bluuebunny/crossref_metadata_2025_split huggingface dataset:
Some physicochemical aspects regarding the synthesis of polyvinyl alcohol
Authors: Dimonie M. , Cincu C. , Oprescu C. , Hubcǎ Gh. 
Published: June 2010

AbstractThe present paper reports some theoretical aspects related to recent technology for the production of polyvinyl alcohol. The procedure involves the polymerization of vinyl acetate in two stages and the alcoholysis of polyvinyl acetate. A model for the calculation of the polymerization degree and grafting degree of vinyl acetate was developed in view of a quantitative evaluation of various possibilities for conducting the polymerization process. The alcoholysis of polyvinyl acetate was studied by conducting the reaction in a Brabender‐type mixer. The dependence of the reaction rate on the catalyst or polymer concentration or on the temperature evidences the important role played by the diffusion processes and supports the idea of the cocatalytic effect of OH groups in the alcoholysis reaction of the polyvinyl acetate in the basic catalysis.
Copolymerization of vinyl chloride with bis(beta‐chloroethyl) vinylphosphonate
Authors: Gallagher R. , Hwa J. C. H. 
Published: June 2010

AbstractBis(beta‐chloroethyl) vinylphosphonate and vinyl chloride were copolymerized free‐radically in water suspension and in toluene solution at 55°C. From compositional analysis of the low‐conversion copolymers, the reactivity ratios of bis(beta‐chloroethyl) vinylphosphonate (r1) and vinyl chloride (r2) were found to be 0.37 ± 0.1 and 0.26 ± 0.05, respectively, indicating that the two monomers have a marked tendency to alternate. From the Q and e values of vinyl chloride, the corresponding Q.e values for the vinylphosphonate are calculated to be 0.23 and 1.73, respectively. Interestingly, the rate of copolymerization is greater than that of homopolymerization, and is also greater when water is present. These copolymerization characteristics are deemed favorable in industrial productions. The copolymers have lower viscosities and glass temperatures than poly (vinyl chloride). From patent literature, the copolymers also show useful flame retardant properties.
Polyquinolines: A class of rigid‐chain polymers
Authors: Beever W. H. , Stille J. K. 
Published: June 2010

AbstractThe reaction product of m‐cresol and phosphorus pentoxide has been shown by 31P‐nmr to consist of an equimolar mixture of mono‐ and di‐m‐cresyl phosphate. A mixture of pure di‐m‐cresyl phosphate and m‐cresol is an excellent polymerization medium for the preparation of polyquinolines via the Friedländer reaction, giving higher‐molecular‐weight polymers than can be obtained from the crude reaction of m‐cresol and phosphorus pentoxide. Spin‐lattice relaxation times T1 have been used to relate the chain mobility of the polymers in solution to the glass transition temperature (Tg) in the solid.
Kinetic aspects of the formation of the ordered phase in stiff‐chain helical polyamino acids
Authors: Miller Wilmer G. , Kou Lee , Tohyama Kohji , Voltaggio Vincent 
Published: June 2010

AbstractThe helical polyamino acids exhibit a two‐component temperature‐composition phase diagram that corresponds well in overall appearance to the Flory prediction for rigid, impenetrable rods. The phase diagram may be characterized as a narrow, typically 1–2%, biphasic region separating the disordered (isotropic) state from the ordered (liquid–crystalline) state, connected to a wide biphasic region in which nearly pure polymer is in equilibrium with nearly pure solvent. Initial studies have been undertaken to deduce the kinetics of formation of the ordered phase, both when the thermodynamically stable state is the ordered state, as well as when it is in an ordered‐disordered biphasic state. The time course of the formation of the ordered phase at different temperatures is reminiscent of analogous studies on polymer crystallization, describable by a nucleation and growth mechanism. Formation of the ordered phase when the final state is the narow biphasic state appears also to follow a nucleation‐growth mechanism. However, when the final state is the wide biphasic region, the morphology of the final state is that of an optically clear, self‐supporting gel, even at very low concentrations (as low as 0.03 wt %). The reasons for and nature of the gel state are believed to be a kinetic phenomenon. The shape of the phase diagram is such that the temperature range of thermodynamic metastability is small and phase separation occurs in the thermodynamically unstable region. In the unstable region the zero activation‐energy spinodal decomposition mechanism dominates the kinetics of phase separation, leading to bicontinuous interconnected phases that have little possibility or driving force to rearrange further. The polymer network structure is proposed to be a bulk thermodynamic phase, characterized by bundles or sheets of polymer between branch points, rather than individual chains as in the usual polymer network. Rheological, electron microscope, and light‐scattering data are presented that support this view. The possibility of other stiff‐chain polymers forming a network structure for similar reasons is discussed.
Properties of the ladder polymer cis‐syndiotactic poly(phenylsilsesquioxane) in solution
Authors: Helminiak T. E. , Berry G. C. 
Published: June 2010

