Three reactive sites on phenol give a 3-D cross-linked network that cannot melt.
Monomers of melamine polymer?
Melamine + formaldehyde.
What do the "6"s in nylon-6,6 mean?
Number of carbon atoms in each monomer (diamine 6, diacid 6).
Use of melamine–formaldehyde?
Unbreakable crockery, Formica laminates.
Why is Kevlar stronger than steel by weight?
Stiff aromatic chains plus extensive inter-chain hydrogen bonding.
What functional groups react to form an amide link?
–COOH + –NH₂ → –CO–NH– + H₂O.
Recall Feynman: explain to a 12-year-old
Imagine sticking paper beads on a string, but every time you stick two beads together a tiny drop of water squeezes out. That's a condensation polymer — long chains made by snapping pieces together and throwing away little water drops. If your beads have two holes you get a long string (nylon, terylene — these melt and can be drawn into fibres). If your beads have three holes, the string ties into a giant 3-D net that can never come apart, so it stays hard forever even when hot — that's Bakelite and Melamine (your unbreakable plates!). Kevlar is a string made of super-stiff beads that hold hands tightly with neighbours, so it's strong enough to stop a bullet.
Dekho, condensation polymers ka funda simple hai: do monomers jab jurte hain to har bond banne par ek chhota molecule (zyadatar paani) bahar nikal jaata hai. Isiliye inhe "step-growth" kehte hain — koi bhi do tukde aapas mein jud sakte hain. Yaad rakhna: monomer ke dono ends par functional group hone chahiye (bi-functional), warna chain lambi nahi banegi.
Ab types: Nylon-6,6 banta hai hexamethylenediamine + adipic acid se (dono mein 6-6 carbon, isliye "6,6"), aur isme amide link hota hai. Nylon-6 sirf ek monomer caprolactam se ring-opening se banta hai. Terylene/PET banta hai ethylene glycol + terephthalic acid se — yahaan ester link hota hai (alcohol + acid), isliye ye polyester hai, polyamide nahi. Kevlar bhi amide hai par aromatic rings ke kaaran bahut strong — bulletproof jackets mein use hota hai (chains ke beech strong hydrogen bonding).
Do special cheezein hain — Bakelite (phenol + formaldehyde) aur Melamine (melamine + formaldehyde). Inke monomers mein teen reactive positions hote hain, isliye ye 3-D cross-linked net banate hain. Net kabhi melt nahi hota, sirf jal jaata hai — inko thermosetting kehte hain. Bakelite se switches/handles, melamine se na tootne wali plates bante hain.
Exam tip: galti mat karna — "6,6" ka matlab carbon count hai, amide links nahi; PET polyester hai polyamide nahi; aur bakelite/melamine garam karne par pighalte nahi. Bas linkage (amide vs ester) aur dimensionality (linear vs 3-D net) yaad rakho, sab clear ho jaayega.
