Polymers: Addition vs Condensation Mechanisms
Polymers are high molecular mass macromolecules formed by the repetition of simpler units called monomers. Understanding the distinction between Addition (Chain-Growth) and Condensation (Step-Growth) polymerization is critical for JEE, NEET, and Board exams.
1. Addition Polymers (Chain-Growth)
Addition polymerization involves the repeated addition of monomer molecules possessing double or triple bonds. No small molecules are eliminated during this process.
Mechanism Types
- Free Radical: Most common (e.g., Polythene, Teflon). Initiated by benzoyl peroxide.
- Cationic: For monomers with electron-donating groups.
- Anionic: For monomers with electron-withdrawing groups.
Figure 1: Common Addition Polymers and their Monomers
2. Condensation Polymers (Step-Growth)
Condensation polymerization involves a repetitive condensation reaction between two bi-functional monomeric units. This process usually eliminates simple molecules like water, alcohol, or HCl.
Key Examples
- Nylon-6,6: Polyamide formed from Hexamethylenediamine + Adipic Acid.
Uses: Bristles for brushes, textile fibers. - Terylene (Dacron): Polyester formed from Ethylene Glycol + Terephthalic Acid.
Uses: Crease-resistant clothes, safety belts. - Bakelite: Phenol-Formaldehyde resin (Cross-linked).
Uses: Electrical switches, handles of utensils.
Figure 2: Major Condensation Polymers and their Synthesis
3. Addition vs Condensation: Exam Cheat Sheet
Key Differences
| Feature | Addition | Condensation |
|---|---|---|
| Monomers | Unsaturated compounds | Bi-functional or Tri-functional |
| By-product | None | Small molecules ($H_2O, HCl$) |
| Polymer Mass | Integral multiple of monomer | Not an integral multiple |
| Chain Growth | Rapid (Chain Reaction) | Slow (Stepwise Reaction) |
Test Your Knowledge (10 Questions)
Select the best answer. Explanations will appear after submission.
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