What is the primary structural feature necessary for a molecule to make it useful in a condensation polymerization reaction ?

Explanation

Condensation polymerization involves a repititive condensation reaction between two bifunctional monomers. The reaction results in the loss of some simple molecule such s as water, alcohol, etc. in such a way that the product of reaction at each step is again a bifunctional compound. Hence, the sequence of condensation goes on resulting in the formation of polymer.