bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Core Delocalization on Intermolecular Interactions in Conjugated Dendrimers
Authors: Beavington R. , Frampton M.J. , Lupton J.M. , Burn P.L. , Samuel I.D.W.
Published: March 2003

Four generations of conjugated dendrimers that contain 1,3,5‐tris(distyrylbenzenyl)benzene cores, stilbene dendrons, and t‐butyl surface groups have been synthesized. The dendrimers were synthesized by coupling benzylphosphonate‐focused dendrons with 1,3,5‐tris(4‐formylstilbenyl)benzene to give the dendrimers in yields in the range 60–82 %. We have probed the optoelectronic properties of the dendrimers by electrochemistry, photoluminescence, and in light‐emitting device structures. We have found that the degree of aggregation is strongly generation dependent. We compared the properties of these benzene‐centered dendrimers with an equivalent family of dendrimers that differs only in having a nitrogen atom as the central unit. We found that the aggregation of dendrimers was strongly dependent on the degree of delocalization across the central unit. The dendrimers with the benzene central unit, which have three localized distyrylbenzene chromophores, were found to aggregate more strongly in the solid state than those with nitrogen as the central unit. In the latter case the electroactive component is comprised of all three distyrylbenzene units and the nitrogen atom.
Self‐Assembled Monolayer Coatings on Nanostencils for the Reduction of Materials Adhesion
Authors: Kölbel M. , Tjerkstra R.W. , Kim G. , Brugger J. , van Rijn C.J.M. , Nijdam W. , Huskens J. , Reinhoudt D.N.
Published: March 2003

Nanostencils (shadow masks with submicrometer apertures in a thin silicon nitride membrane) are promising tools for the facile one‐step generation of nanopatterns of various materials by physical vapor deposition. Evaporation through a shadow mask is accompanied by gradual clogging of the apertures due to adhesion of evaporated material. In order to reduce this effect, nanostencils were coated with alkyl and perfluoroalkyl self‐assembled monolayers (SAMs). The formation and properties of SAMs on planar silicon nitride substrates were studied by contact angle goniometry, X‐ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The SAMs are stable under evaporation of gold at various angles. SAM‐coated nanostencils showed considerably less adhesion of gold compared to bare SixNy stencils.
Engineered Sensitivity of Structured Tin Dioxide Chemical Sensors: Opaline Architectures with Controlled Necking
Authors: Scott R.W.J. , Yang S.M. , Coombs N. , Ozin G.A. , Williams D.E.
Published: March 2003

Structure–property relationships in tin dioxide materials have been studied utilizing a reverse templating strategy to synthesize opaline structures with controlled neck dimensions between spheres. The necking dimensions could be controlled by sintering the parent silica opals at temperatures between 700 and 1050 °C. Inverted polymer opals were synthesized by infiltrating the silica opals with styrene, followed by thermally induced polymerization, and removal of the silica with HF. Tin dioxide opals with controlled microstructures were then synthesized from these inverted polymer opals. The gas sensing response of these materials to carbon monoxide could be understood as a function of the necking diameter in the resulting tin dioxide opals.
Mono‐Bisthienylethene Ring‐Fused versus Multi‐Bisthienylethene Ring‐Fused Photochromic Hybrids
Authors: Luo Q. , Chen B. , Wang M. , Tian H.
Published: March 2003

Novel bisthienylethene‐based tetraazaporphyrin and phthalocyanine hybrids (BTE–TAPs) were prepared as photo‐switching molecules. All new compounds were characterized by mass spectrometry (MS), 1H NMR spectroscopy, elemental analysis, UV‐vis absorption, and luminescence spectroscopy. All BTE–TAP compounds undergo open‐to‐closed and closed‐to‐open ring photoisomerizations in different quantum yields by irradiation with 365 nm or 730 nm light. The near‐IR luminescence of the hybrids can be regulated in a reversible manner by the photoisomerization of the bisthienylethene moiety. These compounds are useful as fluorescent probes and as non‐destructive readouts for erasable memory media. The phosphorescent BTE–TAP–PtII complex was also prepared, and its photochromism and changes in phosphorescence in a polycarbonate film were studied. These properties could give rise to other practical uses of BTE–TAP hybrids.
Composites of Perylene Chromophores and Layered Double Hydroxides: Direct Synthesis, Characterization, and Photo‐ and Chemical Stability
Authors: Bauer J. , Behrens P. , Speckbacher M. , Langhals H.
Published: March 2003

Composites of the tetra‐anion of the perylene dye N,N′‐di(phenyl‐3,5‐disulfonic acid)perylene‐3,4:9,10‐tetracarboxydiimide (PBITS) with layered double hydroxides (LDHs) were formed by direct synthesis (co‐precipitation at constant pH). The LDHs were of the hydrotalcite (Mg–Al–OH and Zn–Al–OH compositions). During synthesis of the hydrocalumite type (Ca–Al–OH), partial destruction of the dye occurs, being more pronounced at higher pH values. The composites were characterized with regard to their composition by elemental and thermal analysis. From UV‐vis spectroscopic data and powder X‐ray diffraction, a structural model is developed for the composites. In the galleries between the hydroxide layers, the chromophore molecules are stacked in an J‐type arrangement. The compounds have brilliant colors and are insoluble in common solvents. With regard to a possible application as pigments, their photostability and their chemical resistance against a typical application environment was tested. The photostability of the dye molecules and their chemical resistance against setting cement are slightly raised by the occlusion within the LDH structure; however, the photostability of the LDH–cement is lower than that of cement colored with the pure perylene dye.
Formation of an Isolated Spherical Three‐Dimensional Nanoparticle Assembly as Stable Submicrometer‐Sized Units by Using an Inorganic Wrapping Technique
Authors: Yonezawa T. , Matsune H. , Kimizuka N.
Published: March 2003