AbstractStudies on the properties of the double‐chain ladder polymer of cis‐syndiotactic poly(phenylsilsesquioxane) (PPSQ) in dilute and concentrated solutions are reported. Data on the intrinsic viscosity [η], the second virial coefficient A2, and the mean‐square radius of gyration 〈s2〉 as functions of molecular weight M, temperature, and solvent lead to the conclusion that the conformation of PPSQ can be modeled with a wormlike chain model with a persistence length ρ of 74 Å. These data cannot be used to assess the extent of intramolecular inflexibility, e.g., resistance to rotational isomerization, of PPSQ. For concentrated solutions (0.05 ⩽ c ⩽ 0.20 g/ml) the limiting viscosity ⩾0 at zero shear rate is proportional to cM for cM < ⩾2Mc and to (cM)3,4 for cM ⩾ ρ2Mc, where Mc = 9120. The product Xc (〈s20/M) × ρ2Mc/ma is equal to 356 × 10−17 for PPSQ, close to the value 400 × 10−17 typical of single‐chain polymers. The reduced flow curve ηK/ϵ0 versus ηCK for the viscosity ϵK as a function of shear rate K is not far different from that for single‐chain polymers—here, the time constant ηC is equal to η0R0 with R0 the limits of the recovery function RK, at small K(R0 is often denoted Je0). The values of ηc are intermediate to ηc for a flexible single‐chain polymer and the relaxation time ηR for rotatory diffusion of a rigid coil. Plots of RK versus K superpose with plots of the transient recovery R0(ϑ) with ϑ = K−1 over the limited range ηCK < 1 where ϑ is the recovery time (R0(ϑ) goes to R0 for large ϑ), similar to behavior found with solutions of single‐chain polymers.
Properties of an optically anisotropic heterocyclic ladder polymer (BBL) in dilute solution
Authors: Berry G. C. 
Published: June 2010

AbstractLight scattering, intrinsic viscosity, gel‐permeation chromatography, and fluorescence depolarization measurements are reported on dilute solutions of a heterocyclic polymer (BBL) prepared by polymerization of 1, 4, 5, 8‐naphthalene tetracarboxylic acid with 1, 2, 4, 5‐tetraaminobenzene. The light‐scattering data on fractions of the polymer giving the anisotropy δ and the mean‐square radius of gyration s2 are discussed in terms of equations for the scattering from polydisperse anisotropic polymer. It is concluded from the dependence of δ and 〈s2〉 on the molecular weight that the polymer has a nearly rodlike conformation. The intrinsic viscosity data are analyzed in terms of relations for rods and wormlike chains. The fluorescence emission anisotropy is found to be so sensitive to molecular‐weight distribution that analysis in terms of molecular parameters is prohibited. Association that can occur under certain circumstances is discussed.
Production, characterization, and solution properties of dextran fractions of narrow molecular weight distributions
Authors: Basedow Arno Max , Ebert Klaus Heinrich 
Published: June 2010

AbstractFractional solution, fractional precipitation, and fractionation by incompatibility with polyethylene glycol are described for the preparation of dextran fractions in the molecular weight (MW) range from 10,000 to 500,000. Polydispersity (Mw/Mn) was about 1.1 at low MWs, increasing up to 1.3 for high MWs. Dextran fractions of lower polydispersity (<1.05) were obtained with preparative GPC on controlled pore glass columns. For the characterization of the dextran fractions, molecular weight distributions (MWD) were determined by GPC on calibrated columns. By combination of low‐angle laser light scattering and GPC absolute MWDs were obtained. Various studies of the properties of solutions of narrow dextran fractions were performed, such as viscosity measurements, calorimetric investigations (heats of solution and dilution) in several solvents, preferential solvation in mixed solvents, and solubility determinations in aqueous solutions of salts and other substances. The results indicate that dextrans with MWs > 2000 are almost perfect statistical coils in solution and that interactions between dextran molecules in solution are small, so that no association occurs. For MWs < 2000 solution properties give support to the assumption that transition to rodlike conformation occurs.
Cross‐linked copolymers of N,N‐diethylacrylamide with improved mechanical properties
Authors: Ulbrich K. , Kopeček J. 
Published: June 2010

