Modeling of Living Cationic Ring-Opening Polymerization of Cyclic Ethers: Active Chain End versus Activated Monomer Mechanism

Living cationic ring-opening polymerization of cyclic ethers in the presence of diol was modeled using the method of moments. A widespread kinetic model was developed based on previous experimental studies. Then, the moment and population balance of reactants were obtained. Modeling results were employed to study the influence of initiator and water amounts (as the impurity) as well as feeding policy in polymerization kinetics and final properties of the polymer. In addition, the sensitivity of modeling results to initiation, backbiting, and finally propagation via activated monomer reactions were investigated. Results showed the population of chains is the function of their precursors. In a typical polymerization, chains with diol functionality are the majority. Therefore, most of the polymerized monomers are incorporated into those chains. This makes the chains with diol functionality the determining group in Molecular Weight Distribution (MWD). The kinetics of polymerization and properties of the reactor’s product are highly dependent on the ratio of the rate of propagation via the Activated Monomer (AM) mechanism to the rate of propagation via active chain end (ACE). An increase in this ratio decreases the probability of occurrence of backbiting reaction. Therefore, cyclic dimers are less formed and MWD narrows. On the other hand, decreasing this ratio results in less diol reacted with protonated monomers. Consequently, the rate of regeneration of the initiator and hence the rate of polymerization is decreased. These findings give complete facts about the ring-opening syntheses of polyethers and are valuable for evolving new grades as well as optimization current processes.

کلیدواژه ها:

Ring-opening ، kinetic model ، Cyclic ethers ، Molecular weight distribution (MWD) ، Method of moments