Addition polymers — polyethene, PVC, PTFE (Teflon), polypropylene, polystyrene, PMMA, polyacrylonitrile

4.6.2 · Chemistry › Polymers

Addition polymer KYA hota hai?

"Addition" KYU? Kyunki monomer sirf jod diya jaata hai — kuch alag nahin hota. Isko condensation polymers (nylon, polyester) se compare karo jo ek chhota molecule jaise $H_{2} O$ bahar nikaalte hain. Yeh sabse zyada kaam aane wala distinction hai.

Chain actually kaise badhti hai? (Free-radical mechanism, scratch se samjho)

Hum rule ko build karenge, ratta nahin lagaayenge. Ethene $C H_{2} = C H_{2}$ lo.

Step 1 — Initiation. Ek peroxide initiator do radicals mein toot jaata hai (species jinmein ek unpaired electron hota hai, jo dot ke roop mein likha jaata hai): $R - O - O - R ⟶ 2 R - O ∙$

Yeh step kyun? Radical electron-hungry hota hai. $C = C$ ke $π$ electrons dheelay hote hain aur pakadna aasaan hota hai — perfect prey.

Step 2 — Propagation. Radical double bond ke ek carbon par attack karta hai. Ek $π$ electron radical ke electron ke saath pair hota hai nayi bond banane ke liye; doosra $π$ electron door wale carbon par nayi radical ban jaata hai: $R O ∙ + C H_{2} = C H_{2} ⟶ R O - C H_{2} - C H_{2} ∙$ $R O - C H_{2} - C H_{2} ∙ + C H_{2} = C H_{2} ⟶ R O - C H_{2} - C H_{2} - C H_{2} - C H_{2} ∙$

Yeh step kyun? Radical bas chain ke end par move karta rehta hai aur monomers khaata rehta hai — ek self-perpetuating "chain reaction". Isliye ise chain-growth kehte hain.

Step 3 — Termination. Do radical chain-ends milte hain aur apne electrons pair kar lete hain (combination), growth rok dete hain.

Net result, chain ends ko ignore karke: $n C H_{2} = C H_{2} peroxide, high P, T - [C H_{2} - C H_{2}]_{n} -$

Figure — Addition polymers — polyethene, PVC, PTFE (Teflon), polypropylene, polystyrene, PMMA, polyacrylonitrile

Yeh family: $X$ badlo, plastic badlo

Polymer	Monomer	$X$ group	Repeat unit	Key use (KYU)
Polyethene (PE)	ethene $C H_{2} = C H_{2}$	H	$- C H_{2} - C H_{2} -$	bags, bottles; sasta, inert
PVC	chloroethene (vinyl chloride) $C H_{2} = C H C l$	Cl	$- C H_{2} - C H C l -$	pipes, insulation; rigid, flame-resistant
PTFE (Teflon)	tetrafluoroethene $C F_{2} = C F_{2}$	sab F	$- C F_{2} - C F_{2} -$	non-stick pans; C–F bond super-strong, inert, low friction
Polypropylene (PP)	propene $C H_{2} = C H (C H_{3})$	CH₃	$- C H_{2} - C H (C H_{3}) -$	crates, ropes; tough, high m.p.
Polystyrene (PS)	styrene $C H_{2} = C H (C_{6} H_{5})$	C₆H₅	$- C H_{2} - C H (C_{6} H_{5}) -$	cups, packaging; rigid, easily foamed
PMMA (acrylic/Perspex)	methyl methacrylate	$- C O O C H_{3}$ + CH₃	$- C H_{2} - C (C H_{3}) (C O O C H_{3}) -$	"glass" substitute; transparent, shatter-resistant
PAN	acrylonitrile $C H_{2} = C H (C N)$	CN	$- C H_{2} - C H (C N) -$	acrylic fibre (sweaters); wool-jaisa, carbon-fibre precursor

Worked Examples

Common Mistakes (Steel-manned)

80/20 — woh 20% jo 80% marks dilaata hai

Addition = $C = C$ monomer, koi chhota molecule nahin khoता.
Double bond kholo → neighbours se single bonds → repeat unit in $- []_{n} -$ .
7 monomers ↔ polymers ↔ uses ki table dil se yaad karo.
C–F bond strength PTFE ki inertness explain karta hai; branching LDPE vs HDPE explain karti hai.

Recall Feynman: ek 12-saal ke bacche ko samjhao

Socho ki har monomer ek aisa baccha hai jo apne dono haath khud apne saath pakde hua hai (woh "pakadna" double bond hai). Jab ek teacher (radical) kisi bacche ko tap karta hai, baccha apna ek haath chhodta hai aur uski jagah agले bacche ka haath pakad leta hai. Woh baccha phir apna haath free karta hai aur agla pakad leta hai, aur yaise hi — ek giant human chain ban jaati hai, aur kisi ki ek bhi ungli nahin jaati (koi atoms nahin phekte). Agar bacche alag alag dastane pehne ho (Cl, F, ek phool CH₃, ek balloon C₆H₅), toh chain alag behave karti hai — isliye usi ek trick se hume bags, pipes, non-stick pans, aur foam cups milte hain.

Flashcards

Addition polymer ko kya define karta hai?

Unsaturated (

C = C

) monomers ka repeated addition bina koi chhota molecule khoye; repeat unit = monomer.

Polyethene ka monomer kya hai?

Ethene,

C H_{2} = C H_{2}

PVC ka monomer kya hai?

Chloroethene (vinyl chloride),

C H_{2} = C H C l

PTFE/Teflon ka monomer kya hai?

Tetrafluoroethene,

C F_{2} = C F_{2}

PTFE itna inert aur non-stick kyun hai?

Bahut strong, chhote C–F bonds + low surface friction, chemically unreactive.

Polypropylene ka monomer kya hai?

Propene,

C H_{2} = C H (C H_{3})

Polystyrene ka monomer kya hai?

Styrene (phenylethene),

C H_{2} = C H (C_{6} H_{5})

PMMA (Perspex) ka monomer kya hai?

Methyl methacrylate.

PAN ka monomer aur use kya hai?

Acrylonitrile

C H_{2} = C H (C N)

; acrylic fibres / carbon-fibre precursor.

LDPE aur HDPE mein farq kya hai?

LDPE branched → low density, flexible; HDPE linear → dense, rigid, stronger.

Addition polymerisation mein C=C ka kya hota hai?

Yeh single bonds mein khul jaati hai jo neighbouring monomers ko link karti hain.

Free-radical addition polymerisation ke teen steps kya hain?

Initiation, propagation, termination.

Repeat unit se monomer kaise dhundhen?

Repeat unit ke do backbone carbons ke beech

C = C

wapas daalo.

M = 42000 wali PE ke liye n kitna hai (ethene M=28)?

1500 units.

Addition vs condensation ka key difference kya hai?

Addition koi atoms nahin khoता (C=C monomers); condensation ek chhota molecule bahar nikalti hai (e.g.

H_{2} O

Connections

Condensation polymers — nylon, polyester
Free-radical mechanism
Alkenes and the C=C double bond
Intermolecular forces and polymer properties
HDPE vs LDPE — structure and density
Carbon fibre from PAN