Search this site

A team from the Johnson, Craig, and Kulik labs introduce a new class of polymer metal–organic cage (polyMOC) gels featuring polyethylene glycol (PEG) strands of varied length cross-linked through bis-pyridyl-carbazole-based M6L12 cubes, where M is Pd(II), Pt(II), or mixtures thereof. The work introduces a novel MOC architecture for polyMOC design, shows that polyMOCs can be prepared from mixtures of Pd(II)/Pt(II), and demonstrates that polyMOCs display unique relaxation behavior due to their multivalent junctions, offering a strategy for controlling polyMOC properties independently of their polymer components. Article Link

A team from the Craig and Kulik groups crosslinked polybutadiene backbone polymers by complexation with two different metal salts. Though dynamic mechanical analysis (DMA) and small-angle X-ray scattering (SAXS) indicate that the crosslinking density and topology of the two materials are the same, the material crosslinked with copper ions exhibits a higher extensibility and fracture energy than the polymer crosslinked with iron. Article Link

The Johnson lab reports bifunctional silyl ether (BSE)-containing high-density polyethylene (HDPE)-like materials synthesized through a one-pot catalytic ring-opening metathesis polymerization (ROMP) and hydrogenation sequence. The crystallinity of these materials can be adjusted by varying the BSE concentration or the steric bulk of the Si-substituents, providing handles to control thermomechanical properties. Article Link

A team from the Olsen lab measured the gel point of an end-linked poly(ethylene glycol) gel during forward (bond forming) and reverse (bond breaking) gelation and degelation processes to interrogate how the gel point scales with synthesis concentration, where decreased concentration leads to an increased prevalence of inelastic loops. The experiments and simulations show that forward and reverse gel points diverge as the gel system becomes more dilute, suggesting that kinetic effects cause a departure from the percolation behavior in defect-rich gels. Article Link

A team from the Olsen lab updated a kinetic graph theory (KGT) model to account for off-stoichiometric reactive groups and side reactions by adding two fitting parameters representing the relative rate of competing side reactions and the probability of side cross-linking events. This model is useful in systems where the cross-linking chemistry yields more complex reaction networks, making it relevant to many classes of polymer network chemistry where classical theories may not adequately capture network behavior. Article Link

A team from the Olsen, Rubinstein, and Craig labs explore the question of reactivity-guided fracture in otherwise indistinguishable end-linked networks by tuning the relative composition of strands with two different mechanochemical reactivities. Increasing the substitution of less mechanochemically reactive (“strong”) strands into a network comprising more reactive (“weak”) strands has a negligible impact on the fracture energy until the strong strand content reaches approximately 45%, at which point the fracture energy sharply increases with strong strand content. Coarse-grained fracture simulations agree closely with the tearing energy trend observed experimentally, confirming that weak strand scissions dominate the failure until the strong strands approach percolation. Article Link

Professors Alshakim Nelson and Stephen Craig write the "Stimuli-responsive materials" section for the 2023 Soft Matter Roadmap. 'Stimuli-responsive' refers to materials that undergo a meaningful change in properties (the response) when subjected to a change in external environment (the stimulus). They discuss how various forms of energy and the introduction or removal of matter can in be coupled to an ever-increasing range of responses. Article Link

A team from the Steinmetz and Craig labs built an internal polymer “backbone” using a maleimide cross-linker to covalently interlink viral coat proteins inside the capsid cavity, while the native VLPs are held together by only noncovalent bonding between subunits. Endoskeleton-armored VLPs exhibited significantly improved thermal stability, increased resistance to denaturants, and enhanced mechanical performance. Article Link

The Kalow lab, in collaboration with the Air Force Research Laboratory, synthesized two oligosiloxane-based epoxy networks that provide fast dynamic bond exchange. The resulting polymer networks provided access to fast stress-relaxation times (1–10 min) at temperatures of only 130 °C with excellent reprocessability. This work provides a framework to utilize epoxy acids and siloxanes for dynamic materials, and the low viscosity of the siloxane monomers may offer further advantages for composite manufacturing processes. Article Link

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 NSF Center for Chemical Innovation, NSF Center for Sustainable Polymers (CSP) in collaboration with Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO)

A team from the Nelson and Craig labs demonstrate 3D printed, elastomeric ionogels comprising covalent adaptable networks (CANs) for modular sensor assemblies. The modular components can be combined and assembled on-demand into customized piezoionic sensors. This study highlights the benefits of dynamic covalent networks toward decentralized manufacturing, wherein a modular approach enables customization of 3D printed parts without the need for modifying the original design. Article Link

Shu Wang, former Craig & Rubinstein graduate student (and founding member of NSF 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!