Recent work has demonstrated that temporary crosslinks in polymer networks generated by chemical “fuels” afford materials with large, transient changes in their mechanical properties. This can be accomplished in carboxylic‐acid‐functionalized polymer hydrogels using carbodiimides, which generate anhydride crosslinks with lifetimes on the order of minutes to hours. Here, the impact of the polymer network architecture on the mechanical properties of transiently crosslinked materials was explored. Single networks (SNs) were compared to interpenetrated networks (IPNs). Notably, semi‐IPN precursors that give IPNs on treatment with carbodiimide give much higher fracture energies (i.e., resistance to fracture) and superior resistance to compressive strain compared to other network architectures. A precursor semi‐IPN material featuring acrylic acid in only the free polymer chains yields, on treatment with carbodiimide, an IPN with a fracture energy of 2400 J/m2, a fourfold increase compared to an analogous semi‐IPN precursor that yields a SN. This resistance to fracture enables the formation of macroscopic complex cut patterns, even at high strain, underscoring the pivotal role of polymer architecture in mechanical performance.
- Award ID(s):
- 1749730
- PAR ID:
- 10088290
- Date Published:
- Journal Name:
- Chemical Communications
- Volume:
- 55
- Issue:
- 14
- ISSN:
- 1359-7345
- Page Range / eLocation ID:
- 2086 to 2089
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Abstract Recent work has demonstrated that temporary crosslinks in polymer networks generated by chemical “fuels” afford materials with large, transient changes in their mechanical properties. This can be accomplished in carboxylic‐acid‐functionalized polymer hydrogels using carbodiimides, which generate anhydride crosslinks with lifetimes on the order of minutes to hours. Here, the impact of the polymer network architecture on the mechanical properties of transiently crosslinked materials was explored. Single networks (SNs) were compared to interpenetrated networks (IPNs). Notably, semi‐IPN precursors that give IPNs on treatment with carbodiimide give much higher fracture energies (i.e., resistance to fracture) and superior resistance to compressive strain compared to other network architectures. A precursor semi‐IPN material featuring acrylic acid in only the free polymer chains yields, on treatment with carbodiimide, an IPN with a fracture energy of 2400 J/m2, a fourfold increase compared to an analogous semi‐IPN precursor that yields a SN. This resistance to fracture enables the formation of macroscopic complex cut patterns, even at high strain, underscoring the pivotal role of polymer architecture in mechanical performance.
-
more » « less
Abstract Metal‐coordinated hydrogels can form a percolated network with transient bonds due to metal ions‐functional group coordination. Each metal ion can link with more than one ligand, leading to intricate speciation of bonding modes. While the mechanics of transient gels made with four‐arm polymers are often studied, less is known about how increasing the number of arms affects the modulus. Using shear rheology, the modulus of hydrogels prepared from four‐, six‐, and eight‐armed poly(ethylene glycols), functionalized with histidine ligands that complex with nickel (II) ions is measured. These gels have matched polymer wt.% and varied pH to compare their moduli. It is considered whether the modulus can be described by established polymer network models by calculating the speciation of metal‐coordinated cross‐links and then incorporating it into a phantom network prediction. This study finds that 1) increasing the number of polymer arms increases the modulus, 2) the phantom network allows reasonable modulus approximation for four‐arm and six‐arm gels, and 3) the modulus of eight‐arm gels exceeds the phantom network prediction. Since polymer cores act as chemical cross‐links and metal‐coordinated cross‐links form network strands, it is possible that increasing the number of metal‐coordinated linkages per molecule reinforces the chemical cross‐link at the polymer core.
-
more » « less
Abstract Biochemical systems make use of out‐of‐equilibrium polymers generated under kinetic control. Inspired by these systems, many abiotic supramolecular polymers driven by chemical fuel reactions have been reported. Conversely, polymers based on transient covalent bonds have received little attention, even though they have the potential to complement supramolecular systems by generating transient structures based on stronger bonds and by offering a straightforward tuning of reaction kinetics. In this study, we show that simple aqueous dicarboxylic acids give poly(anhydrides) when treated with the carbodiimide EDC. Transient covalent polymers with molecular weights exceeding 15,000 are generated which then decompose over the course of hours to weeks. Disassembly kinetics can be controlled using simple substituent effects in the monomer design. The impact of solvent polarity, carbodiimide concentration, temperature, pyridine concentration, and monomer concentration on polymer properties and lifetimes has been investigated. The results reveal substantial control over polymer assembly and disassembly kinetics, highlighting the potential for fine‐tuned kinetic control in nonequilibrium polymerization systems.
-
more » « less
Abstract A critical barrier to overcome in the development of solid‐state electrolytes for lithium batteries is the trade‐off between sacrificing ionic conductivity for enhancement of mechanical stiffness. Here, a physically cross‐linked, polymer‐supported gel electrolyte consisting of a lithium salt/ionic liquid solution featuring a fully zwitterionic (ZI) copolymer network is introduced for rechargeable lithium‐based batteries. The ZI scaffold is synthesized using a 3:1 molar ratio of 2‐methacryloyloxyethyl phosphorylcholine and sulfobetaine vinylimidazole, and the total polymer content is varied between 1.1 and 12.5 wt%. Room‐temperature ionic conductivity values comparable to the base liquid electrolyte (≈1 mS cm−1) are achieved in ZI copolymer‐supported gels that display compressive elastic moduli as large as 14.3 MPa due to ZI dipole–dipole cross‐links. Spectroscopic characterization suggests a change in the Li+coordination shell upon addition of the zwitterions, indicative of strong Li+···ZI group interactions. Li+transference number measurements reveal an increase in Li+conductivity within a ZI gel electrolyte (
nearly doubles). ZI gels display enhanced stability against Li metal, dendrite suppression, and suitable charge–discharge performance in a graphite|lithium nickel cobalt manganese oxide cell. Fully ZI polymer networks in nonvolatile, ionic liquid‐based electrolytes represent a promising approach toward realizing highly conductive, mechanically rigid gels for lithium battery technologies.
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C8CC09823A
