecule eliminated at each bond, and nucleic acids are chains of nucleotides joined by phosphodiester links. Our post on biomolecules in chemistry covers these.
Worked example 1: nylon-6,6 repeat unit
Molar masses from PubChem: hexamethylenediamine, C₆H₁₆N₂, is 116.20 g/mol, and adipic acid, C₆H₁₀O₄, is 146.14 g/mol.
One repeat unit uses one of each monomer and forms two amide links, so two water molecules (2 × 18.015 = 36.03 g/mol) are lost.
Repeat unit mass = 116.20 + 146.14 − 36.03 = 226.31 g/mol. That matches the formula C₁₂H₂₂N₂O₂.
A nylon-6,6 chain of molar mass 22,630 g/mol therefore has about 22,630 / 226.3 = 100 repeat units.
Worked example 2: polythene
Ethene is 28.05 g/mol. No atoms are lost in addition polymerisation, so the repeat unit is also 28.05 g/mol. A chain of 28,000 g/mol has about 28,000 / 28.05 ≈ 1,000 repeat units.
Common mistakes
Nylon-6 is not made like nylon-6,6. Nylon-6 comes from a single monomer, caprolactam, a ring that opens. Check how your source classifies it, and do not invent a second monomer.
Copolymer versus two monomers. A copolymer has two or more different monomer units in its chain. Make sure you can give the textbook example your syllabus uses.
Forgetting the lost water in repeat-unit masses.
Assuming all condensation polymers lose water. Some lose HCl or methanol, depending on the starting groups.
If you would rather see a chain grow than read about it, the Fermi Simulation Lab has interactive simulations for ideas that are easier to see than read, and the Fermi Concept Library covers every concept in chemistry if you need to revise functional groups first.
A practice routine
List eight polymers from the JEE Advanced list and your notes, with monomers, and mark each addition or condensation.
Draw the repeat unit for each and do the formula check.
Calculate three repeat-unit masses and one degree of polymerisation.
For proteins and DNA, name the link and the small molecule lost.
Start with alkene polymerisation, which links straight to our post on addition to alkenes.