AbstractBy using radical solution copolymerization of N,N‐diethylacrylamide and N‐tert‐butylacrylamide in the presence of a small amount of the cross‐linking agent, gels were prepared swollen to equilibrium in water at 25°C and possessing much better mechanical properties (elongation at break, stress at break) than those of the cross‐linked poly‐(N,N‐diethylacrylamide) alone. This is probably due to an increased possibility of hydrophobic interactions of copolymers. At the same time, the effect of the comonomer structure on the mechanical properties of the resulting gel is considered. The equilibrium degree of swelling of the gels steeply decreases with increasing temperature. Some parameters are compared which characterize the three‐dimensional network prepared both by the cross‐linking polymerization of N,N‐diethylacrylamide and by its copolymerization with N‐tert‐butylacrylamide (moduli of elasticity, X parameters, concentration of elastically effective chains, crosslinking effectivity, etc.), and the effect of these quantities on the gel properties is discussed.
On biological (anticoagulant) activity of heparin the high productive method for fractionation of commercial heparin
Authors: Noreika R. , Stepaniukiene E. , Lashas L. 
Published: June 2010

AbstractA universal high productive chromatographic system is proposed for fractionation of com‐ mercial preparations of heparin. The system is suitable for the characterization on an analyti‐ cal scale and fractionation on a large scale of different preparations of heparin.
The biologic activity of polyanions: Past history and new prospectives
Authors: Regelson William 
Published: June 2010

AbstractThe toxicology of synthetic polyanions relates to molecular weight. This developed from experience with pyran copolymer (divinyl ether maleic anhydride copolymer), which was tested clinically as an antitumor agent and found to be too toxic for continued clinical trial. Synthetic polyanions of low molecular weight are potent stimuli to macrophage phagocytic function and possess antitumor activity. Increased host resistance to pathogens including bacteria, fungi, viruses, and trypanosomes is seen. In contrast to lower‐molecular‐weight fractions, higher‐molecular‐weight samples inhibit macrophage function, and apparently increased molecular weight > 15,000 is necessary for antiviral and immunologic stimulating capacity. One possible mechanism for the action of polyanions may relate to redistribution of calcium ions within the cell and increasing cyclic GMP activity. This is a redefinition for the role of polyanions in sol–gel alteration in cytoplasm. The killing effect of the polyanion‐activated macrophage on tumor cells resembles that of the polyanion on the nucleus. Polyanions may be potent controllers of the stability of DNA within the nucleus and can act to derepress cells to turn on protein synthesis or, alternatively, inhibit enzymes involved in virus synthesis and control of RNA or DNA polymerase. Thus, they are cogent tools in an understanding of the physiology of nuclear interaction. Biological use for these agents can be developed not only in clinical approaches to inhibition of tumor or viral infection, but to eliminate plutonium, and provide selective enzyme inhibition and protein interaction which allows for isolation, neutralization, and characterization of blood and tissue protein and glycoprotein fractions vital for a wide range of pathophysiology.
Polymerization of acetylene monomers by molybdenum compounds fixed on the macromolecular supports
Authors: Kiyashkina Zh. S. , Pomogailo A. D. , Kuzayev A. I. , Lagodzinskaya G. V. , Dyachkovskii F. S. 
Published: June 2010

AbstractThe techniques of heterogenization of homogeneous catalysts (molybdenum halogenized) for acetylene monomers polymerization on polymer supports have been worked out. The latter were carbon‐chain polymers grafted with functional groups. The properties of homogeneous and heterogenized catalytic systems have been compared. Heterogenized catalysts induce formation of the greatest amount of high‐molecular polyphenylacetylene. Some assumptions (on basis of MMD polymer analysis) about the mechanism of acetylene monomers polymerization by use of such catalysts have been suggested.
Metal‐containing co‐ordination polymers. VII. Studies on the structure of complexes formed in the reaction of a semicrystalline polyester with mgo
Authors: Vancsó‐Szmercsányi I. , Székely‐Pécsi Zs. , Kalló A. 
Published: June 2010

