bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ethylene polymerization with iron‐based diimine catalyst supported on MCM‐41
Authors: Zhang Mingge , Xu Hong , Guo Cunyue , Ma Zhi , Dong Jinxiang , Ke Yucai , Hu Youliang 
Published: December 2004

AbstractA mesoporous molecular sieve MCM‐41 supported iron‐based diimine catalyst (MC) was prepared for the first time. The kinetic behavior of ethylene polymerization with MC was studied. The effects of Al/Fe molar ratio and various cocatalysts on the catalytic activity and properties of the polyethylene obtained were investigated. The results showed that good catalytic activities can be reached with cocatalyst methylaluminoxane (MAO) and triethylaluminium (TEA). Ethylene polymerization with MC gave polymers with higher molecular weight, melting temperature and onset temperatures of decomposition (Tonset) and better morphology than those obtained with the corresponding homogeneous catalyst. Copyright © 2004 Society of Chemical Industry
Further studies on styrene/styrene derivative copolymerizations using combined diphenylzinc‐additive initiator systems
Authors: Rabagliati Franco M , Pérez Mónica A , Rodríguez Francisco J , Caro Carlos J , Crispel Nicolás 
Published: December 2004

AbstractA combination of diphenylzinc, a metallocene and methylaluminoxane (Ph2Zn‐metallocene‐MAO) is a suitable initiator system for the polymerization of styrene and for its copolymerization with para‐alkyl substituted styrenes. This paper reports new experimental results which reinforce our previous findings indicating that polymerization processes are initiated by monomer coordination to active species resulting from these particular combined systems. Polymerization propagates by a cationic pathway. Further to our previous observation that the I+ inductive effect of para‐substituents in styrene improves conversion to polymer, we now find that methyl substitution on the vinyl double bond of styrene, in spite of the I+ inductive effect and as a result of increased steric hindrance, makes the polymerization process difficult. On the other hand, the replacement of titanocenes by zirconocenes or hafnocenes generates Ph2Zn‐metallocene‐MAO initiator systems which are also able to induce homo‐ and copolymerization, but with lower yields and producing practically amorphous polymers. The efficiency of our Ph2Zn‐metallocene‐MAO initiator systems follows the order titanocene > zirconocene > hafnocene, at least for the studied metallocenes. Copyright © 2004 Society of Chemical Industry
In situ polymerization of ethylene with bis(imino)pyridine iron(II) catalysts supported on clay: The synthesis and characterization of polyethylene–clay nanocomposites
Authors: Ray Saptarshi , Galgali Girish , Lele Ashish , Sivaram S. 
Published: December 2004

AbstractPolyethylene–clay nanocomposites were synthesized by in situ polymerization with 2,6‐bis[1‐(2,6‐diisopropylphenylimino)ethyl] pyridine iron(II) dichloride supported on a modified montmorillonite clay pretreated with methylaluminoxane (MAO). The catalysts and the obtained nanocomposites were examined with wide‐angle X‐ray scattering. The exfoliation of the clay was further established by transmission electron microscopy. Upon the treatment of the clay with MAO, there was an increase in the d‐spacing of the clay galleries. No further increase in the d‐spacing of the galleries was observed with the iron catalyst supported on the MAO‐treated clay. The catalyst activity for ethylene polymerization was independent of the Al/Fe ratio. The exfoliation of the clay inside the polymer matrix depended on various parameters, such as the clay content, catalyst content, and Al/Fe ratio. The crystallinity percentage and crystallite size of the nanocomposites were affected by the degree of exfoliation of the clay. Moreover, when ethylene was polymerized with a mixture of the homogeneous iron(II) catalyst and clay, the degree of exfoliation was significantly lower than when the polymerization was performed with a preformed clay‐supported catalyst. This observation suggested that in the supported catalyst, at least some of the active centers resided within the galleries of the clay. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 304–318, 2005
Arenesulfonyl bromides: The second universal class of functional initiators for the metal‐catalyzed living radical polymerization of methacrylates, acrylates, and styrenes
Authors: Grigoras Cristian , Percec Virgil 
Published: December 2004

