Q.How do you explain the functionality of a monomer?

The functionality of a monomer is the number of binding/reactive sites (reactive functional groups or double bonds) present in one molecule of the monomer that can take part in the polymerisation reaction.

• A monomer with two reactive sites (bifunctional), such as a glycol ($HO-CH_2CH_2-OH$) or a diamine/diacid pair (hexamethylenediamine + adipic acid), can link only in a chain fashion at both ends, giving a linear polymer (e.g. a linear polyester, or Nylon 6,6).
• A monomer with three or more reactive sites (trifunctional or higher), such as glycerol or phenol reacting with formaldehyde in Bakelite formation, can link in more than two directions, producing branched and cross-linked, three-dimensional network polymers (e.g. Bakelite, a thermosetting resin). …

Define functionality as the count of reactive groups, then show how the count (2 vs ≥3) controls the polymer architectu …

• Confusing 'functionality' with 'molecular functional group name' rather than the count of reactive sites.
• Forgetting to link functionality to the resulting polymer shape (linear vs network). …