A novel inorganic wrapping technique has been used to create stable, three‐dimensional spherical assemblies of gold nanoparticles. Uniform, crack‐free TiO2 layers of 5 nm thickness could be wrapped around the nanoparticle assemblies using a sol–gel technique. Upon addition of a suitable surfactant these particles are stable in organic media (see Figure: with (right) and without (left) suitable surfactant).
Percolative Mechanism of Aging in Zirconia‐Containing Ceramics for Medical Applications
Authors: Pecharromán C. , Bartolomé J.F. , Requena J. , Moya J.S. , Deville S. , Chevalier J. , Fantozzi G. , Torrecillas R.
Published: March 2003

For biomedical applications, zirconia‐toughened alumina ceramics (see Figure) would be very appropriate materials, provided that the zirconia content is kept below the percolation threshold (upper limit of 16 vol.‐% 3Y‐TZP inside an alumina matrix). That the concept of a percolation threshold is relevant when talking about aging degradation, is demonstrated by comparing specular IR reflectance measurements with aging experiments.
Sodium Perborate—A Convenient Baeyer–Villiger Oxidation Reagent in the Synthesis of the Corey Aldehyde
Authors: Espiritu Maria , Handley Paul N. , Neumann Ralf
Published: March 2003

Sodium perborate tetrahydrate is a cheap, safe and readily available alternative to the commonly used peracetic acid for the Baeyer–Villiger oxidation step of the Corey aldehyde synthesis. Chloroketo acid 1 is smoothly converted by sodium perborate tetrahydrate in formic acid to the chloroketolactone 2 in 66% isolated yield. In contrast to previously reported reactions using other oxidants, the formation of the lactone is completely regioselective in favour of the “bridgehead‐migrated” isomer 2.
Microwave Heating Effects Rapid and Selective Decarboalkoxylation of Mono‐Alkylated Malonates and β‐Ketoesters
Authors: Curran Dennis P. , Zhang Qisheng
Published: March 2003

Brief microwave irradiation of mono‐alkylated malonates and β‐ketoesters at 160–200 °C in wet DMF induces smooth and selective decarboalkoxylation. Observations suggest that this reaction occurs by nucleophilic attack of water at the ester carbonyl carbon (hydrolysis) followed by decarboxylation of the resulting acid. The process occurs despite the absence of traditional acid, base or nucleophile catalysts or reagents.
Catalysis with Soluble Hybrids of Highly Branched Macromolecules with Palladium Nanoparticles in a Continuously Operated Membrane Reactor
Authors: Sablong Rafael , Schlotterbeck Ulf , Vogt Dieter , Mecking Stefan
Published: March 2003

The continuous recovery and recycling of soluble metal nanoparticles by means of ultrafiltration is described, employing hybrids of palladium nanoparticles with highly branched amphiphilic polyglycerol as a catalyst for cyclohexene hydrogenation as a model reaction. In a continuously operated membrane reactor a productivity of 29000 TO over 30 exchanged reactor volumes was observed for nanoparticles of 2.2 nm size, with a maximum rate of 1200 TO h−1. Catalysis by soluble metal complexes can be excluded. After 30 hours of operation, some decrease in activity is observed which is due to deposition of palladium on the ultrafiltration membrane, however this material does not contribute to catalytic activity.
Phenol and Organic Bases Co‐Catalyzed Chemical Fixation of Carbon Dioxide with Terminal Epoxides to Form Cyclic Carbonates
Authors: Shen Yu‐Mei , Duan Wei‐Liang , Shi Min
Published: March 2003

Phenol can efficiently catalyze the reactions of terminal epoxides with carbon dioxide in the presence of catalytic amounts of various organic bases such as 4‐dimethylaminopyridine (DMAP), pyridine, 1,8‐diazabicyclo[5.4.0]undec‐7‐ene, and triethylamine to give the corresponding five‐membered cyclic carbonate in high yields (initial pressure 3.57 MPa; reaction temperature 120 °C). p‐Methoxyphenol with DMAP is the best combination to give the cyclic carbonate in the highest yield.
Catalytic Carbon‐Fluorine Bond Activation with Monocoordinated Nickel‐Carbene Complexes: Reduction of Fluoroarenes
Authors: Kuhl Sébastien , Schneider Raphaël , Fort Yves
Published: March 2003

Monocoordinate nickel/N‐heterocyclic carbene complexes reveal unexpected reactivity towards aryl fluorides. Defluorination reactions were efficiently performed with a β‐hydrogen‐containing alkoxide (3 equiv.) in the presence of 3 mol % of [1:1] Ni(0)/IMes⋅HCl catalyst (IMes=1,3‐dimesitylimidazol‐2‐ylidene).
Asymmetric Synthesis with N‐Heterocyclic Carbenes. Application to the Copper‐Catalyzed Conjugate Addition
Authors: Alexakis Alexandre , Winn Caroline L. , Guillen Frederic , Pytkowicz Julien , Roland Sylvain , Mangeney Pierre
Published: March 2003

Chiral N‐heterocyclic carbenes are good ligands for the copper‐catalyzed conjugate addition of dialkylzinc reagents to various Michael acceptors. With as little as 4% of chiral ligand, the enantioselectivity may reach 93% on cycloheptenone.
Efficient and Eco‐Friendly Process for the Synthesis of Bis(1H‐indol‐3‐yl)methanes using Ionic Liquids
Authors: Yadav J. S. , Reddy B. V. S. , Sunitha S.
Published: March 2003