AbstractThe metal‐catalyzed living radical polymerization of methyl methacrylate,n‐butyl acrylate, and styrene, initiated withp‐toluenesulfonyl bromide and phenoxybenzene‐4,4′‐disulfonyl bromide and catalyzed with CuBr/2,2′‐bipyridine (bpy) and various self‐regulated Cu‐based catalytic systems such as Cu2O/bpy, Cu2S/bpy, Cu2Se/bpy, and Cu2Te/bpy, is reported. Similarities and differences between the arenesulfonyl chloride and arenesulfonyl bromide initiators are discussed. The arenesulfonyl bromide initiators require reduced reaction times to produce polymers in high conversions under milder reaction conditions than the corresponding arenesulfonyl chloride initiators. At the same time, they exhibit 100% initiator efficiency and generate polymers with narrow molecular weight distributions and functional chain ends. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 319–330, 2005
Synthesis and properties of silica/polystyrene/polyaniline conductive composite particles
Authors: Lee Chia‐Fen , Tsai Hung‐Hsin , Wang Lee‐Yih , Chen Chia‐Fu , Chiu Wen‐Yen 
Published: December 2004

AbstractIn this study, silica/polystyrene/polyaniline (SiO2/PS/PANI) conductive composite particles were synthesized by four sequential reactions. The nanosized SiO2 particles were synthesized from tetraethoxysilane (TEOS) by a sol–gel process with water as the solvent medium, followed by a surface modification with triethoxyvinylsilane; then the surface modified SiO2 particles were used as seeds to synthesize SiO2/PS composite particles with soapless seeded emulsion polymerization. Finally, the SiO2/PS particles were used as seeds to synthesize the SiO2/PS/PANI conductive composite particles. The sol–gel process of SiO2, the effect of surface modification, and several other factors that influenced polymerization of styrene in the soapless seeded emulsion polymerization will be discussed. Either potassium persulfate (KPS) or 2,2′‐azobis(isobutyramidine) dihydrochloride (AIBA) was used as the initiator to synthesize the uniform SiO2/PS particles successfully, and the cross‐section morphology of the SiO2/PS particles was found to be of a core–shell structure, with SiO2 as the core, and PS as the shell. The SiO2/PS particles were well dispersed in many organic solvents. In the following step to synthesize SiO2/PS/PANI conductive composite particles, sodium dodecyl sulfate (SDS) played an important role, specifically, to absorb aniline onto the surfaces of the SiO2/PS particles to carry out the polymerization of aniline over the entire surface of the particles. The conductivity of the SiO2/PS/PANI composite particles approached that of semiconductive materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 342–354, 2005
Peeling of polydimethylsiloxane adhesives at low velocities: Cohesive failure
Authors: Piau J.‐M. , Ravilly G. , Verdier C. 
Published: December 2004

AbstractThis work presents results obtained in 90‐degree peeling tests at low velocities in the case of Newtonian adhesives, when failure is cohesive. Peeling experiments are described and consider the influence of the thickness, viscosity, and surface tension of the adhesive, as well as the backing rigidity. A simple model, based on lubrication effects in thin films, is considered and compared with the measurements, when peeling is a two‐dimensional phenomenon. Furthermore, a criterion for predicting the transition between the two‐dimensional regime and the three‐dimensional regime at higher velocities is proposed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 145–157, 2005
The study of the phase diagram and internal energy of the mixed spin‐3/2 and spin‐5/2 ferrimagnetic Ising system with interlayer coupling by effective‐field theory; a simple approach of calculating internal energy
Authors: Zhang Qi , Wei Guozhu , Gu Yongwei 
Published: December 2004

AbstractPhase diagrams and internal energies of a layered Ising system were studied using the effective‐field theory (EFT) with correlations. The results show that the critical temperature becomes larger, while the compensation temperature and the internal energy become smaller with the increase in the interlayer coupling and the crystal‐field. The traditional method to calculate the internal energy of the Ising system by the EFT is based on a differential of its differential operator identity. So an additional differential procedure must be carried out when calculating the internal energy. In this paper, a new function on which the differential operator acts is introduced to solve this problem, without performing the additional differential procedure. The results obtained by the two methods are exactly the same. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dislocation mechanism of quantum dot formation in heteroepitaxial structures
Authors: Vengrenovich R. D. , Gudyma Yu. V. , Yarema S. V. 
Published: December 2004

