bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Concerted H‐Bonding Self‐Assembly‐Based Approach to Ladder Poly(silsesquioxane)
Authors: Deng Kuilin , Zhang Taoyi , Zhang Xiaojing , Zhang Aiqin , Xie Ping , Zhang Rongben 
Published: February 2006

AbstractSummary: A soluble, regular, ethoxy‐capped, ladder poly(silsesquioxane) (EtO‐LPOAS) has been successfully synthesized by means of the concerted H‐bonding template of silanol and amido groups, through a new template monomer M: tetraethoxy disiloxane bisamide compound. EtO‐LPOAS was characterized by X‐ray diffraction (XRD), 29Si NMR spectroscopy and DSC measurements. The results confirm the presence of the regular, ladder structure of EtO‐LPOAS. This synthetic method has opened a new route to other new kinds of functional ladder poly(silsesquioxane)s.Schematic overview of the mechanism for synthesis of EtO‐LPOAS.magnified imageSchematic overview of the mechanism for synthesis of EtO‐LPOAS.
Synthesis and Orientation of Fluorene Containing Reactive Mesogens
Authors: Thiem Heiko , Jandke Markus , Hanft Doris , Strohriegl Peter 
Published: February 2006

AbstractSummary: The synthesis of new fluorene containing photocrosslinkable reactive mesogens is described. Both monodisperse trimers or pentamers and oligomeric mixtures containing two photocrosslinkable acrylate end groups were obtained by Suzuki‐cross‐coupling reactions. The pentamer 12a shows an ideal phase behavior for orientation experiments with a broad nematic phase between the glass transition at −10 °C and 123 °C. In the oligomeric mixtures 14a–g the transition temperature from the nematic to the isotropic phase can be tailored from 100 to 310 °C by adjusting the molecular weight of the oligomers by end‐capping. This process can be easily characterized by MALDI‐TOF spectroscopy. The pentamer 12a and the oligomeric mixture 14c were oriented on rubbed polyimide layers and orientation ratios of 15:1 in photoluminescence were obtained. Experiments with different film thicknesses show that the orientation is not homogeneous throughout the film but decreases with increasing distance from the orientation layer.
magnified image
Optically Transparency and Light Color of Novel Highly Organosoluble Alicyclic Polyimides with 4‐tert‐Butylcyclohexyl Group
Authors: Liaw Der‐Jang , Huang Ching‐Cheng , Chen Wen‐Hsiang 
Published: February 2006

AbstractSummary: Novel optically transparent and highly organosoluble alicyclic polyimides derived from bulky alicyclic diamine containing trifluoromethyl group on either side, 1,1‐bis[4‐(2‐trifluoromethyl‐4‐aminophenoxy)phenyl]‐4‐tert‐butylcyclohexane (BTFAPBC), were prepared. All polymers showed excellent solubility in various organic solvents like N‐methyl‐2‐pyrrolidinone (NMP), N,N‐dimethyl acetamide (DMAc), N,N‐dimethyl formamide (DMF), pyridine, cyclohexanone, and γ‐butyrolactone. The cut‐off wavelength and 80% transmission wavelength for polyimides ranged from 362 to 407 nm and 436 to 492 nm, respectively. Polyimides with alicyclic tert‐butylcyclohexyl cardo and trifluoromethyl substituents exhibited low dielectric constants ranging from 3.38 to 4.07 (at 1 KHz). Inherent viscosities of the polyimides were found to be in the range of 0.52–1.00 dL · g−1. Polyimides showed glass transition temperatures in the range of 231–262 °C, and possessed a coefficient of thermal expansion (CTE) of 66–79 ppm · °C−1. Thermogravimetric analyses of the polyimides revealed high thermal stability and decomposition temperature more than 450 °C in nitrogen atmosphere. The 10% weight loss temperature was found to be in the range of 453–544 and 413–502 °C in nitrogen and air atmospheres, respectively. The polyimide films had a tensile strength ranging from 84 to 100 MPa. The elongation at break varied from 6 to 12% and the tensile modulus varied from 1.1 to 2.1 GPa.Synthesis of diamines, BTFAPBC, BTFAPAd, and BTFAPTC.magnified imageSynthesis of diamines, BTFAPBC, BTFAPAd, and BTFAPTC.
Gradient Structure Polymer Obtained from a Homogeneous Mixture: Synthesis and Mechanical Properties
Authors: Noblet Guillaume , Désilles Nicolas , Lecamp Laurence , Lebaudy Philippe , Bunel Claude 
Published: February 2006

