Abraham Herzog-Arbeitman

Conjugated polymers (CPs) are a class of semiconducting materials in which electrical conductivity and mechanical extensibility can coincide. Despite advances in synthesis and processing, these key properties are typically negatively correlated and derive from the semicrystalline microstructure of the polymer film. Here, we introduce a new strategy to improve the microstructure and mechanical properties of CPs through the introduction of bullvalene‐based fluxional comonomers, in which bonds rearrange constantly at ambient temperatures. By comparing bullvalene‐containing poly(diketopyrrolopyrrole‐thienothiophene) (p(DPP‐TT)) with static controls, we show that fluxional backbones resist thermal annealing induced crystallization, creating smaller crystallites even at low comonomer loadings (5 mol%). While comonomers produce minimal mechanical differences in low‐molecular weight CPs, when the network is reinforced through crosslinking, bullvalene strongly enhances stretchability, yielding a crack onset strain more than twice that of the controls. Additional experiments indicate that crosslinking enables the network to realign micro crystallites under stress to delay crack onset, but only when large crystallites are absent, as in fluxional CPs. Despite the incorporation of non‐conjugated comonomers, electrical mobility remains similar to controls at all levels of strain. This work demonstrates that fluxional components can outperform static analogues as structural modifiers in diketopyrrolopyrrole co‐thienothiophene CPs, leading to significant macroscopic effects.

Conjugated polymers (CPs) are a class of semiconducting materials in which electrical conductivity and mechanical extensibility can coincide. Despite advances in synthesis and processing, these key properties are typically negatively correlated and derive from the semicrystalline microstructure of the polymer film. Here, we introduce a new strategy to improve the microstructure and mechanical properties of CPs through the introduction of bullvalene‐based fluxional comonomers, in which bonds rearrange constantly at ambient temperatures. By comparing bullvalene‐containing poly(diketopyrrolopyrrole‐thienothiophene) (p(DPP‐TT)) with static controls, we show that fluxional backbones resist thermal annealing induced crystallization, creating smaller crystallites even at low comonomer loadings (5 mol%). While comonomers produce minimal mechanical differences in low‐molecular weight CPs, when the network is reinforced through crosslinking, bullvalene strongly enhances stretchability, yielding a crack onset strain more than twice that of the controls. Additional experiments indicate that crosslinking enables the network to realign micro crystallites under stress to delay crack onset, but only when large crystallites are absent, as in fluxional CPs. Despite the incorporation of non‐conjugated comonomers, electrical mobility remains similar to controls at all levels of strain. This work demonstrates that fluxional components can outperform static analogues as structural modifiers in diketopyrrolopyrrole co‐thienothiophene CPs, leading to significant macroscopic effects.

Customizing the toughness of polymer networks independently of their chemical composition and topology remains an unsolved challenge. Traditionally, polymer network toughening is achieved by using specialized monomers or solvents or adding secondary networks/fillers that substantially alter the composition and may limit applications. Here we report a class of force-responsive molecules—tetrafunctional cyclobutanes (TCBs)—that enable the synthesis of single-network end-linked gels with substantially decreased or increased toughness, including unusually high toughness for dilute end-linked gels, with no other changes to network composition. This behaviour arises from stress-selective force-coupled TCB reactivity when stress is imparted from multiple directions simultaneously, which traditional bifunctional mechanophores cannot access. This molecular-scale mechanoreactivity translates to bulk toughness through a topological descriptor, network strand continuity, that describes the effect of TCB reactivity on the consequent local network topology. TCB mechanophores and the corresponding concepts of stress-selective force-coupled reactivity and strand continuity offer design principles for tuning the toughness of simple yet commonly used single-network gels.

Lithium-ion batteries aid in decarbonization through enabling electric vehicles and renewable energy generation, but these applications put increasing demands on the energy density, safety, and cost of the batteries. Polymer electrolytes could improve battery safety but currently do not have sufficient ionic conductivity for ambient operation. To address this challenge, we developed a high throughput platform to increase the speed and scale of polymer electrolyte research by an estimated 100X. We utilized automated formulation and characterization operations, including electrochemical impedance spectroscopy with in situ thickness measurements, to perform a comparison of lithium and sodium salts in poly(ethylene oxide). Our study provides a high-quality, unified reference dataset for the community, and greatly expands available data for sodium-based electrolytes. Secondly, our large dataset allows us to find that the local minima in glass transition temperature that corresponds to maximum ionic conductivity is a colligative property, independent of either anion or cation chemistry.

