Analysis of the Competition between Cyclization and Linear Chain Growth in Kinetically Controlled A2 + B2 Step‐Growth Polymerizations Using Modeling Tools

A mathematical model for the kinetics and chain length development in A2 + B2 step‐growth polymerization with competition between cyclization and linear chain growth is presented. The model requires two kinetic rate constants, one for the several reactions producing linear polymer molecules (k), and another one for chain length dependent cyclization (kc). The model describes well the qualitative behavior of the system, including the effects of initial monomer concentration and ratio of limiting to excess functional groups on degree of cyclization. The model is validated using two polymerization systems, a conventional A2 + B2 polymerization of hexamethylene diisocyanate (HDI) and poly(ethylene glycol) (PEG200), as well as the superacid catalyzed polyhydroxyalkylation of modified isatin and biphenyl. Four different kinetic rate constants for the four reactions producing linear polymer molecules are required in the second case.