Indoles react smoothly with carbonyl compounds in 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([bmim]BF4) or 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([bmim]PF6) ionic liquids under mild reaction conditions to afford the corresponding bis‐indolylmethanes in excellent yields. These ionic liquids can be recovered and recycled in subsequent reactions without any apparent loss of activity.
Synthesis of Functionalised Phenylalanines Using Rhodium Catalysis in Water
Authors: Chapman Christopher J. , Frost Christopher G.
Published: March 2003

The efficient synthesis of substituted phenylalanine‐type amino acids using a rhodium‐catalysed, conjugate addition of arylboronic acids is described. The reactions are run in water and use a low loading (0.5 mol %) of rhodium catalyst.
Catalytic Asymmetric Alkylation in Water in the Presence of Surfactants
Authors: Sinou Denis , Rabeyrin Cedric , Nguefack Christelle
Published: March 2003

Asymmetric palladium‐catalyzed alkylation of 1,3‐diphenyl‐2‐propenyl acetate with dimethyl malonate occurs in water in the presence of surfactants and a base. The efficiency as well as the enantioselectivity of the coupling reaction depend strongly on the nature and the concentration of the surfactant. The highest yield and enantioselectivity (up to 91%) was obtained using Binap as the ligand in the presence of a cationic surfactant, while neutral or zwitterionic surfactants gave poorer results; anionic surfactants gave no reaction at all. The best results were obtained using Na2CO3, NaHCO3, or K2CO3, among the bases used. The highest enantioselectivities were obtained when the reaction was performed in the presence of chiral atropoisomeric diphosphines such as Binap, Biphemp, or MeOBiphep. A supported cationic surfactant was also used successfully in this reaction, allowing an easier separation of the product.
Application of a Homogeneous Dodecakis(NCN‐PdII) Catalyst in a Nanofiltration Membrane Reactor under Continuous Reaction Conditions
Authors: Dijkstra Harm P. , Ronde Niek , van Klink Gerard P. M. , Vogt Dieter , van Koten Gerard
Published: March 2003

A shape‐persistent nanosize dodecakis(NCN‐PdII‐aqua) complex (4b) was applied as a homogeneous catalyst in the double Michael reaction between methyl vinyl ketone and ethyl α‐cyanoacetate under continuous reaction conditions in a nanofiltration membrane reactor. Due to its macromolecular dimensions, the catalyst is retained in the reactor (R=99.5% determined by ICP‐AAS) during catalysis. In addition, the catalyst was found to be stable under the continuous reaction conditions as a constant activity was obtained at prolonged reaction times (26 h, 65 exchanged reactor volumes). The turnover number of the catalyst was thus increased by a factor greater than 40 from 80 (batch) up to >3000 mol/mol Pd. Further development of this technology will allow an increase of the number of (industrial) catalytic processes in which homogeneous catalysts are applied.
(−)‐Sparteine‐Mediated Directed ortho‐Metalation of N‐Cumyl‐N‐ethylferrocenecarboxamide. Versatile Routes to Functionalized Planar Chiral Ferrocenecarboxamides, Amines, Esters and Phosphines
Authors: Metallinos Costa , Szillat Hauke , Taylor Nicholas J. , Snieckus Victor
Published: March 2003

N‐Cumyl‐N‐ethylferrocenecarboxamide 5 provides planar chiral carboxamides 6 in high yield and % ee via (−)‐sparteine‐mediated directed ortho‐metalation. Mild decumylation affords secondary amides 7, which serve as intermediates for a convenient and general route to the venerable Ugi planar chiral ferrocenylamines 13 and as versatile precursors for the preparation of novel chiral ferrocenes 15 and 20. The chiral TMS‐ferrocenyl derivative 7c is used to prepare the enantiomeric (S)‐7f, circumventing the lack of availability of (+)‐sparteine.
One‐Pot Homogeneous and Heterogeneous Oxidation of Glycerol to Ketomalonic Acid Mediated by TEMPO
Authors: Ciriminna Rosaria , Pagliaro Mario
Published: March 2003

Glycerol, an increasingly abundant by‐product of biodiesel production, is selectively converted to ketomalonic acid in one pot at pH 10 using NaOCl as regenerating oxidant in water at 2 °C in the presence of catalytic Br− along with the radical TEMPO (2,2,6,6‐tetramethylpiperidine‐1‐oxyl). The reaction can also be conducted at completion over a sol‐gel silica glass doped with the nitroxyl radical. Considering the stability and versatility of such doped glasses, these materials show real promise as reusable metal‐free catalysts for the conversion of a readily available and renewable biofeedstock into a highly valued compound.
A Simple and Convenient Method for Epoxidation of Olefins without Metal Catalysts
Authors: Klawonn Markus , Bhor Santosh , Mehltretter Gerald , Döbler Christian , Fischer Christine , Beller Matthias
Published: March 2003

An easy method for epoxidation of olefins using bleach (sodium hypochlorite) and either a stoichiometric or catalytic amount of bromide ion has been developed. Without any transition metal catalyst a variety of non‐activated olefins give epoxides in high yields and good selectivity at ambient conditions.
Easily Accessible Ring Opening Metathesis and Atom Transfer Radical Polymerization Catalysts based on Arene, Norbornadiene and Cyclooctadiene Ruthenium Complexes Bearing Schiff Base Ligands
Authors: Opstal Tom , Couchez Katrien , Verpoort Francis
Published: March 2003

