Invited
Block-stereoblock copolymers of poly(ε-caprolactone) and poly(lactic acid)

The stereoregularity of polymers has a major effect on their physical and chemical properties and consequently on their possible applications. Poly(lactic acid) (PLA) is a biodegradable polymer prepared by the catalyzed ring opening polymerization of lactide. Lactide has two stereogenic centers which typically do not epimerize during the polymerization. PLA of different stereoregularities may be formed by choice of the lactide stereoisomer(s) and choice of the catalyst. In addition, a living catalyst may enable the formation of stereoblock- and block-copolymers of PLA of precise microstructures by sequential monomer addition. A suitable catalyst should lack a termination step, and not favor side-reactions such as trans-esterification.

Recently we introduced several families of magnesium catalysts that combine extremely high activity and living nature, giving access to stereoblock-copolymers of poly(lactic acid) of unprecedented microstructures. More recently, we developed a catalyst that polymerizes both lactide and ε-caprolactone with very high activities. With loadings below 0.01%, it can fully consume both monomers under immortal conditions within minutes, enabling the preparation of the novel block-stereoblock copolymers of ε-caprolactone, L-lactide and D-lactide. Employing different alcohols or poly-alcohols as initiators leads to diverse polymer architectures. These living magnesium catalysts show great potential for developing new and uncommon polymeric materials, that exhibit desired thermal/mechanical properties, which are difficult to attain by alternative approaches.

1. T. Rosen, I. Goldberg, V. Venditto and M. Kol, J. Am. Chem. Soc., 2016,138, 12041–12044.
2. T. Rosen, I. Goldberg, W. Navarra, V. Venditto, and M. Kol, Chem. Sci., 2017,8, 5476–5481.
3. T. Rosen, I. Goldberg, W. Navarra, V. Venditto, and M. Kol, Angew. Chem. Int. Ed. 2018,57, 7191–7195.