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Organocatalyzed ring-opening polymerization (O-ROP) of a six-five bicyclic lactone, 4,5- trans -cyclohexyl-fused γ-butyrolactone (4,5-T6GBL), can be topologically selective or living at room temperature, depending on catalyst structure. A screening of (thio)urea [(T)U] and organic base pairs revealed unique trends in reactivity for this monomer as well as the most active catalyst pairs, which were employed as received commercially to produce relatively high molecular weight ( M n up to 106 kDa), low dispersity ( Đ = 1.04) linear poly(4,5-T6GBL) in a living fashion. The ROP using a hybrid organic/inorganic pair of TU/KOMe in neat conditions led to poly(4,5-T6GBL) with even higher molecular weight ( M n = 215 kDa, Đ = 1.04). In comparison to the metal-catalyzed system, (T)U-base pairs exhibited competitive kinetics and reached higher monomer conversions, and their reactions can be performed in air. In addition, the resulting polymers required less purification to produce materials with higher onset decomposition temperature. (T)U-base pairs were selective towards linear polymerization only, whereas triazabicyclodecene can catalyze both polymerization and (quantitative) depolymerization processes, depending on reaction conditions. Cyclic polymers with M n = 41–72 kDa were selectively formed via N-heterocyclic carbene-mediated zwitterionic O-ROP. 

Abstract 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‐NMe₂sidearm. The latter catalyst produces an isotactic stereoblock polymer (P_mup to 0.95) that forms the crystalline sc‐material with aT_mof 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. 

Abstract The development of chemically recyclable polymers promises a closed‐loop approach towards a circular plastic economy but still faces challenges in structure/property diversity and depolymerization selectivity. Here we report the first successful coordination ring‐opening polymerization of 4,5‐trans‐cyclohexyl‐fused γ‐butyrolactone (M1) with lanthanide catalysts at room temperature, producing P(M1) withM_nup to 89 kg mol⁻¹, high thermal stability, and a linear or cyclic topology. The same catalyst also catalyses selective depolymerization of P(M1) back toM1exclusively at 120 °C. This coordination polymerization is also living, enabling the synthesis of well‐defined block copolymer.