Basic Definitions
Polymer: Macromolecular compound formed by combination of large number of simple molecules (monomers).
Monomer → Polymer: Process is called Polymerisation
Note: All polymers are macromolecules but all macromolecules are not polymers (e.g., chlorophyll).
Classification of Polymers
1. Based on Source
Starch, Cellulose, Proteins, Nucleic acids (DNA, RNA)
Polyethene, PVC, Nylon, Teflon, Bakelite
Cellulose derivatives (nitrate, acetate), Vulcanised rubber, Rayon
2. Based on Structure
| Type | Features | Examples |
|---|---|---|
| Linear | High density, high tensile strength | HDPE, Nylon, PVC |
| Branched | Low density, low strength | LDPE, Glycogen |
| Cross-linked | Hard, rigid, brittle | Bakelite, Melamine |
3. Based on Molecular Forces
Weak intermolecular forces, elastic
Ex: Natural rubber
Strong H-bonding/dipole interaction
Ex: Nylon-66, Dacron
Soften on heating, can be remoulded
Ex: Polyethene, PVC
Do not soften, become hard on heating
Ex: Bakelite, Melamine
4. Based on Mode of Polymerisation
| Addition Polymers | Condensation Polymers | |
|---|---|---|
| Mechanism | Chain growth | Step growth |
| By-product | None | H₂O, NH₃, HCl etc. |
| Monomers | Alkenes/alkadienes | Difunctional (–COOH + –NH₂ etc.) |
| Examples | Polyethene, PVC, Teflon | Nylon-66, Dacron, Bakelite |
5. Based on Monomer
Same monomer
Ex: Polyethene ← Ethene
Two or more monomers
Ex: Nylon-66, Buna-S, Saran
Types of Copolymers
–A–B–A–B–A–B–
–A–A–B–A–B–B–A–
–AAAA–BBBB–AAAA–
Branches of one monomer grafted on another
Polymerisation Mechanisms
Chain Growth (Addition) Polymerisation
Free Radical (Most Common)
Initiator: Benzoyl peroxide
Steps: Initiation → Propagation → Termination
Cationic
Initiator: H₂SO₄, BF₃ + H₂O → Carbocation
Anionic
Initiator: K⁺NH₂⁻ → Carbanion
Step Growth (Condensation)
No initiator needed. Slow stepwise reaction with elimination of small molecules.
Important Polymers
| Polymer | Monomers | Type | Use |
|---|---|---|---|
| Polyethene | Ethene | Addition | Bags, bottles |
| PVC | Vinyl chloride | Addition | Pipes, insulation |
| Teflon | Tetrafluoroethene | Addition | Non-stick cookware |
| Nylon-66 | Hexamethylenediamine + Adipic acid | Condensation | Fibres, ropes |
| Dacron (Terylene) | Terephthalic acid + Ethylene glycol | Condensation | Fibres |
| Bakelite | Phenol + Formaldehyde | Condensation | Electrical fittings |
| Melamine | Melamine + Formaldehyde | Condensation | Unbreakable crockery |
Rubber & Vulcanisation
Natural Rubber
Cis-polyisoprene (11,000–20,000 units)
Soft, sticky, low elasticity
Vulcanised Rubber
Heating with sulphur → S-crosslinks
Hard, non-sticky, high elasticity
5% S → Tyre rubber
30% S → Battery case rubber
Effect of Vulcanisation
• High tensile strength
• High elasticity
• Wide temperature range (–40°C to 100°C)
• Insoluble in solvents
Biopolymers
Starch, Cellulose, Proteins, Nucleic acids (DNA, RNA) → Control life processes
JEE/NEET Weightage
1–2 direct questions expected every year.
High probability topics: Classification, Nylon-66, Bakelite, Vulcanisation, Addition vs Condensation, Natural rubber structure.