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.