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.

Harnessing molecular design principles toward functional applications of ion-containing macromolecules relies on diversifying experimental data sets of well-understood materials. Here, we report a simple, tunable framework for preparing styrenic polyelectrolytes, using aqueous reversible addition−fragmentation chain transfer (RAFT) polymerization in a parallel synthesis approach. A series of diblock polycations and polyanions were RAFT chain-extended from poly-( e t h y l e n e o x i d e ) ( P E O ) u s i n g ( v i n y l b e n z y l )trimethylammonium chloride (PEO-b-PVBTMA) and sodium 4-styrenesulfonate (PEO-b-PSS), with varying neutral PEO block lengths, charged styrenic block lengths, and RAFT endgroup identity. The materials characterization and kinetics study of chain growth exhibited control of the molar mass distribution for both systems. These block polyelectrolytes were also demonstrated to form polyelectrolyte complex (PEC) driven selfassemblies. We present two simple outcomes of micellization to show the importance of polymer selection from a broadened pool of polyelectrolyte candidates: (i) uniform PEC-core micelles comprising PEO-b-PVBTMA and poly(acrylic acid) and (ii) PEC nanoaggregates comprising PEO-b-PVBTMA and PEO-b-PSS. The materials characteristics of these charged assemblies were investigated with dynamic light scattering, small-angle X-ray scattering, and cryogenic-transmission electron microscopy imaging. This model synthetic platform offers a straightforward path to expand the design space of conventional polyelectrolytes into gram-scale block polymer structures, which can ultimately enable the development of more sophisticated ionic materials into technology.

As one of the beyond-lithium battery concepts, hybrid metal-ion batteries have aroused growing interest. Here, TiNb2O7 (TNO) and VNb9O25 (VNO) materials were prepared using a high-temperature solid-state synthesis and, for the first time, comprehensively examined in hybrid Mg–Li batteries. Both materials adopt ReO3-related structures differing in the interconnection of oxygen polyhedra and the resulting guest ion diffusion paths. We show applicability of the compounds in hybrid cells providing capacities comparable to those reached in Li-ion batteries (LIBs) at room temperature (220 mAh g–1 for TNO and 150 mAh g–1 for VNO, both at 0.1 C), their operability in the temperature range between −10 and 60 °C, and even better capacity retention than in pure LIBs, rendering this hybrid technology superior for long-term application. Post mortem X-ray photoelectron spectroscopy reveals a cathode–electrolyte interface as a key ingredient for providing excellent electrochemical stability of the hybrid battery. A significant contribution of the intercalation pseudocapacitance to charge storage was observed for both materials in Li- and Mg–Li batteries. However, the pseudocapacitive part is higher for TNO than for VNO, which correlates with structural distinctions, providing better accessibility of diffusion pathways for guest cations in TNO and, as a consequence, a higher ionic transport within the crystal structure.

We studied the structural evolution and cycling behavior of TiNb2O7 (TNO) as cathode in a non-aqueous hybrid dual-salt Mg-Li battery. A very high fraction of a pseudocapacitive contribution to the overall specific capacity makes the material suitable for ultrafast operation in a hybrid battery, comprised 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 Mg 2+ and Li + , while experimentally up to 20% Mg-co-intercalation was observed after battery discharge.In hybrid Mg-Li batteries, TNO shows capacities which are about 40 mAh g -1 lower than in single-ion Libatteries at current densities up to 1.2 A g -1 . This is likely due to a partial Mg co-intercalation, or/and location of Li-cations on alternative crystallographic sites in the TNO structure in comparison to Liintercalation 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 as well as 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.

