Sn(OTf)₂ and Sc(OTf)₃: Efficient and versatile catalysts for the controlled polymerization of lactones

A general and novel method for the controlled synthesis of aliphatic poly-esters is presented. The evaluation of stannous (II) trifluoromethane sulfonate [Sn(OTf)2] and scandium (III) trifluoromethane sulfonate [Sc(OTf)3] as catalysts for the ring-opening polymerization (ROP) of various lactones is described as a route to polyesters under mild and highly selective polymerization conditions. Size exclusion chromatograms of poly(ε-caprolactone) initiated from ethanol in the presence of either Sn(OTf)2 or Sc(OTf)3 demonstrate the facile synthesis of narrowly dispersed products. Predictable molecular weights, typical of a living or controlled polymerization, were obtained with high yields. These catalysts are versatile and applicable toward the ROP of other cyclic (di)esters, including β-butyrolactone, which produces the synthetic analogue of the biopolymer poly(β-hydroxybutyrate).