Concept:The high mechanical strength, crystallinity, and melting point of polyamides arise from regular arrays of intermolecular hydrogen bonds between adjacent linear chains.
Formula / Reaction:$$>\text{C}=\text{O} \cdots\cdots \text{H}-\text{N}< \quad (\text{Inter-chain Hydrogen Bonding})$$
Solution:- The carbonyl oxygen (\(>\text{C}=\text{O}\)) and amide hydrogen (\(-\text{NH}-\)) form strong hydrogen bonds across parallel aligned polymer chains.
- These cohesive forces yield high tensile strength, abrasion resistance, and elastic recovery.
Why other options are incorrect:- Option A: Ether linkages are found in polyethers and increase flexibility while reducing tensile strength.
- Option B: Nylon-6,6 contains aliphatic \(-(\text{CH}_2)_n-\) spacers, not bulky pendant aromatic rings.
- Option C: Terminal groups represent a fraction of the high-molecular-weight chain; strength is governed by main-chain hydrogen bonding.
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