bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular tweezers as synthetic receptors: the effect of pressure and temperature on the formation of host–guest complexes
Authors: Ruloff Robert , Seelbach Uta P. , Merbach André E. , Klärner Frank‐Gerrit 
Published: October 2002

AbstractFor the formation of the supramolecular complexes between the molecular tweezers 1 and 2 and the aromatic guests 3–5 the volumes of reaction ΔV were determined from the pressure dependence of the association constants K by the use of high‐pressure 1H NMR spectroscopy and the enthalpy ΔH and entropy ΔS of reaction from the temperature dependence of K. The small pressure dependence of K and, hence, the small variation of the reaction volumes around the zero value (ΔV ≈ 0 cm3 mol−1) clearly indicate that the contraction in volume resulting from the host–guest association is compensated for by the expansion in volume resulting from the desolvation of the free host and guest which has to proceed during the complexation. The association and desolvation are expected to have similar effects on ΔS compensating each other. The significant deviations of ΔS from the zero value are, however, good evidence that the size of ΔS not only depends on the processes mentioned above but moreover is influenced by other factors such as the conformational mobility of the guest molecule inside the receptor cavity. Copyright © 2002 John Wiley & Sons, Ltd.
Kinetic and spectral investigation of the electron and hydrogen adducts of dihydroxy‐ and dimethyl‐substituted pyrimidines: a pulse radiolysis and product analysis study
Authors: Luke T. L. , Mohan H. , Jacob T. A. , Manoj V. M. , Manoj P. , Mittal J. P. , Destaillats H. , Hoffmann M. R. , Aravindakumar C. T. 
Published: October 2002

AbstractThe reactions of hydrated electrons (eaq−) and hydrogen atoms (H·) with 4,6‐dihydroxy‐2‐methylpyrimidine (DHMP), 2,4‐dimethyl‐6‐hydroxypyrimidine (DMHP), 5,6‐dimethyluracil (DMU) and 6‐methyluracil (MU) were studied at different pH values using pulse radiolysis. The second‐order rate constants obtained for the reaction of eaq− with these systems are in the range (5–10) × 109 dm3 mol−1 s−1 at near, neutral pH. At basic pH, the rate constant values were considerably reduced owing to the electrostatic effect between eaq− and pyrimidine anion. The transient absorption spectra of the electron adducts have distinct absorption maxima at around 300–320 nm. The initial spectrum in the case of DHMP at pH 4.5 was found to undergo a first‐order transformation. Based on the spectral characteristics and the yields of methylviologen radical cation (MV·+) resulted from the electron transfer reaction between the electron adducts and MV2+, it is proposed that a protonated (at oxygen) electron adduct of DHMP is initially formed which undergoes a proton‐ and phosphate‐catalysed transformation to form a reducing C(5) protonated C(6)‐yl radical. Such preferential protonation at C(5) is predominant only with dihydroxypyrimidine systems. At pH 9 and 13, formation of a radical monoanion of DHMP (pKa ≥13) is proposed. The possible attack of eaq− is proposed to be at N(1) or N(3) of DMHP. The resulting electron adduct has a pKa value around 6.0. Similar properties for the electron adducts of DMU and MU [electron attack at O(4)] are proposed. The second‐order rate constants for H· with DHMP, DMHP, DMU and MU were in the range (1.7–28) × 108 dm3 mol−1 s−1. The hydrogen adduct spectra were generally identified as their absorption maxima at 310–380 and 460–510 nm. Formation of C(5)‐protonated C(6)‐yl radical, the same radical that formed after the H+‐and phosphate‐catalysed transformation of the electron adduct, is proposed for DHMP. The possibility of the formation of C(5)‐yl and C(6)‐yl H adducts of DMHP, DMU and MU is discussed. High‐performance liquid chromatography coupled with electrospray mass spectrometry (HPLC‐ES‐MS) has been used to qualitatively analyse the products obtained from the reaction of eaq− with DHMP and DMHP and the results revealed that the products are mainly derived from the C(5) protonated C(6)‐yl radicals via its disproportionation and dimerization reaction. A possible reaction mechanism is proposed for the product formation. Copyright © 2002 John Wiley & Sons, Ltd.
The role of specific interactions in crystalline complex formation. Structural and thermochemical analysis of inclusion compounds of cis‐ and trans‐9,10‐bis(4‐bromophenyl)‐9,10‐dihydroxy‐9,10‐dihydroanthracene with dimethyl sulfoxide
Authors: Brehmer Thomas H. , Kirchner Ralf , Seidel Jürgen , Weber Edwin 
Published: October 2002

