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Polymers are macromolecules formed by repeating units called monomers. They are a vital topic in NEET Organic Chemistry as they appear in both theory and numerical problems. Understanding polymer formulas helps students solve questions efficiently during exams.
What are Polymers?
A polymer is a large molecule made from smaller repeating units. These units are connected via covalent bonds. Polymers can be natural (like proteins, cellulose) or synthetic (like nylon, Teflon).
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1. Addition Polymers
These polymers are formed by the addition reaction of unsaturated monomers (alkenes). No by-products are produced.
Example Formulas:
Polyethylene (PE): nCH₂=CH₂ → –(CH₂–CH₂)–ₙ
Polystyrene (PS): nC₆H₅CH=CH₂ → –(CH₂–CH(C₆H₅))–ₙ
Polyvinyl chloride (PVC): nCH₂=CHCl → –(CH₂–CHCl)–ₙ
Formed by monomers with two functional groups, producing small molecules like water or HCl as by-products.
Examples:
Nylon-6,6: HOOC–(CH₂)₄–COOH + H₂N–(CH₂)₆–NH₂ → –[NH–(CH₂)₆–NH–CO–(CH₂)₄–CO]–ₙ + H₂O
Terylene (Polyester): HO–C₆H₄–COOH + HO–CH₂–CH₂–OH → –[–CO–C₆H₄–CO–O–CH₂–CH₂–O–]–ₙ + H₂O
Here’s a quick reference table for NEET preparation:
| Polymer | Monomer(s) | Type | Formula |
|---|---|---|---|
| Polyethylene | Ethylene (CH₂=CH₂) | Addition | –(CH₂–CH₂)–ₙ |
| Polypropylene | Propylene (CH₂=CH–CH₃) | Addition | –(CH₂–CH(CH₃))–ₙ |
| Polyvinyl chloride | Vinyl chloride (CH₂=CHCl) | Addition | –(CH₂–CHCl)–ₙ |
| Polystyrene | Styrene (C₆H₅–CH=CH₂) | Addition | –(CH₂–CH(C₆H₅))–ₙ |
| Nylon-6,6 | Hexamethylenediamine + Adipic acid | Condensation | –[NH–(CH₂)₆–NH–CO–(CH₂)₄–CO]–ₙ |
| Bakelite | Phenol + Formaldehyde | Condensation | –[–C₆H₄–O–CH₂–]–ₙ |
| Terylene | Ethylene glycol + Terephthalic acid | Condensation | –[–CO–C₆H₄–CO–O–CH₂–CH₂–O–]–ₙ |
Understanding properties helps in MCQ and reasoning-based NEET questions:
Thermoplastics: Softens on heating (PE, PVC)
Thermosetting plastics: Hardens permanently on heating (Bakelite, Melamine)
Biodegradable polymers: Decompose naturally (Polylactic acid)
Non-biodegradable polymers: Resistant to decomposition (Teflon, Nylon)
1. Addition Polymerization:
Involves breaking double bonds of monomers.
Usually initiated by free radicals, heat, or catalysts.
Example: nCH₂=CH₂ → –(CH₂–CH₂)–ₙ
2. Condensation Polymerization:
Two functional groups react, releasing a small molecule.
Example: HOOC–CH₂–COOH + H₂N–CH₂–NH₂ → –[–CO–CH₂–CO–NH–CH₂–NH–]–ₙ + H₂O
Remember Monomer-Polymer pairs: Many NEET questions ask directly about which monomer forms a polymer.
Focus on Condensation vs Addition: Identify the reaction type based on by-products.
Learn abbreviations: PE, PS, PVC, Nylon, Terylene for faster recall.
Understand structures visually: Drawing repeating units helps memorize easily.
Practice numerical problems: Some questions involve molecular weight or degree of polymerization.
Polymers are an essential part of NEET Chemistry. Memorizing formulas, types, and reactions ensures better performance in the organic chemistry section. By revising monomer-polymer pairs and practicing reaction mechanisms, students can tackle both theoretical and numerical problems efficiently. Use this guide from StudentBro.in as a one-stop reference for NEET polymer formulas.
Remember: Consistent practice + formula memorization = better NEET scores in Chemistry.
