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  1. null (Ed.)
    A one pot synthesis is applied to control the chain structure and architecture of multiply dynamic polymers, enabling fine tuning of materials properties by choice of polymer chain length or crosslink density. Macromolecules containing both non-covalent linkers based on quadruple hydrogen-bonded 2-(((6-(3-(6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl)ureido)hexyl)carbamoyl)oxy)ethyl methacrylate (UPyMA), and thermoresponsive dynamic covalent furan–maleimide based Diels–Alder linkers are explored. The primary polymer's architecture was controlled by reversible addition-fragmentation chain transfer (RAFT) polymerization, with the dynamic non-covalent (UPyMA) and dynamic covalent furfuryl methacrylate (FMA) units incorporated into the same backbone. The materials are crosslinked, taking advantage of the “click” chemistry properties of the furan–maleimide reaction. The polymer materials showed stimulus-responsive thermomechanical properties with a decrosslinking temperature increasing with the polymer's primary chain length and crosslink density. The polymers had good thermally promoted self-healing properties due to the dynamic covalent Diels–Alder bonds. Besides, the materials had excellent stress relaxation characteristics induced by the exchange of the hydrogen bonds in UPyMA units. 
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  2. Recent progress on stretchable, tough dual-dynamic polymer single networks (SN) and interpenetrated networks (IPN) has broadened the potential applications of dynamic polymers. However, the impact of macromolecular structure on the material mechanics remains poorly understood. Here, rapidly exchanging hydrogen bonds and thermoresponsive Diels–Alder bonds were included into molecularly engineered interpenetrated network materials. RAFT polymerization was used to make well-defined polymers with control over macromolecular architecture. The IPN materials were assessed by gel permeation chromatography, differential scanning calorimetry, tensile testing and rheology. The mechanical properties of these IPN materials can be tuned by varying the crosslinker content and chain length. All materials are elastic and have dynamic behavior at both ambient temperature and elevated temperature (90 °C), owing to the presence of the dual dynamic noncovalent and covalent bonds. 100% self-healing recovery was achieved and a maximum stress level of up to 6 MPa was obtained. The data suggested the material's healing properties are inversely proportional to the content of the crosslinker or the degree of polymerization at both room and elevated temperature. The thermoresponsive crosslinker restricted deformation to some extent in an ambient environment but gave excellent malleability upon heating. The underlying mechanism was explored by the computational simulations. Furthermore, a single network material with the same crosslinker content and degree of polymerization as the IPN was made. The SN was substantially weaker than the comparable IPN material. 
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  3. Transiently crosslinked dynamic polymer networks are developed, using carbodiimide hydration to link carboxylic acids as anhydrides. From aqueous polymer solutions, non-equilibrium hydrogels are transiently formed, which dissolve upon anhydride hydrolysis. The materials can be refueled using a subsequent injection of carbodiimide. The gels exhibit higher storage moduli compared to transient supramolecular gels as a result of their covalent crosslinks. 
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  4. Abstract

    Dynamic materials (DMs) or dynamers have potential applications across a broad range of material science challenges. These applications include sustainable materials as a part of the circular plastics economy, advanced materials with tailored high stress properties and biomedical agents. DMs are comprised of polymers that crosslinked through reversible covalent and noncovalent linking groups. This group provides reversible bonds, which impart properties such as (re)healing, adaptability, toughness into a material. The nature of the linker dictates the dynamer's stability and dynamic properties, although for many applications one linker alone cannot give materials with complex multiresponsive functions. The combination of multiple dynamic linkers can introduce complementary functionalities into a single material. This combination of linkers enhances the collective material properties by matching their strengths and offsetting the weaknesses, or by selecting linkers for specific functions, such as one linker for rapid exchange and the other to respond to external stimuli. This contribution highlights the possibilities and unique features of materials containing multiple dynamic linkers, reviewing both fundamental discoveries of materials possessing multiple dynamic bonds and applications facilitated by the presence of multiple linking group chemistry.

     
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  5. Abstract

    Dynamically cross‐linked polymer networks have attracted significant interest in recent years due to their unique and improved properties including increased toughness, malleability, shape memory, and self‐healing. Here, a computational study on the mechanical behavior of dynamically cross‐linked polymer networks is presented. Coarse grained models for different polymer network configurations are established and their mechanical properties using molecular dynamics (MD) simulations are predicted. Consistent with the experimental measurements, the simulation results show that interpenetrating networks (IPN) withstand considerably higher stress compared to the single networks (SN). Additionally, the MD results demonstrate that the origin of this variation in mechanical behavior of IPN and SN configurations goes back to the difference in spatial degrees of freedom of the noncovalent cross‐linkers, represented by nonbonded interactions within the two system types. The results of this work provide new insight for future studies on the design of systems with dual dynamic cross‐linkers where one linkage exchanges rapidly and provides autonomic dynamic character, while the other is a stimulus responsive dynamic covalent linkage that provides stability with dynamic exchange on‐demand.

     
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