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 Article Link

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 Free Full Article Link

Single-event Spectroscopy and Unravelling Kinetics of Covalent Domains Based on Cyclobutane Mechanophores Mechanochemical reactions that increase polymer contour length can 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 unraveling 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. Article Link

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. Article Link

Tuesday, February 16th, Dr. Darryl Boyd of the US Naval Research Laboratory will present in the Johnson Group Seminar Series, supported by MONET. This seminar is open to all. Attendees need to register here: https://mit.zoom.us/meeting/register/tJUrcu2rrjwjE9DT9aMu31t4vr5CiCaEBMw6 In 1907, the 1st synthetic polymer, Bakelite, was invented by Leo Baekeland. Since that time, synthetic polymers have become ubiquitous in the daily lives of billions of people around the globe due to their wide-ranging properties and utility. In recent years, polymers' environmental and biological dangers have been increasingly made known to both the scientific community and the general public. Despite the awareness of these dangers, the common slime demonstration has remained a staple for those seeking to introduce polymers in educational settings. In this talk, Dr. Boyd will discuss the current state of environmental polymer contamination and propose alternative ways to introduce polymers into STEM education.

Jeremiah Johnson and his team at MIT reports on a simple strategy to access functional MOF NPs in one pot, using a polyMOF ligand that possesses a polymer block for surface functionalization and a coordination block with tunable multivalency for size control. Yuwei Gu, Mingjun Huang, Wenxu Zhang, Matthew A Pearson, and Jeremiah A. Johnson PolyMOF nanoparticles: dual roles of a multivalent polyMOF ligand in size control and surface functionalization Article Link

Members of the MONET team at MIT offer a unifying review of polymer networks and showcase how a deep understanding of structure‐property relationships can lead to advanced networks with exceptional properties. Yuwei Gu, Julia Zhao, and Jeremiah A. Johnson A unifying review of polymer networks: from rubbers and gels to porous frameworks Article Li nk

Members of the MONET team at Duke have teamed up with the Russian Academy of Sciences to present a conceptual framework for adding molecular details of chain extension and force-coupled bond dissociation to the Lake–Thomas model of tear energy in rubbery crack propagation. Shu Wang, Sergey Panyukov, Michael Rubinstein, and Stephen L. Craig Quantitative Adjustment to the Molecular Energy Parameter in the Lake–Thomas Theory of Polymer Fracture Energy Article L ink

Shu Wang, former Craig & Rubinstein graduate student (and founding member of MONET) has received the Henkel Award for Outstanding Graduate Research in Polymer Science and Engineering. The award is given to recognize a graduate student or recent graduate who has completed an outstanding Ph.D. thesis in polymeric research. The award will be presented during at the American Chemical Society National Meeting in Denver, Colorado, August 21, 2024 in the ACS Division of Polymeric Materials Science and Engineering. Congratulations Shu!

Herb Wakefield and Ana Paula Kitos Vasconcelos were part of the Plastic in the Environment: Leaders and Innovators Collaborating from Australia, New Zealand, and United States (PELICANS) program. This was jointly hosted by our fellow Center for Chemical Innovation, NSF Center for Sustainable Polymers (CSP) in collaboration with Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO)

We officially welcome our newest institution to the Center today! Prof. Juana Mendenhall joins from Morehouse College at the start of Year 3. Welcome Juana!

Curt Waltmann has successfully defended his thesis, "Structure and Assembly of Macromolecular Compartments". Congratulations Dr. Waltmann!