Imide-aryl ether benzoxazole random copolymers

Novel imide-aryl ether benzoxazole copolymers were prepared and their morphology and mechanical properties investigated. A key feature of these copolymers is the incorporation of a benzoxazole moiety by the use of 2,2′-bis[4-(3-aminophenoxy)phenyl]-6,6′-bibenzoxazole or 2,2′-bis[4-(4-aminophenoxy)-phenyl]-6,6′-bibenzoxazole as co-diamines in polyimide syntheses. The preparation of these diamines involved the nucleophilic aromatic substitution of 2,2′-bis(4-fluorophenyl)-6,6′-bibenzoxazole with either 3- or 4-aminophenol in the presence of K₂CO₃. The diamines were co-reacted with various compositions of pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) to synthesize the desired poly(amic acids). Films were cast and cured (350°C) to effect the imide formation, affording films with elongations between 40 and 110% and moduli in the 2000–2750 MPa range. The copolymers exhibited good dimensional (T_g in excess of 300°C) and thermal stability. Wide-angle X-ray diffraction measurements on the copolymers showed that the ordered morphology characteristic of PMDA/ODA polyimide was retained. Improvements in the auto-adhesion were observed, particularly in those copolymers which displayed a T_g.     

Preparation of nanosize Pt clusters using ion exchange of Pt(NH3) 4 2+ inside mesoporous channel of MCM-41

Mesoporous molecular sieve MCM-41 with a Si/Al ratio of 35 was obtained by hydrothermal synthesis using a gel mixture with a molar composition of 6 SiO₂0.1 Al₂O₃1 hexadecyltrimethylammonium chloride 0.25 dodecyltrimethylammonium bromide 0.25 tetrapropylammonium bromide0.15 (NH₄)₂O1.5 Na₂O300 H₂O. The MCM-41 sample was calcined in O₂ flow at 813 K and subsequently ion exchanged with Ca²⁺. A small Pt cluster has been supported on the MCM-41 sample following a procedure using ion exchange of Pt(NH₃) ₄ ²⁺ . The Pt(NH₃) ₄ ²⁺ ion supported on MCM-41 has been activated in O₂ flow at 593 K and subsequently reduced with Fh flow at 573 K, in the same way used for the preparation of a Pt cluster entrapped inside the supercage of zeolite NaY. The resulting Pt cluster supported on the MCM-41 shows hydrogen chemisorption oftotal two H atoms per Pt at 296 K (based on the total amount of Pt) and high catalytic activity for hydrogenolysis of ethane. The chemical shift in¹²⁹Xe NMR spectroscopy of adsorbed xenon indicates that the Pt cluster is located inside the mesoporous molecular sieve.     

Efficient clustering of uncertain data streams

Clustering uncertain data streams has recently become one of the most challenging tasks in data management because of the strict space and time requirements of processing tuples arriving at high speed and the difficulty that arises from handling uncertain data. The prior work on clustering data streams focuses on devising complicated synopsis data structures to summarize data streams into a small number of micro-clusters so that important statistics can be computed conveniently, such as Clustering Feature (CF) (Zhang et al. in Proceedings of ACM SIGMOD, pp 103–114, 1996) for deterministic data and Error-based Clustering Feature (ECF) (Aggarwal and Yu in Proceedings of ICDE, 2008) for uncertain data. However, ECF can only handle attribute-level uncertainty, while existential uncertainty, the other kind of uncertainty, has not been addressed yet. In this paper, we propose a novel data structure, Uncertain Feature (UF), to summarize data streams with both kinds of uncertainties: UF is space-efficient, has additive and subtractive properties, and can compute complicated statistics easily. Our first attempt aims at enhancing the previous streaming approaches to handle the sliding-window model by using UF instead of old synopses, inclusive of CluStream (Aggarwal et al. in Proceedings of VLDB, 2003) and UMicro (Aggarwal and Yu in Proceedings of ICDE, 2008). We show that such methods cannot achieve high efficiency. Our second attempt aims at devising a novel algorithm, cluUS , to handle the sliding-window model by using UF structure. Detailed analysis and thorough experimental reports on synthetic and real data sets confirm the advantages of our proposed method.     

Thermal Conductivity/Diffusivity of Silicon Carbide Whisker Reinforced Mullite

The thermal conductivity and diffusivity of silicon carbide whisker reinforced mullite was shown to increase with whisker content. This effect was much greater for vapor-liquid-solid (VLS) whiskers than for rice-hull (RH) whiskers. This suggests that the thermal conductivity for the VLS whiskers was significantly higher than for the RH whiskers. Due to preferred orientation of the whiskers, thermal conductivity and diffusivity of the composite samples exhibited significant anisotropy.     

