Metal Triflates as Highly Stable and Active Catalysts for the "Immortal" Ring-Opening Polymerization of Trimethylene Carbonate
Résumé
The controlled "immortal" ring-opening polymerization of trimethylene carbonate (TMC) using a two-component catalyst system based on a metal Lewis acid, such as a metal triflate M(OTf)n(M=Ca, Sc, Zn, Al, Bi; OTf=CF3SO3−) or the metallic salt Fe(acac)3, (acac=acetylacetonate) and an alcohol (ROH) as co-initiator and chain-transfer agent, is carried out in bulk at 110-150 °C. As a result of the water-tolerance of these systems, experimental operating conditions do not require any special care. The approach, valorized both with various ROH transfer agents and with either purified or unpurified monomer sources, is highly versatile. Functional telechelic polycarbonates H[BOND]PTMC[BOND]OR, devoid of decarboxylation sequences, are obtained [PTMC=poly(trimethylene carbonate)]. The molar mass of the PTMCs can be readily predicted by a simple model, taking into account the [TMC]0/[ROH]0 ratio and the amount of transferring impurities present in the raw/unpurified reagents. Such simple, air- and moisture-robust catalytic systems, which display quite high activities (TOF up to 28 200 h−1) and productivities (TON up to 45 000) are thus extremely valuable, especially industrially. The performances of these systems are described in comparison to the previously established valuable inorganic and organometallic catalytic systems, namely metal amido complexes ([M{N(SiMe3)2}3]) and [(BDI)Zn{N(SiMe3)2}] (BDI=β-diiminate ligand) derivatives.