The mechanical properties of covalent polymer networks often arise from the permanent end-linking or cross-linking of polymer strands, and molecular linkers that break more easily would likely produce materials that require less energy to tear. We report that cyclobutane-based mechanophore cross-linkers that break through force-triggered cycloreversion lead to networks that are up to nine times as tough as conventional analogs. The response is attributed to a combination of long, strong primary polymer strands and cross-linker scission forces that are approximately fivefold smaller than control cross-linkers at the same timescales. The enhanced toughness comes without the hysteresis associated with noncovalent cross-linking, and it is observed in two different acrylate elastomers, in fatigue as well as constant displacement rate tension, and in a gel as well as elastomers.

The cis- and trans-isomers of a silacycloheptene were selectively synthesized by the alkylation of a silyl dianion, a novel approach to strained cycloalkenes. The trans-silacycloheptene (trans-SiCH) was significantly more strained than the cis isomer, as predicted by quantum chemical calculations and confirmed by crystallographic signatures of a twisted alkene. Each isomer exhibited distinct reactivity toward ring-opening metathesis polymerization (ROMP), where only trans-SiCH afforded high-molar-mass polymer under enthalpy-driven ROMP. Hypothesizing that the introduction of silicon might result in increased molecular compliance at large extensions, we compared poly(trans-SiCH) to organic polymers by single-molecule force spectroscopy (SMFS). Force-extension curves from SMFS showed that poly(trans-SiCH) is more easily overstretched than two carbon-based analogues, polycyclooctene and polybutadiene, with stretching constants that agree well with the results of computational simulations.

Graft copolymers offer a versatile platform for the design of self-assembling materials; however, simple strategies for precisely and independently controlling the thermomechanical and morphological properties of graft copolymers remain elusive. Here, using a library of 92 polynorbornene-graft-polydimethylsiloxane (PDMS) copolymers, we discover a versatile backbone-pendant sequence-control strategy that addresses this challenge. Small structural variations of pendant groups, e.g., cyclohexyl versus n-hexyl, of small-molecule comonomers have dramatic impacts on order-to-disorder transitions, glass transitions, mechanical properties, and morphologies of statistical and block silicone-based graft copolymers, providing an exceptionally broad palette of designable materials properties. For example, statistical graft copolymers with high PDMS volume fractions yielded unbridged body-centered cubic morphologies that behaved as soft plastic crystals. By contrast, lamellae-forming graft copolymers provided robust, yet reprocessable silicone thermoplastics (TPs) with transition temperatures spanning over 160 °C and elastic moduli as high as 150 MPa despite being both unentangled and un-cross-linked. Altogether, this study reveals a new pendant-group-mediated self-assembly strategy that simplifies graft copolymer synthesis and enables access to a diverse family of silicone-based materials, setting the stage for the broader development of self-assembling materials with tailored performance specifications.

We studied the structural evolution and cycling behavior of TiNb₂O₇ (TNO) as a cathode in a nonaqueous hybrid dual-salt Mg–Li battery. A very high fraction of pseudocapacitive contribution to the overall specific capacity makes the material suitable for ultrafast operation in a hybrid battery, composed of a Mg-metal anode, and a dual-salt APC–LiCl electrolyte with Li and Mg cations. Theoretical calculations show that Li intercalation is predominant over Mg intercalation into the TNO in a dual-salt electrolyte with Mg²⁺ and Li⁺, while experimentally up to 20% Mg cointercalation was observed after battery discharge. In hybrid Mg–Li batteries, TNO shows capacities which are about 40 mA h g^–1 lower than in single-ion Li batteries at current densities of up to 1.2 A g^–1. This is likely due to a partial Mg cointercalation or/and location of Li cations on alternative crystallographic sites in the TNO structure in comparison to the Li-intercalation process in Li batteries. Generally, hybrid Mg–Li cells show a markedly superior applicability for a very prolonged operation (above 1000 cycles) with 100% Coulombic efficiency and a capacity retention higher than 95% in comparison to conventional Li batteries with TNO after being cycled either under a low (7.75 mA g^–1) or high (1.55 A g^–1) current density. The better long-term behavior of the hybrid Mg–Li batteries with TNO is especially pronounced at 60 °C. The reasons for this are an appropriate cathode electrolyte interface containing MgCl₂ species and a superior performance of the Mg anode in APC–LiCl electrolytes with a dendrite-free, fast Mg deposition/stripping. This stable interface stands in contrast to the anode electrolyte interface in Li batteries with a Li anode in conventional carbonate-containing electrolytes, which is prone to dendrite formation, thus leading to a battery shortcut.