Question bank — Condensation polymers — nylon-6,6, nylon-6, terylene (PET), bakelite, melamine, Kevlar

False. It releases roughly one water per amide bond formed; for $n$ repeat units that is about $(2n-1)$ waters, not a fixed 6. The two 6's count carbons in the monomers, not waters.

False. Both lose water, but the linkage differs: PET forms an ester ($-CO-O-$) from acid + alcohol, nylon forms an amide ($-CO-NH-$) from acid + amine. Class is defined by the linkage, so PET is a polyester and nylon a polyamide.

True. With a single "hand" it reacts once and then has nothing left to continue — it caps the chain (a dead end), so it can only terminate, never extend.

False. Its three reactive sites on phenol build a 3-D cross-linked network — one giant molecule with no free chains to slide — so on heating it chars rather than melts. That is the definition of a thermoset.

False. Nylon-6 comes from caprolactam by ring-opening; the ring simply opens and links, so no water is spat out at each join. It is still a polyamide because the repeat unit carries amide links.

Misleading, so effectively false. The backbone bonds matter, but the exceptional strength comes from rigid aromatic chains packing straight plus extensive inter-chain hydrogen bonds holding sheets together.

True. Both use a monomer with three reactive sites (three $-N{H}_2$ on melamine, three ring positions on phenol) that cross-link with formaldehyde into a hard 3-D thermoset network.

False. The eliminated molecule is a small molecule, not always water — e.g. an acid-chloride route to Kevlar eliminates $HCl$, and nylon-6 (ring-opening) eliminates essentially nothing per join.

Wrong count. The two carboxyl carbons ($C$ in each $COOH$) must be added to the four $C{H}_2$ carbons → 6 total, which is exactly why nylon-6,6 has its second "6".

Wrong monomer. Ethylene glycol is an alcohol and belongs to PET. Nylon-6,6 needs an amine partner: hexamethylenediamine $H_{2}N(C{H}_2{)}_{6}N{H}_2$ + adipic acid.

Wrong mechanism. An ester needs one $-OH$ from the acid and one $-H$ from the alcohol to leave as water; a carbon–oxygen bond then forms between the two different partners, not between two identical $-OH$s.

Wrong category. "Plastic" is casual language; the technical split is thermoplastic vs thermoset. Its 3-D network makes it a thermoset.

Wrong linkage. Benzene rings appear in both, but Kevlar joins an acid to an amine → amide link, making it an aromatic polyamide (aramid), not a polyester.

Wrong. Caprolactam is a ring already carrying both an $-NH$ and a $C=O$, so it self-links; nylon-6 is famous for using a single monomer.

Wrong position. The $-OH$ activates the ring by Electrophilic aromatic substitution at the ortho and para positions (2 ortho + 1 para = three sites), not at the carbon already holding the oxygen.

Because a chain needs to grow from both ends — two "hands" let each monomer hold a neighbour on each side; with one hand it would only ever cap.

Three reactive directions weave a 3-D cross-linked net — a single giant molecule with no independent chains to slide past one another, so it cannot flow or melt.

Because at each linkage a small molecule leaves (water/HCl), so that lost mass is missing from the repeat unit — the fingerprint that distinguishes condensation from addition polymers.

The flat, rigid benzene rings resist rotation and bending, so the backbone stays straight and extended, letting chains line up and hydrogen-bond into strong sheets.

A trace of water is used to open the first ring and start the reaction; it is catalytic/initiating, not stoichiometrically released at every join like in nylon-6,6.

Their monomers are strictly bi-functional (two hands each), so they can only make linear chains — no third hand exists to cross-link into a net; hence they are thermoplastic fibres.

Condensation is an equilibrium; taking away the water product pulls the reaction toward more bond formation (Le Chatelier), giving longer chains.

The mono-amine acts as a chain-stopper — it caps whichever end it reaches, so chains stay short and no high polymer forms.

The third "hand" introduces a branch/cross-link point, so the material shifts toward a network and loses the clean, meltable, fibre-drawing behaviour of a linear thermoplastic.

Because pieces join any-to-any — mostly monomers joining into dimers and trimers first; long chains only appear near the end, when nearly all ends have reacted (this is characteristic step-growth behaviour).

No. Both are polyamides, but nylon-6 has repeat unit $[-NH(C{H}_2{)}_{5}CO-]$ from one monomer, while nylon-6,6 alternates a diamine and a diacid — different repeat structure, different packing and melting point.

$HCl$, not water — the acid chloride's $Cl$ leaves with the amine's $H$; it is still a condensation forming the same Kevlar amide link.

Phenol offers exactly three activated positions (two ortho, one para) via Electrophilic aromatic substitution; that hard cap of three is precisely what enables a 3-D net and no more.

No. A single acid group can only form an ester at one end — you'd get a small ester, not a chain. Terylene needs the di-acid terephthalic acid so both ends can link.