Classification — natural vs synthetic; addition vs condensation; thermoplastic vs thermosetting

4.6.1 · Chemistry › Polymers

1. Source: Natural vs Synthetic vs Semi-synthetic

YE classification kyun? Ye batata hai raw material ki economics aur biodegradability. Natural wale usually biodegrade ho jaate hain; zyaadatar synthetics nahi hote.

2. Mode of synthesis: Addition vs Condensation

Ye chemist ki favourite axis hai kyunki ye mechanism ke baare mein hai.

Derivation: addition mein mass kyun conserve hota hai

Ethene lo. $CH_{2} = CH_{2}$ ka π-bond toot ta hai; woh do electrons ek nayi σ-bond banate hain agle monomer se:

$n CH_{2} = CH_{2} ⟶ - repeat unit (CH_{2} - CH_{2}) -_{n}$

By-product kyun nahi? Kuch bhi hata nahi — double bond sirf "khulta" hai aur dobara connect ho jaata hai. Isliye: $mass of polymer = n \times mass of monomer$ Monomer $C_{2} H_{4}$ (28) aur repeat unit $C_{2} H_{4}$ (28) — bilkul same. ✔

Derivation: condensation mein mass kyun kho jaata hai

Ek diol + diacid lo jo polyester bana rahe hain. Har ek ester bond bante waqt ek water nikaalta hai:

$HO-R-OH + HOOC-R’-COOH \to HO-R-O-CO-R’-COOH + H_{2} O$

$n$ diol + $n$ diacid se ek lamba chain bane toh $(2 n - 1)$ links bante hain → $(2 n - 1)$ waters kho jaate hain. Bade $n$ ke liye, ≈ $2 n$ choti molecules eliminate hoti hain.

Figure — Classification — natural vs synthetic; addition vs condensation; thermoplastic vs thermosetting

3. Thermal behaviour: Thermoplastic vs Thermosetting

Yeh farq kyun? Ye is baat par depend karta hai ki chains ko kya hold karta hai:

Thermoplastic → heat se weak forces tooto → reversible.
Thermosetting → strong covalent crosslinks todne padenge → decomposition ke bina possible nahi → irreversible.

Forecast-then-Verify

Flashcards

Addition aur condensation polymer mein kya farq hai

Addition: C=C monomers bina koi atom khoye add hote hain (repeat unit = monomer formula). Condensation: bifunctional monomers ek choti molecule (H₂O/HCl/NH₃) eliminate karke join hote hain.

Thermosetting plastics reheating par melt kyun nahi hote

Unke paas strong covalent crosslinks ka 3-D network hota hai jo heat nahi tod sakti, isliye ye soft hone ki jagah char/decompose ho jaate hain.

Thermoplastics remould kyun HO SAKTE HAIN

Unki chains sirf weak intermolecular forces se held hoti hain jo heating par dhili pad jaati hain, phir cooling par dobara bann jaati hain.

Ek-ek example do: natural, synthetic, semi-synthetic

Cellulose (natural); polythene (synthetic); cellulose acetate/rayon (semi-synthetic).

Kya Bakelite addition hai ya condensation, thermoplastic hai ya thermosetting

Condensation (phenol + formaldehyde, H₂O lose karta hai); thermosetting.

Teflon teeno axes par kaise classify hota hai

Synthetic, addition (CF₂=CF₂ se), thermoplastic.

Nylon-6,6 formation mein kaunsi choti molecule eliminate hoti hai

Water (–NH₂ aur –COOH ke beech amide bond formation mein).

Addition polymerisation mein mass kyun conserve hota hai

π-bond sirf khulta hai nayi σ-bonds banane ke liye; kuch bhi nahi hata, isliye monomer aur repeat unit ka formula same hota hai.

Kya 'addition vs condensation' aur 'thermoplastic vs thermosetting' related hain

Nahi, ye independent axes hain — ek mechanism ke baare mein hai, doosra crosslinking/thermal behaviour ke baare mein.

Semi-synthetic polymer ki definition

Ek naturally occurring polymer jo chemically modify kiya gaya ho, e.g. cellulose nitrate (gun cotton).

Recall Feynman: 12-saal ke bachche ko samjhao

LEGO imagine karo. Addition plastics jaise identical bricks ko click karna — click karte waqt table se kuch nahi girta. Condensation plastics jaise bricks ko glue karna jahan har baar ek choti glue ki bund nikaali jaati hai (woh bund = kho gayi water). Ab melting ke baare mein: thermoplastic chocolate chain jaisi hai — garam karo toh soft ho jaati hai, baar baar reshape kar sakte ho. Thermosetting cake baking jaisi hai — ek baar batter ko cake banao, zyada garam karo toh bas jalti hai; kabhi batter mein wapas nahi ho sakti. Cake ke ingredients permanently lock ho gaye (yahi crosslinking hai).

Connections

Addition Polymerisation Mechanism — C=C monomers ka radical/ionic chain growth.
Condensation Polymerisation — step growth, polyesters & polyamides.
Natural Rubber and Vulcanisation — natural addition polymer jo sulphur ke saath crosslinking se thermoset ban jaata hai.
Intermolecular Forces — thermoplastic softening explain karta hai.
Biodegradable Polymers — natural vs synthetic aur waste management se jodta hai.
Copolymers — jab do monomers combine hote hain (e.g. Buna-S).