In the synthesis of a polyester through condensation polymerization, how would an increase in the molar ratio of diol to dicarboxylic acid affect the molecular weight of the resulting polymer and the byproducts formed during the reaction?

When the ratio of diol to dicarboxylic acid is increased, the acid becomes the limiting reagent, so the polymer chains can grow longer before an acid group stops further growth, raising the average molecular weight. Because fewer acid molecules are available, the number of condensation steps—and thus the amount of water released—is reduced, so the reaction produces less water per mole of polymer formed. The excess diol remains unreacted and can be recovered or may act as a chain‑terminating agent if it reacts with a terminal acid group, but it does not generate additional water. For example, a 2:1 diol‑to‑acid ratio will give a higher‑MW polyester and produce roughly half as much water as a 1:1 ratio, while leaving extra diol in the mixture. This explains why controlling the stoichiometry is key to tailoring polymer weight and byproduct output.