Class 12 polymers Notes for IIT JEE & NEET

Addition polymerisation involves monomers with double bonds joining together without losing any atoms — the repeating unit has the same formula as the monomer. Condensation polymerisation involves bifunctional monomers reacting with loss of small molecules like water. Nylon and Terylene are condensation polymers; PVC and Teflon are addition polymers.

Nylon-6,6, Bakelite, Terylene, and PVC consistently appear in JEE Main. Questions typically ask for the monomer, linkage type (amide, ester), or classification (thermoplastic vs thermosetting). Nylon-6,6 and Bakelite alone have appeared in 6+ JEE Main papers in the last decade.

Vulcanisation is the process of heating natural rubber with sulphur at around 150°C. The sulphur atoms form cross-links between the cis-polyisoprene chains. This makes rubber harder, more elastic, and resistant to heat and cold — properties that raw natural rubber does not have. It is directly asked in both JEE Main and NEET.

PHBV (Poly-β-hydroxybutyrate-co-β-hydroxyvalerate) is the most important biodegradable polymer in the Class 12 syllabus. Its monomers are 3-hydroxybutanoic acid and 3-hydroxypentanoic acid. It is used in packaging and medical devices. NEET frequently asks for its monomer names, so memorise the full IUPAC names.

The degree of polymerisation (n) is the number of repeating monomer units in a polymer chain. A higher degree of polymerisation means a longer chain and generally higher molecular mass. For JEE Advanced, you may need to distinguish between number-average molecular mass and weight-average molecular mass.