AbstractSummary: The synthesis of a polymer that exhibits a gradient in mechanical properties, by means of a new method recently developed in our laboratory, is described. The synthesis involves two commercial resins, Laromer® LR 8986 and Laromer® LR 9000. In a first step, an acrylic double bond photopolymerization gradient is created under UV exposure thanks to the decay of UV light intensity through the sample thickness. In a second step, a thermal crosslinking reaction is realized to form a polyurethane network in order to set the obtained gradient. The experimental conditions required to obtain and keep the gradient are investigated by FT‐IR and UV spectroscopies. Thus, an 80% acrylic double bond conversion gradient is obtained in the ultimate 5 mm thick material. Dynamic mechanical analysis reveals an important difference between both sides of the material, the irradiated surface being hard at ambient temperature, meanwhile the underside remains soft.Acrylic double bond conversion after 3 min of irradiation at 30 °C on materials of various thicknesses.magnified imageAcrylic double bond conversion after 3 min of irradiation at 30 °C on materials of various thicknesses.
Synthesis of Cross‐Linked Comb Polysiloxane for Polymer Electrolyte Membranes
Authors: Karatas Yunus , Kaskhedikar Nitin , Burjanadze Marina , Wiemhöfer Hans‐Dieter 
Published: February 2006

AbstractSummary: A series of comb‐like polysiloxanes was prepared as the base polymer for solvent‐free polymer electrolyte membranes. Hydrosilylation of poly(methylhydrosiloxane) (PMHS) was used to substitute hydrogen by the two types of side groups tetraethylene glycol allyl methyl ether and allyltrimethoxysilane (ATMS) with varying molar ratios between 5 and 40 mol‐% ATMS. The ATMS side groups served to cross‐link as‐prepared polymer electrolyte membranes after dissolving lithium trifluoromethylsulfonate (triflate) or lithium bis(trifluoromethylsulfonyl)imide. The ionic conductivities of these salt‐in‐polymer membranes prepared with a constant concentration of 10 wt.‐% lithium triflate showed a maximum conductivity of 4.6 × 10−5 S · cm−1 at 30 °C for 10 mol‐% ATMS substitution. In another series of experiments with the ATMS substitution held constant at 10 mol‐%, the salt concentration was varied yielding a maximum conductivity of 1.4 × 10−4 S · cm−1 at 30 °C for 12.5 wt.‐% lithium triflate.
magnified image
A Facile Method for Controlling the Molecular Weight of Hyperbranched Light‐Emitting Polymers
Authors: He Qingguo , Huang Hongmin , Bai Fenglian , Cao Yong 
Published: February 2006

AbstractSummary: Two series of hyperbranched conjugated polymers were synthesized via an A3 + B2 type Wittig reaction. The molecular weights of the polymers were successfully tuned by simply changing the feed ratio of the monomers. Polymers with higher molecular weights presented more efficient photoluminescence, higher thermal stability and higher performance of LEDs.
magnified image
Introducing a Flat Model of the Silica‐Supported Bis(imino)pyridyl Iron(II) Polyolefin Catalyst
Authors: Han Wei , Müller Christian , Vogt Dieter , Niemantsverdriet Hans (J. W.) , Thüne Peter C. 
Published: February 2006

AbstractSummary: A well‐defined flat model of a supported homogeneous polyolefin catalyst is prepared on the basis of an immobilized bis(imino)pyridyl iron complex on a super flat silica surface. The amount of supported catalyst precursor is quantified using XPS. This model catalyst remains active over extended periods, i.e., an average activity of 0.25 × 103 kg PE · (molCat · h · bar)−1 is obtained for 24 h of ethylene polymerization. The morphology of the nascent polyethylene film is investigated by SEM.A side‐view SEM image of the PE produced from the supported bis(imino)pyridyl Fe catalyst.magnified imageA side‐view SEM image of the PE produced from the supported bis(imino)pyridyl Fe catalyst.
Styrene Emulsion Polymerization above the CMC: New Evidence on Particle Nucleation by means of AFFFF
Authors: Carro Shirley , Herrera‐Ordonez Jorge 
Published: February 2006