AbstractReferring to a crucial problem in crystal engineering and co‐crystallization of host–guest complexes, whether the non‐covalent supramolecular interactions existing in a pre‐crystalline solution state may determine the subsequent crystal structure, the particular inclusion properties of host compounds 1, cis‐ and 2, trans‐9,10‐bis(4‐bromophenyl)‐9,10‐dihydroxy‐9,10‐dihydroanthracene, with dimethyl sulfoxide (DMSO) were studied by using x‐ray structure analysis and calorimetric methods. Both hosts form crystalline inclusion complexes with DMSO showing 2:3 (1·DMSO) and 1:4 (2·DMSO) host:guest composition. The crystal structure of 1·DMSO (2:3) is dominated by a strong bifurcated acceptor‐type H bond interaction involving 1 and one of the DMSO molecules. Titration calorimetric investigations in solution also confirm the formation of a stable 1·DMSO (1:1) complex unit, suggesting that for crystal nuclei of 1·DMSO (2:3) the pre‐formed 1:1 host–guest complex is the relevant building block while the additional molecules of DMSO fill lattice voids. In contrast, compound 2 with a trans configuration of the two hydroxy groups gives much weaker complexation with DMSO in solution, which is in agreement with single H‐bond interaction, also realized in the crystal structure of the respective inclusion complex. Thermal decomposition (TG–DSC) measurements of the crystalline complexes supply supporting data for these findings. Copyright © 2002 John Wiley & Sons, Ltd.
Kinetics and thermodynamics of heat conduction microcalorimetry
Authors: Blandamer Michael J. , Cullis Paul M. , Gleeson Peter T. 
Published: October 2002

AbstractHeat conduction microcalorimetry offers an important technique in the context of physical organic chemistry for the study of chemical reactions in solution. The thermodynamic basis of the technique is discussed. Model reaction schemes are used in an examination of the dependence on time of the rate of heat production. The impact of rate constants and enthalpies of reaction on the recorded dependence is reviewed for first‐ and second‐order reactions. Copyright © 2002 John Wiley & Sons, Ltd.
Determination of the hydrolysis rate of AOT in AOT–isooctane–water microemulsions using sodium­nitroprusside as chemical probe
Authors: García‐Río L. , Hervés P. , Leis J. R. , Mejuto J. C. , Pérez‐Juste J. 
Published: October 2002

AbstractThe alkaline hydrolysis of sodium nitroprusside, [Fe(CN)5NO]2−, to yield [Fe(CN)5NO2]4− was studied in water in oil (w/o) AOT–isooctane–water microemulsions [AOT = sodium bis(2‐ethylhexyl) sulphosuccinate]. Kinetic data show an initial increase of absorbance at 415 nm, due to the formation of [Fe(CN)5NO2]4−. Following this initial increase, the absorbance started to decrease after a period of time which depends on the particular experimental conditions and returned to the initial value. This anomalous behaviour was interpreted as a result of competitive AOT hydrolysis consuming HO− ions and regenerating [Fe(CN)5NO]2−. The influence of the microemulsion composition on the kinetic results was interpreted in terms of pseudophase formalism, assuming a uniform distribution of HO− and [Fe(CN)5NO]2− ions in the aqueous pseudophase. Analysis of the absorbance–time profiles enables us to obtain the second‐order rate constants for hydrolysis of [Fe(CN)5NO]2− in the water droplet, $\font\smc=cmr10 scaled 800\def\sc#1{\hbox{\smc #1}} = k_{1}^{\rm NP} = 0.108\,\sc{M}^{-1}\hbox{ s}^{-1}$ (half that reported in pure water) and the second‐order rate constant for hydrolysis of the surfactant (AOT), $\font\smc=cmr10 scaled 800\def\sc#1{\hbox{\smc #1}} = k_{2}^{\rm AOT}=4.4\times 10^{-4} \, \sc{M}^{-1} \hbox{ s}^{-1}$, in the microemulsion. Copyright © 2002 John Wiley & Sons, Ltd.
Synthesis of model linear tetrablock quaterpolymers and pentablock quintopolymers of ethylene oxide
Authors: Ekizoglou Nikos , Hadjichristidis Nikos 
Published: October 2002

AbstractMultiblock copolymers of ethylene oxide, with four and five different blocks, were synthesized by the sequential anionic polymerization of styrene, isoprene, 2‐vinyl pyridine, t‐butyl methacrylate, and ethylene oxide with benzyl potassium as an initiator. The monomer sequence was based on the relative nucleophilicity of the active centers. Characterization of the multiblock copolymers by size exclusion chromatography (with refractive‐index and UV detectors), membrane osmometry, and NMR spectroscopy confirmed that benzyl potassium is an efficient initiator for the synthesis of well‐defined multiblock multicomponent copolymers of ethylene oxide. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2166–2170, 2002
One‐ and two‐dimensional NMR characterization of N‐vinyl‐2‐pyrrolidone/methyl acrylate copolymers
Authors: Brar A. S. , Kumar Rajeev 
Published: October 2002

