Polymers and Biomolecules

Why This Chapter Matters

Polymers and Biomolecules together give 5-7 marks in CBSE Class 12 boards. Classification of polymers, important synthetic polymers, and structure/function of biomolecules (carbohydrates, proteins, nucleic acids, vitamins) are tested.

Polymers

1. Classification

By source:

Natural: starch, cellulose, rubber, proteins, silk.

Synthetic: nylon, Bakelite, PVC, polythene.

Semi-synthetic: cellulose acetate, rayon.

By structure:

Linear: high density polyethylene, nylon, PET.

Branched: low density polyethylene (LDPE).

Cross-linked (network): Bakelite, vulcanised rubber (hard, infusible).

By mode of polymerisation:

Addition polymers: addition of monomer without loss of small molecules.

Condensation polymers: monomers join with loss of small molecules (H₂O, HCl).

2. Important Polymers

Polymer	Monomer(s)	Type	Uses

|---|---|---|---|

Nylon-6,6	Hexamethylenediamine + adipic acid	Condensation	Fibres, ropes
Nylon-6	Caprolactam	Ring-opening	Fibres
Dacron/Terylene	Ethylene glycol + terephthalic acid	Condensation polyester	Textile, bottles
Bakelite	Phenol + formaldehyde	Condensation (network)	Electrical fittings
Buna-S (SBR)	Butadiene + styrene	Copolymer (addition)	Tyres
Buna-N (NBR)	Butadiene + acrylonitrile	Copolymer	Oil-resistant seals
LDPE	Ethylene	Addition (free radical)	Plastic bags
HDPE	Ethylene	Addition (Ziegler-Natta)	Pipes, containers
Teflon (PTFE)	Tetrafluoroethylene	Addition	Non-stick coating
PVC	Vinyl chloride	Addition	Pipes, wires
Polystyrene	Styrene	Addition	Thermocol

Natural rubber: cis-polyisoprene. Soft, elastic but not durable.

Vulcanised rubber: rubber + sulphur (3-5%) → cross-links → harder, durable, elastic.

Biomolecules

3. Carbohydrates

Polyhydroxy aldehydes or ketones OR their derivatives.

Classified by: monosaccharides, oligosaccharides (2-10 units), polysaccharides (>10 units).

Monosaccharides: Glucose (aldohexose), Fructose (ketohexose), Ribose (aldopentose).

Glucose: C₆H₁₂O₆. Open chain (Fischer) and cyclic forms (Haworth).

Glucose forms cyclic hemiacetal (glucopyranose) with C-1 aldehyde attacking C-5 OH.

Disaccharides:

Sucrose: glucose+fructose (α-1,β-2 glycosidic bond). Non-reducing (no free anomeric carbon).

Maltose: glucose+glucose (α-1,4 bond). Reducing sugar.

Lactose: glucose+galactose. Reducing sugar.

Polysaccharides:

Starch: amylose (linear, α-1,4) + amylopectin (branched, α-1,4 and α-1,6).

Glycogen: like amylopectin but more branched. Animal storage.

Cellulose: β-1,4 glycosidic bonds. Cannot be digested by humans.

Chitin: N-acetylglucosamine units. Fungal walls, insect exoskeletons.

4. Proteins

Polymers of α-amino acids joined by peptide bonds (CO-NH).

20 standard amino acids. Essential (9 must come from diet): MVTLHITWF (Val,Met,Thr,Leu,His,Ile,Trp,Phe,Lys).

Protein structure:

Primary: amino acid sequence.

Secondary: α-helix (H-bonds within chain) or β-pleated sheet (H-bonds between chains).

Tertiary: 3D folding (disulphide bonds, hydrophobic interactions).

Quaternary: association of multiple polypeptide chains (haemoglobin = 4 chains).

Denaturation: Loss of 3D structure due to heat, pH change, organic solvents. Disrupts secondary and tertiary but NOT primary structure.

Enzymes: Biological catalysts (mostly proteins). Highly specific. Active site binds substrate.

5. Nucleic Acids

DNA and RNA (see genetics chapter). Built from nucleotides (base+sugar+phosphate).

6. Vitamins

Organic micronutrients required in small amounts for normal metabolism.

Vitamin	Name	Deficiency Disease

|---|---|---|

A	Retinol	Night blindness
B₁	Thiamine	Beriberi
B₂	Riboflavin	Cheilosis, glossitis
B₆	Pyridoxine	Anaemia
B₁₂	Cyanocobalamin	Pernicious anaemia
C	Ascorbic acid	Scurvy
D	Calciferol	Rickets (children), Osteomalacia (adults)
E	Tocopherol	Sterility (rare)
K	Phylloquinone	Poor blood clotting

Fat-soluble vitamins: A, D, E, K (stored in fat — can accumulate and cause toxicity).

Water-soluble vitamins: B-complex and C (excess excreted in urine, less risk of toxicity).

PYQs (CBSE)

CBSE 2023: What is vulcanisation of rubber? How does it improve properties?

Vulcanisation: heating raw rubber with sulphur at 100-180°C. Sulphur forms cross-links between rubber chains.

Improvement: increased tensile strength, hardness, resistance to heat and organic solvents; retains elasticity.

CBSE 2022: What is the difference between DNA and RNA?

DNA: deoxyribose sugar, ATGC bases, double helix, found mainly in nucleus, stores genetic info.

RNA: ribose sugar, AUGC bases (U instead of T), usually single-stranded, found in nucleus and cytoplasm, involved in protein synthesis.

Revision Notes

POLYMERS:
Addition: no byproduct | Condensation: lose H₂O or HCl
Linear (HDPE,nylon) | Branched (LDPE) | Network (Bakelite)
NYLON-6,6: hexamethylenediamine+adipic acid
DACRON: ethylene glycol+terephthalic acid
Vulcanised rubber: S cross-links → harder, durable

CARBOHYDRATES:
Glucose=C₆H₁₂O₆ (aldohexose) | Fructose (ketohexose)
Sucrose (non-reducing) | Maltose, Lactose (reducing)
Starch: amylose(linear)+amylopectin(branched)
Glycogen: animal starch | Cellulose: β-1,4 (indigestible)

PROTEIN STRUCTURE:
1°=sequence | 2°=helix/sheet(H-bonds) | 3°=3D folding | 4°=multiple chains
Denaturation: disrupts 2°+3°, NOT 1°

VITAMINS:
Fat-soluble: A,D,E,K | Water-soluble: B-complex,C
A→night blindness | C→scurvy | D→rickets | K→poor clotting