A stretchable, mechanically robust polymer exhibiting shape-memory-assisted self-healing and clustering-triggered emission

Malleable, Ultrastrong Antibacterial Thermosets Enabled by Guanidine Urea Structure

Dynamic covalent polymers (DCPs) that strike a balance between high performance and rapid reconfiguration have been a challenging task. For this purpose, a solution is proposed in the form of a new dynamic covalent supramolecular motif-guanidine urea structure (GUAs). GUAs contain complex and diverse chemical structures as well as unique bonding characteristics, allowing guanidine urea supramolecular polymers to demonstrate advanced physical properties. Noncovalent interaction aggregates (NIAs) have been confirmed to form in GUA-DCPs through multistage H-bonding and π-π stacking, resulting in an extremely high Young's modulus of 14 GPa, suggesting remarkable mechanical strength. Additionally, guanamine urea linkages in GUAs, a new type of dynamic covalent bond, provide resins with excellent malleability and reprocessability. Guanamine urea metathesis is validated using small molecule model compounds, and the temperature dependent infrared and rheological behavior of GUA-DCPs following the dissociative exchange mechanism. Moreover, the inherent photodynamic antibacterial properties are extensively verified by antibacterial experiments. Even after undergoing three reprocessing cycles, the antibacterial rate of GUA-DCPs remains above 99% after 24 h, highlighting their long-lasting antibacterial effectiveness. GUA-DCPs with dynamic nature, tuneable composition, and unique combination of properties make them promising candidates for various technological advancements.

Synthesis of Photoresponsive Fast Self-healing Polyolefin Composites by Nickel-Catalyzed Copolymerization of Ethylene and Lignin Cluster Monomers

Polymers may suffer from sudden mechanical damages during long-term use under various harsh operating environments. Rapid and real-time self-healing will extend their service life, which is particularly attractive in the context of circular economy. In this work, a lignin cluster polymerization strategy (LCPS) was designed to prepare a series of lignin functionalized polyolefin composites with excellent mechanical properties through nickel catalyzed copolymerization of ethylene and lignin cluster monomers. These composites can achieve rapid self-healing within 30 seconds under a variety of extreme usage environments (underwater, seawater, extremely low temperatures as low as -60 °C, organic solvents, acid/alkali solvents, etc.), which is of great significance for real-time self-healing of sudden mechanical damage. More importantly, the dynamic cross-linking network within these composites enable great re-processability and amazing sealing performances.

Mechanically Ultra-Robust Fluorescent Elastomer for Elaborating Auxetic Composite

Fluorescent elastomers are predominantly fabricated through doping fluorescent components or conjugating chromophores into polymer networks, which often involves detrimental effects on mechanical performance and also makes large-scale production difficult. Inspired by the heteroatom-rich microphase separation structures assisted by intensive hydrogen bonds in natural organisms, an ultra-robust fluorescent polyurethane elastomer is reported, which features a remarkable fracture strength of 87.2 MPa with an elongation of 1797%, exceptional toughness of 678.4 MJ m-3 and intrinsic cyan fluorescence at 445 nm. Moreover, the reversible fluorescence variation with temperature could in situ reveal the microphase separation of the elastomer in real time. By taking advantage of mechanical properties, intrinsic fluorescence and hydrogen bonds-promoted interfacial bonding ability, this fluorescent elastomer can be utilized as an auxetic skeleton for the elaboration of an integrated auxetic composite. Compared with the auxetic skeleton alone, the integrated composite shows an improved mechanical performance while maintaining auxetic deformation in a large strain below 185%, and its auxetic process can be visually detected under ultraviolet light by the fluorescence of the auxetic skeleton. The concept of introducing hydrogen-bonded heteroatom-rich microphase separation structures into polymer networks in this work provides a promising approach to developing fluorescent elastomers with exceptional mechanical properties.

