When Monomers with at least two functional groups react to form a polymer and produce a byproduct, it is called polycondensation.
The polycondensation can work only properly if the byproduct is taken away continuously.
Otherwise a low polymerisation degree leads to an end of the polycondensation.
A polycondensate with a high molar mass can be produced only with a reaction conversion of more than 99 %.
Furthermore the quantity needs to fit the stoichiometric ratio of the reaction.