bluuebunny/crossref_metadata_2025_split huggingface dataset:
When tethered chains meet free ones; the stability of polymer wetting films on polymer brushes
Authors: Maas Joost H. , Leermakers Frans A.M. , Fleer Gerard J. , Stuart Martinus A. Cohen 
Published: April 2003

AbstractWe present a combined experimental and theoretical self‐consistent field (SCF) investigation of the wetting behavior of a polystyrene melt (composed of chains with degree of polymerization P) on top of a polystyrene brush (composed of chains with length N) grafted onto a silica surface. The control variables are the grafting density σ of the brush chains and the length of mobile chains P. Experiments show in agreement with the theory that there is a window of complete wetting. Both at very low and at high grafting densities the system remains partial wet. At large degree of polymerization P, there is a difference between the experimental and theoretical results. Theory predicts partial wetting only, whereas the window of complete wetting persists in the experiments even when P >> N. This difference is attributed to the double‐well structure of the disjoining pressure as revealed by the SCF theory. With this type of disjoining pressure it is conceivable that a metastable zero contact angle remains present for very long times.
Effects of temperature on neutron scattering from aqueous solutions of hydrophobically modified poly(ethylene oxide)
Authors: Beaudoin Emmanuel , Borisov Oleg , Lapp Alain , François Jeanne 
Published: April 2003

AbstractThe effect of temperature on the structure of aqueous dispersions of hydrophobically end‐capped poly(ethylene oxide) (PEOM) was investigated by small angle neutron scattering (SANS). Polymers with hydrogenated or deuterated n‐octadecyl end‐groups were studied in heavy water or in a mixture heavy water / water, respectively. In the latter case the PEO chains were selectively matched. In all the cases, the scattering curves were characterised by a main peak which revealed organisation of polymers into micelles consisting of hydrophobic cores surrounded by repulsive PEO coronae. Measurements were performed in the semi‐dilute regime where micelles coronae overlap. At constant polymer concentration, an increase in temperature leads to decreasing solvent strength of water for the PEO chains and decreasing repulsion between the PEO coronae. As a result, the intensity of the peak in a mixture of water /heavy water decreases with temperature On the contrary, in heavy water, the peak of the scattered intensity increases with increasing temperature. This scattering behaviour is interpreted on the basis of a scaling theory of the semi‐dilute solutions of star‐like polymer micelles.
New poly(silanes‐siloxanes) via hydrosilation in supercritical CO2 and subsequent crosslinking
Authors: Zhou Hui , Venumbaka Sreenu R. , Fitch III John W. , Cassidy Patrick E. 
Published: April 2003

AbstractIn order to obtain crosslinkable, low dielectric, low Tg materials, the hydrosilation polymerization was carried out in supercritical carbon dioxide (SC CO2) using Karstedt's catalyst, and a series of new fluorine‐containing poly(carbosilane/siloxane) were synthesized and characterized. The molecular weights of polymers obtained in SC CO2 were notably greater than those obtained in benzene. Hydrolysis and thermal curing of these polymers leads to materials considerably higher molecular weight which retain their low Tg values.
Novel silicon‐based alternating copolymers: synthesis, photophysical properties, and tunable EL colors
Authors: Kim Hwan Kyu , Paik Kyung Lim , Baek Nam Seob , Lee Youngil , Yoshino Katsumi 
Published: April 2003

AbstractWe synthesized novel silicon‐based alternating copolymers for tunable electroluminescent (EL) colors by Heck synthetic method. Their thermal, photophysical and electroluminescent properties were studied. Most of them exhibited a blue‐green EL color at the operating voltage of lower than 12 V. Unusually, we observed the white EL color from a EL device based on SiPhPVK. From photophysical studies and the time‐resolved PL spectroscopies, it might be attributed to the formation of stabilized excited state in SiPhPVK. Furthermore, in order to reduce the operating voltage of their LED with increasing the electron affinity of the main chain in silicon‐based alternating copolymers, we synthesized the silicon‐based copolymers containing electron transporting oxadiazole units in main chain. We also studied their photophysical and electroluminescent properties.
Formation of intragap states and achieving balance in carrier mobilities for a PPV derivative bearing the carbazole pendants
Authors: Kim Kyungkon , Park Yongsup , Lee Cheol Eui , Jang Jae Won , Jin Jung‐Il 
Published: April 2003

