Closed-loop recycling of tough epoxy supramolecular thermosets constructed with hyperbranched topological structure.

The regulation of topological structure of covalent adaptable networks (CANs) remains a challenge for epoxy CANs. Here, we report a strategy to develop strong and tough epoxy supramolecular thermosets with rapid reprocessability and room-temperature closed-loop recyclability. These thermosets were constructed from vanillin-based hyperbranched epoxy resin (VanEHBP) through the introduction of intermolecular hydrogen bonds and dual dynamic covalent bonds, as well as the formation of intramolecular and intermolecular cavities. The supramolecular structures confer remarkable energy dissipation capability of thermosets, leading to high toughness and strength. Due to the dynamic imine exchange and reversible noncovalent crosslinks, the thermosets can be rapidly and effectively reprocessed at 120 °C within 30 s. Importantly, the thermosets can be efficiently depolymerized at room temperature, and the recovered materials retain the structural integrity and mechanical properties of the original samples. This strategy may be employed to design tough, closed-loop recyclable epoxy thermosets for practical applications.

Surface hybrid self-assembly, mechanism, and crystalline behavior of a carboxyl-ended hyperbranched polyester/platinum complex.

The self-assembly of hyperbranched polymers has attracted much attention because of their wide application. In this article, we report a new facile surface self-assembly method for a carboxyl-ended hyperbranched polyester/platinum complex (HTD-3-Pt) and obtain ordered structural microrods with a length of 10-20 µm and a width of 1 µm. The length and diameter of the self-assembled microrods could be increased to 300-600 µm and 4-5 µm, respectively, by hierarchical self-assembly. The main factors affecting the morphology of the self-assemblies, including temperature, time, solvent and solubility parameter, and relative humidity were discussed by transmission/reflection polarizing optical microscopy (TRPOM), SEM, and HRSEM. The indications for the coordination bond (-COOPt) included the appearance of a new peak at 1606 cm(-1) and its shifting to 1634 cm(-1) in the FT-IR spectra, the disappearance of the C 1s peak at about 288.6 eV, and the increase in the O 1s electron binding energy in the XPS spectra. Furthermore, an interesting crystal property of the HTD-3-Pt self-assemblies was discovered and confirmed by XRD. The study results from the surface self-assembly mechanism suggest that the coordination induction of the platinum ion play a key role in driving microphase separation between the intermolecular chains and end groups of the HTD-3-Pt to form the microrod self-assemblies. Another interesting finding was that HTD-3-Pt showed a higher catalytic activity for hydrosilylation than did a traditional homogeneous catalyst.

NUV-pumped red-emitting Ca9MnK(PO4)7 phosphor: energy transfer and charge compensation.

The development of novel Mn-based phosphor hosts has received increasing interest in the search for highly efficient red emitting phosphors for white LED applications. In this study, Ca9MnK(PO4)7, a compound with the ß-Ca3(PO4)2-type structure, was successfully synthesized by a high-temperature solid-state reaction process. The Eu2+-doped Ca9MnK(PO4)7 phosphor exhibits a broadband red emission peaking at 650 nm. The optimal excitation wavelength is 395 nm, which matches that of commercial ultraviolet (NUV) chips. Codoping Ce3+ ions into the Ca9MnK(PO4)7:Eu2+ phosphor efficiently improves Mn2+ luminescence. Here, Ce3+ acts as a charge compensator rather than a sensitizer and substantially increases the effective number of Eu2+ and finally improves the red emission of Mn2+. The charge compensation mechanism is also verified by codoping some optically inert rare earth ions (Ln3+) including Y3+, La3+ and Gd3+. The results demonstrate that these developed Ca9MnK(PO4)7:Eu2+, Ln3+ phosphors have great potential for application in NUV-based white LEDs. The energy transfer approach combined with the charge compensation technique is valuable for improving the performance of the red-emitting Ca9MnK(PO4)7:Eu2+ phosphor, which can further be used in developing other Mn-based phosphors.

Methylene-Bridged Tridentate Salicylaldiminato Binuclear Titanium Complexes as Copolymerization Catalysts for the Preparation of LLDPE through [Fe]/[Ti] Tandem Catalysis.