AbstractStructural changes are detected by x‐ray diffractometry when a semicrystalline polyester of molecular weight of about 1000 having free carboxyl and hydroxyl end groups is reacted with MgO. The ratio of MgO to the COOH end groups alters the diffractograms. Supplementary structural studies were performed by various electron microscopic techniques. Differences were also detected in the supermolecular structure as a function of the MgO to COOH ratio. Furthermore, at the equivalent ratio a fiber‐forming solution can be prepared; while the equimolar ratio results in a gel‐like system. This is in accordance with our previous conclusions about the mechanism of the reaction (association), i.e., at a molar ratio of the COOH group to MgO of 2:1 (equivalent amounts) the forming of aCOO− Mg2+ −OOClinkage is preferred; while in the case of an equimolecular amount of COOH and MgO, the possibility of the association of other groups of the polyester chain (such as CO groups and alcoholic end groups) increases creating associates of greater size.
A new support for whole cell immobilization
Authors: Vijayalakshmi M. A. , Marcipar A. , Cochet N. 
Published: June 2010

AbstractA new support for whole‐cell immobilization based on crosslinked pectate with iminodiacetate as polydentate spacer and iron is proposed. Microorganisms of the strains Escherichia coli, Staphiloccoccus aureus, Saccharomyces cereviseae, and Candida tropicalis have been immobilized on this matrix. Immobilization capacity of the support, conditions of adsorption, and differences in respiration between free and fixed cells have been evaluated. Using scanning electron microcopy, electron micrographs of the support and of cells fixed on the support were prepared in order to examine fixation in detail. It was found that it is possible to immobilize an important active biomass, with a very strong binding strength, between cells and support, without the inherent diffusional limitations encountered in other methods. Respiration measurements showed increased oxygen demand by immobilized cells.
Investigation of interaction between methemoglobin and polymethacrylates containing imidazole or hydrophobic side chains by means of epr spectroscopy
Authors: Pommerening K. , Ristau O. , Kühn M. , Mohr P. , Štamberg J. , Beneš M. 
Published: June 2010

AbstractMacroporous polymethacrylates containing imidazole groups as well as hydrophobic side chains adsorb methemoglobin (metHb). The protein‐matrix interaction was investigated by means of an electron paramagnetic resonance (EPR) spectroscopy. The adsorption of metHb to the imidazole containing matrices occurs by complex formation with the iron of the prosthetic group. In case of steric hindrance or long spacers, this complex formation is not primarily responsible for the adsorption. The binding of metHb to hydrophobic side chains clearly demonstrates the presence of a metHb‐H2O‐metHb‐OH mixture. Moreover, the protein‐matrix interaction induces conformational changes in the protein component. In this case, additional signals in the EPR spectra indicate the formation of a cytochrome P450‐like structure.
Molecular aspects of affinity chromatography
Authors: Mohr P. , Pommerening K. , Kühn M. 
Published: June 2010

AbstractAffinity chromatography is based on the well‐known specific interaction between biomacromolecules and between biomacromolecules and low‐molecular partners. To separate the one component (bioaffine component), the complementary bioaffinant has to be attached chemically to a solid‐phase support. This interaction, however, can be disturbed considerably by the linkage of one partner to the insoluble matrix. Some molecular aspects of this interaction discussed in a summarized presentation of our investigations are: (1) conformational state of immobilized biomacromolecules; (2) nonspecific interaction between matrix and bioaffine component; (3) steric factors; and (4) interaction between spacer and/or carrier and bioaffine components.
Application of macroporous sorbents in antioxidants determination
Authors: Šmejkal František , Popl Milan , Čihová Alena 
Published: June 2010

AbstractFor LC separation of antioxidants with differently sterically shielded polar groups, a selective interactions solute‐mobile phase may be utilized. Improvement of the separation in the reversed‐phase LLC can be achieved by means of utilization of the various interaction profiles of some solvents. In this study, reversed‐phase LLC with a macroporous gel, Separon SE, was applied for characterization of the retention behavior of some antioxidants and for the determination of these compounds in rubber and plastics.
Equilibrium and nonequilibrium dynamics of sorption and chromatography on ion exchangers with polyelectrolyte surface layer
Authors: Samsonov G. V. , Elkin G. E. 
Published: June 2010

