Constructed by supramolecular polymer-metal coordination driven self-assembly – Organic nanocapsules network
Organometallic nanocapsules (MONC), metal organic frameworks (MOF), the organic metal cage (MOC) and metal-organic polyhedra (MOP) is a hot topic of recent research in the field of metal-organic material. MONC unique geometry and large internal voids so that it can be applied to separate, related catalysis, energy storage and biomedicine. However, most crystalline powder MONC polydisperse, brittle material is discontinuous, which limits their application. More and more studies will be integrated into the supramolecular polymer metal – organic hybrid material to construct a structure, such hybrid materials not only retains the rigid frame nanostructures, and polymers having flexibility, machinability and other features. While the related work has been reported, but the chemically modified ligand is extremely complex, resulting in chain length of the polymer matrix component and difficult to adjust. In addition, the self-assembly behavior polyMOC / MOP is also difficult to simulate and study at the molecular level, which is detrimental to improving the performance of materials through molecular design. 
Recently, US Department of Chemistry, University of Missouri Jerry L. Atwood Bin Hua, Zhejiang University team and teamwork in the JACS [123 ] published \”Construction of Polymeric Metal-Organic Nanocapsule Networks via Supramolecular Coordination-Driven Self-Assembly\” 123] on [. oF MONCs based monomer as pyrogallol aromatics, which with polyethylene glycol (PEG) polymerized to build a new polymer metal – organic nanocapsules network (polyMONC). MONC may be interconnected with a hydroxyl group on the PEG chains, resulting in spontaneous assembly made polyMONC gel (Scheme 1). Mechanical properties of the gel may also be adjusted by different molecular weight or changing the ratio of PEG PEG:MONC. Due to the dynamic nature of coordination bonds, supramolecular polymer gels also have unique characteristics such as self-healing properties and stimuli responsive. The authors also discuss in depth from a molecular point of the polymerization mechanism polyMONC.
crystal and EG @ MONC DEG @ MONC Typical solvents are prepared in the hydrothermal synthesis technique. EG @ MONC crystal structure, nanocapsules six propyl pyrogallol aromatics (PGC3) and 24 Mg
2+
configuration, cubo-octahedral geometry similar (Figure 1a). Nanocapsules formed from eight [Mg3O3] three metal clusters which Mg-O distance of 2.00 to 2.09Å, O-Mg-O angle 81.8-102.3 °, Mg-O-Mg angle of 138.3-139.1 °. Molecules within the crystal structure of the hydrogen bonding interactions as well, the distance between oxygen atoms is very short, from 2.46 to 2.51Å. Since nanocapsules is electrically neutral, so 48 phenolic groups is deprotonated to balance the positive charge of Mg 2+ . The remaining 24-hydroxy held together by hydrogen bonds. Thus, the nanocapsules 96 is a metal – oxygen coordination bonds and hydrogen bonds suture 24, to keep high stability. Mg 2+ octahedral ligands equatorial position oxygen atom PgC3 filling (FIG. 1b). EG outside ligand, and there are 12 [Mg3O3] clusters coordinated other capsules, each capsule and connected with six adjacent nanocapsules, thereby forming a crosslinked backbone (FIG. 1c). DEG @ MONC crystal structure has two types MONC, 24 thereof by Mg 2+ and 6 PgC3 composition. The two differ in that the outer axial MONC ligand. External axial ligands include four type A DEG molecules, each capsule is connected to two adjacent capsules. B-type ligands comprises an external 12 DEG, two and two molecules of pyridine nitrate ion (FIG. 1d). In addition, each capsule and six capsules connecting adjacent (FIG. 1e and 1f). And various EG @ MONC DEG @ MONC stacking structure, the degree of crosslinking is different, indicating that PEG crosslinking MONC with different molecular weights, the resultant mechanical properties of the polymer change.
of the PEG chain using a flexible linker was prepared as polyMONC. Scanning electron microscopy (SEM) display non-crosslinked MONC without the formation of large aggregates (FIG. 2a) rule, and EG @ MONC cube can be observed even at the nanoscale, because small crystals are formed (FIG. 2b) . PEG400 @ MONCs a diameter of about 70 nm is formed small nanoparticles (FIG. 2C), indicated that MONCs crystallization is suppressed, and the complex-forming colloidal particles PEG400. PEG8000 @ MONCs form a polymer matrix embedding the nanoparticles, colloidal nanoparticles can be wound together with polyMONC ligand (FIG. 2d). OF also a transmission electron microscope (the TEM), scanning transmission electron microscope (STEM), NMR spectroscopy, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis ((TGA) further characterized polyMONC, results showed that PEG is capable of forming the cross-MONC joint, MONC have high thermal stability.
acetonitrile solution of a high concentration (15 wt%) of at polyMONC maintained at 110 ° C, cooled slowly to room temperature to give a dark opaque gel, and the gel is not generated control experiments, show MONC gelled essential .SEM image, the microstructure of the gel is nanofiberInterconnected porous three-dimensional network structure is formed. The porous structure so that it is of great significance in the potential applications of science and technology related fields body adsorption, catalysis and the like. Small angle X-ray scattering (the SAXS) further confirmed the presence of MONC (FIG. 3b) gel.
or PEG of different molecular weights used to prepare different polyMONC PEG8000 and varying the ratio of MONC. When the PEG molecular weight is too small or MONCs: PEG ratio is too low, polyMON a viscous gel rather than a sol. May be due to (i) a low molecular weight PEG chains shorter and rigid, extending the chain entanglement and more difficult, and (ii) when MONCs: too low, the degree of crosslinking is lowered PEG, is difficult to form a gel. Using PEG6000 (MONCs: PEG = 1: 6), PEG8000 (MONCs: PEG = 1: 4 or 1: 6) and PEG10000 (MONCs: PEG = 1: 6) polyMONC prepared can form a gel (gel 1-4 ), the gel obtained showed an elastic solid (G \’> G \”). Furthermore, the gel 1-4 G\’ is G\’gel-2> G\’gel-1> G\’gel-3> G \’gel-4, show that with MONCs: PEG ratio increase or decrease the molecular weight of PEG, the higher the degree of crosslinking of the gel due to the dynamic characteristics of coordination bond, a gel having self-healing properties is made polyMONC stimuli and responses. after capabilities (FIG. 4b). the gel-3 sample was cut into three segments, and each segment contact each other, discrete segments immediately adhered to each other. the samples were incubated for 5 minutes, which is completely healed, no cracks were found at the symphysis. such can reversibly gel sol process of heating and cooling – gel transition (FIG. 4c), the dynamic nature of the system indicates that polyMONCs and reversible
of the drive coordinated by supramolecular self-assembly of the nanocapsules polyMONC successfully prepared. The author first studied the use of small molecule linker EG and DEG-based crosslinking behavior MONC skeleton. The PEG is then used as a bridging ligand to form a polymeric nanocapsules polyMONC, polyMONC form a gel. Benefit from the dynamic characteristics of coordination bonds, these gels exhibit stimulus responsiveness and self-healing properties. This work not only developed a coordinated drive by self-assembly, the new policy MONC functionalized, and reveals the polymerization mechanism polyMONC from the perspective of the molecule. Since a plurality of metal can be – constructed ligand supramolecular assembly compositions, this method can be further developed polyMONC gel having a novel function (magnetic, electric conductivity, catalytic action, etc.).
