Design and Synthesis of Hyperbranched Aromatic Polymers for Catalysis.

Aromatic polymers such as poly(ether sulfone), poly(ether ketone), and polyimide have been widely used in industry due to their thermal, mechanical, and chemical stabilities. Although their application to catalysis has been limited, the introduction of a hyperbranched architecture to such aromatic polymers is effective in developing catalytic materials that combine the advantages of homogenous and heterogeneous catalysts. This review article overviews the recent progress on the design and synthesis of hyperbranched aromatic polymers. Several acid catalyzed reactions and the aerobic oxidation of alcohols have been demonstrated using hyperbranched aromatic polymers as catalysts. The advantage of hyperbranched polymers against linear polymers is also discussed.

Star-Shaped Thermoresponsive Polymers with Various Functional Groups for Cell Sheet Engineering.

This study demonstrates the facile preparation of poly(N-isopropylacrylamide) (PNIPAM)-immobilized Petri dishes by drop-casting a star-shaped copolymer of hyperbranched polystyrene (HBPS) possessing PNIPAM arms (HBPS-g-PNIPAM) functionalized with polar groups. HBPS was synthesized via reversible addition-fragmentation chain transfer (RAFT) self-condensing vinyl polymerization (SCVP), and HBPS polymers with different terminal structures were prepared by changing the monomer structure. HBPS-g-PNIPAM was synthesized by the grafting of PNIPAM from each terminal of HBPS. To tune the cell adhesion and detachment properties, polar functional groups such as carboxylic acid and dimethylamino groups were introduced to HBPS-g-PNIPAM. Based on surface characterization using scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy (XPS), and contact angle measurements, the advantage of the hyperbranched structure for the PNIPAM immobilization was evident in terms of the uniformity, stability, and thermoresponsiveness. Successful cell sheet harvesting was demonstrated on dishes coated with HBPS-g-PNIPAM. In addition, the cell adhesion and detachment properties could be tuned by the introduction of polar functional groups.

Active site formation mechanism of carbon-based oxygen reduction catalysts derived from a hyperbranched iron phthalocyanine polymer.

Carbon-based cathode catalysts derived from a hyperbranched iron phthalocyanine polymer (HB-FePc) were characterized, and their active-site formation mechanism was studied by synchrotron-based spectroscopy. The properties of the HB-FePc catalyst are compared with those of a catalyst with high oxygen reduction reaction (ORR) activity synthesized from a mixture of iron phthalocyanine and phenolic resin (FePc/PhRs). Electrochemical measurements demonstrate that the HB-FePc catalyst does not lose its ORR activity up to 900°C, whereas that of the FePc/PhRs catalyst decreases above 700°C. Hard X-ray photoemission spectra reveal that the HB-FePc catalysts retain more nitrogen components than the FePc/PhRs catalysts between pyrolysis temperatures of 600°C and 800°C. This is because the linked structure of the HB-FePc precursor has high thermostability against nitrogen desorption. Consequently, effective doping of active nitrogen species into the sp (2) carbon network of the HB-FePc catalysts may occur up to 900°C.

Theoretical characterization of X-ray absorption, emission, and photoelectron spectra of nitrogen doped along graphene edges.

K-edge X-ray absorption (XAS), emission (XES), and photoelectron (XPS) spectra of nitrogen doped along graphene edges are systematically investigated by using first-principles methods. In this study we considered pyridinium-like, pyridine-like, cyanide-like, and amine-like nitrogens at armchair and zigzag edges and pyrrole-like nitrogen at armchair edge as well as graphite-like nitrogen at graphene interior site. Our results indicate that nitrogen configuration and its location (armchair or zigzag edge) in nitrogen-doped graphene can be identified via the spectral analysis. Furthermore, some controversial spectral features observed in experiment for N-doped graphene-like materials are unambiguously assigned. The present analysis gives an explanation to the reason why the peak assignment is usually made differently between XPS and XAS.

Cylindrical Nanostructure of Rigid-Rod POSS-Containing Polymethacrylate from a Star-Branched Block Copolymer.

