bluuebunny/crossref_metadata_2025 huggingface dataset:
Disparity in use of orthotopic liver transplantation among blacks and whites
Authors: Reid Andrea E. , Resnick Maria , Chang YuChiao , Buerstatte Nathan , Weissman Joel S.
Published: June 2004

Orthotopic liver transplantation (OLT) is the best treatment for end-stage liver disease. Limited data exist on the access of minorities to OLT. The aim of this study was to determine whether disparities exist among black and white OLT patients. Data were collected from the United Network for Organ Sharing on black and white 18-70 year-old OLT waiting list registrants (n = 29,013) and OLT recipients (n = 15,805) between 1994 and 1998. Standardized transplant ratios were generated by comparing the racial distribution of OLT patients with the US population. Demographic and clinical characteristics of OLT registrants were compared by race. Multivariate analyses were performed to identify predictors of time to OLT and the likelihood of dying or receiving OLT within 4 years, controlling for severity of illness and other factors. The standardized transplant ratio for black OLT recipients (0.65) was significantly lower than the standardized transplant ratio for white OLT recipients (1.05). Blacks were younger and sicker than whites. After adjustment for severity and other factors, time to OLT among recipients did not differ by race (P > .05). Blacks were more likely to die or become too ill for OLT while waiting (P < .001). Blacks were less likely to receive OLT within 4 years (P < .001). In conclusion, adult blacks were underrepresented among OLT patients. Although waiting times were similar once listed, black race affected outcomes while awaiting OLT. The process of referral and evaluation for OLT should be investigated further. (Liver Transpl 2004;10:834-841.)
Consumption of dietary supplements in a liver transplant population
Authors: Neff Guy W. , O’Brien Christopher , Montalbano Marzia , DeManno Antoinette , Kahn Stephanie , Safdar Kamran , Nishida Seigo , Tzakis Andreas
Published: June 2004

The extensive use of alternative medicine products, herbal remedies, and vitamins in large doses has reached an all time high in the general public. Some agents are reported and advertised as immune stimulants and may interfere with patients suffering from immune modification, autoimmune diseases, or transplant recipients. In this report, we will present an investigation into the use of herbal remedies and vitamins in our liver transplant population. We performed an investigation using a questionnaire to determine the use of herbal products and vitamins in our liver transplant population. Medical records were reviewed for each liver transplant recipient that admitted to consuming herbal products or vitamins. Information collected included patient demographics, transplant related information, laboratory tests, outcomes, and herbs or vitamin products used. A total of 290 patients completed and returned the questionnaire. We found 156 admitting to taking more than a standard multivitamin and/or an herbal remedy. All patients were treated with steroids for allograft rejection and experienced a recurrence of amino transaminases following the removal of steroids. Further investigation into dietary supplements using a patient questionnaire form revealed that nearly 50% of patients admitted to using vitamins following transplantation, while 19% used herbal remedies combined with vitamins, most admitting to silymarin. One recipient was ingesting colostrum and required admission for the management of allograft rejection, while 5 patients had consumed large amounts of echinacea or CoEnzyme Q-10 and experienced elevations in their transaminases that resolved with discontinuation of the herb. The review also identified 4 patients with primary biliary cirrhosis and with transaminase elevation (mean values of aspartate aminotransferase and alanine aminotransferase levels of 88 and 95, respectively). All recipients were consuming vitamins, in particular high doses of vitamin E (tocopherol), more than 1 gram per day. All of the transplant recipients were instructed to discontinue all vitamin E products and the amino transaminases resolved over the following 30 to 60 days. In conclusion, this information reveals that a significant proportion of our liver transplant recipients consume herbal remedies. The results of this report suggest that transplant teams need to question each recipient about the use of herbal and vitamin remedies and educate them regarding the potential hazards. (Liver Transpl 2004;10:881-885.)
Bacteremias in liver transplant recipients: Shift toward gram-negative bacteria as predominant pathogens†
Authors: Singh Nina , Wagener Marilyn M. , Obman Asia , Cacciarelli Thomas V. , de Vera Michael E. , Gayowski Timothy
Published: June 2004

During the 1990s, gram-positive bacteria emerged as major pathogens after liver transplantation. We sought to determine whether the pathogens associated with bacteremias in liver transplant recipients have changed. Patients included 233 liver transplant recipients transplanted between 1989 and 2003. The proportion of all infections due to bacteremias increased significantly over time (P < .0001). Of other major infections, a trend toward a decrease in fungal infections (P = .089) and a significant decrease in cytomegalovirus (CMV) disease (P = .0004) were documented. Whereas the proportion of bacteremias due to gram-negatives increased from 25% in the period of 1989-1993 to 51.8% in 1998-03, that of gram-positive bacteria decreased from 75% in the period of 1989-93 to 48.2% in the period of 1998-2003. Methicillin-resistant Staphylococcus aureus (MRSA), Klebsiella pneumoniae, and Pseudomonas aeruginosa were the most frequent pathogens in bacteremic patients. The incidence of bacteremias due to MRSA and Pseudomonas aeruginosa has remained unchanged (P < .20); however, that due to enteric gram-negative bacteria, particularly Klebsiella pneumoniae has increased (P = .02). Klebsiella pneumoniae isolates in the current quartile were not clonally related. In conclusion, bacteremias as a proportion of all infections in liver transplant recipients have increased significantly over time, due in part to a decline in infections due to other major pathogens, e.g., fungi, primarily Candida species, and CMV. Gram-negative bacteria have emerged as predominant pathogens in bacteremic liver transplant recipients. (Liver Transpl 2004;10:844-849.)
Oxidation of niobium particles embedded in a sintered ceramic matrix
Authors: Tommaselli M. A. G. , Mariano N. A. , Pallone E. M. J. A. , Kuri S. E.
Published: June 2004

