bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular weight distribution of metallocene polymerization with long chain branching using a binary catalyst system
Authors: Zhu Shiping , Li Dean 
Published: April 2003

AbstractIn metallocene polymerization, termination by β‐hydride elimination generates polymer chains containing unsaturated vinyl groups at their chain ends. Further polymerization of these macromonomers produces branched polymers. Material properties of the branched polymers not only depend on molecular weight and branching density, but also on chain structure. This work presents analytical expressions to predict the bivariate distribution of molecular weight and branching density for polymer chains having dendritic and comb structures. It is shown that when a single metallocene catalyst is used the formation of dendritic polymers is favored with only a very small fraction of highly branched chains assuming comb structure. The use of a binary catalyst system is therefore proposed to obtain high content of comb polymers. One catalyst generates macromonomers and the other yields in‐situ branching. It is found that the comb polymers give much narrower molecular weight distributions than dendritic polymers with same branching densities.
Protruding chain at a sharp penetrable interface
Authors: Cifra Peter 
Published: April 2003

AbstractA single protruding chain at a sharp discontinuity of the quality of the surrounding medium was shown by Monte Carlo (MC) simulations to be a good model representing semiquantitatively the major macroscopic features of polymer interfaces such as the interface thickness. This is in accord with early original theoretical suggestions. Compared to multichain simulations of a polymer/polymer interface it is clear that the protruding chain is not completely adequate to represent a diffuse multichain interface. The results on a protruding chain, however, indicate the proper interfacial thickness as obtained by MC simulations in multichain systems. The microscopic results (such as deformation, orientation of coils at the interface and chain end segregation into the interface) are similar to those obtained in multichain polymer interfaces. None of the investigated interface properties exhibits a dependence on the total chain length of the protruding chain.
The effect of tethered polymers on the conformation of a lipid membrane
Authors: Birshtein Tatiana M. , Zhulina Ekaterina B. 
Published: April 2003

AbstractWe consider the effect of tethered macromolecules on the stability of the flat conformation of a lipid bilayer in a dense brush regime when anchored chains are significantly overlapped. On the basis of a scaling approach we have shown that redistribution of polymer chains from inner to outer layers reduces the free energy of the system and stabilizes spherically bent configurations of the membrane.
Flavonoids: Promising anticancer agents
Authors: Ren Wenying , Qiao Zhenhua , Wang Hongwei , Zhu Lei , Zhang Li 
Published: April 2003

AbstractFlavonoids are polyphenolic compounds that are ubiquitously in plants. They have been shown to possess a variety of biological activities at nontoxic concentrations in organisms. The role of dietary flavonoids in cancer prevention is widely discussed. Compelling data from laboratory studies, epidemiological investigations, and human clinical trials indicate that flavonoids have important effects on cancer chemoprevention and chemotherapy. Many mechanisms of action have been identified, including carcinogen inactivation, antiproliferation, cell cycle arrest, induction of apoptosis and differentiation, inhibition of angiogenesis, antioxidation and reversal of multidrug resistance or a combination of these mechanisms. Based on these results, flavonoids may be promising anticancer agents. © 2003 Wiley Periodicals, Inc. Med Res Rev, 23, No. 4, 519–534, 2003
Genetic variability: The key problem in the prevention and therapy of RNA‐based virus infections
Authors: Figlerowicz Magdalena , Alejska Magdalena , Kurzyńska‐Kokorniak Anna , Figlerowicz Marek 
Published: April 2003

AbstractDespite extraordinary progress that has recently been made in biomedical sciences, viral infectious diseases still remain one of the most serious world health problems. Among the different types of viruses, those using RNA as their genetic material (RNA viruses and retroviruses) are especially dangerous. At present there is no medicine allowing an effective treatment of RNA‐based virus infections. Many RNA viruses and retroviruses need only a few weeks to escape immune response or to produce drug‐resistant mutants. This seems to be the obvious consequence of the unusual genetic variability of RNA‐based viruses. An individual virus does not form a homogenous population but rather a set of similar but not identical variants. In consequence, RNA‐based viruses can easily adapt to environmental changes, also those resulting from immune system response or therapy. The modifications identified within viral genes can be divided into two groups: point mutations and complex genome rearrangements. The former arises mainly during error‐prone replication, whereas RNA recombination and generic reassortment are responsible for the latter. This article shortly describes major strategies used to control virus infections. Then, it presents the various mechanisms generating the genetic diversity of RNA‐based viruses, which are most probably the main cause of clinical problems. © 2003 Wiley Periodicals, Inc. Med Res Rev, 23, No. 4, 488–518, 2003
Beneficial effects of creatine supplementation in dystrophic patients
Authors: Louis Magali , Lebacq Jean , Poortmans Jacques R. , Belpaire‐Dethiou Marie‐Claude , Devogelaer Jean‐Pierre , Van Hecke Paul , Goubel Francis , Francaux Marc 
Published: April 2003