AbstractQuantum dot formation during heteroepitaxial growth of 3D islands in Stranski–Krastanow mode is described. The island size distribution function is shown to become narrower, and the dispersion decreases markedly for dislocation growth mechanism with subsequent separation of dislocations from the island base. Probable reasons for slowing down of Ostwald ripening are also discussed. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Polaron effect on the binding energy of hydrogenic impurities in a cylindrical quantum dot
Authors: Wang Rui‐Qiang , Xie Hong‐Jing , Yu You‐Bin 
Published: December 2004

AbstractThe binding energy of a shallow hydrogenic impurity in a cylindrical quantum dot (QD) is investigated by using a variational method, where a two‐parameter trial wave function is introduced to consider the anisotropic nature of the QD system. We have taken into consideration the influence of the confined longitudinal optical (LO) phonons as well as the side‐surface (SSO) and top‐surface (TSO) optical phonons. Our calculations are performed within the effective‐mass approximation for an infinitely deep confinement potential system model. Numerical calculation shows that the binding energy of an impurity is greatly modified by the electron–phonon interactions and the phonon contribution to the impurity binding energy is dependent on the QD sizes (radius and height). It is noted that we obtain about a 4% higher impurity binding energy than that based on a one‐parameter trial wave function. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photon echo studies of biexcitons and coherences in colloidal CdSe quantum dots
Authors: Colonna Anne E. , Yang Xiujuan , Scholes Gregory D. 
Published: December 2004

AbstractNonlinear optical properties of colloidal quantum dots are studied to elucidate the significance and nature of many‐body effects. Two‐pulse photon echo studies of nanocrystalline CdSe quantum dots are reported for samples dispersed in a poly(butylmethacrylate) film (4.4 K). Oscillations are observed in the experimental data that are attributed to 1S3/21Se–2S3/21Se biexciton cohererences. Signals are simulated using a phenomenological model based on the many‐body description of the dynamics (the average polarization model). It is found that the electronic coherences and the nonlinear response originating from biexciton source terms are important, but their manifestation in the photon echo signals is strongly influenced by the interplay between homogeneous and inhomogeneous line broadening. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comment on “Orbital ordering and orbital fluctuations in transition metal oxides” [phys. stat. sol. (b) 236, No. 2, 281–288 (2003)]
Authors: Radwanski R. J. , Ropka Z. 
Published: December 2004

AbstractWe argue that the 3A2 state considered by Oleś in phys. stat. sol. (b) 236, 281 (2003) for the d2 system occurring in the V3+ ion in V2O3 and LaVO3 as well as in the Ti2+ ion in TiO and in many other oxides is wrong. The proper ground state is 3T1g – its 9‐fold degeneracy is further split in a crystal by intra‐atomic spin–orbit interactions and lattice distortions. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Scaling behavior of ground‐state energy cluster expansion for linear polyenes
Authors: Griffin L. L. , Wu Jian , Klein D. J. , Schmalz T. G. , Bytautas L. 
Published: December 2004

AbstractGround‐state energies for linear‐chain polyenes are additively expanded in a sequence of terms for chemically relevant conjugated substructures of increasing size. The asymptotic behavior of the large‐substructure limit (i.e., high‐polymer limit) is investigated as a means of characterizing the rapidity of convergence and consequent utility of this energy cluster expansion. Consideration is directed to computations via: simple Hückel theory, a refined Hückel scheme with geometry optimization, restricted Hartree–Fock self‐consistent field (RHF‐SCF) solutions of fixed bond‐length Parisier–Parr–Pople (PPP)/Hubbard models, and ab initio SCF approaches with and without geometry optimization. The cluster expansion in what might be described as the more “refined” approaches appears to lead to qualitatively more rapid convergence: exponentially fast as opposed to an inverse power at the simple Hückel or SCF–Hubbard levels. The substructural energy cluster expansion then seems to merit special attention. Its possible utility in making accurate extrapolations from finite systems to extended polymers is noted. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Effect of hindered piperidine light stabilizer molecular structure and UV absorber addition on the oxidation of HDPE. Part 2: Mechanistic aspects—molecular modeling and electron spin resonance spectroscopy study
Authors: Liauw Christopher M. , Quadir Angela , Allen Norman S. , Edge Michele , Wagner Alan 
Published: December 2004