The toughness of ceramic materials can be improved through the inclusion of metallic particles in the ceramic matrix. The plastic deformation of the particles limits the rupture of the ceramic matrix. Al2O3‐Nb composites show the ability of niobium to form a strong bond with Al2O3, but the poor resistance to oxidation of niobium hinders the use of niobium for high temperature applications. The study of the oxidation mechanism was done using thermogravimetric analysis under an oxygen atmosphere in order to obtain the oxidation reaction rate constants of the Al2O3‐Nb composite. At the beginning the oxidation kinetics are linear, probably due to a great availability of oxygen. Later on, the oxidation mechanism showed to be parabolic, indicating that the process depends on the oxygen diffusion through the ceramic matrix.
Investigations of an ethanolamine‐based corrosion inhibitor system for surface treatment of reinforced concrete
Authors: Ngala V. T. , Page C. L. , Page M. M.
Published: June 2004

Laboratory investigations were performed to assess the efficacy of a proprietary ethanolamine‐based corrosion inhibitor system when applied to the surface of reinforced concrete specimens that were chloride‐contaminated to varying extents in the presence or absence of carbonation. The corrosion responses of embedded steel bars at various depths of cover were monitored electrochemically during a controlled programme of cyclic wetting and drying undertaken for several months prior to the inhibitor treatment and for approximately eighteen months thereafter. Gravimetric measurements of the quantities and distribution of corrosion on the steel were also made on completion of the exposure tests. Analysis of aqueous extracts from treated concrete revealed that the ethanolamine component of the inhibitor system penetrated to depths of more than 15 mm within the concrete. It was found that, for inhibitor‐treated specimens, there was some reduction in the corrosion rate of pre‐corroding steel at low cover depths in non‐carbonated concrete with modest levels of chloride contamination. At higher levels of chloride contamination and in carbonated specimens, however, the ethanolamine‐based inhibitor was apparently ineffective under the conditions investigated.
Preparation of Scratch‐ and Abrasion‐Resistant Polymeric Nanocomposites by Monomer Grafting onto Nanoparticles, 4
Authors: Bauer Frank , Sauerland Volker , Ernst Horst , Gläsel Hans‐Jürgen , Naumov Sergej , Mehnert Reiner
Published: June 2004

To obtain transparent, scratch‐ and abrasion‐resistant coating materials a high content of nanosized silica and alumina filler was embedded in radiation‐curable acrylate formulations by acid catalyzed silylation using trialkoxysilanes. 29Si magic angle spinning (MAS) NMR spectroscopy and matrix‐assisted laser desorption/ionisation time‐of‐flight mass spectrometry (MALDI‐TOF MS) were used to elucidate the structure of the surface‐grafted methacryloxypropyl‐, vinyl‐, and n‐propyltrimethoxysilane. 29Si MAS NMR measurements revealed a predominance of T2 and T3 structures of silicon atoms, i.e., silane oligomers have been formed by an extensive loss of water. For methacryloxypropyltrimethoxysilane, the proportion of the highly condensed T3 silicon atoms was estimated to be 75%. In accordance with these NMR findings, MALDI‐TOF MS showed highly condensed oligomeric siloxanes of more than 20 monomeric silane units. The degree of silane condensation is higher on alumina than on silica, irrespective to the addition of maleic acid as catalyst. Moreover, completely condensed silsesquioxanes, e.g., octamers, decamers, and dodecamers, were detected. Based on the observed MS pattern, a ladder‐like arrangement of two linked siloxane chains forming connected eight‐membered rings is proposed, which is similar for all of the condensed organosilanes under study. The grafted polysiloxanes lead to an organophilation of inorganic nanofillers and improve their dispersibility in acrylate suspensions.

Proposed ladder‐like arrangement of the T3 structure of silicon atoms in polysiloxanes grafted on the silica surface.

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Proposed ladder‐like arrangement of the T3 structure of silicon atoms in polysiloxanes grafted on the silica surface.
Self‐Assembly of Porphyrin‐Centered Amphiphilic Star Block Copolymer into Polymeric Vesicular Aggregates
Authors: Jin Ren‐Hua
Published: June 2004

Polymeric vesicular aggregates with spherical and tubular shapes were formed from the self‐assembly of a porphyrin‐centered amphiphilic star poly(oxazoline) [poly(phenyloxazoline)‐block‐poly(methyloxazoline)] in an DMF/water mixture containing excess DMF. The aggregates were evaluated by means of UV‐Vis, fluorescent, 1H NMR spectroscopies, and optical microscopy. The driving force to induce the vesicular aggregates is the interactions between poly(phenyloxazoline) segments which were insoluble in DMF rich aqueous medium.

Polymeric vesicular aggregates with spherical and tubular shapes were formed from the self‐assembly of a porphyrin‐centered amphiphilic star poly(oxazoline) [poly(phenyloxazoline)‐block‐poly(methyloxazoline)] in an DMF/water mixture.