AbstractThe effect of creatine (Cr) supplementation on muscle function and body composition of 12 boys with Duchenne muscular dystrophy and three with Becker dystrophy was evaluated by a randomized double‐blind cross‐over study (3 g Cr or maltodextrin daily for 3 months, with wash‐out period of 2 months). After placebo, no change was observed in maximal voluntary contraction (MVC) and resistance to fatigue, whereas total joint stiffness (TJS) was increased by ∼25% (P < 0.05). The patients receiving Cr did not show any change in TJS, improved MVC by 15% (P = 0.02), and almost doubled their resistance to fatigue (P < 0.001). In patients still independent of a wheelchair (n = 5), bone mineral density increased by 3% (P < 0.05), and urinary excretion of collagen type I cross‐linking N‐telopeptide declined to about one third (P < 0.001) after Cr. No adverse effect was observed. Thus, Cr may provide some symptomatic benefit in these patients. Muscle Nerve 27: 604–610, 2003
Polymer blends containing liquid crystal polymers
Authors: Ballauff Matthias 
Published: April 2003

AbstractPolymer blends can be either composed of mixtures of flexible components, of a stiff chain and a flexible macromolecule, or of two stiff‐chain polymers. All three cases may be dealt with in terms of the Flory lattice model. Special attention is paid to the influence of liquid crystalline order on the miscibility of the two polymers. For isotropic mixtures all three cases may be described in terms of the usual Flory–Huggins approximation. If a nematic phase is formed the miscibility of blends of rigid rods with flexible macromolecules (molecular composites) is strongly reduced because of entropic reasons. Highly ordered mixture of two stiff‐chain polymers in melt can be described in terms of the regular solution theory leading to the same miscibility criterion as is valid for two flexible polymers. All deductions are compared to recent experimental work.
Preparation of polyimides utilizing the diels–alder reaction. I. Bis(3,4‐dimethylenepyrrolidyl) arylenes with bismaleimides
Authors: Ottenbrite Raphael M. , Yoshimatsu Akira , Smith Joseph G. 
Published: April 2003

AbstractBis(exocyclic)dienes were prepared by the reaction of 2,3‐dibromomethyl‐1,3‐butadiene with aromatic diamines. The diamines were 4,4′‐methylene dianiline, 4,4′‐oxy dianiline, benzidine, and α, α′‐bis(4‐aminophenyl)‐p‐isopropyl benzene (EPON HPT 1061). Polymers were synthesized by the Diels–Alder reaction of these bisdienes with bis(4‐maleimidylphenyl) methane. Flexible films were obtained for diene: dienophile ratios ranging from 0.7 : 1 to 0.8 : 1. Films were found to be insoluble in organic solvents and those cured above 120°C were insoluble in concentrated sulfuric acid. The polymers were characterized by IR, TGA, and elemental analysis.
Thermal and nuclear magnetic relaxation studies of water–sodium polystyrene sulfonate systems
Authors: Hatakeyama T. , Hatakeyama H. 
Published: April 2003

AbstractThe phase transition behavior of water–sodium polystyrene sulfonate (NaPSS) systems was investigated by differential scanning calorimetry (DSC), 1H and 23Na nuclear magnetic resonance spectroscopy (NMR) in a temperature range from 150 to 330 K, and in a water content (Wc = grams of water/gram of dry sample) range from 0 to 2.5. With slow cooling from the isotropic liquid state, the system formed the liquid crystalline state and the crystalline state. The temperature range of the liquid crystalline state became broader with deceasing Wc. When the system contained an excess amount of free water, the liquid crystalline state was not observed. The 1H longitudinal relaxation time (T1) of the system showed a minimum value in the temperature range where the liquid crystalline state was observed. At the same time, the 1H transverse relaxation time (T2) dropped at the transition temperature from the isotropic liquid to the liquid crystalline state (T*). The correlation time (τc) was calculated using modified Woessner's equations. The variation of τc as a function of temperature agreed well with the phase diagram obtained from DSC. The 23Na T1 and T2 values were correlated with Wc and temperature. The activation energy was calculated to be from 20 to 25 KJ/mol depending on Wc. The formation of the liquid crystalline phase of NaPSS is affected by 10–20 water molecules, which can be categorized as freezing bound water.
Thermolysis of reactive oligo(p‐phenylene sulfide) containing disulfide bond
Authors: Oyaizu Kenichi , Katoh Junya , Suzuki Fumiaki , Jikei Mitsutoshi , Yamamoto Kimihisa , Nishide Hiroyuki , Tsuchida Eishun 
Published: April 2003