A group of four mixed ligand ruthenium(II)‐Schiff base complexes has been synthesized and characterized. These complexes are easily accessible from [RuCl2(p‐cymene)]2, [RuCl2(NBD)]n, [RuCl2(COD)]x and salicylaldimine salts. They have been found to serve as good catalyst precursors for ring‐opening metathesis polymerization (ROMP) and atom transfer radical polymerization (ATRP) of different vinyl monomers. The catalytic activity and the control over the produced polymer can be dramatically improved after the addition of additives such as Et2AlCl and (n‐Bu)2NH.
Mono‐ and Bidentate Phosphine Ligands in the Palladium‐Catalyzed Methyl Acrylate Dimerization
Authors: Zimmermann Jörg , Tkatchenko Igor , Wasserscheid Peter
Published: March 2003

The influence of several phosphine ligands on the activity, selectivity and stability of the catalytic system Pd(acac)2, ligand, [HOEt2][BF4] was studied in the dimerization of methyl acrylate (MA). It was found that the catalyst's activity increased with increasing the basicity of the monodentate ligands used, whereas bulky phosphines lowered the linearity of the dimers and the reaction rates. With chelating P N‐, P P‐, and P As‐ligands the Pd‐catalyst could be efficiently stabilized during the reaction. The use of 1‐dibutylphosphino‐2‐dimethylaminoethane as ammonium tetrafluoroborate salt allowed the highest overall activity.
Rhodium‐Catalysed Asymmetric Hydroformylation of Unsaturated Nitriles
Authors: Lambers‐Verstappen Mariëlle M. H. , de Vries Johannes G.
Published: March 2003

Asymmetric hydroformylation of crotononitrile (1) and ally cyanide (2) was probed with the view to develop a synthesis for (R)‐4‐amino‐2‐methyl‐butan‐1‐ol. Hydroformylation of 1 under a variety of conditions mainly led to hydrogenated product. Hydroformylation of 2 with Rh/tris(2,4‐di‐tert‐butylphenyl) phosphite gave good selectivity to the formylated nitrile with an n/iso of 77:23. Asymmetric hydroformylation of 2 could be accomplished in 66% ee using Rh/(R,S)‐BINAPHOS.
Synthesis ofN‐Acetyl‐α‐aminobutyric AcidviaAmidocarbonylation: A Case Study
Authors: Gördes Dirk , Neumann Helfried , von Wangelin Axel Jacobi , Fischer Christine , Drauz Karlheinz , Krimmer Hans‐Peter , Beller Matthias
Published: March 2003

The synthesis ofN‐acetyl‐α‐aminobutyric acid by amidocarbonylation of propionaldehyde with acetamide in the presence of palladium catalysts is studied in detail. The influence of various reaction conditions and compositions (e.g., the co‐catalysts acid and bromide) on the yield ofN‐acetyl‐α‐aminobutyric acid is shown. For the first time it is demonstrated that the palladium‐catalyzed amidocarbonylations of aldehydes can be run with significantly lower halide concentrations (<30 mol %) without a major yield decrease. While phosphine‐free catalyst systems give best yields at low CO pressure, phosphine‐ligated palladium catalysts lead to better yields at higher CO pressure. At low palladium loadings (<0.1 mol %), unwanted condensation reactions of propionaldehyde become increasingly competitive.
Interstitial deletion of the short arm of chromosome 1: Attempt to establish a clinical phenotype (46,XX,del (1)(p22p32))
Authors: Mircher Clotilde , Rethore Marie‐Odile , Lespinasse James , Fert‐Ferrer Sandra , Lundsteen Claes , Kirchoff Maria
Published: March 2003

A girl with a de novo interstitial deletion of the short arm of chromosome 1 (46,XX,del (1)(p22p32) is described with moderate developmental delay and minor phenotypic abnormality. These clinical manifestations are compared to previously reported patients with interstitial deletion of chromosome 1, in an attempt to identify a clinical phenotype which seems quite different from the syndrome linked to more terminal deletion of chromosome 1p, and perhaps from more proximal 1p deletion phenotype. © 2003 Wiley‐Liss, Inc.
Poland anomaly—report of an unusual family
Authors: Shalev Stavit A. , Hall Judith G.
Published: March 2003

A family with classical Poland anomaly presenting in the son and a partially affected mother is reported. We hypothesize that Poland anomaly has a multifactorial basis involving vascular compromise in early development. Two possible predisposing factors are aberrant vascular formation and thrombophilia. The investigation of our family has not demonstrated an abnormality in coagulation, therefore, we surmise that an inherited structural variant of blood vessel formation is responsible. © 2003 Wiley‐Liss, Inc.
Cover Picture: Aluminum Dihydroxide with Terminal OH Groups: An Unprecedented Congener of Boronic Acid (Angew. Chem. Int. Ed. 10/2003)
Authors: Bai Guangcai , Peng Ying , Roesky Herbert W. , Li Jiyang , Schmidt Hans‐Georg , Noltemeyer Mathias
Published: March 2003

This week's catch is an unprecedented aluminum compound of the form [LAl(OH)2], prepared via the hydrolysis of [LAlI2] in a two‐phase toluene/liquid ammonia system. The solid‐state structure reveals a weakly hydrogen‐bonded dimer; electrostatic potential analysis indicates that electrophilic attack at the oxygen sites is preferred, and that π‐electron density is increased upon formation of the dimer. More details of this congener of RB(OH)2 are given in the Communication by H. W. Roesky and co‐workers on page 1132ff.
Copper Carbene Complexes: Advanced Catalysts, New Insights
Authors: Kirmse Wolfgang
Published: March 2003

