Stereoselective polymerization of functional β-lactones: PolyHydroxyAlcanoates (PHAs) with controlled architecture
Keywords: ring-opening polymerization, sequence-controlled polyester, stereoselectivity, catalytic engineering, rare-earth catalysts
Ring-opening polymerization (ROP) of β-lactones affords synthetic polyhydroxyalkanoates (PHAs) that are promising alternatives to current fossil-based plastics. Our group has a longstanding experience in the ROP of functional chiral β-lactones mediated by stereoselective catalytic systems. In particular, our yttrium complexes stabilized by dianionic tripodal bisphenolate ligands are highly active for the controlled ROP of such rac-β-lactones under mild conditions. Tuning the steric and –more rewardingly- electronic effects of the substituents of their phenolates ligand enables to modify at will the tacticity of the resulting PHAs from iso- to syndio-enriched, according to a « chain-end » mechanism, and to provide functional stereoregular PHAs with enhanced thermo-mechanical properties. Furthermore, syndioselective catalytic systems provide perfectly alternated coPHAs from mixtures of comonomers of a same chemical type but of opposite configuration. Such sequence-controlled polyesters featuring the precise enchainment of the comonomers are prone to various applications (e.g. encoding).
Functional polymer materials
Keywords: ring-opening metathesis polymerization (ROMP), non-isocyanate polyurethane (NIPU), polyhydroxyurethane (PHU), polysiloxanes, catalytic engineering.
Polyurethanes (PUs) are currently industrially prepared from the polyaddition of diols with toxic diisocyanates. Current efforts towards the design of non-isocyanate PUs (NIPUs) mainly rely on the polyaddition of a 5-membered cyclic biscarbonate and a diamine, thereby affording polyhydroxyurethanes (PHUs). We have been developing α,ω-telechelic functional polyolefins, prepared by the tandem ring-opening metathesis (ROMP) / cross-metathesis (CM) polymerization of cyclic olefins, performed in the presence of a difunctionnal (FG = functional group = 5CC, 5-membered dithiocarbonate, azalactone, epoxide, oxetane, trialkoxysilyl) alkene chain transfer agent (CTA). Further polyaddition of such α,ω-difunctional polymers with di- or polyamines affords original NIPUs/PHUs. In particular, hydrolysis of α,ω-bis(trialkoxysilyl)telechelic polymers provide a 3-D network with valuable adhesives properties .
Molecular Alkalyne-Earth Complexes for Homogeneous Catalysis
Keywords: alkaline-earth metals, homogeneous catalysis, hydroelementation, dehydrocoupling.
The synthetic molecular chemistry of the large alkaline earths (Ae = Ca, Sr and Ba) is booming. It is now established that the reactivity of these earth-abundant metals is different from that of their lighter magnesium analogue. Many examples now exist in the recent literature of catalytic processes using low Ae catalyst loadings and mild conditions. Beyond the design of original architectures constructed around these metals, we have shown that stable, well-defined complexes of the large alkaline earths act as competent homogeneous catalysts for a broad range of atom-efficient catalysed reactions. For instance, they allow for the chemoselective creation of C–N (amines) and C–P (phosphines) bonds through the controlled hydroamination and hydrophosphination of alkenes. We have also implemented them to create bonds between heteroelements (Si, N, O, etc.) in the dehydrogenative couplings of mono/poly-amines with hydrosilanes, boranes, borinic acids etc. These green processes that release little or no by-products are optimized to generate highly valuable molecular products or polymer materials.