A novel tandem catalysis system consisted of salicylaldiminato binuclear/mononuclear titanium and 2,6-bis(imino)pyridyl iron complexes was developed to catalyze ethylene in-situ copolymerization. Linear low-density polyethylene (LLDPE) with varying molecular weight and branching degree was successfully prepared with ethylene as the sole monomer feed. The polymerization conditions, including the reaction temperature, the Fi/Ti molar ratio, and the structures of bi- or mononuclear Ti complexes were found to greatly influence the catalytic performances and the properties of obtained polymers. The polymers were characterized by differential scanning calorimetry (DSC), high temperature gel permeation chromatography (GPC) and high temperature 13C NMR spectroscopy, and found to contain ethyl, butyl, as well as some longer branches. The binuclear titanium complexes demonstrated excellent catalytic activity (up to 8.95 × 106 g/molTi·h·atm) and showed a strong positive comonomer effect when combined with the bisiminopyridyl Fe complex. The branching degree can be tuned from 2.53 to 22.89/1000C by changing the reaction conditions or using different copolymerization pre-catalysts. The melting points, crystallinity and molecular weights of the products can also be modified accordingly. The binuclear complex Ti2L1 with methylthio sidearm showed higher capability for comonomer incorporation and produced polymers with higher branching degree and much higher molecular weight compared with the mononuclear analogue.

Stabilization of the mesomorphic phase in a self-assembled two-component system.

We reported here the two-component self-assembling building blocks capable of forming lyotropic liquid crystal and liquid-crystalline physical gel. One of the components has a molecular characteristic of C(3)-symmetrical trisureas containing three azobenzene groups, which can form liquid-crystal phase in a temperature range of 133-215 degrees C. Another one has a trisamide core, which can self-aggregate to fibrous network through hydrogen bonds of amide moieties. The mixture of these two components performs lyotropic liquid crystal as well as liquid-crystalline physical gel in a temperature range larger than that of sole compound, suggesting that the cooperation of hydrogen bonds between these components stabilizes the mesophase of the assembly. The mechanism of formation of the mesophase was investigated by infrared spectra and small-angle X-ray scatterings.

Synthesis, characterization and olefin polymerization behaviors of phenylene-bridged bis-ß-carbonylenamine binuclear titanium complexes.

Binuclear and multinuclear complexes have attracted much attention due to their unique catalytic performances for olefin polymerization compared with their mononuclear counterparts. In this work, a series of phenyl-bridged bis-ß-carbonylenamine [O-NSR] (R = alkyl or phenyl) tridentate ligands and their binuclear titanium complexes (Ti2L1-Ti2L5) were synthesized and characterized by 1H NMR, 13C NMR, FTIR and elemental analysis. The molecular structure of ligand L2 (R = n Pr) and its corresponding Ti complex Ti2L2 were further investigated by single-crystal X-ray diffraction, which showed that each titanium coordinated with six atoms to form a distorted octahedral configuration along with the conversion of the ligand from ß-carbonylenamine to ß-imino enol form. Under the activation of MMAO, these complexes catalyzed ethylene polymerization and ethylene/α-olefin copolymerization with extremely high activity (over 106 g mol (Ti)-1 h-1 atm-1) to produce high molecular weight polyethylene. At the same time, wider polydispersity as compared with the mononuclear counterpart TiL6 was observed, indicating that two active catalytic centers may be present, consistent with the asymmetrical crystal structure of the binuclear titanium complex. Furthermore, these complexes possessed better thermal stability than their mononuclear analogues. Compared with the complexes bearing alkylthio sidearms, the complex Ti2L5 bearing a phenylthio sidearm exhibited higher catalytic activity towards ethylene polymerization and produced polyethylene with much higher molecular weight, but with an appreciably lower 1-hexene incorporation ratio. Nevertheless, these bis-ß-carbonylenamine-derived binuclear titanium complexes showed much higher ethylene/1-hexene copolymerization activity and 1-hexene incorporation ratios as compared with the methylene-bridged bis-salicylaldiminato binuclear titanium complexes, and the molecular weight and 1-hexene incorporation ratio could be flexibly tuned by the initial feed of α-olefin commoners and catalyst structures.

Morphological and X-ray diffraction studies of crystalline hydroxyapatite-reinforced polycaprolactone.