AbstractWe have found by NEXAFS spectroscopic studies that a PPV derivative (CzEh‐PPV) bearing the carbazole pendants form new intragap states when contacted with calcium metal. Moreover, the polymer exhibited much more balanced mobilities of holes and electrons than PPV and MEH‐PPV. Such characteristics are believed to bring about low turn‐on electric field and improved efficiency for the LED device fabricated with the polymer.
Topological polymer chemistry: classification and construction of nonlinear polymer architectures
Authors: Tezuka Yasuyuki 
Published: April 2003

AbstractA systematic classification of nonlinear polymer architectures is formulated by reference to constitutional isomerism in a series of alkanes (CnH2n+2), monocycloalkanes (CnH2n) and polycycloalkanes (CnH2n−2, CnH2n−4, etc). And a variety of topologically unique polymers, such as monocyclic and polycyclic polymers, cyclic telechelics (kyklo‐telechelics), cyclic macromonomers and polymeric topological isomers have been constructed by means of an “electrostatic self‐assembly and covalent fixation” strategy. In this process, new telechelic polymer precursors having moderately strained cyclic onium salt groups carrying multifunctional carboxylate counteranions have been prepared as key polymer precursors. The unique electrostatic self‐assembly, formed particularly in a dilute solution, was covalently fixed through the ring‐opening reaction by heating, to produce a variety of nonlinear polymer architectures in high efficiency.
Fluorescence study for the electrostatic interaction and aggregation in dilute polar solution of polyelectrolytes
Authors: Sun Qilong , Ren Biye , Liu Xinxing , Zeng Fang , Liu Ping , Tong Zhen 
Published: April 2003

AbstractFluorescence decay and quenching of pyrene labels on copolymers of 2‐acrylamido‐2‐methylpropanesulphonic acid (AMPS) and N,N‐dimethylacryl‐amide (DMAA) were observed in dilute salt‐free aqueous solutions as a function of the mole fraction FAMPS of AMPS from 0 to 0.896. Monoexponential and biexponential decays were found for the samples of FAMPS < 0.35 and samples of FAMPS > 0.35, respectively. The fast decay component is 80% and the averaged lifetime <τ> and lifetime τ1 of the fast decay decreased with increasing FAMPS. Quenching efficiency of Cu2+, CH3NO2, and dinitrobenzene to the pyrene label was investigated in the framework of Stern‐Volmer plot. The quenching effects of Cu2+ included both of dynamic and static ones, the latter was due to the condensed Cu2+. For the neutral quenchers, the quenching rate constant kq increased when FAMPS < 0.449 then decreased, showing a decline of accessibility to the pyrene label. I1/I3 value in salt‐free dilute aqueous solution and in DMSO solution decreased obviously with an increase in FAMPS, indicating that the labeled fluorophore experienced a decrease in polarity of its microenvironment with increasing charge density of the polymer. This I1/I3 decrease was enhanced with increasing the polymer concentration and adding salt NaCl up to 0.75 mol/L showed no effect on the appearance of this decrease. These results were interpreted consistently with the counterion condensation concept, where condensed counterions induced the “temporal” aggregation of less‐polar in the polyelectrolyte solutions surrounding the pyrene labels.
Living ring‐opening polymerization of cyclic thiocarbonate
Authors: Endo Takeshi , Nemoto Nobukatsu , Sanda Fumio 
Published: April 2003

AbstractThis work deals with the cationic ring‐opening polymerization of a cyclic thiocarbonate, 5,5‐dimethyl‐1,3‐dioxane‐2‐thione (1). The polymerization was carried out with 2 mol% of trifluoromethanesulfonic acid, methyl trifluoromethanesulfonate, boron trifluoride etherate, or triethyloxonium tetrafluoroborate as an initiator to afford the polythiocarbonate with the narrow molecular weight distribution (Mn = 11200‐31000, Mw/Mn = 1.04‐1.15). The molecular weight of the obtained polymer could be controlled by the feed ratio of the monomer to the initiator and increased when the second monomer was added to the polymerization mixture after quantitative consumption of 1 in the first stage, supporting that the cationic ring‐opening polymerization of 1 proceeded via a living process.
Synthesis of branched polymers by means of anionic polymerization. 11. anionic synthesis of densely branched polystyrenes carrying double branches in each repeating unit
Authors: Hirao Akira , Ryu Sang Wong 
Published: April 2003