Controlling the selectivity of reactive intermediates is a major goal of organic chemists. Carbenes generated by thermal or photochemical extrusion of nitrogen from diazo compounds defy external control and tend to give complex product mixtures. However, the catalyzed decomposition of diazo compounds gives rise to highly selective “carbenoids” which have found extensive application in synthesis although little is known of their precise nature. On the other hand, a large variety of carbene metal complexes have been prepared and characterized which more or less lack carbenoid reactivity. Structural evidence for the transients of catalyzed diazo decomposition is becoming available through experiment and computation. Although the present report focuses on copper complexes, outstanding results with other metals are also covered.
meso Compounds: Stepchildren or Favored Children of Stereoselective Synthesis?
Authors: Hoffmann Reinhard W.
Published: March 2003

After more than a quarter of a century of development, the methodology of stereoselective synthesis appears to be fully matured. In line with this, the potential that meso compounds offer in stereoselective synthesis is clearly recognized. The use of meso compounds in synthesis is, however, in no way commensurate with this potential, because, ironically, the synthesis of meso compounds in the first place is a problem of stereoselective synthesis. Present‐day methodology does not provide many useful solutions to this problem. This Review therefore addresses the strategies available for the synthesis of more elaborate meso compounds whose stereogenic centers have a distance >1,4 between them. meso Compounds with more than four stereogenic centers are also considered. The criteria used in choosing from several strategies in the synthesis of such compounds are discussed.
Direct Synthesis of Propylene Oxide with CO2 as the Solvent
Authors: Danciu Tiberiu , Beckman Eric J. , Hancu Dan , Cochran Robert N. , Grey Roger , Hajnik Dennis M. , Jewson Jennifer
Published: March 2003

The oxidant H2O2 is generated in situ in this clean, one‐step conversion of propylene into propylene oxide. Contrary to expectations, the catalyst—palladium on titanium silicalite—does not require methanol for activity, and solvent‐based side reactions are avoided by conducting the reaction in CO2.
Drying and semidrying oil macromonomers. III. Styrenation of sunflower and linseed oils
Authors: Akbas T. , Beker Ü. G. , Güner F. S. , Erciyes A. T. , Yagci Y.
Published: March 2003

Styrenation of drying and semidrying oils, namely sunflower and linseed oils, via the macromer technique was studied. For this purpose, the macromonomers of the oils were prepared by transesterification of methyl methacrylate (MMA) with the corresponding partial glycerides (PG). Subsequent styrenation was achieved by free radical copolymerization of the macromonomers with styrene using benzoyl peroxide as the initiator. The viscosity and the film properties of the products were studied and compared. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2373–2376, 2003
Synthesis and characterization of novel grafted amphoteric poly(propylene) fabrics
Authors: Mosleh S. , Gawish S. M.
Published: March 2003

Novel grafted amphoteric poly(propylene) (PP) fabrics were prepared by γ‐irradiation, which induced grafting of methacrylic acid (MA) onto PP fabric. A subsequent reaction of PP–MA grafted chains with freshly prepared (3‐chloro‐2‐hydroxylpropyl)amine or diamine chloride compounds followed by purification yielded the corresponding amphoteric PP fabrics. The latter were characterized by elemental microanalysis for the determination of the percentage nitrogen. Fourier transform infrared and scanning electron microscopy were performed on methacrylic and amphoteric PP fabrics. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2504–2510, 2003
Effects of blend ratio and vulcanizate powders on the processability of silicone rubber/fluororubber blends
Authors: Ghosh Arun , Kumar B. , Bhattacharya A. K. , De S. K.
Published: March 2003

While silicone rubber has a much lower shear viscosity than that of fluororubber, the viscosity of silicone rubber/fluororubber blends is closer to that of silicone rubber. All rubber compositions show pseudoplastic behavior. While the viscosity of a 50/50 silicone rubber/fluororubber blend increases on replacement of the silicone rubber by silicone rubber vulcanizate powder (SVP), the effect of fluororubber replacement by the corresponding fluororubber vulcanizate powder (FVP) on the shear viscosity is less pronounced. The difference in viscosity between SVP‐replaced silicone rubber and FVP‐replaced fluororubber becomes less prominent at higher shear rates. Fluororubber exhibits a higher extrudate die swell than that of silicone rubber. The die swell of the silicone rubber/fluororubber blends is higher than are the figures obtained by the additivity rule. Replacement of constituent rubbers in the blend by the corresponding vulcanizate powders causes an increase in the die swell. While the silicone rubber extrudate surface is smooth, the fluororubber extrudate shows melt fracture. The extrudate surfaces of the silicone rubber/fluororubber blends are similar to that of the silicone rubber extrudate. Replacement of constituent rubbers by the corresponding vulcanizate powders increases the roughness of the extrudate surface, which is more prominent in the case of silicone rubber replacement by SVP. SVP can replace 50% of silicone rubber and FVP can replace 75% of fluororubber in the 50/50 silicone rubber/fluororubber blend. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2377–2387, 2003
A novel synthesis method for the preparation of aromatic poly(imide benzoxazole) from trimellitic anhydride chloride and bis(o‐aminophenol)
Authors: Hsu Steve Lien‐Chung , Chang Keng‐Chuan , Huang Yuan‐Pin , Tsai Shih‐Jung
Published: March 2003