Morphological and mechanical properties of hydroxyapatite (HAP)-reinforced polycaprolactone (PCL) were studied. The objective was to examine how morphological features alter the bulk mechanical properties in our laboratory-synthesized HAP-reinforced PCL. HAP crystals were synthesized by hydrolysis of mixtures of calcium and phosphate salts in the laboratory with wet chemical methods. The properties of the commercially available hydroxyapatite (HAP(1)) are compared with that of laboratory-synthesized hydroxyapatite (HAP(2)). The HAP crystals and composition were characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared spectrometry (FTIR). The HAP(1) and HAP(2) crystals were dispersed into polymers to examine the mechanical behavior of bioactive composites, and the interfacial interactions between the polymer and HAP crystals are addressed. The FTIR results confirmed that the two forms of HAP crystals are consistent in terms of the functional chemical groups. The wide angle X-ray diffraction study was performed to determine the crystallinity of the bioactive composites. It was observed that the crystallinty of HAP-filled PCL steadily increased as the filler concentration increased. Generally, HAP(2) has a particle size considerably smaller than HAP(1) and the composite derived had higher modulus than conventional HAP-filled polymers. This increase in modulus is attributed to better interfacial interaction. Bioresorbability tests performed on HAP particles found that the synthesized HAP had higher resorption rates. It is clear that the mechanical properties are influenced by the particle size and therefore by the processing method used.

A facile method to prepare monodispersed CdS/SiO2 composite microspheres and investigation on their photocatalytic properties.

This article presents a facile method to prepare CdS/SiO(2) composite microspheres and their good catalytic properties. In our method, monodispersed SiO(2) particles bearing amino groups (-NH(2)) were synthesized at first and then used as carriers to load nanosized CdS particles to form CdS/SiO(2) composite microspheres. With the addition of CdAc(2) solution to the SiO(2) dispersion, Cd(2+) was attracted to the surfaces of the SiO(2) particles through coordination interaction, and then thioacetamide was added to the dispersion. By heating, S(2-) released and reacted with the Cd(2+), CdS/SiO(2) composite microspheres were obtained accordingly. The photocatalytic properties of the as-prepared composite microspheres were investigated as well. It was found that the composite microspheres have excellent photocatalytic activities for the degradation of dyes comparing with the commercial P-25 TiO(2) catalysts. After using and recycling for three times, the photocatalytic performance still remained very well.

Supramolecule-regulated photophysics of oligo(p-phenyleneethynylene)-based rod-coil block copolymers: effect of molecular architecture.

Three new topology-varied rod-coil block copolymers, comprising the same oligo(p-phenyleneethynylene) (OPE) rod components and the same coil components, were synthesized by atom-transfer radical polymerization. Their photophysical properties were systematically studied and compared in consideration of their solid-state structures and self-assembly abilities. These copolymers have similar intrinsic photophysical properties to the OPE rods, as reflected in dilute solution. However, their photophysical properties in the solid state are manipulated to be dissimilar by supramolecular organization. Wide-angle X-ray diffraction (WAXD) and atomic force microscopy (AFM) data demonstrate that these copolymers possess different self-assembly abilities due to the molecular-architecture-dependent pi-pi interactions of the rods. Hence, the aggregates in the solid state are formed with a different mechanism for these copolymers, bringing about the discrepancy in the solid-state luminescent properties.

Silver nanoparticles capped by oleylamine: formation, growth, and self-organization.

Nearly monodisperse silver nanoparticles have been prepared in a simple oleylamine-liquid paraffin system. Intensive study has found that the formation process of silver nanoparticles could be divided into three stages: growth, incubation, and Ostwald ripening stages. Ultraviolet-visible spectroscopy, transmission electron microscopy (TEM), and high-resolution TEM have all demonstrated the occurrence of Ostwald ripening, which could result in better control over the size and size distribution of silver nanoparticles. SAXS (small-angle X-ray scattering) results show that the as-obtained silver nanoparticles can self-assemble into ordered arrays. The possible reduction mechanism of silver ions by oleylamine is related to the Ag+-mediated conversion of primary amines to nitriles.

Low-temperature strategy to synthesize highly ordered mesoporous silicas with very large pores.

By employing a novel low-temperature synthetic pathway, highly ordered cubic mesoporous materials with hitherto the largest pores (up to 27 nm) and unit cells (up to 44 nm) have been successfully obtained.

Isolation and identification of surface-bound acetone enolate on Ni(111).

A surface-bound acetone enolate species has been synthesized on Ni(111) between 260 and 340 K by two different routes catalyzed by surface Ni and O atoms: deprotonation of acetone and deacetylation of acetylacetone. The reaction pathways and surface species have been identified using reflection absorption infrared spectroscopy (RAIRS) in combination with isotopic substitution and density functional theory (DFT) calculations. Acetone enolate exhibits characteristic vibrational absorption bands at 1260, 1353, and 1545 cm-1 arising from mixed modes that involve CC stretching, CH3 bending, and CO stretching. This work conclusively proves the existence of stable acetone enolate species on a metal single-crystal surface and provides its first detailed characterization.