Microphase‐separated structure of telechelic urethane acrylate anionomers and their network in various solvents

Telechelic urethane acrylate anionomer (UAA) chain showed less viscosity and polyelectrolyte behavior in water than dimethyl acetamide (DMAc) because of hydrophobic aggregation. UAA networks prepared in different solvents (water and DMAc) exhibited very different swelling behaviors in the same swelling medium, which can be interpreted as due to the very different microstructures formed in the solvents. UAA networks prepared with water (UAHG networks) had microphase‐separated hydrophilic and hydrophobic domains, whereas UAA networks synthesized with DMAc (UADG networks) had relatively homogeneous network structures. The mechanical property of the UAHG and UADG networks, measured with a dynamic mechanical analyzer, was also very sensitive to the solvent type used during the crosslinking reaction. UAHG networks with a microphase‐separated structure had a higher modulus than UADG networks. The results of the mechanical property measurements showed that water was a much better solvent for the hydrophilic hard segments of UAA chain than DMAc, even though DMAc dissolved both hydrophilic and hydrophobic segments of UAA chain. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2081–2095, 2000     

Binding of uranyl ion by 2,2′-dihydroxyazobenzene attached to a partially chloromethylated polystyrene

A 2,2′-dihydroxyazobenzene (DHAB) derivative was attached to a chloromethylated cross-linked polystyrene derivative in view of high affinity of DHAB for uranyl ion. Chloromethyl groups of the resin were converted to quaternary ammonium ions by treating with tertiary amines. Capacity of the resins for uranyl-uptake was measured, revealing that about 20 mg of uranium can be complexed to 1 g of the resins. Formation constants (K_f) for uranyl complexes of the resins were determined. In the presence of >0.1 M bicarbonate ion at pH 8.10, log K_f of about 15 was obtained. As bicarbonate concentration was lowered, K_f decreased considerably. Degrees of uranyl-uptake from rapidly flowing uranyl solutions were measured, and the results suggested that rate of uranyl-uptake may not impose a major barrier to application of the resins in uranium extraction from seawater. Uranium extraction from seawater with the resins was carried out on the east coast of Korean peninsula. The amount of uranium extracted from seawater was about 10 µg/g resin. This is not satisfactory for economical processes of uranium recovery from seawater. Results of the present study, however, suggested that modification of the DHAB-containing resins can improve uranyl-binding ability, probably leading to economical recovery of uranium from seawater. In addition, simulation of uranyl-binding processes in seawater with the laboratory procedures developed in this study was satisfactory. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3169–3177, 1999     

Growth and Optical Properties of Tm:GdVO4 Single Crystal

Thulium-doped gadolinium vanadate (Tm:GdVO₄) single crystal has been successfully grown by a modified Czochralski (CZ) technique. Effective distribution coefficient of Tm was determined to be 0.74. Absorption characterization was performed in the 800 nm region and the maximum absorption peak was found at 799 nm for p polarization. Fluorescence spectra for tuning at the maximum absorption were obtained around 1.8-2.0µm region with 100 nm bandwidth. This suggests that a Tm:GdVO₄ crystal is expected as a new promising LD pumped solid-state laser in the 2µm region.     

Self-Assembly of a Molecular Floral Lace with One-Dimensional Channels and Inclusion of Glucose

A three-dimensional network with one-dimensional channels (see picture) has been self-assembled from the nickel(II ) complex of cyclam and 1,3,5-benzenetricarboxylate in water through hydrogen-bond formation. The channels have an appropriate diameter (10.3 Å) to include D -glucose with a formation constant of K_f=(1.38±0.01)×10⁴ M ⁻¹. Under similar conditions maltose is not included.     

Partially imidized poly[(amic ester)-alt-imide]: A novel polyimide pregursor

Partial imidization of poly[(amic ester)-alt-(amic acid)], a precursor for the “strictly alternating” copolyimides, was performed via selective chemical imidization of amic acid units in the copolymer precursor. The resulting, poly[(amic ester)-alt-imide], showed superior properties such as an excellent solution stability, good processibility and improved optical transparency, which are essential for the use as a precursor for the polyimide.     