A poly(imide benzoxazole) was prepared directly from trimellitic anhydride chloride and 2,2‐bis(3‐amino‐4‐hydroxyphenyl)hexafluoropropane (BisAPAF) monomers in a two‐step method. In the first step, a poly(hydroxyamide amic acid) precursor was synthesized by the low‐temperature solution polymerization in an organic solvent. Subsequently, thermal cyclodehydration of the poly(hydroxyamide amic acid) precursor at 350°C produced the corresponding poly(imide benzoxazole). The inherent viscosity of the precursor polymer was 0.22 dL/g. The cyclized poly(imide benzoxazole) showed a glass transition temperature (Tg) at 329°C and a 5% weight loss temperature at 530°C in nitrogen and at 525°C in air. The poly(imide benzoxazole) is amorphous as evidenced by the wide‐angle X‐ray diffraction measurement. The structures of the precursor polymer and the fully cyclized polymer were characterized by Fourier transform infrared (FTIR) and proton nuclear magnetic resonance spectroscopy (1H NMR). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2388–2391, 2003
Analysis of surface degradation of silicone rubber due to tracking—A physicochemical approach
Authors: Sarathi R. , Maheswar Rao Uma
Published: March 2003

The tracking phenomenon for silicone rubber material under AC and DC voltages, with ammonium chloride as the contaminant, has been studied. The tracking phenomenon is explained in detail with a leakage current measurement. The tracking time depends on the conductivity and the flow rate of the contaminant. The surface condition of the aged specimens was characterized with contact angle measurements. The thermal and chemical stabilities of the material were identified with a methodical experimental study. Physicochemical analysis by wide‐angle X‐ray diffraction (WAXD), thermogravimetric differential thermal analysis (TG‐DTA), and the differential scanning calorimetry (DSC) indicated that the mechanism of the tracking process is due to surface degradation. The tracking time is different for AC and DC voltages. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2392–2399, 2003
Surface modification of thermotropic poly(oxybenzoate‐co‐oxynaphthoate) copolyester by remote oxygen plasma for copper metalization
Authors: Lim Sang Kyoo , Inagaki N.
Published: March 2003

Poly(oxybenzoate‐co‐oxynaphthoate) (POCO) film surfaces were modified with remote oxygen plasma, and the effects of the modification on the adhesion between the copper layer and POCO were investigated. The remote‐oxygen‐plasma treatment led to a noticeable decrease in the contact angle, which was mainly due to the CO functional groups on the surface. The modification of the POCO surface by remote oxygen plasma was effective in improving the adhesion with copper metal. The peel strength for the copper metal/POCO system was enhanced from 10 to 127.5 mN/5 mm by the surface modification. The failure mode of the copper metal/POCO system was an interface layer between the oxidized micro‐POCO fibril surface and the copper metal layer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2400–2408, 2003
Temperature‐dependence modeling of highly crosslinked polymer networks
Authors: Yin S. , Pizzi A.
Published: March 2003

The dependence on the temperature of the state of a highly crosslinked polymer network can be modeled as a function of well‐defined molecular‐level network parameters to yield a simple applied model equation. The tightness and strength (modulus of elasticity) of the crosslinked networks formed, as well as any further tightening of the network due to further curing, can easily be compared with the parametersA,M, and α (the coefficient of branching) and them/Eratio and, therefore, with parameters directly related to molecular‐level characteristics of the system. The crosslinking contribution to the network is represented byAandM, the former representing the frequency of crosslinking and the latter having the dimensions of an energy. The ratiom/E, that is, the ratio of the average number of degrees of freedom of chain segments between crosslinking nodes (m) to the average energy of nonbonded atom interactions between the same segments (E), and α model the noncrosslinked contribution to the characteristics of the network. These are the same parameters that appear in the simple equation modeling the dependence of the characteristics of the network on the temperature within a limited temperature range. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2416–2426, 2003
New developments in flame retardancy of glass‐reinforced epoxy composites
Authors: Kandola Baljinder K. , Horrocks A. Richard , Myler Peter , Blair Dana
Published: March 2003

This work involves the development of novel glass fiber–reinforced composite materials containing a commercially available epoxy resin, a phosphate‐based intumescent, and inherently flame‐retardant cellulosic (Visil, Sateri) and phenol–formaldehyde (Kynol) fibers. The intumescent and flame‐retardant fiber components were added both as additives in pulverized form and fiber interdispersed with the intumescent as a fabric scrim for partial replacement of glass fiber. Thermal stability, char formation, and flammability properties of these novel structures were studied by thermal analysis, limiting oxygen index, and cone calorimetry. The results are discussed in terms of effect of individual additive component on thermal degradation/burning behavior of neat resin. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2511–2521, 2003
Role of cationic polyacrylamide in fiber‐CaCO3 pigment interactions
Authors: Alince B. , Bednar F.
Published: March 2003

It is believed that the action of cationic polyacrylamide as a retention aid for incorporating pigment particles into a paper is based on its ability to form a polymeric bridge between particles and pulp fiber suspended in water. When the polymer is added to a mixture of fibers and pigments, this process is complicated by the different rates of polymer adsorption on the fibers and the pigment particles, the rate of collision between them, and the charge reversal of the polymer from the hydrolysis. To elucidate under which conditions the polymer can form a bridge, the processes of polymer adsorption and pigment–fiber interaction were separated. A deposition of pigment particles onto fibers suspended in water was investigated, using both components pretreated with the polymer. The results indicated that polymer adsorbed on fiber can form a bridge with untreated pigment particles regardless of the polymer charge. On the other hand, negatively charged hydrolyzed polymer adsorbed on the pigment does not form a bridge with untreated fiber. When both the fiber and the pigment are pretreated, the bridge formation depends on their surface coverage by polymer and its charge. No deposition takes place when both components are sufficiently coated by anionic hydrolyzed polymer, which indicates electrosteric repulsion. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2409–2415, 2003
Physical, mechanical, and biocompatibility evaluation of three different types of silicone rubber
Authors: Fallahi D. , Mirzadeh H. , Khorasani M. T.
Published: March 2003