AbstractN‐vinyl‐2‐pyrrolidone/methyl acrylate (V/M) copolymers were prepared by free‐radical bulk polymerization using benzoyl peroxide as an initiator. The copolymer composition of these copolymers was calculated from 1H NMR spectra. The radical reactivity ratios for N‐vinyl‐2‐pyrrolidone (V) and methyl acrylate (M) were rV = 0.09, rM = 0.44. These reactivity ratios for the copolymerization of V and M were determined using the Kelen–Tudos and nonlinear least‐squares error‐in‐variable methods. The 13C{1H} and 1H NMR spectra of these copolymers overlapped and were complex. The complete spectral assignment of the 13C and 1H NMR spectra were done with distortionless enhancement by polarization transfer and two dimensional 13C‐1H heteronuclear single quantum correlation spectroscopic experiments. The two‐dimensional 1H‐1H homonuclear total correlation spectroscopic NMR spectrum showed the various bond interactions, thus inferring the possible structure of the copolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2225–2236, 2002
Epoxy‐functionalized, low glass‐transition temperature latex. I. Synthesis, characterizations, and polymer interdiffusion
Authors: Tronc Frédéric , Liu Ronghua , Winnik Mitchell A. , Eckersley Sarah T. , Rose Gene D. , Weishuhn J. M. , Meunier D. M. 
Published: October 2002

AbstractResults are presented on the synthesis and characterization of epoxy‐functionalized poly(butyl acrylate‐co‐methyl methacrylate) latex dispersions. Two pairs of latex dispersions, of low and high molecular weights, were prepared by semicontinuous emulsion polymerization. In each pair, one latex was labeled with phenanthrene, a donor for nonradiative energy‐transfer (ET) experiments, and the other was labeled with anthracene, the acceptor. Films were prepared from 1:1 mixtures of donor‐ and acceptor‐labeled latex, and ET experiments were used to study the rate and extent of polymer diffusion in these films. A complicating feature of these experiments was that, even in the absence of an externally added crosslinking agent, the films began to gel as soon as they were formed. The rate of gel formation increased with increasing temperature but never reached 100% under the conditions of these experiments. The presence of a gel fraction caused the rate of polymer diffusion to slow down. An important parameter affecting the rate of diffusion is the amount of time the films are held at relatively low temperatures (4 and 25 °C) before being annealed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2609–2625, 2002
Characterization of the surface content, hydrolysis ratio, and condensation degree of polyalkoxysiloxane segregated to the surface of a polyurethane crosslinked film by X‐ray photoelectron spectroscopy
Authors: Tomita R. , Urano S. , Kohiki S. 
Published: October 2002

AbstractWe report, using an electron spectrometer equipped with both monochromatized Al Kα and unmonochromatized Mg Kα sources, the quantitative characterization of the surface content, hydrolysis ratio, and condensation degree of polyalkoxysiloxane segregated to the surface of a polyurethane crosslinked film consisting of acryl polyol, polyisocyanate, and polyalkoxysiloxane. Unmonochromatized Mg Kα X‐ray irradiation extremely accelerated the decomposition of alkoxy groups of polyalkoxysiloxane. The surface content and hydrolysis ratio were determined from C 1s, Si 2p, and N 1s spectral intensities measured with monochromatized Al Kα X rays after decomposition by unmonochromatized Mg Kα X‐ray irradiation. The condensation degree was determined by the kinetic energy of the silicon KLL Auger electron after decomposition. We applied the established characterization method for a polyurethane film containing polyalkoxysiloxane. After 20 days, the surface content of polyalkoxysiloxane was greater than 60 wt %, the hydrolysis ratio ranged from 0.8 to 0.95, and the higher hydrolysis ratio resulted in a larger condensation degree. The hydrophilicity of the film surface became higher as the surface content and hydrolysis ratio increased, and the crack density became higher as the condensation degree increased. A method for characterizing the practical properties of coating film surfaces containing polyalkoxysiloxane was established. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2917–2926, 2002
Synthesis of a new amino acid/sulfur dioxide copolymer and its use in aqueous two‐phase polymer systems
Authors: Ali Sk. Asrof , Al‐Muallem Hasan A. , Wazeer Mohamed I. M. 
Published: October 2002