AbstractSummary: The number (N) and size distribution of particles (PSD) of a styrene emulsion polymerization above the CMC were studied by means of asymmetric flow‐field flow fractionation (AF4). Bimodal PSDs were obtained, suggesting that coagulation of the primary particles is not as extensive as would be expected, according to the coagulative mechanism. AF4 allowed it to be demonstrated that N is constant during interval II, and that the resolution limit of other particle sizing techniques can lead to erroneous mechanistic inferences, from the evolution of N.Particle size distribution measured at low conversion for the emulsion polymerization of styrene, obtained by AF4 and DLS. The initial surfactant (S0), initiator (I0) and monomer (M0) concentrations are indicated in the figure.magnified imageParticle size distribution measured at low conversion for the emulsion polymerization of styrene, obtained by AF4 and DLS. The initial surfactant (S0), initiator (I0) and monomer (M0) concentrations are indicated in the figure.
Strain Field Analysis and Kinetics of Crack Propagation of Binary Triblock Copolymer Blends
Authors: Satapathy Bhabani Kumar , Staudinger Ulrike , Weidisch Roland , Lach Ralf , Janke Andreas , Knoll Konrad 
Published: February 2006

AbstractSummary:The crack toughness behaviour of binary styrene‐butadiene (SB) triblock copolymer blends of a thermoplastic block copolymer (LN3) and a thermoplastic elastomer (LN4) with different molecular architecture was studied using essential work of fracture (EWF) concept and was correlated to the morphological features from transmission electron microscopy (TEM). An increase in the crack toughness behaviour between 60 and 80 wt.‐% LN3 has been observed and is attributed to a change from cylindrical to lamellar morphology. The time‐resolved crack propagation studies have offered new dimensions to understand the kinetic aspects of fracture behaviour while the strain field analysis has explained the time‐dependent deformation behaviour to characterise the time dependence of the strain energy dissipation modes.Load‐displacement diagrams of non essential work of fracture values of LN3/LN4 blends.magnified imageLoad‐displacement diagrams of non essential work of fracture values of LN3/LN4 blends.
Precise Block‐Copolymers by Efficient Coupling of End‐Functionalized Polymers Using Phosgene
Authors: Cotiuga Irina , Picchioni Francesco , Agarwal Uday S. , Staal Bastiaan B. P. , Vekemans Jef A. J. M. , Lemstra Piet J. 
Published: February 2006

AbstractSummary: We report the synthesis of well‐defined block copolymers by covalent coupling of hydroxy end‐functionalized polymers. Using the high volatility of the coupling agent phosgene as compared to the solvent, very high conversion (up to 96%) is obtained in a one‐pot reaction with as little as 10−5 moles of each of the reacting polymers, even without prior purification of the as‐received reagents. This has potential as an alternative to the currently practiced method of sequential living polymerization of constituent monomers, with the added advantage of direct knowledge and control over the length distribution of each block.Coupling of end‐functionalized polymers using phosgene to form block copolymers of controlled composition.magnified imageCoupling of end‐functionalized polymers using phosgene to form block copolymers of controlled composition.
One‐Pot Fabrication of Supramolecular Polymer Particles via Situ Polymerization Stringed Assembly of a Two‐Monomer Microemulsion
Authors: Wang Yongxin , Qiu Zhaobin , Yang Wantai 
Published: February 2006

AbstractSummary: A novel method, situ polymerization stringed assembly (SPSA), is proposed to prepare stable solid or hollow supramolecular polymer particles, which are assembled by numerous nanoparticles. By this method, the fabrication of primary nanoparticles (poly(methyl methacrylate), PMMA), the linkers (polyvinylpyrrolidone, PVP, chains) between the nanoparticles, and the final assembled solid or hollow particles could be achieved in just one‐pot by methyl methacrylate (MMA)/N‐vinylpyrrolidone (NVP) microemulsion polymerization under UV irradiation. The structures of the supramolecular particles can be changed from solid to hollow by tuning the mass ratio of MMA/NVP in the microemulsion. AFM, TEM, and SEM experiments are performed to identify the results.AFM image of the PMMA/PVP solid particles obtained from the photopolymerization of the microemulsion containing 20 wt.‐% MMA, 10 wt.‐% NVP, and 5 × 10−2 wt.‐% BP.magnified imageAFM image of the PMMA/PVP solid particles obtained from the photopolymerization of the microemulsion containing 20 wt.‐% MMA, 10 wt.‐% NVP, and 5 × 10−2 wt.‐% BP.
Nanocomposite Dendrimers Based on Cyclic Phosphazene Cores: Amorphous Materials for Electroluminescent Devices
Authors: Sudhakar Sundarraj , Sellinger Alan 
Published: February 2006