AbstractWe have demonstrated the first successful synthesis of well‐defined densely branched polystyrenes carrying double branches in each of all repeating unit of backbone polymer by the coupling reaction of 1,1‐diphenylethylene‐end‐capped polystyryllithiums with novel polystyrene derivatives having two benzyl bromide moieties in each monomer unit. The coupling reaction efficiently and quantitatively proceeded without any steric limitations to introduce two polystyrene branches in each repeating unit under certain conditions in THF at −40°C. Thus, a series of 36.4‐ and 181‐arm densely branched polystyrenes were synthesized (Mw = 365 ∼ 2 000 kg/mol, Mw/Mn = 1.01 ∼ 1.03). In the 36.4‐arm branched polystyrenes thus synthesized, the maximum Mw value of the introduced polystyrene as a branch segment was 55.1 kg/mol. The experimental g‘ values of the 36.4‐arm branched polystyrenes deterimined in the range of 0.14 ∼ 0.15 were very close to the value of 0.13 calculated from the empirical equation previously reported by Roovers.
Approaches to conjugated polymers via solid state polymerization
Authors: Sandman Daniel J. , Kim Ik‐Bum , Njus Jeffrey M. , Lee Dong‐Chan , Cholli Ashok L. , Sahoo Sangrama 
Published: April 2003

AbstractTopochemical solid state polymerization is a method of obtaining fully crystalline macromolecules. Herein, approaches to conjugated polymers via new solid state polymerizations and the properties of materials, especially polydiacetylenes(PDA), obtained via solid state polymerization are discussed. Our attempts to polymerize cyanoalkynes and to define the thermal reaction product of a dicyanodiazepine are presented. Certain PDA exhibit absorption, likely charge‐transfer, at energies below the exciton. Nanocrystals of PDA‐DCH react with liquid bromine to give the mixed polyacetylene PDA‐DCHBr6 whose visible spectrum exhibits structure not observed in spectra of bulk crystals of PDA‐DCHBr6. The thermochromic PDA of the dialkylurethanes of 5,7‐dodecadiyn‐1,12‐diol were studied by variable temperature solid state 13C nmr. The upfield shift of the acetylene carbons as the temperature is raised above that of the thermochromic phase transition indicates the role of mechanical strains in achieving thermochromism.
Fluorescence and biochemical characterization of glycated hemoglobin
Authors: Vigneshwaran Nadanathangam , Bijukumar Gopalakrishnapillai , Karmakar Nivedita , Anand Sneh , Misra Anoop 
Published: April 2003

AbstractIsoelectric focusing (IEF) of glycated hemoglobin (GHb) was carried out in ultra‐thin polyacrylamide gels to separate the hemoglobin‐advanced glycation endproducts (Hb‐AGEs) from the hemoglobin‐A1C (HbA1C) fraction. Precast polyacrylamide gels (Ampholine® PAGplate) were used in Pharmacia LKB Multiphor II for this purpose. The separated bands for Hb‐AGE and HbA1C based on their isoelectric point (pI), were confirmed with the purifed fractions obtained from the cation exchange chromatographic technique. From the calibration curve, the pI values were found to be 6.748 and 6.495 for HbA1C and Hb‐AGE, respectively. The lowering of pI values for glycated hemoglobin, when compared to unglycated hemoglobin (pI = 6.852), can be attributed to the glycation at the amino terminals of the peptide chains. Increased reduction in pI value for Hb‐AGE can be attributed to the effect of glycation of amino groups at various sites on the peptide chains, apart from the terminal amino groups. Fluorescence analysis was carried out for the purified fraction of Hb‐AGE which showed the formation of a new fluorophor adduct having the excitation and emission maxima at 308 nm and 345 nm, respectively. Time‐dependent formation of Hb‐AGE under in vitro conditions was monitored by fluorescence (308/345 nm) over a period of 120 days, which showed its formation only after 3 weeks of incubation.
Multipolymers with Fischer‐Tropsch olefins
Authors: Tincul Ioan , Smith Jaco , van Zyl Pieter 
Published: April 2003

AbstractMultipolymers consisting of ethylene, 1‐heptene, 3‐methylpentene and 4‐methylpentene were prepared with a heterogeneous Ziegler‐Natta catalyst. The polymers were prepared in such a way that the molar fraction of the comonomers remained the same. Copolymers of ethylene/1‐heptene and ethylene/4‐methylpentene were prepared in order to study the changes in polymer characteristics as one moves from an ethylene/linear alpha olefin copolymer through ethylene multipolymers to an ethylene/4‐methylpentene copolymer. The mechanical, rheological and application properties showed expected trends.
Synthesis and characterization of novel soluble and thermally stable polyamides based on pyridine monomer
Authors: Mehdipour‐Ataei Shahram , Heidari Hani 
Published: April 2003

