Comparison of Effects of Different Sacrificial Hydrogen Bonds on Performance of Polyurethane/Graphene Oxide Membrane

Processing robust mechanical properties is important for elastomeric materials. In this work, different molecular weights of polyethylene glycols (PEG) were used to modify graphene oxide (GO) in order to study the relationship between the number of hydrogen bonds and the properties of the polyurethane/graphene oxide membrane. The fact of PEG was successfully grafted onto the surface of GO was certified by Fourier transform infrared spectra, Raman spectra, X-ray photoelectron spectroscopy. The graft ratio was indicated by thermogravimetric analysis. The presence of hydrogen bonds in PUR/MGO composites membrane was proved by the cyclic loading-unloading test and stress relaxation test. The thermal stability and low-temperature resistance performance of PUR/MGO had been improved compared with PUR/GO. When the molecular weight of PEG grafted on the surface of GO was 600, the tensile strength and elongation at break of the composite membrane were optimal. The reason for the improvement of physical and mechanical properties was that the dispersion of filler in the rubber matrix and the compatibility between filler and rubber had been improved.

Molecularly engineered dual-crosslinked elastomer vitrimers with superior strength, improved creep resistance, and retained malleability

Preparation of covalently crosslinked elastomers with an integration of high mechanical performance, enhanced creep resistance and retained malleability by incorporating quadruple hydrogen bonds into dynamic boronic ester bonds crosslinked SBR.

Facile strategy to incorporate amidoxime groups into elastomers toward self-crosslinking and self-reinforcement

Amidoxime modification of NBR and the formation of a multi-crosslinking network structure by self-crosslinking of AO-NBR.

Tandem metathesis depolymerization and cyclopolymerization toward flexible-rigid block copolymer with unique damping properties

Metathesis depolymerization (MDP) of natural rubber (NR) was readily conducted to afford depolymerized NR (dNRx) bearing the living chain end, which can initiate metathesis cyclopolymerization (MCP) of 1,6-heptadiyne monomers to...

Mechanically Robust Elastomers Enabled by a Facile Interfacial Interactions-Driven Sacrificial Network

Strength and toughness are usually mutually exclusive for materials. The sacrificial bond strategy is used to address the trade-off between strength and toughness. However, the complex construction process of sacrificial network limits the application of sacrificial network. This work develops a facile strategy to construct an interfacial interactions-driven sacrificial network. The authors' group finds that there are the interfacial interactions between arginines (A) aggregates and molecular chains. Such interfacial interactions result in the mechanical properties of samples having a strong dependence on extension rates, which shows that A aggregates construct a network structure by interfacial interactions. The interfacial interactions between A aggregates and chains improve the strength of samples; while the A aggregate network driven by interfacial interactions preferentially ruptures to dissipate large energy for the improvement of fracture toughness, which can be considered as a sacrificial network. Therefore, their designed elastomers have both high strength and high toughness. This work provides an easier strategy for the construction of sacrificial networks, which can promote the industrial application of sacrificial networks in elastomer materials.

Enzymatic and Chemical Approaches for Post-Polymerization Modifications of Diene Rubbers: Current state and Perspectives

Diene rubbers are polymeric materials which present elastic properties and have double bonds in the macromolecular backbone after the polymerization process. Post-polymerization modifications of rubbers can be conducted by enzymatic or chemical methods. Enzymes are environmentally friendly catalysts and with the increasing demand for rubber waste management, biodegradation and biomodifications have become hot topics of research. Some rubbers are renewable materials and are a source of organic molecules, and biodegradation can be conducted to obtain either oligomers or monomers. On the other hand, chemical modifications of rubbers by click-chemistry are important strategies for the creation and combination of new materials. In a way to expand the scope of uses to other non-traditional applications, several and effective modifications can be conducted with diene rubbers. Two groups of efficient tools, enzymatic, and chemical modifications in diene rubbers, are summarized in this review. By analyzing stereochemical and reactivity aspects, the authors also point to some applications perspectives for biodegradation products and to rational modifications of diene rubbers by combining both methodologies.

High-Temperature-Aging Induced Sequential Recovery of Shape Memory Nitrile Butadiene Rubber Composites

The sacrificial bonds in natural materials have inspired the preparation of shape memory polymer (SMP), which can be prepared through the construction of dual cross-linking networks in a polymer matrix. With the rise of 4D printing technology, fine control over the shape recovery of SMPs, especially control over the recovery time, is urgently needed. In this study, the high-temperature aging method is adopted to tune the shape recovery time of dual cross-linked SMPs. Shape memory acrylonitrile butadiene rubber composite (i.e., NBR-C) is prepared by introducing Zn²⁺-C≡N coordination bonding and sulfur covalent cross-linking networks into the rubber matrix and then thermal aging at 180 °C for various time frames. Aging increases the covalent cross-linking density, ruptures rubber chains, and generates imine structures. Moreover, the composition of the coordination bonding network becomes diversified because of the formation of coordination bonds between imines and Zn²⁺ ions. The mechanical "tough-brittle" transition of aged NBR-C is observed, and its glassy temperature increases with aging time, which in turn changes the shape recovery time at the same recovery temperature. On the basis of these findings, the special shape memory rubber components with sequential recovery are fabricated by partially aging the NBR-C strings. This methodology provides novel solutions for the preparation of sequential SMP products without programming heating design or using redundant chemical materials. We believe that this work will be able to help promote comprehensive research of SMPs and widen applications of SMPs in the industry.

