Polymers: JEE Advanced PYQ, 2007–2026

Answer: (A)

Teflon is poly(tetrafluoroethene). Tetrafluoroethene is CF2=CF2, and addition polymerisation opens the double bond. Each monomer adds a -CF2-CF2- unit to the chain, so the repeat unit is -(CF2-CF2)-.

Answer: (A)

Both polymers have ester linkages and form by condensation with loss of water, so the linkage alone does not explain the difference. NCERT names aliphatic polyesters such as PHBV as biodegradable. Terylene's backbone contains benzene rings, which make it rigid and resistant to attack. The wrong options mix up the type of polymerisation, the linkage, and the monomer composition.

Answer: (A)

A linear chain of 150 monomers has 150 − 1 = 149 ester bonds. Each repeat unit is –O–CH(R)–CH2–CO–, with R = CH3 for 3-hydroxybutanoate and R = CH2CH3 for 3-hydroxypentanoate. Methyl groups come from 100 R = CH3 groups and 50 terminal CH3 of the ethyl groups, giving 150. The end groups –OH and –COOH contain no CH3, and the backbone CH2 groups are not CH3.

Answer: (A)

Principle: in a carboxylic acid, the carbon of -COOH is C1. Greek letters label the carbon bearing the substituent: alpha is C2, beta is C3, gamma is C4. Since 3-hydroxybutanoic acid has its -OH on C3, it is a beta-hydroxy acid.

Answer: (A)

Nylon-6,6 is a condensation polymer, and each amide (–CO–NH–) link formed releases one H2O. A linear chain of N monomer units contains N−1 links. Here N = 200 (100 diamine + 100 diacid), so there are 199 amide bonds and 199 water molecules. Counting 200 treats it as a ring, and counting 100 or 99 uses repeat units instead of monomer molecules.

Answer: (A)

In a condensation polyester each monomer unit in the chain is the acid minus one H2O. The 3-hydroxybutanoic acid unit (C4H8O3, 104) becomes –O–CH(CH3)–CH2–CO–, C4H6O2, with M = 86. The 3-hydroxypentanoic acid unit (C5H10O3, 118) becomes C5H8O2, with M = 100. For a 4 : 1 ratio, take 5 units: mass = 4(86) + 100 = 444 g and carbon = 4(4) + 5 = 21 atoms = 252 g. So %C = 252/444 × 100 ≈ 56.8%. Using the monomer masses gives 47.2%. Miscounting carbon gives 54.1%. Reversing the ratio gives 59.3%.

Answer: (B)

Principle: PHB is a homopolymer, meaning it is made from a single type of monomer. Its monomer is 3-hydroxybutanoic acid, CH3CH(OH)CH2COOH, which condenses through its -OH and -COOH groups to form polyester chains. Apply: the name 'poly-β-hydroxybutyrate' signals a four-carbon hydroxy acid with the hydroxyl on the β-carbon (carbon 3), so the monomer is 3-hydroxybutanoic acid. Lactic acid belongs to PLA, the 4-hydroxybutanoic acid option has the wrong -OH position, and 3-hydroxypentanoic acid is the second monomer of PHBV, not of PHB.

Answer: (B)

Microbial depolymerases and esterases act by hydrolysis, so the chain needs a hydrolysable link such as an ester or amide. PHBV has an ester in every repeat unit, and cleavage gives 3-hydroxy acids that cells can oxidise to CO2 and H2O. Polythene has only non-polar C–C and C–H bonds that these enzymes cannot cleave. Molar mass, branching and the copolymer-versus-homopolymer distinction do not decide whether a polymer is biodegradable.

Answer: (A)

The repeat unit of PHB is C4H6O2, with M = 48 + 6 + 32 = 86 g/mol. The reaction is C4H6O2 + x O2 → 4CO2 + 3H2O. Oxygen atoms on the right are 8 + 3 = 11, and the unit supplies 2, so 9 must come from O2, which gives x = 4.5. The sample contains 8.6/86 = 0.100 mol of repeat units, so O2 = 0.45 mol, and V = 0.45 × 22.4 = 10.08 L. Ignoring the internal oxygen gives 12.32 L. Ignoring hydrogen gives 8.96 L. Using 104 g/mol gives 8.34 L.

Answer: (A)

Cellulose is the linear polymer of beta-D-glucose, formed by condensation of glucose units with loss of water. Starch and glycogen use alpha-D-glucose instead, and this difference in anomeric configuration gives the two polymers different properties.