AbstractOligo(phenylene sulfide) (OPS) containing one disulfide bond at the end of the chain, which was obtained by the oxidative polymerization of diphenyl disulfide, had a relatively low Td10%(temperature for 10% weight loss) of 412 °C because of degradation of the disulfide bond. But this thermal cleavage of the disulfide bond promoted the curing reaction through thiophenoxy radical formation. OPS was allowed to react with diiodobenzene at 220 °C. The thermal stability of OPS was improved through the consumption of the disulfide bond and the coupling of the chain.
Role of solvent in the compatibility of a vinylchloride–vinylacetate–maleic acid terpolymer and nitrocellulose blends
Authors: Banerjee Amar Nath , Chattopadhyay Saumya 
Published: April 2003

AbstractThe compatibility of cast films of a vinylchloride–vinylacetate–maleic acid terpolymer (VMCH) and nitrocellulose (NC) blends is influenced by solvents. Transparent films of VMCH/NC blends are obtained when cast from solvents such as tetrahydrofuran or cyclohexanone, whereas hazy films are obtained when cast from solvents such as acetone or ethylacetate. Visible spectroscopy and phase morphology were used to analyse the compatibility–incompatibility of the blend. Differential scanning calorimetry (DSC) studies demonstrate that the transparent film is compatible, but the hazy film is incompatible. Fourier transform infra‐red (FTIR) studies establish that a greater interaction is observed between the polymer pair in case of the compatible blend than in the case of the incompatible blend.A solvent dependency of blend compatibility is reflected in this study. The conformational state of the polymers in solution, which is responsible for the compatibility phenomena, may depend on the donor number and/or Taft‐β value of the solvent. The greater the donor number and/or the Taft‐β value, the higher may be the level of interaction between the solvent and the polymer molecules, which in turn may give a compatible blend after removal of the solvent.
Phase transition of layer structure of poly(1,4‐benzenedithiol‐co‐1,4‐diethynylbenzene) by photon mode
Authors: Kobayashi Eiichi , Ohashi Toyoshi , Furukawa Junji 
Published: April 2003

AbstractThe effect of light wavelength on the phase transition of the layer structure of poly(1,4‐benzenedithiol‐co‐1,4‐diethynylbenzene) was studied under an air atmosphere at 18–22°C. The thin layer polymer crystals were prepared by solid state polymerization, and the amount of the layer structure was evaluated by an X‐ray diagram. A monochromatic light with a wavelength in the region of ca. 500–600 nm was used as a light source. The amount of the layer structure was found to be altered by light. There were three characteristic wavelengths at 545.6, 567.8 and 590.1 nm, inducing pronounced peak intensities in the X‐ray diagram. On the other hand, at 501.1, 539.6, 571.8 and 588.1 nm the light made the peak intensity decrease steeply. The phase transition was induced by a photon mode, but not by a heat mode. The amount of the layer structure was altered linearly with increasing irradiation time up to 60 min. However, over 60 min the change became dull. The total energy given to the polymers during the irradiation was about 24 X 10−3 J/cm2. Accordingly, the phase transition occurs with a high sensitivity to the light. The polymers were irradiated alternately by the light of 545.6 nm and 571.8 nm at intervals of 60 min, respectively. The amount of the layer structure was controlled reversibly by the light.
Polarization and viscosity measurements of ferroelectric liquid crystalline monomer polymer mixtures
Authors: Bömelburg Jan , Heppke Gerd , M.‐Hollidt Jörg 
Published: April 2003

AbstractMeasurements of spontaneous polarization, tilt angle and response time on mixtures of a ferroelectric side chain polyacrylate with a low molecular mass liquid crystal of a very similar structure are reported. From the obtained values the rotational viscosity for the ferroelectric switching process is calculated. All mixtures exhibit an Arrhenius‐like temperature dependence of the rotational viscosity, the values for the polymer being three orders of magnitude higher than for the low molecular mass compound.
Controlled release of 4‐hydroperoxycyclophosphamide from the fatty acid dimer‐sebacic acid copolymer
Authors: Buahin Kwame G. , Judy Kevin D. , Hartke Carol , Domb Abraham J. , Maniar Manoj , Colvin O. Michael , Brem Henry 
Published: April 2003

