Chapter 8 – Polymers (JEE Chemistry)
1. Introduction to Polymers
Polymers are large molecules formed by the combination of many small repeating units
called monomers.
Polymer = Monomer + Monomer + Monomer + ...
The word polymer comes from Greek words:
- Poly = many
- Mer = unit
2. Monomers
Monomers are small molecules which join together to form polymers.
They usually contain double bonds or functional groups.
Example: Ethene $(CH_2=CH_2)$ is a monomer for polyethylene.
3. Classification of Polymers
(a) Based on Source
| Type | Examples |
|---|---|
| Natural | Cellulose, Starch, Proteins |
| Semi-synthetic | Rayon, Cellulose acetate |
| Synthetic | Polythene, PVC, Nylon |
4. Classification Based on Structure
| Structure | Description | Example |
|---|---|---|
| Linear | Straight chains | HDPE |
| Branched | Side chains present | LDPE |
| Cross-linked | 3D network | Bakelite |
5. Classification Based on Mode of Polymerization
(a) Addition Polymerization
In addition polymerization, monomers add together without loss of any molecule.
$n(CH_2=CH_2) \rightarrow (-CH_2-CH_2-)_n$
Examples:
- Polythene
- Polypropylene
- PVC
(b) Condensation Polymerization
In condensation polymerization, monomers combine with elimination of small molecules
like $H_2O$, $HCl$, or $NH_3$.
$nH_2N-(CH_2)_6-NH_2 + nHOOC-(CH_2)_4-COOH \\
\rightarrow (-NH-(CH_2)_6-NH-CO-(CH_2)_4-CO-)_n + 2nH_2O$
6. Classification Based on Intermolecular Forces
| Polymer Type | Properties | Examples |
|---|---|---|
| Elastomers | Elastic, flexible | Rubber |
| Fibres | Strong, high tensile strength | Nylon, Terylene |
| Thermoplastics | Soft on heating | Polythene |
| Thermosetting | Hard, infusible | Bakelite |
7. Important Synthetic Polymers
Polythene
$n(CH_2=CH_2) \rightarrow (-CH_2-CH_2-)_n$
PVC
$n(CH_2=CHCl) \rightarrow (-CH_2-CHCl-)_n$
Nylon-6,6
Hexamethylene diamine + Adipic acid → Nylon-6,6
Bakelite
Bakelite is a thermosetting polymer made from phenol and formaldehyde.
8. Biodegradable Polymers
Biodegradable polymers decompose naturally by microorganisms.
- PHBV
- PLA
9. Rubber
Natural Rubber
Isoprene → cis-1,4-polyisoprene
Vulcanization
Vulcanization is the process of heating rubber with sulfur to improve elasticity and strength.
10. Common JEE Examination Points
- Difference between addition and condensation polymers
- Identification of monomers
- Thermoplastic vs thermosetting
- Uses of polymers
11. Final Revision Checklist
You have mastered this chapter if you can:
- Classify polymers correctly
- Identify polymerization type
- Write polymer structures
- Recall examples and uses
- Differentiate thermoplastics and thermosets