Catalyst-Sidearm-Induced Stereoselectivity Switching in Polymerization of a Racemic Lactone for Stereocomplexed Crystalline Polymer with a Circular Life Cycle.

Construction of robust, stereocomplexed (sc) crystalline material, based on a recently discovered infinitely recyclable polymer system, requires blending of enantiomeric polymer chains produced from respective enantiopure, fused six-five bicyclic lactones. Herein, the stereoselective polymerization of the racemic monomer by yttrium catalysts bearing tetradentate ligands is reported, where the tethered donor sidearm switches the heteroselectivity of the catalyst to isoselectivity when it is changed from the β-OMe to β-NMe2 sidearm. The latter catalyst produces an isotactic stereoblock polymer (Pm up to 0.95) that forms the crystalline sc-material with a Tm of up to 171 °C. This sc-material can be fully depolymerized back to rac-monomer in a quantitative yield and purity, thus establishing its circular life cycle.