Preparation of multi-temperature responsive elastomers by generating ionic networks in 1,2-polybutadiene using an anionic melting method

The development of reversible networks in elastomers provided unique inspiration for the design of advanced polymers with excellent properties. In this paper, we adopted an anionic melting method to introduce carboxylate groups into 1,2-polybutadiene (1,2-PB), using maleic anhydride as a modifier, and sodium hydride (NaH), calcium hydride (CaH2), and lithium aluminum hydride (LiAlH4) as metallization reagents. Na-Based, Ca-based, and Li/Al-based ionic bond networks were constructed in the covalently crosslinked 1,2-PB. The effects of the electronegativity and valence of the metal ions on the strength and reversible temperature of the ionic network were studied. Payne effect was shown by rheological tests, demonstrating the interactions between the ionic networks and rubber chains. The reforming temperature for these ionic networks was studied by stress-relaxation analysis, and shape memory experiments were performed based on these temperatures. This concept provides novel inspiration for the design of high-performance and temperature-adaptive elastomers.

Recyclable, Self-Healing, Thermadapt Triple-Shape Memory Polymers Based on Dual Dynamic Bonds

Fabricating a single polymer network with a combination of a multi-shape memory effect (multiple-SME), solid-state plasticity, recyclability and self-healing behavior remains a challenge. We designed imine bond and ionic hydrogen bond dual cross-linked polybutadiene (PB) networks. The resulting PB networks showed a triple-shape memory effect, where imine bonds could be used to fix the permanent shape and ionic hydrogen bonds and glass transition acted as the transition segments for fixing/releasing the temporary shapes. Additionally, the dual dynamic bonds offered PB networks outstanding solid-state plasticity, recyclability and self-healing behavior. This strategy provides some insights for preparing shape memory polymers integrating multiple-SME and multi-functionality.

Elastomer Reinforced with Innate Sulfur-Based Cross-Links as Ligands

Although the incorporation of sacrificial bonds into an elastomer is an effective way to provide a combination of high strength and high fracture toughness, this method normally involves complicated chemical processes. The coordination between metal ions and polysulfides has been documented. However, the potential of polysulfide structures in vulcanizates as ligands has long been neglected. Using innate sulfur-based cross-links, we show how weak and nonpolar elastomers achieve significant reinforcement without modification of the backbone. By simply soaking vulcanizates into solutions containing metal ions, dual ions are simultaneously introduced into the vulcanizate to generate coordinations with different bond strengths, resulting in an unprecedented high modulus. Overall, this work presents a universal yet high-efficiency reinforcing strategy to prepare high-performance elastomers without additional chemical modifications, which should promote comprehensive research and industrial application of sacrificial bond strategies for elastomers.

Enhancing Mechanical and Thermal Properties of Polyurethane Rubber Reinforced with Polyethylene Glycol-g-Graphene Oxide

This paper attempted to achieve the purpose of increasing the tensile strength and toughness of polyurethane rubber (PUR) simultaneously by introducing polyethylene glycol (PEG) onto the surface of graphene oxide (GO) to introduce hydrogen bond interactions into the PUR-GO system. GO was grafted with PEG and added to PUR by mechanical blending. The polyethylene glycol-g-graphene oxide (MGO) was characterized by infrared spectroscopy, Raman spectroscopy, X-ray diffraction, and thermogravimetric analysis. The PUR/MGO composites were tested by tensile testing machine, thermogravimetric analysis, dynamic thermal analysis, and scanning electron microscopy. The results demonstrated that PEG was successfully grafted onto the surface of GO and the grafting rate was about 37%. The grated PEG did not affect the crystalline structure of GO. The addition of MGO could improve the thermal stability of PUR vulcanizate. After the addition of GO, the glass transition temperature (Tg) of vulcanizate was shifted to higher temperature. However, the Tg of vulcanizate reinforced by MGO was shifted to lower temperature. The strength and toughness of vulcanizate were significantly improved by adding MGO. The reason was that the hydrogen bond interactions between MGO and PUR were destroyed and the hidden length was released during the strain process. A lot of energy was consumed, and thus the strength and toughness of PUR vulcanizate were improved.

Simultaneously improved dielectric and mechanical properties of silicone elastomer by designing a dual crosslinking network

A homogenous silicone dielectric elastomer with simultaneously improved dielectric and mechanical properties is synthesized by designing a dual crosslinking network.

The emerging applications of click chemistry reactions in the modification of industrial polymers

Click chemistry reactions have been applied to the modification of major industrial polymers by analysing the synthetic approaches and the resulting material properties.

Progress in bio-inspired sacrificial bonds in artificial polymeric materials

Mimicking natural structures has been highly pursued in the fabrication of synthetic polymeric materials due to its potential in breaking the bottlenecks in mechanical properties and extending the applications of polymeric materials. Recently, it has been revealed that the energy dissipating mechanisms via sacrificial bonds are among the important factors which account for strong and tough attributes of natural materials. Great progress in synthesis of polymeric materials consisting of sacrificial bonds has been achieved. The present review aims at (1) summarizing progress in the mechanics and chemistry of sacrificial bond bearing polymers, (2) describing the mechanisms of sacrificial bonds in strengthening/toughening polymers based on studies by single-molecule force spectroscopy, chromophore incorporation and constitutive laws, (3) presenting synthesis methods for sacrificial bonding including dual-crosslink, dual/multiple-network, and sacrificial interfaces, (4) discussing the important advances in engineering sacrificial bonding into hydrogels, biomimetic structures and elastomers, and (5) suggesting future works on molecular simulation, viscoelasticity, construction of sacrificial interfaces and sacrificial bonds with high dissociative temperature. It is hoped that this review will provide guidance for further development of sacrificial bonding strategies in polymeric materials.