Stereospecific carbene polymerization with oxygenated Rh(diene) species.

Polymers bearing polar functionalities are important materials, since they exhibit beneficial properties with respect to adhesion, paint/printability and surface properties. Commercial synthesis of these materials is mainly based on radical processes, which (so far) only allow poor control over the stereochemistry of the resulting polymers. 2 ] Stereo-controlled polymerisation generally requires (transition) metal catalysis. However, to the best of our knowledge there are no catalysts known that can polymerise 1,2-difunctionalized olefins such as fumarates or maleates, certainly not in a stereocontrolled manner (even controlled radical polymerisation of di-functionalized polar vinyl monomers is not trivial and an unsolved problem to date). Therefore, the synthesis of high molecular weight and stereoregular densely functionalized spcarbon chain (co)polymers containing a polar substituent at every carbon atom of the polymer backbone is currently restricted to the Rh-mediated carbene polymerisation techniques recently developed in our group (C1 polymerisation; see Scheme 1). 3 ] These (co)polymers reveal interesting and unexpected material properties, such as thermotropic and lyotropic liquid crystallinity, gel-formation, a broad thermal stability range, and a high storage modulus up to high temperatures. Such polymers are not accessible from (1,2-difunctionalised) olefins, and any future application of these new materials 5 ] therefore relies on increasing the efficiency of the carbene polymerisation reaction. The reaction mechanism of this intriguing carbene polymerisation reaction has been the subject of intensive investigations in our group, but the exact nature of the polymer forming Rh-species remained thus far elusive. Recently we discovered that partial oxidation of pre-catalyst 2 (Scheme 1) leads to markedly improved polymer yields and a higher amount of active Rh species, [ 6 ] but the underlying reason was poorly understood.