A nanostructure consisting of rectangular polyhedral oligomeric silsesquioxane (POSS) nanodomains packed into a hexagonal lattice was observed in POSS-containing A2B star-branched polymers. The A2B star-branched polymers, which comprised polystyrene (A) and bulky POSS-containing poly(methacrylate) (PMAPOSS) (B) units, were synthesized by anionic polymerization and addition reaction. The self-assembled structures of the A2B star-branched polymers were studied via transmission electron microscopy (TEM) and small- and wide-angle X-ray scattering (SAXS and WAXS, respectively). It was found that a rectangular nanostructure was packed into a hexagonal arrangement of nanodomains for a PMAPOSS volume fraction of 40 vol. % in the star-branched polymer. In addition, the cylinder-like nanostructure of bulky POSS observed, which is not observed in the case of PS-b-PMAPOSS diblock copolymers, was formed owing to the curvature effect, which is the result of the branched architecture of the copolymer.

Organic macromolecular high dielectric constant materials: synthesis, characterization, and applications.

Hyperbranched and dendritic architectures have been targeted for various applications such as sensing, drug delivery, optical limiting, and light harvesting. One interesting development in this area has focused on utilizing the existence of long-range delocalization in hyperbranched structures to achieve high dielectric constants. In this Feature Article, we will review the creation and development of this concept, and we highlight our recent research progress in this aspect. In particular, we discuss (1) synthetic methods for a particular group of hyperbranched polymers; (2) detailed optical and electronic characterization of this group of hyperbranched polymers, revealing the design criteria for achieving a good combination of high dielectric constant and minimum loss in such materials; and (3) the importance and potential applications of these materials.

Pt-free cathode catalysts prepared via multi-step pyrolysis of Fe phthalocyanine and phenolic resin for fuel cells.

Pt-free cathode catalysts for polymer electrolyte membrane fuel cells have been prepared by multi-step pyrolysis of FePc and PhRs, in the best of which show extensively high initial cell performance and good durability compared to other present precious-metal-free cathode catalysts to date.

Synchrotron grazing incidence X-ray scattering study of the morphological structures in thin films of a polymethacrylate diblock copolymer bearing POSS moieties.

The morphological structures in thin films of a diblock copolymer of methyl methacrylate and polyhedral oligomeric silsesquioxane (POSS) functionalized methacrylate (PMMA-b-PMAPOSS) with a volume ratio of 13/87 were investigated in detail by using synchrotron grazing incidence small and wide-angle X-ray scattering (GISAXS and GIWAXS). In addition, its thermal properties were studied. Thin films of this diblock copolymer were found to undergo phase-separation during solvent-annealing with carbon disulfide and post thermal annealing. To quantitatively analyze the scattering data, GISAXS and GIWAXS formulas were derived and applied. Our detailed analysis found that cylinders of PMMA blocks are induced to form in the diblock copolymer films by solvent-annealing and are hexagonally packed in the PMAPOSS matrix, in which the cylinders are oriented vertically with respect to the film plane. In the solvent-annealed films, both the PMMA cylinders and the PMAPOSS matrix are featureless, i.e., amorphous. However, the post thermal annealing process induces aggregation of the POSS moieties, which results in the formation of crystals with an orthorhombic lattice unit cell. These crystals were found to consist of PMAPOSS block chains in a helical conformation in which the molecular PMAPOSS cylinders are aligned in the film plane. The formation of these crystals is induced by the ordering ability of the POSS moieties. The crystals were found to melt above 190 degrees C during heating and subsequent cooling. In contrast, the hexagonally packed structure of the PMMA cylinders in the solvent-annealed and post thermally annealed films was found to be retained during the heating and the subsequent cooling. In addition, the scattering analysis provides detailed structural parameters. The 2D GISAXS and GIWAXS patterns were reconstructed from the determined structural parameters by using the derived scattering formulas, and found to be in good agreement with the experimental patterns. Moreover, a model for the structure of the films of the diblock copolymer is proposed.