AbstractThe first in this series of papers explored the effect of the structural characteristics of 2,2,6,6‐tetramethylpiperidine‐based hindered amine light stabilizers (HALS) on the thermal and photostabilization of high‐density polyethylene. In the second part, the energies (stabilities) of the nitroxyl radicals and various intermediate species have been predicted using AccuModel® and related to stabilization performance and electron spin resonance (ESR) spectral data. Nitroxyl radicals with low predicted stability generally afforded improved thermal and photostabilization. ESR spectra were used to obtain values of nitroxyl radical concentration ([>NO·]) and g‐factor as a function of pre‐aging time for combinations of pre‐aged HDPE and >NH HALS. Demethylation reactions of > N‐methyl HALS resulted in uselessly weak ESR spectra. The HALS that afforded poor thermal oxidative stabilization gave rise to pronounced minima in [>NO·] that coincided with a maximum in hydroperoxide concentration. The g‐factor values indicated that a predominant nitroxyl canonical form generally promoted superior thermal oxidative stabilization, whereas a predominance of the dipolar N·+O− form promoted superior photo‐oxidative stabilization. These trends may be related to greater radical‐scavenging and peroxide‐trapping effects, respectively. Molecular modeling and ESR spectra can therefore provide valuable insight into the effectiveness of HALS and stabilization mechanisms. J. Vinyl Addit. Technol. 10:159–167, 2004. © 2004 Society of Plastics Engineers.
Pathoarchitectonic pattern of iso‐ and allocortical lesions in juvenile and adult neuronal ceroid‐lipofuscinosis
Authors: Braak H. , Braak E. 
Published: December 2004

ConclusionJuvenile and adult forms of NCL reveal a pronounced and specific involvement of nerve cells generating isocortico‐isocortical projections and isocortico‐entorhinal connections. They also show a specific destruction of the nerve cells generating the perforant path. Additional changes are seen in a deep entorhinal layer receiving a feedback projection from the hippocampus. Within the hippocampal formation, the CA4/CA3 projection cells necessary for intrahippocampal processing of the data are markedly changed. This lesion pattern leads to a partial or complete interruption of the flow of information from the isocortex to the hippocampal formation. It is assumed that the pathoarchitectonic pattern contributes to the development of personality changes and cognitive impairment, both frequently seen even in early stages of NCL.
Linkage analysis of late‐infantile neuronal ceroid‐lipofuscinosis (CLN2) using markers on chromosome 16p
Authors: Williams R. , Mitchison H. , McKay T. , Järvelä I. , Gardiner R. M. 
Published: December 2004

ConclusionThese results provide further evidence of non‐allelic genetic heterogeneity within the disorders grouped together as the neuronal ceroid‐lipofuscinoses. There are at least three mutations at different loci involved in the pathogenesis of these disorders. The discrepancy in the extent of the regions excluded using data from the families with classical CLN2 and families with Finnish variant late‐infantile NCL is due to the smaller number of families segregating for Finnish variant late‐infantile NCL.
Novel glycine conjugates in medium‐chain acyl‐CoA dehydrogenase deficiency
Authors: Pitt J. J. 
Published: December 2004

SummaryThe glycine conjugates of isocaproic, 4‐methylhexanoic, 7‐hydroxyoctanoic and 8‐hydroxyoctanoic acids have been identified in the urine of children with medium‐chain acyl‐CoA dehydrogenase (MCAD) deficiency using gas chromatography‐mass spectrometry of the trimethylsilyl derivatives. A quantitative study showed that the glycine conjugates of isocaproic and 4‐methylhexanoic acids were excreted during acute episodes and in smaller amounts when subjects were asymptomatic. The glycine conjugates of 7‐hydroxyoctanoic and 8‐hydroxyoctanoic acids were detectable during acute episodes. None of the conjugates was detected in controls or controls receiving a diet containing medium‐chain triglycerides. It is suggested that the glycine conjugates of isocaproic acid and 4‐methylhexanoic acid are metabolites of branched‐chain fatty acids and that they are specific for MCAD deficiency.
Improved identification of heterozygotes for phenylketonuria using blood neopterin and biopterin
Authors: Alós T. , Bel Y. , Cabello M. L. , Catalá J. L. , Dalmau J. , Ferré J. , García A. M. , Ruiz‐Vázquez P. 
Published: December 2004