Charge-driven complexation of polyelectrolytes in water is a fundamental phase separation phenomenon that is prevalent in nature and across the high-value technology landscape.Condensed ionic biopolymers often rely on multiple non-covalent driving forces in patterned sequences to carefully preserve hierarchical structure and direct emerging function, and while synthetic polyelectrolyte complex (PEC) assemblies have sought to emulate and recapitulate such associative capabilities into applications, molecular engineering design strategies to precisely modulate monomeric building blocks remain vastly limited. Here we describe an experimentally convenient and versatile approach to construct patterned PECs, comprising well-defined charged macromolecules with both ionic styrene and neutral maleimide units alternating in the chain sequence. The controlled chemical structure of the alternating polyelectrolytes directly impacted the physical properties of bulk complex assemblies, demonstrated by elevated salt resistance and differences in viscoelastic relaxation and stiffness. Analogously, by engineering alternating diblock polyelectrolyte architectures for micelle self-assembly, the kinetic formation and stability pathways of PEC micelles were tailored without modifying nanoparticle size, attributed to the reduction in charge density and increased core hydrophobicity. We conclude by showing how multiple segments of donor/acceptor styrene-maleimide blocks can be incorporated into model polyelectrolyte chains in semi-batch reactions, enabling avenues to further explore sequencecontrolled polymers that regulate placement of N-substituted maleimides in polymer encryption endeavors. This unique copolymerization approach integrates appealing aspects of precision polymer synthesis with programmable self-assembly for advancing new directions in chemistry, physics, and engineering related to the complexation of oppositely-charged designer polymers.

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with exceptional mechanical resilience, self-healing properties, and processability have been reported recently. [16] Although hydrogel composites remain useful materials for sensor and biomedical applications, broad use is restricted by their operating temperature range (0−100 °C), long-term stability, and the need for watersoluble reagents.Conductive organogel composites have received comparatively little attention despite the ability to support a wide range of polymers and fillers, exhibit conductivities between 10 −4 and 10 mS cm −1 , [17] and maintain useful mechanical and electrical properties at temperature extremes without solvent evaporation or freezing. [18] Furthermore, the synthetic tunability of organogels provides access to a diverse range of materials. For example, dynamic organogels can be synthesized with reversible covalent bonds or secondary interactions such as hydrogen bonding to facilitate self-healing, network reversion, or sensing capabilities. [19][20][21][22][23][24][25][26][27] Variability in solvent, polymer, and filler selection allows access to materials mimicking the mechanical properties of hydrogel composites and soft conductive elastics, and enables performance inaccessible to either system alone such as stimuli responsivity and temperature stability. Recyclable hemiaminal dynamic covalent networks (HDCNs) formulated with insulating polyethylene glycol (PEG) and conductive fillers present advantages in applications such as pressure and chemical sensors, antistatic technologies, and other flexible electronics. [27][28][29][30][31][32] A survey of conductive nanoparticles was added to HDCN organogels during their synthesis in N-methyl-2-pyrrolidone (NMP): "long" (10 µm × 12 nm) multi-walled carbon nanotubes (MWCNTs), four types of carbon black (Black Pearls L (BPL), 9A32, XC72, XC72R), and graphite. Microscale behaviors were first established through rheology. HDCN composites remained in a dynamic state, underwent stress relaxation up to 2 h after formation, and had relaxation stretching parameters close to zero (β = 0.01−0.09, R 2 ≈ 0.95, Table S1, Supporting Information), independent of solvent and filler choice. The stretched relaxation behavior was attributed to hierarchical and continuous segmental relaxation from the dynamic heterogeneity of transient networks. Transient covalent crosslinks and supramolecular interactions are active throughout the gel at various length scales and stages of relaxation, changing the kinetics of chain motion as a function of their fluctuation, and creating a wide distribution of relaxation behaviors over long time periods. [33][34][35][36][37] Notably, β values for composites were comparable to the matrix alone (β = 0.02), suggesting uniform filler Conductive OrganogelsAs the use of automation in industry accelerates, the development of flexible, electrically conducting materials with the requisite environmental resilience for impact-resistant sensors, foldable electronics, and electrostatic shielding are needed; simultaneously, recyclability fo...

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.