Nylon-6,6 and Kevlar

Nylon-6,6 and Kevlar are both polyamides, but their monomers give them very different properties.Nylon-6,6 is made from hexane-1,6-diamine and hexanedioic acid (or hexanedioyl dichloride). The name comes from the six carbon atoms in each monomer.n H₂N(CH₂)₆NH₂ + n HOOC(CH₂)₄COOH → [-NH(CH₂)₆NH-CO(CH₂)₄CO-]_n + (2n − 1) H₂OKevlar is made from benzene-1,4-diamine and benzene-1,4-dicarboxylic acid (or benzene-1,4-dicarbonyl dichloride). Its repeating unit is [-NH-C₆H₄-NH-CO-C₆H₄-CO-]_n.The benzene rings make Kevlar chains flat and rigid. The chains line up side by side and form many hydrogen bonds between the C=O and N-H groups of neighbouring chains, giving a material that is very strong for its mass. Nylon-6,6 has flexible (CH₂) sections, so it is strong but also stretchy.Uses: nylon-6,6 is used for clothing, carpets, ropes and fishing line; Kevlar is used in bulletproof vests (body armour), protective helmets and to reinforce tyres.Worked example. Find M_r of the nylon-6,6 repeating unit, C₁₂H₂₂N₂O₂: (12 × 12.0) + (22 × 1.0) + (2 × 14.0) + (2 × 16.0) = 144 + 22 + 28 + 32 = 226.