Q.Draw the repeat unit of nylon-6,6 and identify the type of linkage that joins successive monomer units.

Nylon-6,6's repeat unit is $\big[-\text{NH--}(\text{CH}_2)_6\text{--NH--CO--}(\text{CH}_2)_4\text{--CO--}\big]_n$, built by condensing hexamethylenediamine's two $-\text{NH}_2$ groups with adipic acid's two $-\text{COOH}$ groups. Each condensation between an $-\text{NH}_2$ and a $-\text{COOH}$ forms an amide linkage, $-\text{CO--NH}-$ (the same functional linkage that joins amino acids into proteins, where it is called a peptide bond), with loss of one water molecule per linkage. Two amide linkages occur per repeat unit shown above (one at each end, joining it to the neighbouring units on either si …

Locate the new bond formed at each condensation step between the two monomers' reactive groups, …

Calling the linkage an 'ester' linkage (that is polyester's linkage, formed from $-\text{OH}$ and $-\text{COOH}$, not $-\text{NH}_2$ and $-\text{COOH …