AbstractSummary: A new family of solution‐processable, photoluminescent, nanocomposite dendrimers based on cyclic phosphazene (CP) cores have been prepared and characterized. The synthetic approach is based on the preparation of bromoaromatic‐functionalized CP cores by reacting selected bromophenolic compounds with the commercially available hexachlorocyclotriphosphazene in yields >90%. The bromophenyl‐functionalized CP cores are then reacted with N‐p‐tolylpyren‐1‐amine using Buchwald‐Hartwig amination chemistry to give the dendrimers of interest in yields >90%. The resultant dendrimers have high glass transition (>165 °C) and decomposition temperatures (>465 °C), are monodisperse (PDI < 1.05), have high purity via common chromatographic techniques, have high photoluminescent quantum efficiencies (83%), and form defect‐free amorphous films via spin/dip coating. A comparison to their molecular analogues is also provided to demonstrate the superior properties of the new nanocomposite dendrimers.Structure of the cyclic phosphazene dendrimers.magnified imageStructure of the cyclic phosphazene dendrimers.
Novel Metal‐Polyurethane Complexes with Enhanced Antimicrobial Activity
Authors: Francolini Iolanda , Ruggeri Valeria , Martinelli Andrea , D'Ilario Lucio , Piozzi Antonella 
Published: February 2006

AbstractSummary: The silver coating of polymers has been intensively investigated in the last few decades as an effective non‐resistance‐inducing strategy to prevent medical device‐related infections. We have developed a completely new approach to incorporate silver ions in polymers by the synthesis of a carboxylated polyurethane able to coordinate Ag+. The obtained polymers possess mechanical properties suitable for the development of medical devices, without any risk of loss of activity. To minimize the risk of increasing antibiotic resistance, the metal ion‐containing polymers are loaded with ciprofloxacin, which possesses a different mechanism of antimicrobial action, thus a system able to inhibit Staphylococcus epidermidis and Pseudomonas aeruginosa growth for at least one month is developed.SEM images showing a mature S. epidermidis biofilm on the surface of the carboxylated polyurethane (left) and the surface of the silver ion‐containing polyurethane free from bacterial colonization (right) after 48 h of incubation.magnified imageSEM images showing a mature S. epidermidis biofilm on the surface of the carboxylated polyurethane (left) and the surface of the silver ion‐containing polyurethane free from bacterial colonization (right) after 48 h of incubation.
Interactions between pairs of antimalarial drugs studied by experimental and ab initio13C NMR chemical shifts
Authors: Casabianca Leah B. , de Dios Angel C. 
Published: February 2006

AbstractThe interactions between the antimalarial drugs chloroquine (CQ) and amodiaquine (AQ), chloroquine and quinine (QN), and amodiaquine and quinine are studied by 13C NMR. Experimental changes in chemical shift are compared to nucleus‐independent chemical shifts to determine the best structure of the complex formed by each drug pair in solution. Structures of the CQ–AQ and CQ–QN complexes are found to be similar to those found previously for the drug dimers. On the other hand, the best solution structure for the AQ–QN complex suggests that the quinoline rings of the two drugs are at an angle with respect to each other. Copyright © 2006 John Wiley & Sons, Ltd.
Conformational analyses of 2,3‐dihydroxypropanoic acid as a function of solvent and ionization state as determined by NMR spectroscopy
Authors: Drake Michael D. , Harsha Alex K. , Terterov Sergei , Roberts John D. 
Published: February 2006

AbstractVicinal 1H1H coupling constants were used to determine the conformational preferences of 2,3‐dihydroxypropanoic acid (1) (DL‐glyceric acid) in various solvents and its different carboxyl ionization states. The stereospecific assignments of J12 and J13 were confirmed through the point‐group substitution of the C‐3 hydrogen with deuterium, yielding rac‐(2SR,3RS)‐[3‐2H]‐1, and the observation of only J13 in the 1H NMR spectra. While hydrogen bonding and steric strain may be expected to drive the conformational equilibrium, their role is overshadowed by a profound gauche effect between the vicinal hydroxyl groups that mimics other substituted ethanes, such as 1,2‐ethanediol and 1,2‐difluoroethane. At low pH, the conformational equilibrium is heavily weighted toward the gauche‐hydroxyl rotamers with a range of 81% in DMSO‐d6 to 92% in tert‐butyl alcohol‐d10. At high pH, the equilibrium exhibits a larger dependence upon the polarity and solvating capability of the medium, although the gauche effect still dominates in D2O, 1,4‐dioxane‐d8, methanol‐d4, and ethanol‐d6 (96, 89, 85, and 83% gauche‐hydroxyls respectively). The observed preference for the gauche‐hydroxyl rotamers is believed to stem primarily from hyperconjugative σCH → σ*COH interactions. Copyright © 2006 John Wiley & Sons, Ltd.
Effect of rapidly relaxed electron spin anisotropically coupled to nearby nuclear partners
Authors: Werbelow Larry 
Published: February 2006

