Polyamide chemistry: nylon-66 is manufactured from which pair of monomers?

Introduction / Context:
Nylons are polyamides formed by condensation reactions between diamines and diacids (or by ring-opening of lactams). Naming such as “66” reflects the number of carbons in each monomer. Properly identifying monomers clarifies polymer structure and properties (melting point, crystallinity, moisture uptake).

Given Data / Assumptions:

• Nylon-66: the first “6” denotes a C6 diamine; the second “6” denotes a C6 diacid.
• Industrial route involves salt formation followed by polycondensation.

Concept / Approach:
Hexamethylene diamine (HMD, 6 carbons) and adipic acid (AA, 6 carbons) form the nylon-salt that, upon condensation with removal of water, yields nylon-66. Caprolactam is used for nylon-6 (not 66), DMT and ethylene glycol form PET polyester, and maleic anhydride combinations lead to other polyesters or copolymers.

Step-by-Step Solution:

Verification / Alternative check:
Polymer chemistry texts consistently specify HMD + adipic acid for nylon-66, with melting point near 255–265 °C depending on grade.

Why Other Options Are Wrong:

• Caprolactam: monomer for nylon-6 via ring opening.
• Maleic anhydride + HMD: not nylon-66.
• DMT + EG: polyester (PET), not a polyamide.

Common Pitfalls:
Confusing nylon-6 with nylon-66 due to similar names; remember “6-6” denotes two C6 monomers.

Final Answer:
Adipic acid and hexamethylene diamine