Understanding heterogeneous Zn-gallate catalyzed copolymerization of propylene oxide and CO2

We investigated the polymerization mechanism of a highly active heterogeneous Zn-gallate catalyst used for propylene oxide (PO) homopolymerization and PO/CO 2 copolymerization. The molecular weights of poly(propylene oxide) (PPO) and poly(propylene carbonate) (PPC) can be controlled by varying the ratio of chain transfer agents (CTAs) to PO. CTAs of varying acidity and structure provided insight into their interaction with catalytic sites. Theoretical calculations on a heterogeneous zinc hydroxide slab model for Zn-gallate revealed that polymerization is initiated by the reaction of PO with a hydroxyl group located within the zinc hydroxide lattice. Further energy barrier calculations and polymerizations at varying CO 2 pressures explained the kinetic preference for PPC formation over PPO at high CO 2 pressure.