AbstractNucleophilic aromatic substitution reaction of 4‐aminophenol and also 5‐amino‐1‐naphthol with 2,6‐dichloropyridine in N‐methyl‐2‐pyrrolidone (NMP) as solvent, in the presence of potassium carbonate, afforded two aromatic ether diamines. Eight soluble, thermally stable polyamides were prepared by polycondensation reaction of the obtained diamines with aromatic and aliphatic diacid chlorides including terephthaloyl chloride (TPC), isophthaloyl chloride (IPC), adipoyl chloride (AC), and sebacoyl chloride (SC). The prepared monomers and polymers were characterized by conventional spectroscopic methods. Physical and thermal properties of the polymers, such as thermal behavior, thermal stability, solution viscosity, and solubility behavior were also studied.
New materials by polymerisation of olefins and styrene with metallocene catalysts
Authors: Kaminsky Walter , Tran Phu‐Dennis , Weingarten Ulrich 
Published: April 2003

AbstractMetallocenes are highly active catalysts for the production of precisely designed polyolefins and engineering plastics. Especially zirconocene/methylalumoxane (MAO) catalysts and half‐sandwich titanium complexes have opened a frontier in the area of new polymer synthesis and processing. The materials obtained show different microstructures, tacticities and properties compared with conventional polymers. Alternating ethene/propene polymers show lower glass transition temperatures than random copolymers. Constrained geometry catalysts are useful for the synthesis of norbornene/ethene copolymers.
Copper‐mediated ATRP of methyl methacrylate in polar solvents using a bifunctional pyridinal diimine ligand
Authors: Iovu Mihaela , Maithufi Norah , Mapolie Selwyn 
Published: April 2003

AbstractThe bifunctional pyridinal diimine ligand, bis(2‐pyridinal)ethylenediimine, was employed in copper‐mediated ATRP of methylmethacrylate using solvents such as acetonitrile, N,N‐dimethyl formamide and dimethylsulfoxide. Solvent polarity was found to play a crucial role in determining the extent of control in the ATRP process. Acetonitrile showed the best control when used at a level of 33 vol.‐%.
The synthesis of HgS and CdS nanoparticles in polymer matrices
Authors: Sreekumari Nair P. , Radhakrishnan T. , Revaprasadu N. 
Published: April 2003

AbstractThe synthesis of CdS nanoparticles in two different polymer matrices ie. polyacrylamide and polystyrene, is described. In addition, we describe the synthesis of HgS nanoparticles in polyacrylamide. Both the CdS and HgS nanocomposites show blue shifts in the optical spectra in relation to the bulk material. The photoluminescence spectra of both materials show broad emission. The transmission electron microscopy (TEM) images confirm the nanocrystalline nature of the CdS and HgS nanocomposites.
The use of selected acrylate and acrylamide‐based surfmers and polysoaps in the emulsion polymerization of styrene
Authors: Tichagwa Lilian , Götz Christian , Tonge Matthew , Sanderson Ron , Pasch Harald 
Published: April 2003

AbstractPolymerizable surfactants (surfmers) 12‐acryloyloxy‐dodecanoic acid and 11‐acrylamidoundecanoic acid and their respective sodium salts were prepared and then polymerized to form their corresponding oligomers using reversible addition‐fragmentation chain transfer (RAFT). Different concentrations of both the surfmers, their sodium salts, and their RAFT oligomers were used as polysoaps in the emulsion polymerization of styrene. Stabilities of the pre‐emulsions before polymerization were determined and compared. After polymerization, particle sizes and polydispersities of the resulting polystyrene latices were determined. Sodium dodecyl sulfate (SDS) was used as a reference surfactant to compare the particle sizes and stabilities of the pre‐emulsions prepared using surfmers and polymeric surfactants (polysoaps) as particle stabilizers.Emulsion polymerization of styrene using these surfmers and polysoaps all led to latices which were stable for a period of more than six months, as indicated by constant particle sizes, whereas latices prepared using the conventional surfactant, SDS, were not as stable.
Study of a new route by which to make fully cured thermoplastic elastomers with plastics and ultrafine powdered rubber
Authors: Zhang Xiaohong , Wei Genshuan , Liu Yiqun , Gao Jianming , Zhu Yicai , Song Zhihai , Huang Fan , Zhang Manli , Qiao Jinliang 
Published: April 2003

AbstractA series of fully cured thermoplastic elastomers (TPEs) have been developed by mixing plastics and fully cured, ultra‐fine powdered rubbers (UFPRs). The fully cured UFPRs were prepared by the irradiation of rubber latexes and drying of the irradiated rubber latexes. The average particle size of the UFPRs ranged from 50 to 500nm. The influences of the dose rate, absorbed dose and content of cross‐linking agent on the cross‐linking of rubber latexes were studied. It was found that a new type of TPEs with excellent properties can be easily made by blending UFPRs with plastics.
Recent advances in the development of Fischer‐Tropsch catalysts at sasol
Authors: Bromfield Tracy C. , Vosloo Anton C. 
Published: April 2003