Preparation and flame resistance properties of revolutionary self-extinguishing epoxy nanocomposites based on layered double hydroxides

Layered double hydroxides/epoxy (LDHs/EP) nanocomposites were prepared from organo-modified LDHs, a diglycidyl ether of bisphenol A monomer (DGEBA) and amine curing agents. The organo-modified LDHs were obtained by ionic exchange of a magnesium-aluminum carbonate LDH in an acid medium. X-ray diffraction and transmission electron microscopy showed a dispersion of the layers at a nanometer scale, indicating the formation of LDH/EP nanocomposites. The thermal degradation and flame resistance properties of LDH/EP nanocomposites, montmorillonite-epoxy (MMT/EP) nanocomposites, LDH/EP microcomposites and aluminum hydroxide-epoxy microcomposites were compared by thermogravimetrical analyses, simultaneous thermal analyses, UL94 and cone calorimeter tests. Only LDH/EP nanocomposites showed self-extinguishing behavior in the horizontal UL94 test; LDH/EP microcomposites and MMT/EP nanocomposites samples burned completely showing that the unique flame resistance of LDH/EP nanocomposites is related to both the level of dispersion and the intrinsic properties of LDH clay. Furthermore, cone calorimeter revealed intumescent behavior for LDH/EP nanocomposites and a higher reduction in the peak heat release rate compared to MMT/EP nanocomposites.     

Allelopathic properties ofPolygonella myriophylla

Polygonella myriophylla is a perennial shrub endemic to the Florida scrub. Striking bare zones surround maturePolygonella stands. Quantitative measurements of root distribution show that fewPolygonella roots extend into the bare zones, supporting the hypothesis that the bare zones result from chemical interference byPolygonella with the growth of other species. Bioassays of soils collected biweekly for one year from beneathPolygonella, the bare zone, and adjacent grassed areas confirm that the germination and growth of grasses is reduced inPolygonella soil and soil from the surrounding bare zone. Compared to adjacent grassed area soil, the average germination of bahiagrass (Paspalum notatum) was 71% inPolygonella soil and 81% in bare zone soil, and average shoot dry weight was 48% inPolygonella soil and 81% in bare zone soil. Seasonal variation in the inhibition of grass germination and growth was not pronounced.     

Preparation and characterization of mesostructured polymer-functionalized sol–gel-derived thin films

The present study attempts to incorporate methacrylate-based polymers into ordered lamellar organic/inorganic nanocomposite films composed of alternating SiO₂/polymer layers. The films are prepared by dip-coating from a solution containing the monomers and silica precursors, thus leading to composite lamellar mesostructured materials through evaporation-induced self-assembly (EISA). A polymerizable coupling agent is added to covalently link the polymers to the silica matrix. The final polymer/SiO₂ hybrid material is obtained by a separate free-radical polymerization step, initiated by UV exposure or thermal treatment. Using trimethoxy(7-octen-1-yl)silane as a coupling agent, a procedure was established that preserved the mesostructure and maintained the swelling properties of the polymers, while acrylate-based coupling agents lead to a significant distortion of the film mesostructure. Structure and composition of the films were studied by X-ray diffraction, NMR and IR.     

Image analysis for interfacial area and cocontinuity detection in polymer blends

A novel image processing method was developed to extract interfacial area concentration measurements from 2D micrographs of immiscible polymer blends. Although this method can be used for analyzing different types of 2D micrographs such as optical or transmission electron microscopy images, it was designed for analyzing scanning electron microscopy (SEM) images. The method operates by detecting edges within the images and using standard image processing operations to selectively eliminate false edges. SEM images of polyethylene oxide/polystyrene (PEO/PS) blends were analyzed using this image processing method to measure the amount of interfacial area in the samples. Interfacial area per unit volume exhibits maxima for blend compositions at the boundary between droplet and cocontinuous morphologies. In addition to the detection of cocontinuity, the interfacial area measurements facilitated by this method may be used in future investigations of blend dynamics, including coalescence, drop deformation, and blend rheology studies. These measurements may also be used to quantify the effects of compatibilizers on blend morphology.     

Sulfonated poly(ether ketone ketone) ionomers as proton exchange membranes

Sulfonated poly(ether ketone ketone) ionomers (SPEKK) with ion‐exchange capacities (IEC) between 0.2 and 3.4 meq/g were prepared by sulfonating PEKK with a mixture of concentrated and fuming sulfuric acids. Sulfonation occurs only on the phenyl rings attached to ether and ketone groups. The glass transition temperature of the dry SPEKK ionomers increased linearly with increasing IEC, and the ionomers were thermally stable to ～250°C, above which desulfonation occurred. Water‐swollen ionomers exhibited microphase separated morphologies, and the average correlation length determined by small angle X‐ray scattering increased with increasing IEC. The proton conductivity of hydrated SPEKK membranes measured by impedance spectroscopy ranged from ～10^–3 to 10^–1 S/cm as the IEC increased from ～1.0 to 2.4 meq/g. Single cell performance curves on membrane‐electrode assemblies (MEA) indicated that the SPEKK membranes approached the performance of Nafion? for an IEC of 2 meq/g. POLYM. ENG. SCI., 45:1081–1091, 2005. © 2005 Society of Plastics Engineers