𝑓 𝑎 ̅ , 𝑓 𝑏 ̅ is number-average functionality of all reactant components A and B before the reaction, which can be calculated by the Carothers equation. As mentioned, the specific composition of the polymer mixture after reaction needs to be calculated. According to Flory-Stockmayer , , , theory, when the component A reacts to component B, one group of A will consume one group of B, resulting in a new component S. If the non-excessive component is consumed completely, the structure of component S will be as follows: