Controlled routes to prepare polyesters and polycarbonates are of interest due to the widespread application of these materials and the opportunities provided to prepare new copolymers. Furthermore, ring-opening copolymerization may enable new poly(ester-carbonate) materials to be prepared which are inaccessible using alternative polymerizations. This review highlights recent advances in the ring-opening copolymerization catalysis, using epoxides coupled with anhydrides or CO2, to produce polyesters and polycarbonates. In particular, the structures and performances of various homogeneous catalysts are presented for the epoxide-anhydride copolymerization. The properties of the resultant polyesters and polycarbonates are presented and future opportunities highlighted for developments of both the materials and catalysts.

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Homodinuclear catalysts have good precedent for epoxide and carbon dioxide/anhydride copolymerizations; in contrast, so far pure heterodinuclear catalysts are unknown. The synthesis and properties of a heterodinuclear Zn(II)/Mg(II) complex coordinated by a symmetrical macrocyclic ligand are reported. It shows high polymerization selectivity, control, and significantly greater activity compared to either of the homodinuclear analogues or any combinations of them. Indeed, compared to a 50:50 mixture of the homodinuclear complexes, it shows 5 times (CO2/epoxide) or 40 times (anhydride/epoxide) greater activity.

Two new homogeneous dinuclear catalysts for the ring-opening copolymerization of phthalic anhydride (PA)/cyclohexene oxide (CHO) and the terpolymerization of phthalic anhydride (PA)/cyclohexene oxide (CHO)/carbon dioxide (CO2) are reported. The catalysts are a di-magnesium (1) and a di-zinc complex (2), both are coordinated by the same macrocyclic ancillary ligand. Both catalysts show good polymerization control and activity (TOF = 97 (1) and 24 (2) h−1), with the di-magnesium complex (1) being approximately four times faster compared to the di-zinc (2) analogue. Their relative reactivity is closely related to that observed for well documented chromium salen/porphyrin catalysts. However, these results represent the first example of a well-defined magnesium catalyst which may be advantageous in terms of obviating use of co-catalysts, low cost, lack of colour and redox chemistry

This article summarizes and reviews recent progress in the development of catalysts for the ring-opening copolymerization of carbon dioxide and epoxides. The copolymerization is an interesting method to add value to carbon dioxide, including from waste sources, and to reduce pollution associated with commodity polymer manufacture. The selection of the catalyst is of critical importance to control the composition, properties and applications of the resultant polymers. This review highlights and exemplifies some key recent findings and hypotheses, in particular using examples drawn from our own research.