"Nylon 66" question?

Question

In "Nylon 66",what does 66 means?

Answer 1

From reference 1:

"Most nylons are condensation copolymers formed by reacting equal parts of a diamine and a dicarboxylic acid, so that peptide bonds form at both ends of each monomer in a process analogous to polypeptide biopolymers. The numerical suffix specifies the numbers of carbons donated by the monomers; the diamine first and the diacid second. The most common variant is nylon 6,6, also called nylon 66, which refers to the fact that the diamine (hexamethylene diamine) and the diacid (adipic acid) each donate 6 carbons to the polymer chain. As with other regular copolymers like polyesters and polyurethanes, the repeating unit consists of one of each monomer, so that they alternate in the chain. Since each monomer in this copolymer has the same reactive group on both ends, the direction of the amide bond reverses between each monomer, unlike natural polyamide proteins which have overall directionality: C terminal → N terminal. In the laboratory, nylon 6,6 can also be made using adipoyl chloride instead of adipic acid."

See also reference 2 for wire diagrams of each molecule.

Answer 2

A polymer widely used in a fibrous form in fabrics as well as solid lumps of plastic (e.g. in chopping boards and bearings). Nylon 66 may be formed from the condensation polymerisation of 1,2-hexadiamine and 1,8-octadioic acid, although modern industrial processes have improved upon these reactions by ionising the reagents to the hexadiammonium and 1,8-octadioate ions before the reaction is undertaken.