Understanding Alkali Cation-Assisted Ring-Opening Polymerization of Macrocyclic Carbonate: Kinetics and Thermodynamics

Control over polymerization thermodynamics and kinetics enables the generation of polymers with on-demand properties. This is exemplified by the ring-opening polymerization of tetraethylene glycol carbonate (4EGMC) using an alkali cation (M⁺)-based binary catalytic system at ambient temperature. By introducing a guanidine catalyst [(1,5,7-triazabicyclo[4.4.0]dec-5-ene), TBD], the alkali cation-assisted ring-opening polymerization of macrocyclic carbonate was ca. 120-270 times faster than the reaction without an alkali cation, M⁺ (0.16-0.36 min^-1 with M⁺ vs 0.001 min^-1 without M⁺). Moreover, the interaction between 4EGMC and M⁺ led to an increase in the ring strain, supported by both bench experiments and computational simulations. This interaction altered the driving force of polymerization from the change of entropy to enthalpy, which revealed the pivotal role of alkali cations in regulating the ring-opening polymerization of macrocyclic carbonate.