Hyperbranched polysiloxysilane nanoparticles: surface charge control of nonviral gene delivery vectors and nanoprobes.

New hyperbranched polysiloxysilane (HBPS) materials containing terminal carboxylic acid and quaternary ammonium groups were designed and synthesized to obtain fluorescent-dye-encapsulated nanoparticles. These polymers exhibited desirable characteristics, including amphiphilicity for nanoparticle formation, and contained various terminal groups for surface-charge control on the nanoparticles or for further bioconjugation for targeted imaging. Nanoprobes composed of polysiloxysilane nanoparticles encapsulating two-photon dyes were also prepared for optical bioimaging with controlled surface charge density (zeta potential) for modulation of cellular uptake. Intracellular delivery of these structurally similar polysiloxysilane nanoparticles, with substantially different surface charges, was investigated using confocal and two-photon fluorescence microscopy as well as flow cytometry. Finally, the use of these nanoparticles as efficient gene delivery vectors was demonstrated by means of in vitro transfection study using beta-galactosidase plasmid and pEGFP-N1 plasmid and the most efficient combination was obtained using HBPS-CN30:70.

One-Step Direct-Patterning Template Utilizing Self-Assembly of POSS-Containing Block Copolymers.

We report the self-assembly of organic-inorganic block copolymers (BCP) in thin-films by simple solvent annealing on unmodified substrates. The resulting vertically oriented lamellae and cylinders are converted to a hard silica mask by a single step highly selective oxygen plasma etching. The size of the resulting nanostructures in the case of cylinders is less than 10 nm.

Spin-assembled nanolayer of a hyperbranched polymer on the anode in organic light-emitting diodes: the mechanism of hole injection and electron blocking.

We introduced a spin-assembled nanolayer of hyperbranched poly(ether sulfone) with sulfonic acid terminal on top of an indium-tin oxide anode in organic light-emitting diodes. This results in great improvement in luminous efficiency, better than that of devices using a commercially available conducting polymer composition as a hole-injection layer. The effect of the nanolayer was investigated by impedance spectroscopy, photovoltaic measurement for built-in-potential, and transient electroluminescence. We concluded that the high luminous efficiency resulted from the efficient electron-blocking by the nanolayer and hole-injection assisted by the accumulation of electrons at the interface. This result implies that, for an efficient hole-injection layer, the electron-blocking capability should be incorporated in addition to the hole-injection and -transport capability.

Novel bipolar bathophenanthroline containing hosts for highly efficient phosphorescent OLEDs.

The electronic structures of eight bathophenanthroline derivatives were elucidated by DFT calculations, and four representatives of which CZBP, m-CZBP, m-TPAP, and BPABP were synthesized and employed as the hosts to afford highly efficient phosphorescent OLEDs. The calculated molecular orbital energies agree well with the experimental results, which further demonstrates that the localization of HOMO and LUMO at the respective hole- and electron-transporting moieties is desirable in bipolar molecular designs.

High frequency dielectric response in a branched phthalocyanine.

We describe the dielectric effects in a novel branched phthalocyanine system. The synthesis and characterization of the hyperbranched structure are provided. The dielectric constant was approximately 45 over many decades of frequency, and the dispersion was small up to 1 MHz. The losses experienced in this novel material were very small (close to 0.001) at high frequency. The mechanism of this novel effect in the branched structure involves a delocalized polaronic state which takes advantage of the strong intramolecular interactions in the system.

Self-assembled lamellar nanostructures of wholly aromatic rod-rod-type block molecules.

Wholly aromatic rod-rod type di- and triblock molecules, oligo(ether sulfone)-b-oligo(ether ketone)s (OES-OEK), were synthesized to study a solid-state self-assembled nanostructure. The OES and OEK segments in the block molecules form segregated crystalline domains. The energy-filtering transmission electron microscopy images revealed that the di- and triblock OES-OEK co-oligomers formed lamellar nanostructures with a periodicity of approximately 9 and 13 nm, respectively. [structure: see text].