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1. Living Coordination Polymerization of a Six‐Five Bicyclic Lactone to Produce Completely Recyclable Polyester

   https://doi.org/10.1002/anie.201808003  

   Zhu, Jian‐Bo; Chen, Eugene Y. ‐X. (August 2018, Angewandte Chemie International Edition)

   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. 

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2. Telechelic all-cis polycyclooctene via catalytic stereoretentive ROMP for the synthesis of polylactide-based ABA triblock copolymers

   https://doi.org/10.1039/D5FD00067J  

   Nicholson, Jake Lee; Gravet, Antoine Clément; Michaudel, Quentin (May 2025, Faraday Discussions)

   Polylactide (PLA) is a commercial and sustainably sourced aliphatic polyester but its applications have been limited by its low toughness. The insertion of a rubbery segment within the PLA backbone is among the promising strategies to enhance the mechanical properties of PLA while retaining sustainability. Herein, we disclose a catalytic stereoretentive ring-opening metathesis polymerization process to access high molar mass (Mnexp up to 127.9 kg/mol) all-cis telechelic polycyclooctene (PCOE) at low catalyst loadings. The use of cis-1,4-diacetoxy-2-butene as a chain-transfer agent in the presence of stereoretentive dithiolate Ru carbenes afforded precise control over the cis content, the molar mass, and the introduction of acetoxy chain ends. Subsequent hydrolysis of the acetoxy motifs followed by chain extension via ring-opening polymerization of D,L-lactide yielded high molar mass (Mnexp up to 105.0 kg/mol) all-cis PLA ABA triblock copolymers. The influence of the molar mass of the all-cis PCOE over the thermal and mechanical properties of the ABA triblock was investigated. 

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3. Cascade Ring Strain Release Polymerization of Cyclohexene Oxide and Derivatives Using a Mono(μ-Alkoxo)bis(alkylaluminum) Initiator

   https://doi.org/10.1021/acs.macromol.3c00473  

   Pedretti, Benjamin J.; Zhu, Congzhi; Watanabe, Hironobu; Aoshima, Sadahito; Lynd, Nathaniel A. (July 2023, Macromolecules)

   Cyclohexene oxide (CHO) is a useful building block for the synthesis of novel materials and is a model substrate for polymerization catalyst development. The driving force for CHO polymerization is derived from its bicyclic structure, which combines the release of the enthalpy from epoxide ring-opening (ca. −15 kcal/mol) and a twist-chair-to-chair conformation shift in the cyclohexane ring (ca. −5 kcal/mol) upon enchainment. The lack of regio-defined functional handles attached to the CHO monomer limits the ability to both pre- and post-functionalize the resultant materials and establish structure–property relationships, which reduces the versatility of currently accessible materials. We report the synthesis of two series of CHO derivatives with butyl, allyl, and halogen substituents in the α and β positions relative to the epoxide ring. Adding substituents to the CHO ring was found to affect polymerization kinetics, with 4-substituted (β) CHO being more reactive than 3-substituted (α) CHO analogs when initiated with a mono(μ-alkoxo)bis(alkylaluminum) pre-catalyst. Polymer thermal properties depended on substituent location and identity. Halogenated CHO rings were most reactive and produced the highest glass transition temperatures in the resultant polymers (up to 105 °C). Density functional theory revealed a possible mechanistic explanation consistent with the observed differences in polymerization rate for the 3- and 4-substituted CHOs derived from a combination of steric and thermodynamic considerations. 

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4. Catalyst-controlled stereoselective cationic polymerization of vinyl ethers

   https://doi.org/10.1126/science.aaw1703  

   Teator, A. J.; Leibfarth, F. A. (March 2019, Science)

   The tacticity of vinyl polymers has a profound effect on their physical properties. Despite the well-developed stereoselective methods for the polymerization of propylene and other nonpolar α-olefins, stereoselective polymerization of polar vinyl monomers has proven more challenging. We have designed chiral counterions that systematically bias the reactivity and chain-end stereochemical environment during cationic polymerization. This approach overrides conventional chain-end stereochemical bias to achieve catalyst-controlled stereoselective polymerization. We demonstrate that this method is general to vinyl ether substrates, providing access to a range of isotactic poly(vinyl ether)s with high degrees of isotacticity. The obtained materials display the tensile properties of commercial polyolefins but adhere more strongly to polar substrates by an order of magnitude, indicating their promise for next-generation engineering applications. 

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5. Cationic Bottlebrush Polymers from Quaternary Ammonium Macromonomers by Grafting‐Through Ring‐Opening Metathesis Polymerization

   https://doi.org/10.1002/macp.201900476  

   Senkum, Hathaithep; Gramlich, William M. (February 2020, Macromolecular Chemistry and Physics)

   Abstract Cationic bottlebrush homopolymers are polymerized using a grafting‐through approach by ring‐opening metathesis polymerization (ROMP) to afford well‐defined polymers. Quaternary ammonium macromonomers (MMs) are prepared by quaternizing tertiary amine MMs synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization. The quaternary ammonium MMs undergo ROMP to target molecular weights (M_n= 30 000–100 000 g mol⁻¹) and a low dispersity (Đ= 1.10–1.30). Halide‐ligand exchange between the third generation Grubbs catalyst (G3) and halide counter ions (bromide and iodide ions) of MMs changes the catalyst activity throughout ROMP, causing it to deviate from pseudo‐first order kinetic behavior; however, the polymerization still follows controlled behavior without significant catalyst termination. Increasing steric bulk of the MMs decreases the polymerization rate as well. Amphiphilic block copolymers are synthesized by sequential polymerization of quaternary ammonium MMs and polystyrene (PS) MMs. Using a PS macroinitiator affords block copolymers with lowerĐvalues as compared to the less active cationic macroinitiator. 

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