\[\begin{array}{cc}\ce{\phantom{…………………..}O}\phantom{………….}\ce{O}\\\phantom{…………………..}||\phantom{………….}||\\
\ce{[- HN – (CH2)6 \underset{\text{Nylon 6,6}}{- NH – C} – (CH2)4 – C -]_{n}}\end{array}\]