AbstractControlled polymeric release of chemotherapeutic agents has shown promise in the management of malignant gliomas. 4‐Hydroperoxycyclophosphamide (4HC), loaded on the fatty acid dimer–sebacic acid copolymer (FAD:SA, 1:1), significantly prolonged survival in rats implanted with F98 and 9L gliomas. Here, we studied the in vitro and in vivo release kinetics in phosphate‐buffered saline and rat brain of 20% 4HC/FAD:SA (wt:wt), the optimal dose for treatment of rat gliomas. In vitro release under infinite sink conditions was steady over the initial 12 hr to a peak of 20–35% of impregnated drug, consistent with early phase control via surface erosion. Release over the next 3 weeks was minimal, consistent with barrier formation around the polymer by an oily fatty acid dimer degradation product and consequent slowing of release. However, the polymer started to disintegrate by day 4, and there were minimal visible remnants by 3 weeks. Thus, a considerable amount of polymer‐carried drug was probably lost in the disintegrating fragments. Also, drug loss is expected from its inherent hydrolytic instability. In vivo release into brain revealed two peak levels of drug at 0–1 hr and 5–20 days. With loaded polymer implanted intraperitoneally or cyclophosphamide injected systemically, peak brain drug levels were measured in 2–8 hr, with substantial decrease by 48 hr without a second peak. Brain levels were substantially higher than blood levels at all time periods. We conclude that FAD:SA (1:1) adequately protects the otherwise labile 4HC, allowing effective and substained drug release in vivo. Furthermore, it should be possible to modify the polymer to adjust the time of peak release for more beneficial therapeutic effects.
Poly(benzylsulfonic acid) siloxane as proton‐conducting electrolyte
Authors: Sanchez J.‐Y. , Denoyelle A. , Poinsignon C. 
Published: April 2003

AbstractA new proton‐conducting polymer electrolyte—poly‐(benzylsulfonic acid)siloxane (PBSS)—has been prepared by sol–gel process. Both the hydrolysis and the condensation reactions of triethoxybenzylsilane have been studied under different catalysis conditions. The basic material—polybenzylsiloxane (PBS)—is always soluble, no matter what the experimental conditions, reaching an average molecular weight—Mw—of 20,000 and a polydispersity index close to 5. Good yields of a water‐soluble polyelectrolyte—PBSS–thermally stable up to 300°C in air according to thermogravimetric analysis (TGA), and for which the exchange capacity is close to 4.4, can be obtained by sulfonation of PBS. Conductivities ranging from 2 × 10−3 to 10−2 S/cm at room temperature have been determined by a.c. impedance spectroscopy. These high conductivities, as well as the tensile strength of the PBSS, allow its use in several electrochemical devices.
Sorption and addition of bromine from aqueous solutions on cis‐1,4‐polyisoprene
Authors: Lewin Menachem , Penhasi Adel 
Published: April 2003

AbstractThe sorption of bromine from bromine water on cis‐1,4‐polyisoprene film and the initial stages of bromination are studied at concentrations of 0.002–0.1 mol/l and temperatures of 15–35°C. The diffusion coefficient of bromine into natural rubber (NR) is 1.3–2.0 × 10−6 cm2/sec for the total sorption and 5–13 × 10−7 cm2/sec for the irreversible sorption. The partition coefficient of bromine between water and rubber increased from 17.3 at 15°C to 37.1 l/kg at 35°C. The chemical potential, enthalpy and change in entropy of partition are, at 25°C, respectively: −1.9 kcal/mol, 6.6 kcal/mol and 28.4 cal/mol. K. The irreversible sorption is due to a charge‐transfer complex between bromine molecules and double bonds of the rubber. The complex is the first stage of the addition reaction, which becomes noticeable at concentrations above 0.012 mol/l. With increasing bromine concentration the concentration of the complex decreases and the added bromine increases. The charge transfer complex appears to change the conformation of the cis‐NR chains so that the bromine addition occurs in the trans‐conformation, as shown by FT–IR spectra. The bromination is accompanied by a marked crystallization effect as illustrated by thermal analysis and WAXS measurements.
Kinetic behavior of UV‐sensitive polymers from modified natural rubber
Authors: Visconte Leila L. Y. , Andrade Cristina T. , Azuma Chiaki 
Published: April 2003

