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1. Metal‐Free Ring‐Opening Metathesis Polymerization with Hydrazonium Initiators**

   https://doi.org/10.1002/anie.202203344  

   Quach, Phong K; Hsu, Jesse H; Keresztes, Ivan; Fors, Brett P; Lambert, Tristan H (June 2022, Angewandte Chemie International Edition)

   Abstract The ring‐opening metathesis polymerization (ROMP) of cyclopropenes using hydrazonium initiators is described. The initiators, which are formed by the condensation of 2,3‐diazabicyclo[2.2.2]octane and an aldehyde, polymerize cyclopropene monomers by a sequence of [3+2] cycloaddition and cycloreversion reactions. This process generates short chain polyolefins (M_n≤9.4 kg mol⁻¹) with relatively low dispersities (Đ≤1.4). The optimized conditions showed efficiency comparable to that achieved with Grubbs’ 2^ndgeneration catalyst for the polymerization of 3‐methyl‐3‐phenylcyclopropene. A positive correlation between monomer to initiator ratio and degree of polymerization was revealed through NMR spectroscopy. 

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2. A bioinspired and degradable riboflavin-containing polypeptide as a sustainable material for energy storage

   https://doi.org/10.1073/pnas.2509325122  

   Li, Shih-Guo; Mohanty, Khirabdhi T; Easley, Alexandra D; Rezenom, Yohannes H; Lim, Soon-Mi; Gillett, Leyla P; Naquin, Stone D; Tran, David K; Nguyen, Tan P; Lutkenhaus, Jodie L; et al (July 2025, Proceedings of the National Academy of Sciences)

   Inspired by Nature, we present a polypeptide-based organic redox-active material constructed from renewable feedstocks, L-glutamic acid (an amino acid) and riboflavin (vitamin B₂), to address challenges with start-to-end-of-life management in energy storage systems (ESSs). The amino acid was utilized to establish a degradable polymer backbone, along which many copies of riboflavin were incorporated to serve as the redox-active pendant groups that enabled energy storage. The overall synthesis involved the ring-opening polymerization (ROP) of anl-glutamic acid-derivedN-carboxyanhydride (NCA) monomer, followed by side chain activation with azides and, finally, click coupling to achieve installation of alkyne-functionalized riboflavin moieties. The steric bulkiness and rich chemical functionality of riboflavin resulted in synthetic complexities that required reaction optimization to achieve the desired polymer structure. Electrochemical characterization of the resultant riboflavin polypeptide, in organic electrolyte, showed quasireversible redox activity with a half-wave potential (E_1/2) ofca.−1.10 Vvs.ferrocene/ferrocenium (Fc/Fc⁺). Cell viability assays revealed biocompatibility, as indicated by negligible cytotoxicity for fibroblast cells. The polypeptide design, consisting of labile amide backbone linkages and side-chain ester functionalities that tethered the riboflavin units to the backbone, enabled hydrolytic degradation to recover building blocks for future upcycling or recycling. This bioinspired strategy advances the development of degradable redox-active polymers and promotes sustainable materials design for circular energy storage technologies. 

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3. Selective electrochemical degradation of bottlebrush elastomers

   https://doi.org/10.1002/pol.20240393  

   Albanese, Kaitlin R; Morris, Parker T; Roehrich, Brian; Read_de_Alaniz, Javier; Hawker, Craig J; Bates, Christopher M (July 2024, Journal of Polymer Science)

   <sc>A</sc>bstract We introduce a simple synthetic strategy to selectively degrade bottlebrush networks derived from well‐defined poly(4‐methylcaprolactone) (P4MCL) bottlebrush polymers. Functionalization of the hydroxyl groups present at the terminal ends of P4MCL side chains withα‐lipoic acid resulted in bottlebrush polymers having a range of molecular weights (M_n = 45–2200 kg mol⁻¹) and a tunable number of reactive dithiolane chain ends. These functionalized chain ends act as efficient crosslinkers due to radical ring‐opening of the dithiolane rings under UV light. The resulting redox‐active disulfide crosslinks enable mild electrochemical or chemical degradation of the SS crosslinks to regenerate the starting bottlebrush polymer. P4MCL side chains and the disulfides can be degraded simultaneously using harsher reducing conditions. This combination of bottlebrush architecture with facile disulfide crosslinking presents a versatile platform for preparing highly tunable elastomers that undergo controlled degradation under mild conditions. 

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4. Ultra‐High Molecular Weight Polydimethylsiloxane Bottlebrushes From Norbornene‐Pyrrolidine Capped Macromonomers

   https://doi.org/10.1002/pol.20250521  

   Cater, Henry L; Liu, Yutong; Page, Zachariah A (September 2025, Journal of Polymer Science)

   ABSTRACT Bottlebrush (BB) polymers with polydimethylsiloxane (PDMS) side‐chains exhibit supersoft moduli (E < 100 kPa) without solvent, making them promising tissue‐mimetic materials for biomedical applications. While larger backbones and side‐chains enhance softness, synthetic limitations have constrained their molecular weight. We report a graft‐through method to access ultra‐high molecular weight PDMS BB polymers (~1–20 million g mol⁻¹). Central to this was the design of a norbornene‐pyrrolidine aryllithium initiator for the anionic ring‐opening of hexamethylcyclotrisiloxane (D3), yielding monofunctionalized PDMS macromonomers (MMs) with molecular weights from 1–30 kg mol⁻¹. Subsequent ring‐opening metathesis polymerization (ROMP) produced BB homopolymers within minutes (t ≤ 5 min) and with low dispersity (Đ < 1.3). The ‐C‐Si‐O‐ linkage between the backbone and side‐chains provided improved chemical stability over earlier ‐C‐O‐Si‐ analogues. These MMs were also used to create a linear‐bottlebrush‐linear block copolymer, forming a supersoft (E = 79 kPa), thermoplastic elastomer with excellent elastic recovery (~96%). This platform enables the synthesis of ultra‐high molecular weight graft (co‐)polymers, advancing the study of extreme structure–property relationships and supporting the development of novel soft materials for bio‐interfacing. 

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5. Highly Conductive Polyoxanorbornene‐Based Polymer Electrolyte for Lithium‐Metal Batteries

   https://doi.org/10.1002/advs.202302932  

   An, So Young; Wu, Xinsheng; Zhao, Yuqi; Liu, Tong; Yin, Rongguan; Ahn, Jung Hyun; Walker, Lynn M.; Whitacre, Jay F.; Matyjaszewski, Krzysztof (September 2023, Advanced Science)

   Abstract This present study illustrates the synthesis and preparation of polyoxanorbornene‐based bottlebrush polymers with poly(ethylene oxide) (PEO) side chains by ring‐opening metathesis polymerization for solid polymer electrolytes (SPE). In addition to the conductive PEO side chains, the polyoxanorbornene backbones may act as another ion conductor to further promote Li‐ion movement within the SPE matrix. These results suggest that these bottlebrush polymer electrolytes provide impressively high ionic conductivity of 7.12 × 10⁻⁴S cm⁻¹at room temperature and excellent electrochemical performance, including high‐rate capabilities and cycling stability when paired with a Li metal anode and a LiFePO₄cathode. The new design paradigm, which has dual ionic conductive pathways, provides an unexplored avenue for inventing new SPEs and emphasizes the importance of molecular engineering to develop highly stable and conductive polymer electrolytes for lithium‐metal batteries (LMB). 

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