Biodegradable photo-crosslinked polycaprolactone/polydopamine elastomers with excellent light driven programmable shape memory and chemical degradation properties

Fabrication of biodegradable shape memory polymer with remotely controllable shape actuation is of great significance in the biomedical field but remains challenging. Herein, we present a simple strategy to fabricate a monolayer-based stretchable and mechanically robust polycaprolactone/polydopamine elastomer via efficient thiol-ene click chemistry. The resultant elastomers exhibit desirable photothermal transfer efficiency and can enable rapid temperature increase over the melting temperature of polymeric matrix, and quantitative results demonstrate that the crosslinked film exhibited excellent shape memory properties with shape fixity (Rf) and shape recovery ratios (Rr) approaching 92.3 % and 95.6 %, respectively. Combined with photo stimuli, anisotropic polymer chain relaxation of the prestretched film can generate asymmetric contractions and eventually give rise to ut out-of-plane bending actuations upon photo stimulation, meanwhile, numerical simulation reveals the interaction mechanism of light with film. Beyond this, we further demonstrate that the bending angle is correlated with the parameters of prestretch strain, film thickness as well as irradiation time, and the maximum value can reach 158° with prestretch strain of 200 % and film thickness of 0.3 mm. In particular, the bent structures could be reversibly deformed into plane state via photo-directed corresponding opposite surfaces. Remarkably, the in vitro degradation properties of the elastomers on PBS-T buffer solutions demonstrated that the degradation was composed of induction stage and acceleration stage. This work will pave way for designing biodegradable light-induced shape memory materials toward biomedical device fields and so on.

Self-Healing Elastomers with Unprecedented Ultrahigh Strength, Superhigh Fracture Energy, Excellent Puncture Resistance, and Durability Based on Supramolecule Interlocking Networks Formed by Interlaced Hydrogen Bonds

Due to the multiple different properties in self-healing elastomers that are mutually exclusive based on the different and contradictory molecule chain structures, simultaneously achieving the ultrahigh mechanical performance and high durability of self-healing elastomers is a great challenge and the goal that has always been pursued. Herein, we report a novel strategy to fabricate a self-healing elastomer by introducing interlaced hydrogen bonds with superhigh binding energy. Distinguishing from the quadruple hydrogen bonds reported already, the interlaced hydrogen bond with a lower repulsive secondary interaction and higher binding energy is composed of two molecule units with different lengths and steric hindrance. Connected by the interlaced hydrogen bonds, a supramolecule interlocking network is formed to lock the polymer chains at room temperature, endowing the poly(urethane-urea) elastomer with an unprecedented ultrahigh strength (117.5 MPa, even higher than some plastics), the superhigh fracture energy (522.46 kJ m-2), and an excellent puncture resistance (puncture force reached 181.9 N). Moreover, the elastomers also exhibited excellent self-healing properties (healing efficiency up to 95.8%), high transparency (the average transmittance up to 91.0%), and good durability (including thermal decomposition resistance, thermal oxidation aging resistance, water resistance, and solvent resistance), providing a theoretical basis and technical reference in the development and broadening the application prospects of self-healing elastomers.

An Analysis of the Self-Healing and Mechanical Properties as well as Shape Memory of 3D-Printed Surlyn® Nanocomposites Reinforced with Multiwall Carbon Nanotubes

This research work studies the self-healing ability, mechanical properties, and shape memory of the polymer Surlyn® 8940 with and without multiwall carbon nanotubes (MWCNTs) as a nanoreinforcement. This polymer comes from a partially neutralized poly(ethylene-co-methacrylic acid) (EMAA) ionomer copolymer. MWCNTs and the polymer went through a mixing process aimed at achieving an excellent dispersion. Later, an optimized extrusion method was used to produce a uniform reinforced filament, which was the input for the 3D-printing process that was used to create the final test samples. Various concentrations of MWCNTs (0.0, 0.1, 0.5, and 1.0 wt.%) were used to evaluate and compare the mechanical properties, self-healing ability, and shape memory of unreinforced and nanoreinforced materials. Results show an enhancement of the mechanical properties and self-healing ability through the addition of MWCNTs to the matrix of polymer, and the specimens showed shape memory events.