Silicone rubber as a valuable biomaterial is widely used in medical applications, but its surface properties and low wettability make serious problems in long‐term implants. This work was undertaken to evaluate the biocompatibility of modified silicone rubber using two different techniques. A blend of poly(acrylamide) and silicone rubber was compared with virgin silicone surfaces as well as with those modified by laser treatment. Physical and mechanical properties of the samples were examined using different techniques. The hydrophilicity of the silicone rubber increased with increasing hydrogel content and decreased as a result of laser treatment. Both fibroblast cell (L929) and platelet behavior in contact with these surfaces were evaluated in vitro. The morphology of fibroblast cells that adhered to the blends was similar to the control. In contrast, on the laser‐treated surfaces fibroblast cells showed different proliferation. On the other hand, fewer platelets adhered to the laser‐treated surface than adhered to the blend and the unmodified PDMS surfaces. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2522–2529, 2003
Precipitation polymerization of methyl methacrylate in tetrahydrofuran with compressed CO2 as antisolvent
Authors: Xu Qun , Han Buxing , Yan Haike
Published: March 2003

Precipitation polymerization of methyl methacrylate (MMA) in tetrahydrofuran (THF) with compressed CO2 as an antisolvent was carried out at 335 K up to 8.5 MPa, and the decomposition rate of the initiator, 2,2′‐azobisisobutyronitrile (AIBN), was studied with UV/vis. Gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) were used to determine the average molecular weights and glass transition temperature (Tg), and scanning electron micrography (SEM) was used to observe the morphologies of the product. The results showed that the average molecular weights of the polymer vary considerably with the volume expansion of the solution induced by compressed CO2. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2427–2433, 2003
Enhancement of antifillet cracking performance for no‐flow underfill by toughening method
Authors: Moon Kyoung‐Sik , Fan Lianhua , Wong C. P.
Published: March 2003

Fillet cracking of no‐flow underfill in a flip‐chip device during a reliability test such as thermal shock or thermal cycling has been a serious reliability problem. The effect of toughening agents and modification of epoxy on fillet cracking of no‐flow underfill was investigated. The best epoxy formulation and the appropriate loading level of toughening agent regarding the antifillet cracking performance were found. In the case where the epoxy was modified with polysiloxanes, the second‐phase particle with a submicron particle size was formed and the size of the particle depended on the kind of toughening agent. The morphology was observed by a scanning electron microscopy and confirmed by a dynamic mechanical analyzer measurement. The physical properties such as the fracture toughness, flexual modulus, coefficient of thermal expansion, and adhesion were measured, and the liquid–liquid thermal shock (LLTS) test under −55 to 125°C was performed with different formulations. One of the formulations toughened by amine/epoxy‐terminated polysiloxane, which has higher die shear strength, lower modulus, and higher toughness, passed 1000 cycles of the LLTS test. In order to obtain a high reliable no‐flow underfill, the physical properties of the no‐flow underfill should be well controlled and balanced. Finally, a correlation between physical properties of the no‐flow underfill and the fillet cracking capability for those approaches was discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2439–2449, 2003
Experimental study of the frictional properties of friction spun yarns
Authors: Ramkumar S. S. , Shastri L. , Tock R. W. , Shelly D. C. , Smith M. L. , Padmanabhan S.
Published: March 2003

This article reports the results from a study conducted to characterize the frictional properties of friction spun yarns. The aim of the study was to obtain data on the surface mechanical properties of a variety of friction spun yarns. The study was essential as the surface mechanical properties influence the fabric formation, bonding strength, and high‐performance properties of yarns. The yarns used in the study were made from different fibers and were spun at different speeds. The capstan method was used to obtain the friction force values between the yarns and a glass cylindrical rod. The experiment was conducted at different tensions. The results indicate that the friction of friction spun yarns are influenced by different factors such as the type of fiber and tensions applied. The results obtained help to understand the surface mechanical properties of high‐performance yarns and their influence on the performance characteristics of friction spun yarns. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2450–2454, 2003
Study of thermal stability and ablation behavior of carbon/epoxy‐novolac composites
Authors: Firouzmanesh M. R. , Azar A. Aref
Published: March 2003

The use of carbon/epoxy‐novolac composites as advanced ablative materials for insulation of exit cone of solid‐propellant rocket nozzles are studied. In this article, three types of carbon fabrics are used and their composites are prepared by use of impregnation and hand lay‐up methods. To study the thermal stability and ablation behavior, these composites are tested by thermal tests such as thermogravimetric analysis (TGA) and oxyacetylene standard flame tests; the latter test is one of the most important standard tests of ablative materials. The test apparatus is made according to American standard, ASTM‐E‐285‐80, and over 33 polymeric composites and 3 steel specimens were carried out according to its standards. It is found that the composites that are made up of C‐9750 fabric (high‐strength carbon fabric) in comparison with steel and the other types of carbon fabric specimens have the highest thermal stability and the best ablation behavior. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2455–2461, 2003
Synthesis and characterization of nylons based on hexadecane diacid
Authors: Li Weihua , Yan Deyue
Published: March 2003

