An official website of the United States government
Abstract Within the past two decades, covalent adaptable networks (CANs) have emerged as a novel class of dynamically crosslinked polymers, combining the benefits of thermosets and thermoplastics. Although some CANs with charged side chains have been reported, CANs with negatively charged backbones remain very limited. The integration of permanent charge into the backbones upon their formation could open up important new applications. Here, we introduce a series of aliphatic spiroborate‐linked ionic covalent adaptable networks (ICANs), representing a new category of dynamic ionomer thermosets. These ICANs were synthesized using a catalyst‐free, scalable, and environment‐friendly method. Incorporating lithium or sodium as counter cations in these networks yielded promising ion conductivity without the need of plasticizers. The dynamic nature of the spiroborate linkages in these materials allows for rapid reprocessing and recycling under moderate conditions. Furthermore, their potential as flexible solid‐state electrolytes is demonstrated in a device that maintained robust conducting performance under extreme physical deformation, coupled with effective self‐healing properties. This research opens new possibilities for future development of dynamic ionomer thermosets and their potential applications in flexible electronic devices.
more »
« less
Light‐Induced Living Polymer Networks with Adaptive Functional Properties
Abstract The advent of covalent adaptable networks (CANs) through the incorporation of dynamic covalent bonds has led to unprecedented properties of macromolecular systems, which can be engineered at the molecular level. Among the various types of stimuli that can be used to trigger chemical changes within polymer networks, light stands out for its remote and spatiotemporal control under ambient conditions. However, most examples of photoactive CANs need to be transparent and they exhibit slow response, side reactions, and limited light penetration. In this vein, it is interesting to understand how molecular engineering of optically active dynamic linkages that offer fast response to visible light can impart “living” characteristics to CANs, especially in opaque systems. Here, the use of carbazole‐based thiuram disulfides (CTDs) that offer dual reactivity as photoactivated reshuffling linkages and iniferters under visible light irradiation is reported. The fast response to visible light activation of the CTDs leads to temporal control of shape manipulation, healing, and chain extension in the polymer networks, despite the lack of optical transparency. This strategy charts a promising avenue for manipulating multifunctional photoactivated CANs in a controlled manner.
more »
« less
- Award ID(s):
- 2116298
- PAR ID:
- 10504967
- Publisher / Repository:
- Wiley-VCH GmbH
- Date Published:
- Journal Name:
- Advanced Materials
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Covalent adaptable networks (CANs) represent a novel class of polymeric materials crosslinked by dynamic covalent bonds. Since their first discovery, CANs have attracted great attention due to their high mechanical strength and stability like conventional thermosets under service conditions and easy reprocessability like thermoplastics under certain external stimuli. Here, we report the first example of ionic covalent adaptable networks (ICANs), a type of crosslinked ionomers, consisting of negatively charged backbone structures. More specifically, two ICANs with different backbone compositions were prepared through spiroborate chemistry. Given the dynamic nature of the spiroborate linkages, the resulting ionomer thermosets display rapid reprocessability and closed-loop recyclability under mild conditions. The materials mechanically broken into smaller pieces can be reprocessed into coherent solids at 120 °C within only 1 min with nearly 100% recovery of the mechanical properties. Upon treating the ICANs with dilute hydrochloric acid at room temperature, the valuable monomers can be easily chemically recycled in almost quantitative yield. This work demonstrates the great potential of spiroborate bonds as a novel dynamic ionic linkage for development of new reprocessable and recyclable ionomer thermosets.more » « less
-
Abstract Vitrimers, a class of covalent adaptable networks (CANs), promise sustainability through recyclability and reprocessability, yet suffer from creep under prolonged stress due to dynamic bond exchange. Here, a materials design strategy is reported that integrates polymerization‐induced self‐assembly (PISA) to embed core‐crosslinked nanoparticles within vitrimer networks, yielding hierarchical dual‐crosslinked systems with a reduction of creep susceptibility by up to 90% at 150 °C yet good reprocessability at elevated temperatures (Ea= 246 kJ mol−1). These spherical nanostructures restrict chain mobility and act as rheological modifiers that can be synthetically tuned through core block length. This approach offers precise architectural control, leveraging nanoparticle phase morphology to direct bulk vitrimer properties. This study establishes a new paradigm for creep‐resistant CANs and showcases how PISA can advance vitrimer performance by structurally encoding mechanical robustness and reprocessability.more » « less
-
Dynamic photopolymer networks that take advantage of the thermodynamically controlled reversibility of thiol–succinic anhydride adducts were synthesized from commercial substrates and investigated as a new class of covalent adaptable networks (CANs). Through systematic studies of the catalyst and stoichiometry effects on the exchange dynamics two distinctive exchange mechanisms were found, and then demonstrated to contribute to the overall dynamic characteristics. By varying the catalyst activity, i.e. basicity and/or nucleophilicity, control over the dynamic responsiveness through changes in the type of dynamic covalent chemistry mode (reversible addition vs. reversible exchange) was achieved in otherwise compositionally analogous materials. More specifically, the participation of the associative mechanism (thiol–thioester exchange) in the otherwise dissociative networks, and its relevance on materials properties was demonstrated by dielectric analysis (DEA) and dynamic mechanical analysis (DMA). The activation energies ( E a ) for viscous flow obtained from DMA stress relaxation experiments and from dielectric modulus and loss crossover points were shown to match well between the two techniques. The E a in stoichiometric systems was found to be 110–120 kJ mol −1 , whereas 50% excess thiol systems were characterized by E a ranging 95–105 kJ mol −1 . The thermodynamic equilibrium conversion, estimated in the temperature controlled FTIR, for a stoichiometric 3-mercaptopropionate-succinic anhydride combination was determined at 92 ± 1% at ambient temperature, and decreased to 67 ± 1% at 120 °C within one hour of equilibration time (Δ H ° = −46 ± 5 kJ mol −1 ). Such high potential for reversibility of the thioester anhydride linkages resembles maleimide-furan Diels–Alder networks but has many other attributes that make these CANs of unprecedented value in fundamental research on dynamic materials.more » « less
-
Abstract Vinylogous urethane (VUO) based polymer networks are widely used as catalyst‐free vitrimers that show rapid covalent bond exchange at elevated temperatures. In solution, vinylogous ureas (VUN) undergo much faster bond exchange than VUOand are highly dynamic at room temperature. However, this difference in reactivity is not observed in their respective dynamic polymer networks, as VUOand VUNvitrimers prepared herein with very similar macromolecular architectures show comparable stress relaxation and creep behavior. However, by using mixtures of VUOand VUNlinkages within the same network, the dynamic reactions can be accelerated by an order of magnitude. The results can be rationalized by the effect of intermolecular hydrogen bonding, which is absent in VUOvitrimers, but is very pronounced for vinylogous urea moieties. At low concentrations of VUN, these hydrogen bonds act as catalysts for covalent bond exchange, while at high concentration, they provide a pervasive vinylogous urea ‐ urethane (VU) network of strong non‐covalent interactions, giving rise to phase separation and inhibiting polymer chain dynamics. This offers a straightforward design principle for dynamic polymer materials, showing at the same time the possible additive and synergistic effects of supramolecular and dynamic covalent polymer networks.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/adma.202313961