AbstractDynamic and chromatographic processes of isolation and purification of antibiotics and amino acids on surface‐layer ion exchangers have been investigated. It was shown that the optimum conditions of sorption and desorption on these exchangers can be determined by using a criterion for the regularity of the dynamic process. Theoretical predictions are in agreement with experimental data on the sorption and desorption of slowly diffusing organic ions.
Oxidation of isopropanol catalyzed by polymer‐bound cobalt complexes
Authors: Maternová J. , Setínek K. 
Published: June 2010

AbstractThe oxidation of isopropanol in glacial acetic acid catalyzed by soluble and polymer‐bound cobalt (II) complex ions has been studied. In both cases, the oxidation proceeds as a homolytic reaction and the catalyst acts as an initiator of the decomposition of peroxides to radicals. The oxidation activity of the free‐ and fixed‐cobalt (II) ions increases in the presence of the bromine ion. Heterogenized cobalt (II) ions also catalyze the gas‐phase oxidation of the title alcohol. Their activity is conditioned by the presence of acetic acid in the inner co‐ordination sphere of the metal. The gasand liquid‐phase reactions proceed by the same reaction mechanism.
Stretching calorimetry of some poly(α‐amino acid)s
Authors: Ebert G. , Knispel G. , Müller F. H. 
Published: June 2010

AbstractStretching of poly(α‐amino acid) fibers or films as well as natural occurring protein fibers like wool is accompanied by heat effects due to conformation changes of the macromolecules and by orientation changes, sliding processes, etc. Such phenomena were studied by using a stretching calorimeter.
Thermodynamic properties and glass transition of polystyrene
Authors: Chang Shu‐Sing 
Published: June 2010

AbstractThe heat capacity of a narrow molecular weight distribution polystyrene, National Bureau of Standards—Standard Reference Material 1478, has been determined by a fully automated adiabatic calorimeter from 5 to 380 K for the sample subjected to different thermal history. The number‐average molecular weight of this sample is 35,800 and the dispersity in the molecular weights, Mw:Mn, is 1.045. The heat capacities of the glass and of the liquid of this material are found to be within 0.5% of other atactic polystyrenes over most of the temperature range studied. The glass transition temperature Tg of the annealed glass (cooling rate < 1 K/h) at 366 K and that of the quenched glass (cooling rate about 6 K/min) at 366 K are determined by the intersections of enthalpy‐temperature curves of the glasses with the liquid. The glass transition temperature is slightly higher than that calculated from dilatometrically determined Tgs of a series of low‐polydispersity polystyrenes cooled at 0.1 K/h, but is lower than that from thermal analytically determined Tgs.
Stretching calorimetry and thermoelasticity of rubbers at different temperatures
Authors: Kilian H.‐G. , Höhne G. W. H. , Trögele P. , Ambacher H. 
Published: June 2010

AbstractThe data of isothermal stretching calorimetry on rubbers at different temperatures above room temperature are presented. Based upon the van der Waals equation of state for rubbers calculations can be fitted to the experimental data obtained by simple elongation whereby the thermoelastic behavior is related to a constant thermal expansion coefficient in the unstrained state and to an invariant temperature coefficient of the end‐to‐end distance of the equivalent freely jointed chain.
Effects of ph and electrolytes on absorption and luminescence spectra of water‐soluble polydiacetylenes
Authors: Bhattacharjee H. R. , Preziosi A. F. , Patel G. N. 
Published: June 2010

AbstractWater‐soluble polydiacetylenes, RC—CC—CR, where R is either (CH2)3,4OCONHCH2COOK or (CH2)3,4COOK, undergo visual (yellow ↔ red or purple) reversible conformational (nonplanar ↔ planar) transitions by varying the pH of the solution as well as by the addition of different monovalent electrolytes, such as KCl and LiCl. Polyvalent cations such as Ca2+ cause precipitation of the polymer due to crosslinking. The conformational changes caused by the variations in pHs can be viewed as a gradual ion exchange process, for example, K+ is exchanged with H+ or vice versa. The transition phenomena were studied by visible absorption spectroscopy. The broadest spectral change (465 nm ↔ 575 nm) occurred when the pH of the solution was changed from 9 to 2. The spectral shifts displayed by the additions of electrolytes were rather narrow (465 nm ↔ 515 nm), the corresponding color change being yellow ↔ red only. The luminescence properties (fluorescence only) of these water‐soluble polydiacetylenes were also studied. The fluorescence is pH dependent, being observed only at relatively higher pHs. Both absorption and emission spectra revealed some anomalous phenomena for which explanations are provided through experimental evidence.