DESIGNING CATIONIC ZINC AND MAGNESIUM CATALYSTS FOR COORDINATION–INSERTION POLYMERIZATION OF LACTIDE

Abstract

This review presents a synopsis of the development of cationic zinc and magnesium metal complexes as catalysts for the polymerization of lactones, with the major focus being directed toward the polymerization of lactide. By utilizing an electron-rich, neutral bis(phosphinimine) pincer ligand, cationic complexes with high ambient temperature activity for polymerization of lactide were obtained for the first time. A number of important structure–activity relationships have been established for this new class of catalyst. Recent progress toward P-stereogenic analogues of these cationic catalysts is also summarized.

Keywords:

• catalysis
• cation
• lactide polymerization
• magnesium
• zinc

ACKNOWLEDGMENTS

Numerous outstanding group members, both past and current, have contributed experimentally and intellectually to this work. P.G.H. acknowledges NSERC, GreenCentre Canada, and Canada School of Energy and Environment for funding this research. C.A.W. thanks NSERC and Alberta Ingenuity (Alberta Innovates) for financial support.

Notes

^a [LA]₀ = 0.25 M, C₆H₅Br solvent.

^b Calculated using M _n = [([LA]₀/[I]) × 144.13 × conversion] + 104.1.

^a Calculated based on the observed rate constant (k _obs = 0.00188 s⁻¹) measured under identical conditions, using the equation ln[LA] = –k _obs × t.

^b Calculated using M _n = [([LA]₀/[I]) × 144.13 × isolated yield].

^a Calculated using M _n = [([LA]₀/[I]) × 144.13 × conversion].