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Macromolecular architecture is a critical parameter when tuning polymer material properties. Although the implementation of non-linear polymers in different applications has grown over the years, polymer grafted surfaces such as nanoparticles have traditionally been composed of linear thermoplastic polymers, with a limited number of examples demonstrating a diversity in polymer architectures. In an effort to combine polymer architecturally dependent material properties with polymer grafted particles (PGPs), as opposed to conventional methods of tuning polymer grafting parameters such as the number of chains per surface area (i.e., polymer graft density), a series of bottlebrush grafted particles were synthesized using surface-initiated ring-opening metathesis polymerization (SI-ROMP). These bottlebrush PGPs are composed of glassy, semi-crystalline, and elastomeric polymer side chains with controlled backbone degrees of polymerization (Nbb) at relatively constant polymer graft density on the surface of silica particles with diameters equaling approximately 160 or 77 nm. Bottlebrush polymer chain conformations, evaluated by measuring the brush height of surface grafted polymer chains in solution and the melt, undergo drastic changes in macromolecular dimensions in different environments. In solution, brush heights increase linearly as a function of Nbb, consistent with fully stretched chains, which is confirmed using cryogenic transmission electron microscopy (Cryo-TEM). Meanwhile, brush heights are consistently at a minimum in the melt, indicative of chains collapsed on the particle surface. The conformational extremes for grafted bottlebrush polymers are unseen in any linear polymer chain systems, highlighting the effect of macromolecular architecture and surface grafting. Bottlebrush grafted particles are an exciting class of materials where diversifying polymer architectures will expand PGP material design rules that harness macromolecular architecture to dictate properties.
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This content will become publicly available on March 27, 2026
Redox-Active Polymer-Grafted Particles as Redox Mediators for Enhanced Charge Transport in Solution-State Electrochemical Systems
Efficient charge transport pathways in solutions of redox-active polymers are essential for advancing nextgeneration energy storage systems. Herein, we report the grafting of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) and poly(2,2,6,6-tetramethyl-1-piperidinyloxy-4-yl methacrylate) (PTMA) polymer brushes onto silica particles with different molecular weights and grafting densities, and the impact of these composite particles in solutions of PTMA. The polymer-grafted particles are characterized using Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and dynamic light scattering (DLS) techniques. The grafted polymers have molecular weights of 2.5 kDa and 5.0 kDa, with corresponding grafting densities of 0.688 and 0.378 chains nm−2 for SiO2-PTMA-2.5k and SiO2-PTMA-5k, respectively, with the grafting density decreasing with increasing graft length. To investigate the effect of these composite particles on charge transport in solutions of PTMA, different concentrations of the grafted particles were added to solutions of PTMA of different concentrations (near overlap concentration, C*) in 0.1 M LiTFSI in acetonitrile. Electrochemical analysis reveals that below C* the addition of SiO2-PTMA-5k increases the apparent diffusion coefficient (Dapp) 15.2% to 1.041 × 10−6 cm2 s−1 , the exchange rate constant (kex,app) by 9.5% to 1.546 × 1011 L mol−1 s−1, and the heterogeneous electron transfer rate constant (k0) by 24.6%, to 5.526 × 10−4 cm s−1. These results indicate that the synergistic interactions between unbound PTMA polymer chains in solution and PTMA-grafted particles facilitate interchain charge transfer kinetics. This highlights that grafted redoxactive particles can enhance charge transport without the limitations of polymer-only solutions (e.g., chain entanglement) and presents a promising design strategy for high-performance electrochemical applications, such as redox flow batteries (RFBs).
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- Award ID(s):
- 2104179
- PAR ID:
- 10582550
- Publisher / Repository:
- Royal Society of Chemistry
- Date Published:
- Journal Name:
- Chemical science
- ISSN:
- 2041-6520
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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