SummaryA novel approach that combines information provided by the metabolism of pteridines and that of phenylalanine has been applied to the detection of heterozygotes for phenylketonuria. Phenylalanine, tyrosine, biopterin and neopterin have been measured in serum from normal controls and heterozygotes for classical phenylketonuria, before and after a phenylalanine oral load. Significant differences in neopterin and biopterin mean values in fasting serum and in the mean increase of biopterin induced by the phenylalanine load were found between groups. Inclusion of pteridine data in the discriminant analysis significantly improved the resolution of the classical phenylalanine loading test for the detection of heterozygotes for phenylketonuria.
Juvenile metachromatic leukodystrophy: neurological outcome two years after bone marrow transplantation
Authors: Guffon N. , Souillet G. , Maire I. , Dorche C. , Mathieu M. , Guibaud P. 
Published: December 2004

ConclusionOur patient was not an ideal candidate since she was not clinically completely asymptomatic and presented with abnormal MRI and decreased nerve conduction when the metachromatic leukodystrophy was diagnosed in her older sibling. Nevertheless, 2 years after graft the deterioration did not progress and the MRI improved, while her brother became bed‐ridden within few months after the same initial symptoms.These favourable results need further confirmation after several years since significant differences in course have been observed in siblings (Clarke et al 1989).
Maple syrup urine disease (MSUD): Screening for known mutations in Italian patients
Authors: Parrella T. , Surrey S. , Iolascon A. , Sartore M. , Heidenreich R. , Diamond G. , Ponzone A. , Guardamagna O. , Burlina A. B. , Cerone R. , Parini R. , Dionisi‐Vici C. , Rappaport E. , Fortina P. 
Published: December 2004

SummaryMaple syrup urine disease (MSUD) is an autosomal recessive disease due to deficiency of the branched‐chain α‐ketoacid dehydrogenase (BCKDH) caused by a large number of mutations. In the present study, DNA from Italian patients and their relatives was examined for three point mutations (Y393N in the E1α gene, T841G and G1031A in the E2 gene) and two deletions (−G at the intron/exon border of exon 8 in the E2 gene and an 11 bp deletion in exon 1 of the E1β gene) using the polymerase chain reaction (PCR) followed by allele‐specific oligonucleotide (ASO) hybridization, gene‐scanning size analysis of fluorescent‐tagged PCR products and/or automated DNA sequence analysis. Our results show that two different mutations account for 7 of the 20 mutant MSUD alleles. Two unrelated affected children, two of their parents and one sibling were carriers for the 11 bp deletion in the E1β gene, one patient and her mother were heterozygous for Y393N in E1α, while T841G, G1031A and the −G deletion in E2 were not detected. This study is the first attempt to characterize at a nucleic acid level MSUD mutations in Italy. Our results indicate that additional defects are present in the Italian population and that, unlike the Mennonites, a number of different MSUD mutations exist in Italians.
Prenatal detection of Canavan disease (aspartoacylase deficiency) by DNA analysis
Authors: Elpeleg O. N. , Shaag A. , Anikster Y. , Jakobs C. 
Published: December 2004

SummaryAmniocentesis was performed in four pregnancies at risk for Canavan disease (CD). In all families both parents were of Ashkenazi‐Jewish origin and harboured the C854 mutation in the cDNA of the aspartoacylase gene. Using DNA analysis of the amniotic cells, three fetuses were predicted to be non‐affected and one fetus was predicted to be affected. The concentration ofN‐acetylaspartic acid (NAA) in the amniotic fluid was in agreement with these results. In urine samples of the three newborns predicted to be non‐affected, the concentration of NAA was normal. Tissues of the aborted fetus were not available. We conclude that DNA analysis is probably a reliable method for prenatal diagnosis of CD.