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Polymeric vesicular aggregates with spherical and tubular shapes were formed from the self‐assembly of a porphyrin‐centered amphiphilic star poly(oxazoline) [poly(phenyloxazoline)‐block‐poly(methyloxazoline)] in an DMF/water mixture.
Characterization of Solvation Environment Provided by Dilute Poly(sulfonyl maleic anhydride‐co‐dodecyl vinyl ether) Solutions at Various pH Using Pyrene and 1,3‐Bis(1‐pyrenyl)propane as Fluorescence Probes
Authors: Pandey Siddharth , Redden Rebecca A. , Fletcher Kristin A. , Palmer Christopher P.
Published: June 2004

Solubilization environments afforded by dilute aqueous solutions of poly(sulfonyl maleic anhydride‐co‐dodecyl vinyl ether) [PSMADVE, 1 wt.‐%] at pH 4, 7, and 10 are investigated using pyrene and 1,3‐bis(1‐pyrenyl)propane as fluorescence probes. While pyrene is a common polarity probe, intramolecular excimer formation in 1,3‐bis(1‐pyrenyl)propane makes it an interesting cybotactic region microviscosity probe. Results for pyrene II/IIII indicate that the most hydrophobic solubilization site is afforded at pH 4 followed by pH 10 and pH 7. The dipolarity indicated by pyrene is similar to that observed in m‐ and o‐xylene, toluene, and butyl benzoate. The solvation microenvironment afforded by the PSMADVE solutions is more hydrophobic than that observed within sodium dodecyl sulfate micellar solution. Additionally, further investigation of the relative size of the solubilization site revealed that the polymer solutions promoted intermolecular pyrene excimer formation at relatively low pyrene concentrations, indicating the possibility of localized concentration enhancement within the solvation pockets and/or compartmentalization of the solute molecules. This observation was most prominent at pH 10 and least at pH 7. 1,3‐Bis(1‐pyrenyl)propane intramolecular excimer formation efficiency at pH 4 is slightly higher than that for neat ethylene glycol, while at pH 10 is similar to that observed in 1‐octanol or dimethyl sulfoxide. Anomalously high excimer‐to‐monomer intensity ratio at pH 7 could be due to probe ground state heterogeneity, i.e., the existence of probe moieties in the ground state where the two pyrenyl groups are already aggregated. This is demonstrated by the fluorescence excitation data. Presence of the ground state aggregated form may give rise to anomalously high excimer formation efficiency.

Structures of fluorescence probes pyrene and 1,3‐bis(1‐pyrenyl)propane.

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Structures of fluorescence probes pyrene and 1,3‐bis(1‐pyrenyl)propane.
Effect of a Polymeric Additive on the Pore‐Size Distribution and Shrinking Process of a Hydrogel Network
Authors: Lynch Isuelt , Dawson Kenneth A.
Published: June 2004

A systematic comparison of the effect of architectural modifications to the network structure on the internal microstructure of N‐isopropylacrylamide (NIPA) based hydrogels showed that the addition of a second component to the network significantly increased the proportion of macropores in the network. The second components considered were short poly(N‐isopropylacrylamide) (PNIPAM) chains grafted to the network backbone, high‐molecular‐weight polyacrylamide (PAM) chains, or microsphere particles of PNIPAM. Structures are proposed for each of the modified gel networks taking into account the new structural information. Through a combination of the pore size and network structure data reported here, and with the shrinking data obtained previously, shrinking mechanisms are proposed for each of the modified network structures. In all cases, the enhanced shrinking rates were directly caused by the presence of the second component, which acted as nuclei for shrinking (graft‐PNIPAM and PNIPAM microspheres) or as water‐release channels (PAM gel), and indirectly caused by the second components via their affect on the network microstructure.

Proposed structures for the architecturally modified gels based on the pore‐size information. Graft‐PNIPAM gel. The freely mobile graft chains prevent chains from meeting resulting in larger pores.

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Proposed structures for the architecturally modified gels based on the pore‐size information. Graft‐PNIPAM gel. The freely mobile graft chains prevent chains from meeting resulting in larger pores.
NMR Characterization of Carbazole‐Substituted Norbornene Comonomer 9‐(Bicyclo[2.2.1.]hept‐5‐en‐2‐ylmethyl)‐9H‐carbazole (BHMCZ) and Poly(ethylene‐co‐BHMCZ) Copolymer
Authors: Mustonen Ilpo , Hukka Terttu , Pakkanen Tuula T.
Published: June 2004

Carbazole‐substituted norbornene comonomer 9‐(bicyclo[2.2.1.]hept‐5‐en‐2‐ylmethyl)‐9H‐carbazole (BHMCZ) can be copolymerized with ethylene using the [Ph2C(Ind)(Cp)ZrCl2] catalyst and methylaluminoxane (MAO) cocatalyst system. The microstructures of BHMCZ comonomer and of ethylene–BHMCZ copolymer containing 4.6 mol‐% BHMCZ units in the chain were characterized by one‐dimensional 13C DEPT and two‐dimensional homonuclear 1H‐1H COSY and heteronuclear 1H‐13C HXCO NMR spectroscopy. The BHMCZ comonomer appears as endo and exo stereoisomers, which were identified on the basis of chemical shifts, signal multiplicities, and coupling in the 2D NMR spectra. The NMR information on the BHMCZ isomers was used to assist in the determination of the chemical shifts and microstructure of ethylene–BHMCZ copolymer. The NMR analysis of ethylene–BHMCZ copolymer indicated that exo‐BHMCZ polymerizes with ethylene slightly more readily than does endo‐BHMCZ under the polymerization conditions employed.

Isolated segments of exo(2)‐exo(5)‐exo(6) and endo(2)‐exo(5)‐exo(6) ethylene‐BHMCZ copolymer showing carbon atom numbering.

