Stereoselective polymerization of functional beta-lactones: PolyHydroxyAlcanoates (PHAs) with controlled architecture
Keywords: ring-opening polymerization, sequence-controlled polyester, stereoselectivity, catalytic engineering, rare-earth catalysts
Ring-opening polymerization (ROP) of b-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 b-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-b-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).