Vacuum pyrolysis study of graphite-like pyropolymers from 1,4-diphenyl-1-buten-3-yne

1,4-Diphenyl-1-buten-3-yne was metathesis polymerized over NbCl₅- or TaCl₅-based catalysts followed by pyrolysis to obtain graphite-like pyropolymers. The brown metathesis polymer, poly(1,4-diphenyl-1-buten-3-yne), has the structure of fully conjugated backbone and was annealed at 250°C to obtain partially crosslinked polymer which showed 20% increase of carbon residue on pyrolysis over 400°C than the pyrolyzed poly(1,4-diphenyl-1-buten-3-yne) without annealing. The polymers were characterized by GPC, EA, NMR, XPS, TGA, DSC, FT-IR, laser-Raman, x-ray diffraction, and SEM studies. © 1996 John Wiley & Sons, Inc.     

Suppression of secondary PL emission by indirect photoexcitation

A blend of a newly synthesized polyfluorene(PDHBF) and polyvinylcarbazole(PVK) exhibits a photoluminescence(PL) emission spectrum of PDHBF without an increase in the PL intensity on photoexcitation at 340 nm, the UV-visible absorption maximum of PVK, despite of a substantial spectrum overlap. However, the indirect photoexcitation of the blend suppresses the secondary emission of the PL with the maximum at 520 nm. The chromophores generating the secondary emission are formed when the chromophores are photoexcited above the critical energy level of an excited state. The chromophores formed by the energy transfer have energy lower than the critical energy and fail to form the excimers. A low temperature PL study of the blend in a cryogenic chamber proves that the energy transfer in the system takes place mainly between the excimers of PVK generated by the partially eclipsed dimeric states of two carbazole units and the fluorophores of PDHBF.     

Generalized Killing Ricci tensor for real hypersurfaces in the complex quadric

First we introduce a new notion of generalized Killing Ricci tensor which is equivalent to the notion of cyclic parallel Ricci tensor for real hypersurfaces in the complex quadric $Q^m=S{O}_{m+2}/S{O}_{m}S{O}_2$. Next, in terms of $\mathfrak{A}$-principal or $\mathfrak{A}$-isotropic unit normal vector fields we give a complete classification of real hypersurfaces in $Q^m=S{O}_{m+2}/S{O}_{m}S{O}_2$ with cyclic parallel Ricci tensor.     

A Useful Poly(ethylene oxide)‐poly(propylene oxide)‐poly(ethylene oxide) Triblock Crosslinker in a Diffusion‐Controlled Polymerization Method

Monodisperse micron‐sized polystyrene particles crosslinked with a novel poly(ethylene oxide)‐poly(propylene oxide)‐poly(ethylene oxide) triblock diol diacrylate (t‐BDDA) were produced via simple dispersion polymerization. It was established that the monomer‐diffusible surface characteristics of primary particles played a decisive role in producing the monodisperse crosslinked polymer particles. We named this concept a diffusion‐controlled polymerization method, DPM. Here in this study, particularly, t‐BDDA is proposed as a very useful crosslinker capable of self‐assembling and crosslinking in the process of particle formation and particle growth.     

Impact of microcellular plastics on industrial practice and academic research

Microcellular plastics (MCP) refer to any plastic with tiny bubbles of less than about 50 microns. It is made by subjecting polymers with a large amount of dissolved gas to a thermodynamic instability so as to nucleate a large number of cells instantaneously. MCP has been extruded and injection molded to make various industrial products. The fundamental theory for design of MCP and the processing methods are reviewed. It also discusses the design of equipment, including the die or mold, for MCP processing. The performance of MCP and the advantages of using MCP are presented. Some of industrial applications are also highlighted.