Dynamic Covalent Structure for the Design of Recyclable Polyurethane Based on the Diketone Chemistry.

Herein, the rational design of an enaminone compound is reported which can be easily and conveniently designed and obtained via the reaction of amine and diketone. The dynamic enaminoneamide structure is formed via the reaction between isocyanate and enaminone in fabricating a novel dynamic crosslinked polyurethane. The new kind of polyurethane can be efficiently recycled via the shifting between crosslinked structure and oligomer for the reversible dissociation of the enaminoneamide structure. Besides remolding itself via the thermal treatment, oligomers liberated from recycled-polyurethane can directly take part in constructing a new polyurethane without further purification. Therefore, the recyclability of this polyurethane shows high-value characteristics. The ease with which polyurethane can be produced, used, recycled, and reused without losing value offers a new green solution in designing sustainable polymer materials with a high economic value and a minimal environmental burden.

Skin-Inspired Tough Elastomer with Moisture-Triggered Switchable Mechanical Properties.

Biological tissue usually exhibits good water adaptive mechanical properties, which can maintain high strength and toughness in both wet and dry states. However, synthetic tissue like hydrogel usually becomes hard and brittle in its dry state. Herein, this challenge is met by exploring iron-catechol complex (TA-Fe3+ ) as a great platform combining extremely different polymers (elastomer and hydrogel) to construct new tissue-like soft composite materials with two different continuous phases, which have not yet been reported. In its dry state, the xerogel phase becomes a reinforced segment to increase the strength of PB without losing its toughness. In its wet state, this soft material becomes high performance hydrogel, where hydrogel phase absorbs high water and elastomer phase can sustain high loading. Such heterogeneous phase structures provide a good idea for designing the soft materials, exhibiting a trade-off between its high strength and toughness in both wet and dry states. Furthermore, its shape memory behaviors in both its wet and dry state, which shows a great potential application for complex adaptive shape transformation and engineering application like lifting of heavy objects under remote control due to high photo-thermal transition of TA-Fe3+ is explored.

Wavelength-Selective Photo-Cycloadditions of Styryl-Anthracene.

Light-tunable covalent chemistry is highly urgent in the fields of chemistry, biology, and materials science, especially for the smart materials and surface, due to the spatiotemporal control and feasible operation. Here, a new type of wavelength-selective photo-cycloaddition of styryl-anthracene carboxylic acid (SACA) is reported. Upon the irradiation of 450 nm visible light or 365 nm UV light, SACA can undergo [2+2] or [2+4] photocycloaddition, respectively. Furthermore, the [2+2] photocycloaddition induced by vis-light of 450 nm is reversible and can be disrupted by 365 nm UV light to form dimer-24 which cannot be photo-cleavable. Owing to the feasibility and spatiotemporal characteristics of UV-vis light-controlled photocycloaddition, the SACA possesses potential applications in various areas such as self-assembly, dynamic wrinkles, and fluorescence patterns, which are also explored and exhibited in this work.

Aminoesterenamide Achieved by Three-Component Reaction Heading toward Tailoring Covalent Adaptable Network with Great Freedom.

Covalent adaptable networks (CANs) have recently received extensive interests due to their reprocessability and repairability. Rethinking the libraries of the published CANs, most of them are fabricated by one/two-component reactions and few cases utilize multi-component reactions to construct CANs while multi-component reactions are conductive to tailoring the properties of polymers due to their structural designability and flexible choice of raw materials. A novel kind of dynamic covalent bond named aminoesterenamide is presented through three-component reaction between acetoacetyl, amine and isocyanate. Aminoesterenamide exhibits thermal reversibility through dissociating into vinylogous urethane and isocyanate. When it is used to prepare CANs, the synthesized polymer networks can be reprocessed many times via the exchange reaction between aminoesterenamides. Moreover, the forming of aminoesterenamide involving three starting components imparts CANs with great freedom to tailor their properties. Therefore, the authors believe this method that utilizes three-component reaction to fabricate CANs would bring new stories and perspectives to the exploration of new types of CANs.

A study on mineralization behavior of amino-terminated hyperbranched polybenzimidazole membranes.

Amino-bearing polymers, coated with apatite or similar minerals, have attracted significant attention for their potential in medical applications. In this study, an amino-terminated hyperbranched polybenzimidazole (HBPBI) membrane was used as a substrate for apatite growth. The membrane was soaked in solutions of CaCl2, Na2HPO4 and SBF to yield an apatite coating. The structure and morphology of the layers were characterized by FTIR-ATR, XRD and FESEM. The results indicate that the high densities of amino, imide and imidazole groups on the amino-terminated HBPBI membrane provide active sites for the growth of apatite.

Unzipped multiwalled carbon nanotube oxide/multiwalled carbon nanotube hybrids for polymer reinforcement.

Multiwalled carbon nanotubes (MWNTs) have been widely used as nanofillers for polymer reinforcement. However, it has been restricted by the limited available interface area of MWNTs in the polymer matrices. Oxidation unzipping of MWNTs is an effective way to solve this problem. The unzipped multiwalled carbon nanotube oxides (UMCNOs) exhibit excellent enhancement effect with low weight fractions, but agglomeration of UMCNOs at a relatively higher loading still hampered the mechanical reinforcement of polymer composites. In this paper, we interestingly found that the dispersion of UMCNOs in polymer matrices can be significantly improved with the combination of pristine MWNTs. The hybrids of MWNTs and UMCNOs (U/Ms) can be easily obtained by adding the pristine MWNTs into the UMCNOs aqueous dispersion, followed by sonication. With a π-stacking interaction, the UMCNOs were attached onto the outwalls of MWNTs. The morphologies and structure of the U/Ms were characterized by several measurements. The mechanical testing of the resultant poly(vinyl alcohol) (PVA)-based composites demonstrated that the U/Ms can be used as ideal reinforcing fillers. Compared to PVA, the yield strength and Young's modulus of U/M-PVA composites with a loading of 0.7 wt % of the U/Ms approached ∼145.8 MPa and 6.9 GPa, respectively, which are increases of ∼107.4% and ∼122.5%, respectively. The results of tensile tests demonstrated that the reinforcement effect of U/Ms is superior to the individual UMCNOs and MWNTs, because of the synergistic interaction of UMCNOs and MWNTs.