AbstractThe amine salt N,N‐diallyl‐N‐5‐carbomethoxypentylammonium chloride was copolymerized with sulfur dioxide in dimethyl sulfoxide with ammonium persulfate or 2,2′‐azobisisobutyronitrile and afforded a cationic polyelectrolyte (CPE) with a five‐membered cyclic structure on the polymeric backbone. The CPE, upon acidic hydrolysis of the pendent ester groups, gave a corresponding cationic acid salt (CAS) having the equivalent of chloride salt of 6‐N,N‐diallylammoniohexanoic acid as the monomeric unit. The CAS was converted into an anionic polyelectrolyte (APE) and a polybetaine (PB), having the monomeric unit equivalent of sodium 6‐N,N‐diallylaminohexanoate and 6‐N,N‐diallylammoniohexanoate, by treatment with 2 and 1 equiv of base, respectively. The solution properties of APE were investigated by potentiometric and viscometric techniques. The basicity constant of the amine functionality in APE was apparent and as such followed the modified Henderson–Hasselbalch equation; the protonation of the APE became more and more difficult as the degree of protonation of the whole macromolecule increased. The compositions and phase diagrams of the aqueous two‐phase systems of APE and poly(ethylene glycol) were studied. The PB was found to be insoluble in water, and this paves the way for the potential use of APE in aqueous two‐phase polymer systems for protein purification and its removal and recycling by conversion into PB. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2464–2477, 2002
Pd(0)‐catalyzed polyaddition of bifunctional vinyloxiranes with 1,3‐dicarbonyl compounds: The synthesis of polymers containing hydroxy and carbonyl groups
Authors: Koizumi Toshio , Sakamoto Jun , Gondo Yasuhiko , Endo Takeshi 
Published: October 2002

AbstractThe palladium(0)‐catalyzed polyaddition of bifunctional vinyloxiranes [1,4‐bis(2‐vinylepoxyethyl)benzene (1a) and 1,4‐bis(1‐methyl‐2‐vinylepoxyethyl)benzene (1b)] with 1,3‐dicarbonyl compounds [methyl acetoacetate (4), dimethyl malonate (6), and Meldrum's acid (8)] was investigated under various conditions. The polyaddition of 1 with 4 was carried out in tetrahydrofuran with phosphine ligands such as PPh3 and 1,2‐bis(diphenylphosphino)ethane (dppe). Polymers having hydroxy, ketone, and ester groups in the side groups (5) were obtained in good yields despite the kinds of ligands employed. The number‐average molecular weight value of 5b was higher than that of 5a. The polyaddition of 1b and 6 was affected by the kinds of ligands employed. The corresponding polymer 7b was not obtained when PPh3 and 1,2‐bis(diphenylphosphino)ferrocene were used. The polyaddition was carried out with dppe as the ligand and gave polymer 7b in a good yield. The molecular weight of the polymer obtained from 1b and 8 was much higher than those of polymers 5b and 7b. The polyaddition with Pd2(dba)3 · CHCl3/dppe as a catalyst (where dba is dibenzylideneacetone) produced polymer 9b in a 92% yield (number‐average molecular weight = 45,600). The stereochemistries of all the obtained polymers were confirmed as an E configuration by the coupling constant of the vinyl proton. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2487–2494, 2002
Influence of diluent composition on the porous structure of methacrylate copolymers
Authors: Gawdzik Barbara , Maciejewska Małgorzata 
Published: October 2002

AbstractThe porous structure of copolymers obtained by suspension polymerization has been investigated. Three different copolymers were synthesized—styrene‐divinylbenzene, ethylene glycol dimethacrylate‐divinylbenzene, and 1,4‐phenylene dimethacrylate‐divinylbenzene. All the copolymers were porous. As a pore‐forming diluent, the mixture of toluene (good solvent) and n‐dodecane (nonsolvent) was used. The influence of the composition of two‐component diluent on the porous structure of the copolymers has been examined. Surface areas, pore volumes, pore size distributions, skeletal and apparent densities, and swellability coefficients were determined for the copolymers obtained in the presence of 0, 15, 50, 85, and 100% (v/v) toluene in the mixture with n‐dodecane. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3079–3085, 2002
X‐ray powder diffraction of polymer/layered silicate nanocomposites: Model and practice
Authors: Vaia Richard A. , Liu Weidong 
Published: October 2002