AbstractPhotosensitive copolymers have been obtained by chemical modification of natural rubber. The introduction of the photoreactive cinnamoyl group in different conversions has been carried out by the reaction of natural polyisoprene with maleic anhydride, followed by ring opening and condensation with some oxyalkylcinnamate esters. These reactions gave rise to five polymer series. Each series, for which the anhydride content was kept constant, is constituted of five copolymeric products, differing from each other in the size of the aliphatic chain between the chromophore and the main chain. The photosensitive products were submitted to UV irradiation, and their kinetic behavior has been investigated in order to correlate structural dissimilarities with the dimerization rate constants.
Photosensitive poly(vinyl alcohol) bearing N‐(1‐pyridinio)benzamidate groups
Authors: Nagasawa Jun'ichi , Tamaki Takashi , Ichimura Kunihiro 
Published: April 2003

AbstractPoly(vinyl alcohol) (PVA) bearing N‐(1‐pyridinio)benzamidate (PB) was synthesized through acetalization of PVA and 4‐dimethoxymethyl‐N‐(1‐pyridinio)benzamidate (DMPB) in water. The PB groups in PVA–PB had almost the same proportion of DMPB to the starting PVA. The UV spectrum of PVA–PB shows an absorption band of pyridinium ylide as a shoulder around 300 nm in water, and as a maximum at 315 nm in a film on a quartz plate. These absorption bands decreased on irradiation at 313 nm. The photoreaction of the PVA–PB film proceeds much faster than that of PVA–PB in water. The solution, of PVA‐bearing high‐PB content, became slightly turbid during irradiation. After irradiation the film became insoluble in water, and the soluble fraction of polymer (P̄ = 1700) was 3% at a PB content of 1 mol% and less than 1% at that of more than 2 mol%. This polymer can be applied as a water‐soluble negative photoresist.
Kinetic study of cyanoguanidine resin formation: acid hydrolysis of hydroxymethyl and methoxymethyl cyanoguanidine
Authors: Shiba R. , Takahashi M. 
Published: April 2003

AbstractThe hydrolysis of hydroxymethyl cyanoguanidine and methoxymethyl cyanoguianidine in acidic aqueous media were studied by analyzing the eluted formaldehyde and the reaction products. Dihydroxymethyl cyanoguanidine released two formaldehydes with different rates because one of the two hydroxymethyl groups is intramolecularly interactive through the hydrogen bond. Methanol dissociation from methoxymethyl cyanoguanidine was seven to eight times faster than the dissociation of hydroxymethyl group, and the overall hydrolysis kinetics were similar to those of hydroxymethyl cyanoguanidine.
Complexation of poly(ethylene glycol) with some salts of alkali‐earth metals
Authors: Bekturov Esen , Tolendina Akmaral , Shaikhutdinov Yerenqaip , Dzhumadilov Talkybek 
Published: April 2003

AbstractThe interaction of poly(ethylene glycol) with some salts of alkali‐earth metals (Mg(ClO4)2, BaCl2, SrCl2, SrBr2 and CaCl2) in methanolic solutions was investigated by electroconductivity, viscometry, X‐ray diffractometry and NMR. It was established that the conformation of macromolecules is strongly changed in the presence of Mg(ClO4)2. Chlorides and bromides of alkali‐earth metals have a weak influence on macromolecule size. The formation of amorphous complexes in the PEG–Mg(ClO4)2 system and crystalline complexes in PEG–chloride systems of alkali‐earth metals was shown.
Polymer role in advanced battery technology
Authors: Wada Moriyasu 
Published: April 2003

AbstractA brief introduction to a new generation of sealed, rechargeable battery, a nickel metal hydride battery (Ni‐MH), is presented in connection with the polymer role in battery technology and engineering.Ni‐MH batteries have higher energy density and better environmental friendliness than the conventional sealed nickel cadmium (Ni‐Cd) batteries, and accordingly the importance of the battery is increasing in the area of high‐technology information, communication and audiovideo equipment.In this article it is pointed out that the key technologies for Ni‐MH batteries are: tridimensional nickel foam or mat for the positive nickel electrode substrate made by nickel plating of polyurethane foam or polyester nonwoven fabric; hydrogen‐storage negative electrode treated with hydrophobic polymer; and modified polypropylene nonwoven fabric separator with permanent hydrophilic properties.Moreover, the further importance of polymer science and technology to improve Ni‐MH battery performance is described.