Michael Rubinstein and collaborators at Duke, University of Hokkaido, and the Russian Academy of Sciences have developed a scaling theory of the elasticity of swollen and deswollen polymer networks.Article Link
Nicole Steinmetz and a team at University of California, San Diego formulated cowpea mosaic virus (CPMV) nanoparticles in injectable hydrogels to achieve slow particle release and prolonged immunostimulation, eliciting an antibody response that was sustained over 20 weeks in mouse models.Article Link
Some of the MONET team meet to explore Mission Bay and talk science before the ACS Spring Meeting 2022 in San Diego.
Mechanically Triggered Carbon Monoxide Release with Turn-On Aggregation-Induced Emission
Polymers that release functional small molecules under mechanical stress potentially serve as next-generation materials for catalysis, sensing, and mechanochemical dynamic therapy. To further expand the function of mechanoresponsive materials, the discovery of chemistries capable of small molecule release are highly desirable. In this report, a MONET team details a nonscissile bifunctional mechanophore (i.e., dual mechano-activated properties) based on a unique mechanochemical reaction involving norborn-2-en-7-one (NEO).
Yunyan Sun, William J. Neary, Zachary P. Burke, Hai Qian, Lingyang Zhu, and Jeffrey S. Moore
Toughening hydrogels through force-triggered chemical reactions that lengthen polymer strands
Longer and stronger; stiff but not brittle: Hydrogels are highly water-swollen, cross-linked polymers. Although they can be highly deformed, they tend to be weak, and methods to strengthen or toughen them tend to reduce stretchability. A new paper out of MONET now reports a strategy to create more durable hydrogels. Wang et al. introduce a toughening mechanism by storing releasable extra chain length in the stiff part of a double-network hydrogel. A high applied force triggers the opening of cyclic strands that are only activated at high chain extension.
Zi Wang, Xujun Zheng, Tetsu Ouchi, Tatiana Kouznetsova, Haley Beech, Sarah Av-Ron, Takahiro Matsuda, Brandon Bowser, Shu Wang, Jeremiah Johnson, Julia Kalow, Bradley Olsen, Jian Ping Gong, Michael Rubinstein, and Stephen Craig
Single-event Spectroscopy and Unravelling Kinetics of Covalent Domains Based on Cyclobutane Mechanophores
Mechanochemical reactions that lead to an increase in polymer contour length have the potential to serve as covalent synthetic mimics of the mechanical unfolding of noncovalent “stored length” domains in structural proteins. Here we report the force-dependent kinetics of stored length release in a family of covalent domain polymers based on cis-1,2-substituted cyclobutane mechanophores. The stored length is determined by the size (n) of a fused ring in an [n.2.0] bicyclic architecture, and it can be made sufficiently large (>3 nm per event) that individual unravelling events are resolved in both constant-velocity and constant-force single-molecule force spectroscopy (SMFS) experiments. Replacing a methylene in the pulling attachment with a phenyl group drops the force necessary to achieve rate constants of 1 s–1 from ca. 1970 pN (dialkyl handles) to 630 pN (diaryl handles), and the substituent effect is attributed to a combination of electronic stabilization and mechanical leverage effects. In contrast, the kinetics are negligibly perturbed by changes in the amount of stored length. The independent control of unravelling force and extension holds promise as a probe of molecular behavior in polymer networks and for optimizing the behaviors of materials made from covalent domain polymers.
B. H. Bowser, S. Wang, T. B. Kouznetsova, H. K. Beech, B. D. Olsen, M. Rubinstein, and S. L. Craig, J. Am. Chem. Soc., online access.
Molecular Characterization of Polymer Networks
Polymer networks are complex systems consisting of molecular components. Whereas the properties of the individual components are typically well understood by most chemists, translating that chemical insight into polymer networks themselves is limited by the statistical and poorly defined nature of network structures. As a result, it is challenging, if not currently impossible, to extrapolate from the molecular behavior of components to the full range of performance and properties of the entire polymer network. Polymer networks therefore present an unrealized, important, and interdisciplinary opportunity to exert molecular-level, chemical control on material macroscopic properties. A barrier to sophisticated molecular approaches to polymer networks is that the techniques for characterizing the molecular structure of networks are often unfamiliar to many scientists. Here, we present a critical overview of the current characterization techniques available to understand the relation between the molecular properties and the resulting performance and behavior of polymer networks, in the absence of added fillers. We highlight the methods available to characterize the chemistry and molecular-level properties of individual polymer strands and junctions, the gelation process by which strands form networks, the structure of the resulting network, and the dynamics and mechanics of the final material. The purpose is not to serve as a detailed manual for conducting these measurements but rather to unify the underlying principles, point out remaining challenges, and provide a concise overview by which chemists can plan characterization strategies that suit their research objectives. Because polymer networks cannot often be sufficiently characterized with a single method, strategic combinations of multiple techniques are typically required for their molecular characterization.
S. P. O. Danielsen, H. K. Beech, B. M. El-Zaatari, X. Wang, D. J. Lundberg, G. Stoychev, L. Sapir, S. Wang, Z. Wang, T. Ouchi, P. N. Johnson, Y. Hu, S. L. Craig, J. A. Kalow, J. A. Johnson, B. D. Olsen, and M. Rubinstein, Chem. Rev., 2021.
A collaborative effort from ten(!) MONET researchers has been selected to be featured in ACS Editors’ Choice, through which it is sponsored for immediate, open access by ACS due to its potential for broad public interest, an honor given to only one article from the entire ACS portfolio each day of the year.
PolyDAT: A Generic Data Schema for Polymer Characterization
Tzyy-Shyang Lin, Nathan J. Rebello, Haley K. Beech, Zi Wang, Bassil El-Zaatari, David J. Lundberg, Jeremiah A. Johnson, Julia A. Kalow, Stephen L. Craig, and Bradley D. Olsen
We know now what a molecular substituent effect on reactivity might feel like to the touch, thanks to this work by Shu, Haley, and colleagues! Read all about it in work just published in J. Am. Chem. Soc.
Mechanism Dictates Mechanics: A Molecular Substituent Effect in the Macroscopic Fracture of a Covalent Polymer Network
Shu Wang, Haley K. Beech, Brandon H. Bowser, Tatiana B. Kouznetsova, Bradley D. Olsen, Michael Rubinstein, and Stephen L. Craig
We’re so happy for Julia Kalow and Heather Kulik, recipients of 2021 Sloan Foundation Fellowships in Chemistry!