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Isolated segments of exo(2)‐exo(5)‐exo(6) and endo(2)‐exo(5)‐exo(6) ethylene‐BHMCZ copolymer showing carbon atom numbering.
Surface‐Enhanced Raman Scattering on Molecularly Imprinted Polymers in Water
Authors: Kostrewa Stefan , Emgenbroich Marco , Klockow Dieter , Wulff Günter
Published: June 2004

Molecularly imprinted polymer layers were prepared on SERS‐active surfaces in order to directly monitor the uptake and release of certain substances to this polymer layer by surface enhanced Raman‐scattering (SERS). The imprinting system consisted of either (2S,3S)‐(+)‐di‐O‐benzoyl‐tartaric acid (1) or N‐benzyloxycarbonyl‐(L)‐aspartic acid (2) as templates. As binding site N,N′‐diethyl‐4‐vinylbenzamidine (3) was used which binds in a 2:1 complex to the templates. The release and uptake of the templates to the imprinted polymer could be followed in aqueous solution under physiological conditions (aqueous buffer, ambient temperature). The recorded SERS bands can be unequivocally assigned to the substances taken up, and it is therefore possible to directly detect a certain substance in the imprinted layer. Release and uptake are quick processes occurring within minutes. This method also offers the opportunity to use these layers in chemosensors in which case the stability has to be further increased.

SERS spectra of polymer coatings containing the template N‐benzyloxycarbonyl‐(L)‐aspartic acid (2) on gold and on silver surfaces, Raman spectra of pure 2 (template) and of a HEPES buffer solution (0.1 M, pH 7.3) which was used for the adsorption measurement.

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SERS spectra of polymer coatings containing the template N‐benzyloxycarbonyl‐(L)‐aspartic acid (2) on gold and on silver surfaces, Raman spectra of pure 2 (template) and of a HEPES buffer solution (0.1 M, pH 7.3) which was used for the adsorption measurement.
Synthesis, Characterization, and Polymerization Kinetics of Novel Ladder‐Like Polysilsesquioxanes Containing Side‐Chain Propyl Methacrylate Groups
Authors: Gopala Krishnan P. Santhana , He Chaobin
Published: June 2004

Three ladder‐like polysilsesquioxanes containing side‐chain propyl methacrylate groups have been synthesized successfully by stepwise coupling polymerization. The prepared ladder‐like polymers are polysilsesquioxanes containing 100 mol‐% propyl methacrylate side groups and two copolymers containing 70 mol‐% methyl or phenyl groups and 30 mol‐% propyl methacrylate side groups. They were characterized by FT‐IR, 1H NMR, proton‐decoupled 13C NMR, and 29Si NMR spectroscopies, gel‐permeation chromatography (GPC), wide‐angle X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and thermo‐gravimetric analysis (TGA). Characterization data indicate that these polymers have ordered ladder‐like structures with possible defects. At appropriate conditions, crystals of homopolymer were grown and are in the shape of a parallelogram. All three polymers were cured by 2,2′‐azoisobutyronitrile (1% w/w) and the kinetics for the bulk polymerization of these polysilsesquioxanes was followed by dynamic DSC method. Ozawa and Kissinger methods were used to calculate the activation energy for curing. Both the frequency factor and the activation energy of the homopolymer were found to be higher than the copolymers. Cured samples had a higher thermal stability than uncured samples.

Chemical structure of LPS.

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Chemical structure of LPS.
Correlation between Molecular Architecture, Morphology, and Deformation Behaviour of Styrene/Butadiene Block Copolymers
Authors: Adhikari Rameshwar , Michler Goerg H. , Huy Trinh An , Ivan'kova Elena , Godehardt Reinhold , Lebek Werner , Knoll Konrad
Published: June 2004

The correlation between the molecular architecture, morphology, and micromechanical deformation behaviour of styrene/butadiene (SB) block copolymers with different architectures (linear and star block copolymers, total styrene content, ΦST = 0.74) was studied using dynamic mechanical analysis (DMA), uniaxial tensile testing, scanning force microscopy (SFM), and high voltage electron microscopy (HVEM). Deformation of the individual phases under uniaxial strain at the molecular level was monitored by Fourier transform infrared (FT‐IR) spectroscopy. It was demonstrated that the morphology and deformation behaviour of these block copolymers are strongly influenced by their molecular topology, block symmetry, and the nature of the interface between the component blocks. While the cylindrical morphology (hexagonal polybutadiene (PB) cylinders in polystyrene (PS) matrix) was observed in a symmetric SBS triblock copolymer with ΦST = 0.74, a “two‐component three‐phase” morphology was found in an asymmetric star block copolymer having an equivalent chemical composition and an SBS arm structure. Likewise, an SBS triblock copolymer with a composition identical to the former ones but with highly asymmetric PS end blocks revealed a lamellar morphology. While no locally confined deformation zones were observed in the lamellar block copolymers, the cylindrical block copolymer was found to deform through the formation of highly localised craze‐like deformation zones.

SFM phase images showing lamellae‐like morphology of the star block copolymer ST2, phase difference 25 degrees.

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SFM phase images showing lamellae‐like morphology of the star block copolymer ST2, phase difference 25 degrees.
Kinetic Investigation of the Condensation Reaction of Activated Ester–Amides Containing Oligo(oxyethylene) Segments
Authors: Solaro Roberto , Talamelli Paolo , Carbonaro Laura , Chiellini Emo
Published: June 2004

The kinetics of polycondensation of activated ester–amides, namely pentachlorophenyl α‐amino‐ω‐oligo(ethyleneglycol)succinate hydrochlorides (PSPnNH) having a degree of oligomerization n = 1–3, were investigated in solution in dichloromethane in the presence of excess triethylamine. The large extinction coefficient of the pentachlorophenate formed during the reaction allowed the use of the stopped flow technique. Experimental data resulted in agreement with the existence of concurrent first‐ and second‐order processes, attributable to the intramolecular cyclization and intermolecular polycondensation reactions, respectively. The relative incidence of the cyclization reaction decreased on increasing the monomer concentration and on decreasing the number of oxyethylene units in the monomer. These hypotheses were confirmed by SEC, TLC, FT‐IR, and NMR characterization of the reaction products. The kinetics of PSP3NH are in very good agreement with the predictions of both the collision theory and the condensation theory of linear systems at equilibrium. However, the behavior of shorter chain monomers was opposite to that of the theoretical one, demonstrating that other parameters, such as steric hindrance and solvent interactions, must be taken into proper account. The reported findings clearly evidenced that polymerization of the investigated ester‐amides must be performed in bulk in order to suppress the cyclization reaction and to obtain high‐molecular‐weight polymers.