A series of nylons with long alkane segments between amide groups were synthesized by using hexadecane diacid and various diamines, and the resulting polyamides were characterized comprehensively. It was shown that the molecular weights of nylons 6 16, 8 16, 10 16, and 12 16 in our studies exceed 1.1 × 104, whereas nylons 2 16 and 4 16 have relatively low molecular weights. In addition, the melting temperatures, the decomposition temperatures, and the glass transition temperatures of the nylons obtained were measured. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2462–2467, 2003
Investigation of kinetics of 4‐methylpentene‐1 polymerization using Ziegler–Natta‐type catalysts
Authors: Balaji R. , Kothandaraman H. , Rajarathnam D.
Published: March 2003

The kinetics of 4‐methylpentene‐1 (4MP1) polymerization by use of Ziegler–Natta‐type catalyst systems, M(acac)3‐AlEt3 (M = Cr, Mn, Fe, and Co), are investigated in benzene medium at 40°C. The effect of various parameters such as Al/M ratio, reaction time, aging time, temperature, catalyst, and monomer concentrations on the rate of polymerization and yield are examined. The rate of polymerization increased linearly with increasing monomer concentration with first‐order dependence, whereas the rate of polymerization with respect to catalyst concentration is found to be 0.5. For all cases, the polymer yield is maximum at an Al/M ratio of 2. The activation energies obtained from linear Arrhenius plots are in the range of 25.27–33.51 kJ mol−1. It is found that the aging time to give maximum percentage yield of the polymer varies with the catalyst systems. Based on the experimental results, a plausible mechanism is proposed that envisages a free‐radical mechanism. Characterization of the resulting polymer product, for all the cases, through FTIR, 1H‐NMR, and 13C‐NMR studies, showed isomerized polymeric structures with 1,4‐structure as dominant. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2468–2477, 2003
Studies on mechanical and rheological properties of poly(vinyl chloride) modified with elastomers and rigid organic particles
Authors: Peng Jing , Wei Genshuan , Zhang Yudong
Published: March 2003

Chlorinated polypropylene (CPP) as rigid organic particles and chlorinated polyethylene (CPE) as elastomer were used to modify the properties of poly(vinyl chloride) (PVC) by melt blending. Both mechanical and rheological properties of the PVC blends were investigated. The submicroscopic morphology of the blends was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results demonstrate that when the weight ratio of CPE to CPP is about 6 : 1, a sample with the best impact strength and without obvious decline in tensile strength can be obtained. The impact strength correlates well with SEM morphologies, and TEM micrographs in the necking of the tensile specimen indicate that a cold‐drawing deformation of rigid particles happens as reported by T. Kurauchi and T. Ohta (J Mater Sci 1984, 19, 1699). Therefore, a conclusion can be drawn that CPP particles acting similar to elastic particles can toughen PVC, and the cold‐drawing deformation is the primary reason for toughening the PVC blends. In addition, the addition of CPP can promote the processibility of PVC ternary blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2478–2483, 2003
Use of gradient, critical, and two‐dimensional chromatography in the analysis of styrene‐ and methyl methacrylate‐grafted epoxidized natural rubber
Authors: Graef Sven M. , Van Zyl André J. P. , Sanderson Ronald D. , Klumperman Bert , Pasch Harald
Published: March 2003

The growing number of heterogeneous polymeric species that are being synthesized places increasing demands on existing analytical techniques. Although size‐exclusion chromatography (SEC) has established itself as a powerful analytical tool, it has its limits when complex polymers, e.g., graft copolymers, must be analyzed. In this case, complementary techniques such as gradient HPLC and liquid chromatography at critical conditions (LCCC) are more favorable. The present study describes the synthesis and analysis of methyl methacrylate‐ and styrene‐grafted epoxidized natural rubber by different chromatographic techniques. The grafting efficiency was evaluated by gradient HPLC under normal and reversed phase conditions. Methyl methacrylate‐grafted ENR50 was further analyzed by LCCC, where separation of the rubber and grafted rubber occurred according to chemical composition but was independent of the molar mass of the methyl methacrylate homopolymers. This was followed by the combination of LCCC and SEC, where separation was achieved in two dimensions. Relevant deductions were made of both the chemical composition distribution and the molar mass distribution of the functional groups of methyl methacrylate‐grafted ENR50. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2530–2538, 2003
Monitoring the grafting of epoxidized natural rubber by size‐exclusion chromatography coupled to FTIR spectroscopy
Authors: Van Zyl André J. P. , Graef Sven M. , Sanderson Ronald D. , Klumperman Bert , Pasch Harald
Published: March 2003

The evaluation of heterogeneous polymeric species by a selective, dual detector size‐exclusion chromatography setup can provide accurate results on the incorporation of specific functional groups in copolymers as a function of the molar mass distribution. However, when non‐UV‐absorbing species are used in copolymerization reactions, the dual detector method becomes less reliable. By interfacing a Fourier transform infrared (FTIR) spectrometer with size‐exclusion chromatography (SEC), the problem can be overcome, making it possible to map non‐UV‐absorbing species as a function of the molar mass distribution. Coupling takes place via a solvent‐evaporation stage, which delivers the mobile phase as a dry, solvent‐free polymeric film onto a germanium disk. In this article, styrene and methyl methacrylate were grafted onto epoxidized natural rubber (ENR50) and analyzed by SEC. The accuracy of FTIR as a suitable detector was evaluated by comparing results from a dual detector SEC setup and FTIR coupled to SEC. FTIR proved to be a successful detector for the analysis of non‐UV‐absorbing species. This was consequently followed by the characterization of methyl methacrylate‐grafted ENR50. From the relevant data, Gram–Schmidt and contour plots could be made to indicate the incorporation of methyl methacrylate into the grafted epoxidized natural rubber as a function of the molar mass distribution. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2539–2549, 2003