AbstractSasol's experience of more than 50 years in the field of Fischer‐Tropsch puts it in a unique position to exploit the renewed interest in the utilization of the Fischer‐Tropsch process to convert natural gas to liquids. In order to capitalize on this position, Sasol has made significant improvements to its low temperature and high temperature Fischer‐Tropsch catalysts. A review is given of the development of Sasol's Co‐based catalyst for low temperature Fischer‐Tropsch applications. Sasol has also developed a new Fe‐based catalyst for the high temperature Fischer‐Tropsch process. The advantages of this catalyst compared to the existing catalyst are discussed.
Monitoring thermo‐oxidative degradation of polypropylene by CRYSTAF and SEC‐FTIR
Authors: de Goede Stefan , Brüll Robert , Pasch Harald , Marshall Niall 
Published: April 2003

AbstractSamples of a polypropylene homopolymer have been degraded and analysed with regard to chemical composition, molecular weight distribution and chemical composition distribution. FTIR shows the progress of degradation and a decrease in molecular weight can be observed from SEC. CRYSTAF shows that the chemical heterogeneity of the samples broadens with continuing degradation. SEC‐FTIR reveals that the degraded species are mainly found in the low molecular end of the molecular weight distribution. The spatial heterogeneity of the degradation process has been proven by the analysis of abrased layers.
Kinetic evaluation of various isospecific active sites on MgCl2‐supported Ziegler catalysts
Authors: Nishiyama Isa , Liu Boping , Matsuoka Hitoshi , Nakatani Hisayuki , Terano Minoru 
Published: April 2003

AbstractThe formation, variation and conversion of isospecific active sites were investigated, based on the isotacticity distribution of the polypropenes analyzed by the temperature rising elution fractionation (TREF) method. Stopped‐flow polymerization of propene was carried out with a MgCl2‐supported Ziegler catalyst in the absence or presence of an internal or external electron donor so that the effects and roles of the electron donors could be clarified. The results showed that various kinds of active sites with different isospecificities, including the highest isospecific active sites responsible for producing the highest isotactic fraction (elution temperature: > 112°C) existed, even in the electron donor‐free catalyst system. The isospecificity of the active sites in the donor‐free catalyst might have originated from a surface monolayer multinuclear titanium species, namely an “island” of titanium species. The addition of the external electron donor converted a part of the aspecific and/or low isospecific active sites into the second highest isospecific active sites, but showed no effect on the formation of the highest isospecific active sites, whereas the addition of an internal donor played an important role in creating the highest isospecific active sites as well as suppressing the formation of the aspecific active sites.
Toughening polypropylene with nanoscale rubber particles
Authors: Liu Yiqun , Zhang Manli , Zhang Xiaohong , Gao Jianming , Wei Genshuan , Huang Fan , Song Zhihai , Qiao Jinliang 
Published: April 2003

AbstractA new kind of powdered rubber, ultra‐fine full‐vulcanized powdered rubber (UFPR), was invented and used for toughening polypropylene. The UFPR dispersed well in the PP matrix on a nanoscale. Both toughness and stiffness of PP can be improved by toughening with UFPR. DSC data showed that UFPR has some nucleation effect on PP. When PP was toughened with UFPR and EPDM together, the impact strength showed a synergistic toughening effect.
Characterization of epoxy prepreg SPX 8800 system by isothermal differential scanning calorimetry
Authors: Wang Qian , Storm Birgit K. 
Published: April 2003

AbstractIsothermal Differential Scanning Calorimetry (DSC) was used to study the curing behavior of epoxy prepreg SPX 8800 system, which contains DGEBA/DICY/Diuron (Diglycidyl ether of bisphenol A/Dicyandiamide/Diuron) reinforced by three layers of glass fibre. The rate curves from the DSC study agreed well with those obtained from the isothermal FT Near Infrared (FTNIR) study and similar activation energy was obtained in the range of 92.6 to 87.7 kJ/mol up to 50% total conversion. Modelling of the whole DSC trace with empirical equation dx/dt=kxm(A‐x)n gave relatively good fitting of the experimental curves (the error is lower than 15%.) in the whole studied cure temperature range (75‐110°C) and no significant difference in cure kinetics was observed for both epoxy prepreg and neat resin.