SEC traces of PSP3NH condensation products obtained at different monomer concentrations (Runs P7–P9).

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SEC traces of PSP3NH condensation products obtained at different monomer concentrations (Runs P7–P9).
Copolymers from tert‐Butyl Methacrylate with Trimethylsilyl Methacrylate or Methacrylic Acid: Models for Resist Polymers
Authors: Ferbitz Jens , Mormann Werner
Published: June 2004

Free radical copolymerisation of tert‐butyl methacrylate (1) with trimethylsilyl methacrylate (2) and methacrylic acid (3) has been investigated. Reactivity ratios for methacrylic acid and tert‐butyl methacrylate indicate an azeotropic copolymerisation (r1 = 0.476 ± 0.103; r3 = 0.300 ± 0.032), whereas the two esters show preferential incorporation of 2 (r1 = 0.170 ± 0.050; r2 = 1.170 ± 0.124). Thermal cis‐elimination of isobutylene from the tert‐butyl ester and subsequent formation of six‐membered cyclic anhydride moieties has been studied. For poly(methacrylic acid‐co‐tert‐butyl methacrylate) thermogravimetry could be used to determine copolymer composition. Solvolytic desilylation of the trimethylsilyl ester groups has been investigated as an alternative route to poly(methacrylic acid‐co‐tert‐butyl methacrylate). The tert‐butyl ester is not affected under the conditions of desilylation. Sequence distribution of both copolymers has been calculated using the method introduced by Bruns and Motoc.

Copolymer composition diagram for tert‐butyl methacrylate/methacrylic acid.

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Copolymer composition diagram for tert‐butyl methacrylate/methacrylic acid.
Cloud‐Point Pressure Curves of Ethene/Poly[ethylene‐co‐((meth)acrylic acid)] Mixtures
Authors: Buback Michael , Latz Henning
Published: June 2004

Ethene‐methacrylic acid (MAA) and ethene‐acrylic acid (AA) copolymers of narrow polydispersity and high chemical homogeneity have been synthesized at acid unit copolymer contents up to 9 mol‐% within a continuously operated stirred tank reactor at overall monomer conversions of about 2%. Cloud‐point pressures (CPPs) of mixtures of 3 wt.‐% copolymer in ethene (E) have been measured in an optical high‐pressure cell at pressures and temperatures up to 3 000 bar and 260 °C, respectively. The CPP weakly increases with acid copolymer content up to about 3.5 mol‐%. Toward higher acid contents, the CPP is strongly enhanced, in particular at the lower edge of the experimental temperature range at around 200 °C. This increase in CPP is more pronounced for the AA than for the MAA systems. The data suggest that hydrogen‐bonding interactions are operative in the pressurized E/poly(E‐co‐(M)AA) mixtures at temperatures of 260 °C and perhaps even above. E‐AA and E‐MAA copolymers with acid contents of about 5.6 mol‐% have also been completely methyl‐esterified to yield the associated methyl esters. The CPPs of the resulting E‐methyl acrylate and E‐methyl methacrylate copolymers in mixtures with E are significantly below the CPPs of the corresponding E/poly(E‐co‐(M)AA) systems.

Cloud‐point pressure vs temperature curves for several E/poly(E‐co‐methacrylic acid) systems. The subscripts denote copolymer content in mol‐%. A cloud‐point pressure curve for E/polyethylene (PE) is included for comparison.

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Cloud‐point pressure vs temperature curves for several E/poly(E‐co‐methacrylic acid) systems. The subscripts denote copolymer content in mol‐%. A cloud‐point pressure curve for E/polyethylene (PE) is included for comparison.
New Polymer Syntheses, 112
Authors: Kricheldorf Hans R. , Richter Martin , Steinmann Andreas , Schwarz Gert
Published: June 2004

Bis(4‐chlorophenyl)sebacate (BCPS) was polycondensed with 1,12‐diamino‐4,9‐dioxadodecane or with its bistrimethylsilyl derivative in three different solvents with variation of time and temperature. The highest molecular weights were obtained in dimethylsulfoxide at 60 °C. The highest fraction of cyclic polyamides was detected by MALDI‐TOF mass spectrometry in the samples with the highest molecular weights. Numerous polycondensations of BCPS and 1,13‐diamino‐4,7,10‐trioxatridecane were performed with variation of solvent, time and temperature. Again the best results were obtained in dimethylsulfoxide at 60 °C. The fraction of cyclic polyamides increased with higher average molecular weights of the samples. The MALDI‐TOF mass spectrum of the sample with the highest molar mass (Mn ca. 30 000 Da) exclusively displayed mass peaks of cycles (detected up to 13 000 Da). No side reactions were observed.

MALDI‐TOF mass spectrum (segment) of polyamide 1 prepared by polycondensation of DDD with BCPS in DMSO at 60 °C/48 h (no. 3, Table 1).

