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

Danyang Chen has successfully defended his thesis, "Elasticity and Fracture of Polymer Networks with Entanglements and Weak Crosslinkers". Congratulations Dr. Chen!

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

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

A team from the Schindler and Kulik labs report a visible-light-mediated approach that enables facile access to 1- and 2-azetine-based dimeric lactones of up to 30-membered ring macrocycles. This transformation occurs in one step and deviates from traditional macrolactonization methods. This new method may provide a unique avenue to access biologically interesting synthetic macrocycles. Article Link

A team from the Craig, Kulik, and Johnson labs report the mechanochemically coupled generation of hydrogen flouride (HF) from alkoxy-gem-difluorocyclopropane (gDFC) mechanophores derived from difluorocarbene addition to enol ethers. This latent source of HF resides within a polymer until released in response to a mechanical signal, at which point it be converted in situ to a flouride salt for use in self-immolative polymers, remodeled siloxane elastomers, vitrimer alteration, and degradable polymers. Article Link