What is the repeating unit of nylon 6-6?

http://en.wikipedia.org/wiki/Nylon_6-6

The repeating unit of nylon 6-6 is determined by its chemical structure. To understand the repeating unit of nylon 6-6, we need to break down its name.

"Nylon" refers to a family of synthetic polymers known as polyamides, which are formed by the condensation of a diamine and a diacid or by ring-opening polymerization of lactams. Nylon polymers are known for their toughness, high melting points, and excellent resistance to wear and abrasion.

The numbers "6-6" in nylon 6-6 represent the number of carbon atoms in the diamine and the diacid monomers used to synthesize the polymer. In this case, both the diamine and diacid contain 6 carbon atoms each. This numeric designation differentiates nylon 6-6 from other types of nylon, such as nylon 6, nylon 4-6, and so on.

The specific repeating unit of nylon 6-6 is created by the condensation reaction between hexamethylenediamine (a diamine with 6 carbon atoms) and adipic acid (a diacid with 6 carbon atoms). These two monomers react to form an amide linkage, resulting in the repeating unit of nylon 6-6, which is:

{-NH-(CH₂)₆-NH-CO-(CH₂)₄-CO-}