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MALDI‐TOF mass spectrum (segment) of polyamide 1 prepared by polycondensation of DDD with BCPS in DMSO at 60 °C/48 h (no. 3, Table 1).
Synchrotron X‐Ray Study of Liquid Crystalline Polyoxetanes Containing Two Mesogenic Groups Connected by a Flexible Spacer in the Side Chain
Authors: Campo Aránzazu del , Bello Antonio , Pérez Ernesto
Published: June 2004

The study of the mesophase behaviour of a family of new side chain liquid crystalline polymers by means of synchrotron X‐ray diffraction is reported. These systems contain two bibenzoate rigid units in the side chain that are interconnected through a flexible spacer. A polymerisable oxetane unit is linked to one end of the dimer structure, and a flexible terminal chain is linked to the other end. All the polymers form phases with variable degree of order (from low ordered smectic to crystalline) depending on the chemical constitution of the different segments. The influence of the length, parity, and lateral substitution of the spacers on the transitional parameters and the symmetry of the mesophases that are formed is analysed. Close similarities were found between the phase behaviour of the monomer precursors and the derived polyoxetanes. The arrangement of the mesogens, the flexible groups and the polymeric backbone in the layered structure is discussed with respect to the L/d ratio. Different values were obtained depending on the parity of the central spacer and on the degree of order of the mesophase. Interpenetrated structures, where the flexible groups of different lengths are mixed, seem to be compatible with low ordered smectic phases, but sterically disfavoured when building up highly ordered mesophases.

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Pressure Effects on the Thermodynamics of trans‐Decahydronaphthalene/Polystyrene Polymer Solutions: Application of the Sanchez‐Lacombe Lattice Fluid Theory
Authors: Jiang Shichun , An Lijia , Jiang Bingzheng , Wolf Bernhard A.
Published: June 2004

The cloud‐point temperatures (Tcl's) of trans‐decahydronaphthalene(TD)/polystyrene (PS, Mw = 270 000) solutions were determined by light scattering measurements over a range of temperatures (1–16 °C), pressures (100–900 bar), and compositions (4.2–21.6 vol.‐% polymer). The system phase separates upon cooling and Tcl was found to increase with rising pressure for constant composition. In the absence of special effects, this finding indicates positive excess volume for the mixing. Special attention was paid to the demixing temperatures as a function of pressure for different polymer solutions and the plots in the T‐ϕ plane (where ϕ signifies volume fractions). The cloud‐point curves of polymer solutions under different pressures were observed for different compositions, which demonstrated that pressure has a greater effect on the TD/PS solutions when far from the critical point as opposed to near the critical point. The Sanchez‐Lacombe lattice fluid theory (SLLFT) was used to calculate the spinodals, the binodals, the Flory‐Huggins (FH) interaction parameter, the enthalpy of mixing, and the volume changes of mixing. The calculated results show that modified PS scaling parameters can describe the thermodynamics of the TD/PS system well. Moreover the SLLFT describes the experimental results well.

Pressure dependence of the phase transition temperature for the TD/PS polymer solutions at the indicated compositions (In SI units: 1 bar = 105 N · m−2).

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Pressure dependence of the phase transition temperature for the TD/PS polymer solutions at the indicated compositions (In SI units: 1 bar = 105 N · m−2).
Polyacetylenes Bearing Mesogenic Side Groups: Synthesis and Properties, 2
Authors: Stagnaro Paola , Conzatti Lucia , Costa Giovanna , Gallot Bernard , Tavani Cinzia , Valenti Barbara
Published: June 2004

We report on the synthesis of novel liquid crystalline polyacetylenes derived from monosubstituted acetylene monomers. In the monomers A1OBP‐Acn obtained from 3‐bromo‐1‐propyne, the acetylenic moiety is linked through a very short spacer to a biphenyl mesogenic core. Several linear acyl groups of different length are introduced as tail groups. Most of the monomers show liquid crystalline behavior. Polymerizations are carried out in solution with typical metathesis catalysts based on Mo and W and yield polyacetylenes with fairly high molecular weight (MW), soluble in common organic solvents. Polymers PA1OBP‐Acn are fully characterized in terms of molecular structure, by GPC, FT‐IR, NMR and UV/VIS techniques, and of thermal and morphological behavior, by TGA, DSC, POM and X‐ray diffraction experiments. THF solutions of the polymers show a quite relevant photoluminescence with a broadened maximum located around 450 nm.

POM analysis on monomer A1OBP‐Ac6: crystal transformation on heating at 76 °C.

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POM analysis on monomer A1OBP‐Ac6: crystal transformation on heating at 76 °C.
The Effect of Phase Structure on the Tribological Properties of PA66/HDPE Blends
Authors: Chen Zhao‐Bin , Li Tong‐Sheng , Yang Yu‐Liang , Zhang Yu , Lai Shi‐Quan
Published: June 2004

Summary: In this paper, immiscible, partially miscible and miscible blends of polyamide 66 (PA66) and high density polyethylene (HDPE) were obtained by changing compatibilizer concentrations. Mechanical and tribological properties of materials were tested. It was found that the addition of compatibilizer greatly improved the mechanical properties of PA66/HDPE blends. The wear of PA66/HDPE blends was strongly affected by the phase structure. The best blend for lower friction coefficient and higher wear resistance was the blend with a miscible structure, which significantly improved the tribological properties of PA66 and HDPE. SEM investigations on the worn surface and the steel counterface indicated that, for the immiscible and partially miscible blend systems, the dispersed HDPE particles were pulled out from the worn surfaces during sliding because of the poor adhesion between HDPE and PA66, while this was not observed in the miscible blend system.

SEM micrograph of the worn surface formed by PA66/HDPE blend without HDPE‐g‐MAH.

