Consider the structure of a crosslinked polymer shown in the figure. From the options given, identify the monomers that are used in the synthesis of the polymer.
Show Hint
Urea–formaldehyde and melamine–formaldehyde are classic amino thermosets; the presence of a triazine ring points to \textbf{melamine}.
Step 1: Recognize the repeat unit in the figure.
The depicted network shows a s-triazine ring (six-membered ring with three nitrogens) carrying –NH groups—this is the core of melamine. The network has methylene/ether bridges indicative of a thermoset.
Step 2: Recall the melamine–formaldehyde (MF) resin formation.
Melamine reacts with formaldehyde to form {methylol melamine} (–NH–CH\textsubscript{2}OH) intermediates. On curing/condensation, these create crosslinks via –NH–CH\textsubscript{2}–NH– and –NH–CH\textsubscript{2}–O–CH\textsubscript{2}–NH– bridges, giving a rigid thermoset network that matches the figure.
Step 3: Eliminate distractors.
Benzaldehyde and acetone are not used to make the MF thermoset; ethanol is not an aldehyde for the condensation needed.
Step 4: Conclude.
Therefore, the polymer is a melamine–formaldehyde resin.
Final Answer:
\[
\boxed{\text{Melamine and Formaldehyde}}
\]