AbstractX‐ray powder diffraction in reflection (Bragg–Brentano parafocusing geometry) is extensively used to characterize the structure of polymer/layered silicate nanocomposites (PLSNs). The large basal spacings (d001 > 2.0 nm) necessitates the collection of data at scattering angles (2θ) of less than 10°. The calculation of an ideal scattering profile for PLSNs provides an avenue to ascertain the influence of experimental parameters and the arrangement, organization, concentration, and composition of constituents on the experimentally observed pattern. This enables better experimental technique, more complete utilization of the scattering data, insight into inconsistencies between scattering and microscopy, and minimization of incorrect interpretation or overinterpretation of data. Because of the strong θ dependence of theoretical and experimental factors at low values of 2θ, careful sample preparation and data evaluation are necessary and should be complemented by microscopic observations, especially for PLSNs with low volume fractions of organically‐modified layered silicates (OLS) that are suspected of having exfoliated morphologies. X‐ray powder diffraction in reflection alone is insufficient to completely characterize and ascribe PLSN morphology. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1590–1600, 2002
Synthesis and structural characterizations of [chromophore]+‐saponite/polyurethane nanocomposites
Authors: Wang Wu‐Jing , Chin Wei‐Kuo , Wang Wan‐Ju 
Published: October 2002

AbstractIn this study, three chromophores—p‐nitroaniline, 4‐(4‐nitrophenylazo)aniline, and 4‐[(E)‐2‐{4‐[(E)‐2‐(4‐nitrophenyl)‐1‐diazenyl]phenyl}‐1‐diazenyl]aniline—were intercalated into layered aluminosilicate saponite and then dispersed into the polyurethanes matrix. The intercalated chromophore/saponite complexes were examined by inductively coupled plasma emission and element analysis technologies. The molecular orbital package computation simulation and X‐ray diffraction (XRD) analysis showed that possible configurations of chromophore ions on the gallery surfaces of saponite suggest that the chromophore molecules lie parallel to the basal planes of silicate as an inclined paraffin structure or as pseudo‐multilayers. The XRD and transmission electron microscopy analysis indicated that the delamination of organoclay in the polyurethanes matrix exhibited nanolayers, exfoliated structure, or both. In particular, even at high doping levels up to 15 wt % of organoclay, the [chromophore]+‐saponite/polyurethanes film did not display a macroscopic aggregation of layered silicates and showed high transparency. The thermal stability of chromophore was significantly enhanced as intercalated into the layered aluminosilicate saponite, and the glass‐transition temperature of [chromophore]+‐saponite/polyurethanes nanocomposites proportionally increased with increased clay content. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1690–1703, 2002
Study of the interfacial structure in epoxy bilayer films using neutron reflection
Authors: Yim H. , Kent M. S. , Jeon H. S. , Smith G. 
Published: October 2002

AbstractThe interfacial structure in thin epoxy bilayer films was investigated with neutron reflection. For each experiment, a mixture of crosslinker and deuterated resin was spun onto a chemically similar, fully cured, protonated epoxy film. The reflectivity measurements were performed before and after curing the top epoxy film. We focused on the extent of penetration of the components of the top layer into the network of the bottom layer. The effect of the cure temperature of each layer was examined. In addition, the effect of the initial molecular weight of the oligomers in the top layer was probed by the partial curing of the mixture before spinning. As deposited, the components of the top layer penetrated the bottom layer to an extent that was largely independent of the aforementioned factors. The principal observation was that an additional penetration occurred with curing. This additional penetration was dependent upon both the molecular weight of the top layer and the cure temperature of the top layer relative to the glass‐transition temperature of the bottom layer. A decrease in the thickness of the top layer with curing was also observed, which likely indicates some evaporation of oligomers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1709–1718, 2002
Characterization of volume strain of poly(vinylidene fluoride) under creep test
Authors: Elkoun S. , G'Sell C. , Cangemi L. , Meimon Y. 
Published: October 2002

AbstractPoly(vinylidene fluoride) (PVDF) was subjected to a creep test performed at constant true stress. The use of an original method to control and adjust, in real time, the stress allowed the assessment of volume changes occurring during the test. The adaptation of Bucknall's model enabled us to excerpt the component related to microstructural modifications from the whole volume strain. Mechanisms inducing volume strain are temperature dependent. Above −40 °C and below 80 °C, that is, in between both glass transitions of PVDF, a linear increase of volume strain was observed as a result of polymer damage via the crazing phenomenon. In addition, this region is characterized by the presence of two distinct domains that could be attributed to either nucleation and propagation of voids or to an increase of the number of potential sites for nucleation resulting from microstructural modifications taking place during the test. On the contrary, above the secondary glass transition, a regular decrease of volume strain was observed. It was assigned to a material densification as a result of molecular orientation of the amorphous chain segments. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1754–1759, 2002