A team from the Johnson lab use ring-opening metathesis polymerization to synthesize terpolymers of (1) a “functional” monomer (e.g., a polyethylene glycol macromonomer or dicyclopentadiene); (2) a monomer containing an electrophilic pentafluorophenyl (PFP) substituent; and (3) a cleavable monomer based on a bifunctional silyl ether. This method is shown to be effective for deconstruction of polyethylene glycol (PEG) based graft terpolymers in organic or aqueous conditions as well as polydicyclopentadiene (pDCPD) thermosets, significantly expanding upon the versatility of bifunctional silyl ether based functional polymers. Article Link

A team from the Klausen, Kulik, and Craig labs report the preparation of a new class of oligosilane dienes and their acyclic diene metathesis (ADMET) polymers. Their data suggest that substitution of carbon with silicon in linear polymers will have a substantial effect on the mechanical properties of materials, and motivates the design of polymer networks with heavier carbon analogues that will be future synthetic targets.  Article Link

A team from the Olvera de la Cruz and Kalow labs combined coarse-grained molecular dynamics simulations with a Monte Carlo method to investigate the topological structural changes, microscopic dynamics, and linear rheology of unentangled side-chain-linked vitrimers in conjunction with the sticky Rouse model (SRM). The results indicated that the linear rheology of unentangled vitrimers with a fast bond-exchange rate can be analyzed via a single-chain approach based on the SRM. Article Link

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

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