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SEM micrograph of the worn surface formed by PA66/HDPE blend without HDPE‐g‐MAH.
Kinetic Study of Hindered Amine Light Stabilizer Photografting in Poly(propylene) Films under Natural Weathering and Accelerated UV Conditions: Effect of Additive Concentration
Authors: Kaci Mustapha , Hebal Ghania , Touati Naima , Rabouhi Aida , Zaidi Lynda , Djidjelli Hocine
Published: June 2004

Full Paper: The objective of this work is aimed at determining the kinetics of HALS photografting in PP films as a function of the additive concentration under both natural weathering and accelerated UV conditions. The stabilizer studied had a single structure that combined HALS and a UV absorbing unit detectable at 308 nm in the UV spectrum of PP, capable of inducing a photoreaction with the polymer matrix. The kinetics of HALS photografting on PP films at various additive concentrations was determined by direct spectroscopic measurements on film samples through the absorption band of the stabilizer positioned at 308 nm in the UV spectra, which was attributed to the highly conjugated methylenic double bond. The content of free HALS was determined as a function of exposure time by UV spectroscopy for all the additive concentration ratios used. It is shown that the kinetics of HALS photografting increase with a decrease in the additive concentration ratio. The whole grafting process under conditions of natural weathering occurred in the PP film after almost 350 h of exposure, while approximately 20 h were necessary under accelerated UV conditions. Moreover, these kinetics are well described by a third order polynomial model, validated by a maximum value of the coefficient of correlation close to unity. This was also confirmed by a comparison of the time values measured at 50% of the total grafting calculated from the model with those observed experimentally. This finding was consistent with the data obtained on the free HALS content determined by UV spectroscopy.

The percentage of HALS photografting in PP films as a function of time under natural weathering, determined by UV spectroscopy.

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The percentage of HALS photografting in PP films as a function of time under natural weathering, determined by UV spectroscopy.
The Reinforcement of Elastomeric Networks by Fillers
Authors: Bokobza Liliane
Published: June 2004

Summary: The mechanisms involved in rubber reinforcement are discussed. A better molecular understanding of these mechanisms can be obtained by combining characterization of the mechanical behavior with an analysis of the chain segmental orientation accompanying deformation. While the strain dependence of the stress is the most common quantity used to assess the effect of filler addition, experimental determination of segmental orientation can be used to quantify the interfacial interactions between the elastomeric matrix and the mineral inclusions.

SEM micrograph of natural rubber containing 10 wt.‐% of organomodified clay.

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SEM micrograph of natural rubber containing 10 wt.‐% of organomodified clay.
Some properties of monotone rearrangement with applications to elliptic equations in cylinders
Authors: Berestycki H. , Lachand‐Robert T.
Published: June 2004

This paper is concerned with properties and applications of monotone rearrangement as defined in [18]. Unlike the Schwarz and Steiner symmetrization, in the monotone rearrangement framework, the inequality for the Dirichlet integral holds for all functions in H1 (not only H10). Further, we state and prove a necessary and sufficient condition for equality to hold in this inequality.

These properties allow us to give several applications of monotone rearrangement to semilinear elliptic equations. We study such problems in cylinders with general boundary conditions (Neumann, mixed and Robin type). For these problems, we establish the existence of solutions which are monotone in one direction. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Enveloppes polynômiales d'ensembles compacts invariants
Authors: Bou Attour Latifa , Faraut Jacques
Published: June 2004

We consider the following problem: letVℂbe a finite dimensional vector space, andUbe a compact group of ℂ‐linear automorphisms ofVℂ. The polynomial envelope$ \hat Q $of a compact setQ⊂Vℂis defined as

where 𝒫(Vℂ) denotes the space of holomorphic polynomial functions onVℂ. The problem is to determine the polynomial envelope of a compact set which isU‐invariant. We solve the problem whenUis the isotropy subgroup at the origin of the automorphism group of a bounded symmetric domain of tube type. The case of a domain of type II has been solved by C. Sacré [1992], and, for a domain of type IV, it has been solved by L. Bou Attour [1993]. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Locally boundedly A‐p‐convex algebras
Authors: El Kinani A. , Oudadess M.
Published: June 2004

We consider locally p‐convex algebras the bornologies of which coincide with the ones of p‐normed or multiplicatively p‐convex topologies. Two new classes of these algebras are introduced here. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The finite Hilbert transform and weighted Sobolev spaces
Authors: Elliott David , Okada Susumu
Published: June 2004

The boundedness of the finite Hilbert transform operator on certain weighted Lp spaces is well known. We extend this result to give the boundedness of that operator on certain weighted Sobolev spaces. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Slow and fast convergence to local dimensions of self‐similar measures
Authors: Olsen L.
Published: June 2004

LetKandμbe the self‐similar set and the self‐similar measure associated with an iterated function system with probabilities (Si, pi)i=1,…,Nsatisfying the Open Set Condition. Let Σ = {1, …,N}ℕdenote the full shift space and letπ: Σ →Kdenote the natural projection. The (symbolic) local dimension ofμatω∈ Σ is defined by$ \lim _{n} { {\log \mu K _{\omega \vert n}} \over {\log {\rm diam} \, K_{\omega \vert n} } } $whereKω|n=S○ … ○S(K) forω=ω1ω2… ∈ Σ, and the (symbolic) multifractal spectrum ofμis defined by

where dim denotes the Hausdorff dimension. In this paper we study the speed with which the ratio$ { {\log \mu K _{\omega \vert n}} \over {\log {\rm diam} \, K_{\omega \vert n} } } $converges. In particular, we prove that for all (sufficiently large) speedsγ, the set of points

for which the ratio log$ { {\log \mu K _{\omega \vert n}} \over {\log {\rm diam} \, K_{\omega \vert n} } } $converges to its limit with speed equal toγ, has full dimension. i.e.

(© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On many‐sorted algebraic closure operators
Authors: Climent Vidal Juan , Soliveres Tur Juan
Published: June 2004

A theorem of Birkhoff‐Frink asserts that every algebraic closure operator on an ordinary set arises, from some algebraic structure on the set, as the corresponding generated subalgebra operator. However, for many‐sorted sets, i.e., indexed families of sets, such a theorem is not longer true without qualification. We characterize the corresponding many‐sorted closure operators as precisely the uniform algebraic operators. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A remark on the Riemann‐Hilbert problem with a vanishing coefficient
Authors: Virtanen J. A.
Published: June 2004

This paper concerns the existence of nontrivial solutions of the Riemann‐Hilbert problem with a continuous coefficient whose values belong to two rays in the complex plane. Our results extend those recently obtained by E. Shargorodsky and J. F. Toland [6]. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Impact of the Atmosphere on the Reactivity of Peroxidic Species upon Photooxidation of Polymers
Authors: Fraïsse Frédéric , Kumar Ashutosh , Commereuc Sophie , Verney Vincent
Published: June 2004

Summary: This paper gives an account of preliminary results about the impact of an oxidative atmosphere on peroxidation. Attention is focused on the level, nature, and reactivity of (hydro)peroxides with respect to the oxidative component concentration. Our main result is surprising: a lower peroxidation rate occurs, but a higher content of hydroperoxides are formed in air than in pure oxygen atmospheres. The results may lead to an approach to understand the influence of atmospheric factors on the outdoor weathering of polymers.

The device used to measure the oxygen uptake of the systems studied here.

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The device used to measure the oxygen uptake of the systems studied here.
Novel Biodegradable Copolymers with a Periodic Sequence Structure Derived from Succinate Butan‐1,4‐diol, and Butan‐1,4‐diamine
Authors: Abe Hideki , Doi Yoshiharu
Published: June 2004

Summary: Novel biodegradable copolymers derived from succinate, butan‐1,4‐diol, and butan‐1,4‐diamine were synthesized by two‐step polycondensation reactions. The obtained copolymers had a periodical‐sequence structure consisting of ester and amide units, and the melting temperatures of the periodic copolymers increased with an increase in amide content. The crystalline structure of the periodic copolymers differs from that of butylene succinate homopolymer (PBS), and these results suggest that the periodically introduced amide units are included in the crystalline phase forming a novel crystalline structure.

Periodic copolyester‐amides derived from succinate, butane‐1,4‐diol, and butan‐1,4‐diamine

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Periodic copolyester‐amides derived from succinate, butane‐1,4‐diol, and butan‐1,4‐diamine
Precise arguments on the distribution of stereospecific active sites on MgCl2‐supported ziegler‐natta catalysts
Authors: Liu Boping , Nitta Takashi , Nakatani Hisayuki , Terano Minoru
Published: June 2004

The stereospecific nature of active sites on various MgCl2‐supported Ziegler‐Natta catalysts was investigated by stopped‐flow technique combined with temperature rising elution fractionation (TREF) method. A modified three‐sites model with precise description of the stereospecific nature of various types of active sites stemmed from surface titanium species, Al‐alkyl compounds, Mg‐compounds and electron donors has been proposed. It was demonstrated that the isospecificity of active sites strongly depends on the bulkiness of the ligands situated at the two most important ligand positions for construction of asymmetry and chirality of the active sites with steric hindrance. In general, there may exist both monometallic and bimetallic sites in heterogeneous Ziegler‐Natta catalyst system. The kinds of active titanium species with different chemical structures on this catalyst system should be limited, whereas, the non‐discrete distribution of isospecificity of active sites could be considered to generate from the numerous types of steric and electronic effects from the surroundings of active titanium species as well as large number of reversible and dynamic transformation reactions simultaneously occurred on the heterogeneous catalyst surface.
Surface physico‐chemical state of CO‐prereduced Phillips CrOx/SiO2 catalyst and unique polymerization behavior in the presence of Al‐alkyl cocatalyst
Authors: Liu Boping , Fang Yuwei , Nakatani Hisayuki , Terano Minoru
Published: June 2004

In this work, a CO‐prereduced Phillips CrOx/SiO2 catalyst (PC600/CO) was characterized by X‐ray photoelectron spectroscopy (XPS) and temperature programmed desorption with mass spectrometer (TPD‐MS) in comparison with a calcined catalyst (PC600). It was found that surface chromate Cr(VI) species had not been completely reduced into Cr(II) species, meanwhile, CO and CO2 still strongly adsorbed on the PC600/CO catalyst. Subsequently, the unique real‐time profiles of ethylene polymerization rate using PC600/CO in the presence of TEA indicated the existence of two types of active sites: the first type derived from the desorption of CO or CO2 from Cr(II) species by alkyl‐Al and featured with fast activation, higher activity and fast decay; the second type generated from the further reduction of residual chromate Cr(VI) species by alkyl‐Al and featured with slow activation, lower activity and slow decay.
New polymers by copolymerization of ethylene and norbornene with metallocene catalysts
Authors: Kaminsky Walter , Tran Phu‐Dennis , Werner Ralf
Published: June 2004

To increase the thermal stability of metallocene‐methylaluminoxane catalysts. pentalene bridged zirconocenes and a constrained geometry catalyst were used for the copolymerisation of ethene and norbornene. The constrained geometry catalyst is stable in solution up to 90°C. Surprisingly the molecular weight of the copolymers increases with higher incorporation rates of norbornene. Glass transition temperatures of 120°C are reached. The microstructure of the cyclic olefin copolymers material is more alternating.