Ring-opening polymerizations and copolymerizations of epoxides using aluminum- and boron-centered catalysts

This review provides an overview of ring-opening polymerization (ROP) and copolymerization (ROCOP) reactions of epoxides catalysed by aluminum- and boron-containing compounds. We also highlight some recent examples based on the heavier group 13 elements, gallium and indium. ROP of epoxides yields polyethers whereas ROCOP of epoxides with CO2 yields polycarbonates (or polycarbonate-ethers). More recently, copolymerizations of epoxides with cyclic anhydrides have been performed to yield polyesters or gradient polyester-ether copolymers. Controlled reactions, yielding polymers with narrow dispersities, can be performed using neutral, cationic, bifunctional and bimetallic aluminum complexes. In some cases, co-catalysts (e.g. added nucleophiles) are needed to enhance reactivity and chain transfer agents can be used to control molecular weights and end-groups of polymers. More recently, trialkyl- and triarylboranes have been used as catalysts in these reactions. Given the variety of polymers that can be obtained via controlled ROP of epoxides in the presence or absence of co-monomers, it is expected that new discoveries using group 13 compounds as catalysts will continue in the foreseeable future.