AbstractIn practice, many situations arise when a perturbed nuclear spin relies upon the aid of a rapidly relaxed spin neighbor in order to realize thermal equilibrium. Conventional treatments view the efficiently relaxed spin as part of the ‘lattice’, invoke the secular approximation, and consider the associated time correlation of the lattice variables, phenomenologically. Recently, an ab initio perturbative approach has been proposed for investigation of these spin systems. In this work, a similar formalism is applied to the scenario, in which nuclear spin relaxation is effected via an anisotropically coupled, efficiently relaxed, spin. Interesting conflicts with standard theory are revealed. Furthermore, although left mostly unexplored, this approach lends insight into numerous related aspects of magnetic relaxation including separation of timescales, distinction between spin and spatial averaging, paramagnetic relaxation, Curie spin relaxation, and the dynamic frequency shift. Copyright © 2006 John Wiley & Sons, Ltd.
Calculating protein structures directly from anisotropic spin interaction constraints
Authors: Smurnyy Yegor , Opella Stanley J. 
Published: February 2006

AbstractProtein structure determination by solid‐state NMR of aligned samples relies on the fundamental characteristics of the anisotropic nuclear spin interactions present in isotopically labeled proteins. Progress in the implementation of algorithms that calculate protein structures from the orientational constraints in the chemical shift and heteronuclear dipolar coupling interactions is described using both simulated and experimental data. Copyright © 2006 John Wiley & Sons, Ltd.
1H/29Si cross‐polarization NMR experiments of silica‐reinforced polydimethylsiloxane elastomers: probing the polymer–filler interface
Authors: Iuliucci Robbie , Taylor Craig , Hollis W. Kirk 
Published: February 2006

AbstractPolydimethylsiloxane (PDMS) elastomers reinforced with fumed silica exhibit unusual strength characteristics that are necessary for their designed applications. The microscopic details of the surface interaction between the polymer and silica are not well characterized. 1H/29Si cross‐polarization (cp) experiments are used to characterize cured and uncured samples of Dow Corning silastic 745. Changes to the cp dynamics upon curing are evident by the variation in peak intensities in the variable contact‐time spectra of the two samples. Estimates of the cp relaxation parameters are reported for the cured sample. Additional information can be obtained by expanding the 1H/29Si cp to a two‐dimensional heteronuclear correlation experiment. Dramatic differences between the cured and uncured 1H/29Si HetCor spectra are observed that are not visible in the 1D spectra. These changes can be rationalized as a dehydration of the silica surface and an increased hardening of the polymer after the curing process. Furthermore, isolation of the NMR signal corresponding to nuclei at or near the polymer–filler interface may be achieved in the 2D 1H/29Si HetCor spectrum. Copyright © 2006 John Wiley & Sons, Ltd.
Modeling the 13C chemical‐shift tensor in organic single crystals by quantum mechanical methods: finite basis set effects
Authors: Sefzik Travis H. , Fidler Jacqueline M. , Iuliucci Robbie J. , Facelli Julio C. 
Published: February 2006

AbstractThe influence of using finite basis sets to calculate 13C magnetic shieldings were explored using the Hartree‐Fock and the B3LYP hybrid density functional methods. The shielding values were compared in a linear least‐squares fashion for a test group of 102 13C complete chemical‐shift tensors determined from 14 organic single crystals. Pople's basis sets allow for the addition of polarization and diffuse functions in a straightforward way, allowing the examination of 81 combinations at the double and triple zeta level. Dunning's correlation‐consistent basis sets were explored as well. The errors associated with predicting the shielding values were found to be largely systematic as revealed by the analysis of the determined regression parameters between calculated chemical shieldings and experimental chemical shifts. Expansion of the basis set leads to a convergence of these regression parameters to their ideal values. The random errors, however, do not decrease by employing larger basis sets; therefore, given the appropriate regression parameters, a small basis description such as 3‐21G can be adequate in predicting the relative magnetic‐shielding values, i.e. the chemical shifts. Furthermore, in certain cases the inclusion of unbalanced diffuse and polarization functions can significantly degrade the predicted shielding rmsd. Unless employed carefully, these functions do not justify their computational expense. The chemical‐shift distance is used to evaluate shielding predictions in individual tensor components. The analysis of the chemical‐shift's distance between calculated and experimental data indicates an orientational dependence on the magnitude of errors and suggests the use of the shift anisotropy as a useful fiduciary mark to optimize model chemistries for magnetic‐shielding calculations. Copyright © 2006 John Wiley & Sons, Ltd.