Block-StereoBlock Copolymers of Poly(ε-Caprolactone) and Poly(Lactic Acid)

The sequential addition of monomers to a living polymerization catalyst is a promising method of copolymerization of cyclic esters, which enables the preparation of precise microstructures with predetermined block constitution and length. A suitable catalyst should lack a termination step, and not favor side-reactions such as trans-esterification between polymer chains. We have recently introduced several families of magnesium catalysts that combine extremely high activity and living nature, thereby giving access to stereoblock copolymers of poly(lactic acid) of unprecedented microstructures.^1,2 In this presentation, we will describe a new variety of these catalysts, that is able to polymerize a broad scope of lactones, and in particular ε-caprolactone (εCL).³ This catalyst retains the extremely high activity in lactide (LA) polymerization, as well as with ε-caprolactone polymerization: with loadings below 0.01%, it can fully consume both monomers under immortal conditions within minutes, with trans-esterification side reactions reduced to minimum. The preparation of the novel block-stereoblock copolymers of εCL, L-LA and D-LA which feature high degrees of crystallinity and enhanced thermal properties due to stereocomplexes formation will be described. Employing different alcohols or poly-alcohols as initiators leads to diverse polymer architectures. These living magnesium catalysts show great potential in developing new and uncommon polymeric materials, which are difficult to attain by alternative approaches.

1. Rosen, T.; Goldberg, I.; Venditto, V.; Kol, M. J. Am. Chem. Soc. 2016, 138, 12041-12044.
2. Rosen, T.; Goldberg, I.; Navarra, V.; Venditto, V.; Kol, M. Chem. Sci. 2017, 8, 5476-5481.
3. Rosen, T.; Goldberg, I.; Navarra, V.; Venditto, V.; Kol, M. In preparation.