Borane-Mediated (Co)Polymerization of Oxygenated Monomers and Novel Applications Derived From
With the exception of poly(propylene oxide) (PPO) and poly(propylene carbonate) (PPC) that can be obtained using the same double metal cyanide catalyst (DMC), other polyethers and polycarbonates generally require specific catalysts, either alkali bases for polyethers and complex organometallic systems for polycarbonates.
Several organocatalysts have been specifically designed over the last twenty years for the polymerization of epoxides in an attempt to ditch metallic systems but they could never be successfully applied to the synthesis of polycarbonates.
In a recent addition we have shown that upon associating alkyl boron to various onium salts not only polyethers but also a whole range of polycarbonates resulting from the copolymerization of epoxides with carbon dioxide (CO2) can be synthesized with excellent catalytic activity. The role of boron centers is twofold: as a Lewis acid alkyl boron interacts with the anionic growing species, curbs their reactivity, forming an ate complex of moderate reactivity; boron also independently activates epoxides, enhancing their reactivity. As a result PPO could be generated free of any side reactions using such boron-based systems and PPC as well.
The presentation will actually discuss the potential, the activity, the respective advantages and limitations of two families of boron-based systems: the bicomponent family of boron-based systems associates alkyl boron with various onium salts; in the bifunctional family boron centers and anions responsible for the (co)polymerization initiation are included in a same molecule.
Besides epoxides and CO2, these systems were also found efficient at (co)polymerizing a whole range of oxygenated monomers, such as anhydrides, cyclic esters, isocyanates and aldehydes.