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1. Diffusion of Bottlebrush Polymer-Grafted Nanoparticles: The Role of Matrix Molecular Weight

   https://doi.org/10.1021/acs.macromol.5c02957  

   Indeglia, Benjamin N; Sevening, Jensen N; Hickey, Robert J; Winey, Karen I (January 2026, Macromolecules)

   Nanoparticle diffusion in a polymer matrix is known to be sensitive to the surface chemistry and size of the nanoparticles, and this study explores the effect of grafted polymers on the nanoparticles. We report the diffusion coefficients of nanoparticles grafted with bottlebrush polymers in melts of linear polymers. These bottlebrush polymer-grafted nanoparticles (PGNs) are comprised of large silica NPs (radius 80 nm) grafted with various backbone degrees of polymerization and fixed polystyrene side chains (4.2 kDa) to give bottlebrush molecular weights of 80–388 kDa. The polymer matrix is polystyrene (100 or 425 kDa), and nanoparticle diffusion was studied at 170 °C. After annealing a trilayer sample, time-of-flight secondary ion mass spectrometry (ToF-SIMS) measured the cross-sectional PGN concentration profiles and extracted diffusion coefficients. The PGNs with high bottlebrush molecular weights relative to the matrix polymer display core–shell diffusion behavior, wherein the shell thickness is comparable to the grafted bottlebrush thickness. Surprisingly, when the bottlebrush molecular weight is smaller than the matrix polymer, the PGNs diffuse 10–100 times faster than predicted, which we attribute to a local decrease in viscosity associated with disentanglement of the matrix polymer near the large nanoparticles. 

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2. Polymers on nanoparticles: structure & dynamics

   https://doi.org/10.1039/C8SM02110D  

   Hore, Michael J. (February 2019, Soft Matter)

   Grafting polymers to nanoparticle surfaces influences properties from the conformation of the polymer chains to the dispersion and assembly of nanoparticles within a polymeric material. Recently, a small body of work has begun to address the question of how grafting polymers to a nanoparticle surface impacts chain dynamics, and the resulting physical properties of a material. This Review discusses recent work that characterizes the structure and dynamics of polymers that are grafted to nanoparticles and opportunities for future research. Starting from the case of a single polymer chain attached to a nanoparticle core, this Review follows the structure of the chains as grafting density increases, and how this structure slows relaxation of polymer chains and affects macroscopic material properties. 

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3. A Generalized Machine-Learning Framework for Developing Alchemical Many-Body Interaction Models for Polymer-Grafted Nanoparticles

   https://doi.org/10.1021/acs.jctc.5c00901  

   Zhang, Melody Yiyuan; Lee, Shih-Kuang Alex; Glotzer, Sharon C; Lindsey, Rebecca K (October 2025, Journal of Chemical Theory and Computation)

   Polymer-grafted nanoparticles (PGNs) serve as highly customizable building blocks for technologically relevant self-assembled nanomaterials. Physics informed Inverse design strategies are crucial for expediting exploration of the massive associated design space by identifying optimal PGN attributes such as polymer length and grafting density to meet a target self-assembled structure. However, their success hinges on accurate description of how PGN interactions vary as a function of both particle positions and physical attributes. We introduce a framework to meet this need. Specifically, we develop an “alchemical” ML-IAM that describes how PGN interactions vary as a function of both inter-PGN distances and tunable PGN attributes, simultaneously. This model is an extension of the physics-informed and explicitly many-bodied ChIMES model. The resulting extended ChIMES (X-ChIMES) model is trained on PMF data for PGNs with varied polymer ligand length. We enable efficient training data generation by combining the forward-reverse steered molecular dynamics enhanced sampling approach with a grid-sampling scheme in the HOOMD-blue software package. We demonstrate the efficacy of ChIMES for generating CG models for PGNs with fixed design attributes, the development of the X-ChIMES model, and the application of the X-ChIMES model that enhances digital alchemy inverse-design simulations using HOOMD-blue and the ChIMES Calculator. This is the first application of ChIMES in modeling CG systems and coupling with an inverse design method to target nanomaterial self-assembly. 

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4. Role of Surface-Grafted Polymers on Mechanical Reinforcement of Metal–Organic Framework–Polymer Composites

   https://doi.org/10.1021/acsapm.3c01195  

   Yang, Xiaozhou; Hu, Yongtao; Bonnett, Brittany L; Blosch, Sarah E; Cornell, Hannah D; Gibbons, Bradley; Santos, Claudio Amaya; Ilic, Stefan; Morris, Amanda J (October 2023, ACS Applied Polymer Materials)

   Utilizing metal–organic frameworks (MOFs) as reinforcing fillers for polymer composites is a promising strategy because of the low density, high specific modulus, and tunable aspect ratio (AR). However, it has not been demonstrated for the MOF-reinforced polymer composite using MOFs with high AR and polymer-grafted surface, both of which are extremely important factors for efficient load transfer and favorable particle–matrix interaction. To this end, we designed an MOF–polymer composite system using high AR MOF PCN-222 as the mechanical reinforcer. Moreover, we developed a synthetic route to graft poly(methyl methacrylate) (PMMA) from the surface of PCN-222 through surface-initiated atomic transfer radical polymerization (SI-ATRP). The successful growth of PMMA on the surface of PCN-222 was confirmed via proton nuclear magnetic resonance and infrared spectroscopy. Through thermogravimetric analysis, the grafting density was found to be 0.18 chains/nm2. The grafted polymer molecular weight was controlled ranging from 50.3 to 158 kDa as suggested by size exclusion chromatography. Finally, we fabricated MOF–polymer composite films by the doctor-blading technique and measured the mechanical properties through the tension mode of dynamic mechanical analysis. We found that the mechanical properties of the composites were improved with increasing grafted PMMA molecular weight. The maximum reinforcement, a 114% increase in Young’s modulus at 0.5 wt % MOF loading in comparison to pristine PMMA films, was achieved when the grafted molecular weight was higher than the matrix molecular weight, which was in good agreement with previous literature. Moreover, our composite presents the highest reinforcement measured via Young’s modulus at low weight loading among MOF-reinforced polymer composites due to the high MOF AR and enhanced interface. Our approach offers great potential for lightweight mechanical reinforcement with high AR MOFs and a generalizable grafting-from strategy for porphyrin-based MOFs. 

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5. From Fully Stretched to Collapsed Chains: Bottlebrush Polymer Grafted Particles

   https://doi.org/10.1021/acs.macromol.4c00881  

   Sevening, Jensen N; Nupnar, Nehal; Adhikary, Soumyanil; Reifsnyder_Hickey, Danielle; Swulius, Matthew T; Koerner, Hilmar; Hore, Michael_J A; Hickey, Robert J (October 2024, Macromolecules)

   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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