bluuebunny/crossref_metadata_2025_split huggingface dataset:
Critical association and thermoreversible gelation of some selected polymers
Authors: Burchard Walther , Lang Peter , Schulz Liane , Coviello Tommasina 
Published: March 2011

AbstractThe study of associating polymers is complicated by the fact that at a finite concentration only an apparent molar mass is directly measured. This apparent molar mass deviates from the true one because of thermodynamic interaction. In a good solvent the repulsive interaction can be fully described in terms of the second virial coefficient, which can be measured at very low concentrations, and a correction can be made for the true molar mass. The technique has been successively applied to β‐galactosidase in a phosphate buffer and to cellulose 2,5‐acetate in acetone.The gel point could be determined, and critical behavior was found in very good agreement with percolation prediction. Two other methods were employed and tested. One is based on the condition that the longest relaxation time must diverge at the gel point, and correspondingly the translational diffusion coefficient should go to zero. The second criterion consists of the prediction that power law behavior should be observed for the time correlation function of dynamic light scattering as well as for the frequency dependent storage and loss moduli.These predictions were indeed found to hold for two polysaccharides which form thermoreversible gels in water at a fairly low salt concentration. The two polysaccharides are the Tamarind seeds polysaccharide in 1M Na2SO4 and an exopolysaccharide from Rhizobium leguminosarum, strain 8002 in 0.1M NaCl solutions respectively.
Classical light scattering studies on structure formation in polymer solutions
Authors: Gohlke Ulrich , Rother Gudrun , Otto Andreas , Hartmann Juergen 
Published: March 2011

AbstractThe scattered light is very sensitive to the presence of supermolecular structures in polymer solutions, offering the possibility to study structure formation in situ by classical light scattering and to characterize the generated particles. An improved analysis of light scattering data yields information on the structure type, polydispersity of the systems, particle mass and size as well as the degree of swelling. The flocculation process of ampholytic modified poly(acrylonitrile) was investigated in dependence on the pH‐value and the content of different salts in the solvent. Results obtained give a deeper insight into the flocculation mechanism.
Structure rheological investigations of segment interaction in polymer solutions of the network type
Authors: Schurz Josef 
Published: March 2011

AbstractThe solution structure of flexible chain polymers is described in terms of an equivalent entanglement network characterized by its apparent chain element A'. Such networks can exhibit free penetration of polymer segments, hindered penetration or no penetration at all. The segment interaction effects a hindrance to penetration. It can be characterized by the concentration dependence of the mass of network strand Me resp. the entanglement density ν. Another parameter is the entanglement fraction ß, which describes the ratio of the entanglements actually formed to that possible in case of free penetration. Experimental results with different polymers illustrate these ideas.
Determination of microscopic interaction parameters of ternary polymer solutions with light scattering data
Authors: Kappeler Ch. , Schäfer L. 
Published: March 2011

AbstractUsing a renormalized form of the Random Phase Approximation (or Tree Graph Approximation) we analysed data on the zero angle scattering intensity and the apparent radius of gyration for the system polystyrene‐poly(methyl methacrylate)‐bromobenzene. Since the microscopic parameters of this system are known from the analysis of the zero‐angle scattering data, the theory yields a parameterfree prediction of the apparent radius of gyration which fits the data very well. To show the influence of renormalization we also analyse the data by an unrenormalized version of RPA.
Studies on main ‐ chain liquid ‐ crystalline model oligomers of defined length and structure
Authors: Seliger H. , Eppel M. , Göldner E. , Kittel I. , Ludwig A. , Schorr R. 
Published: March 2011

AbstractOligomers of defined sequence and structure modelling main chain LC polymers were prepared a) by solution synthesis; b) by a novel liquid phase synthesis using two monomethoxy‐poly (ethylene glycol) supports. Benzyl‐ and tert.butyl‐groups were used as orthogonal pair of protecting groups for route a), and also as compatible anchor groups for carriers in route b). Depending on chain structure and end groups, at least ca. 3 mesogenic elements are required to allow for LC phase transitions. The phase behaviour of oligomers with free carboxylic ends can be explained by their association tendency.
Poly(methyl methacrylate) dispersions in decane stabilized by a diblock copolymer
Authors: Stejskal Jaroslav , Kratochvíl Pavel 
Published: March 2011

AbstractIn a dispersion polymerization, the monomer is miscible with the reaction medium, while the resulting polymer is insoluble under the same conditions. The macroscopic precipitation of the polymer is prevented by a steric stabilizer. Methyl methacrylate was polymerized in decane in presence of polystyrene‐block‐poly(ethylene‐co‐propylene) and spherical dispersion particles of poly(methyl methacrylate) (PMMA) were obtained. The static light scattering yielded molar masses of particles in the range 4 × 107 to 7 × 109 g mol−1. Dynamic light scattering provided the hydrodynamic radii from 60 to 190 nm and also information on the non‐uniformity of the particles. The relations between the characteristics of the dispersion particles (concentration of components, particle mass and dimensions, molar mass of PMMA chains, surface density of stabilizing chains, etc.) were looked for. The kinetics of polymerization seems to be only little affected by the colloidal character of the system.
Solution properties of complexes between oxygen‐ and nitrogen‐containing polymers and alkali metal salts
Authors: Bekturov Esen A. , Dzhumadilov Talkybek K. 
Published: March 2011

AbstractThe results of investigations of the complexation of polymer ethers and polybases with alkali metal salts in organic solvents are discussed. The influence of different factors as nature of polymers, salts and solvents on the complexation process is considered.
Lanthanide metal polymer complexes. Synthesis, characterization and application
Authors: Okamoto Yoshi 
Published: March 2011

AbstractOur recent results on the investigation of lanthanide metal polymer complexes were presented. Luminescence properties of Tb3+ or Eu3+ ‐polycarboxylate complexes in aqueous solution were investigated. The excitation band near 300 nm for Tb or Eu(polyacrylate) solutions were drastically enhanced by the addition of hydroxy radical generating reagents as well as ultrasonic irradiation. These spectral changes were attributed to the energy transfer from chromophore molecules formed by generated hydroxy radicals in both systems. Since the increase in the luminescence intensity was proportional to the hydroxy radical concentration, the Eu3+ or Tb3+ (PAA) system can provide a convenient method for the determination of hydroxy radical concentration in aqueous solution. We have also utilized lanthanide metal ion complexes as a luminescent emitter in electroluminescence (EL) devices. The configuration of the EL cell and experimental results were discussed.
Synthesis of new conducting poly(2,5‐thienylene)s containing alkylhydroxy and alkylester side chains
Authors: Delia Casa C. , Salatelli E. , Andreani F. , Costa Bizzarri P. 
Published: March 2011

AbstractThe chemical synthesis of new electroconducting poly(2,5‐thienylene)s containing alkylhydroxy and alkylester side‐chains in the β‐position of the thiophene rings is reported. The polymers were obtained by oxidative homopolymerization or copolymerization of 2‐(3‐thienyl)ethanol and 2‐(3‐thienyl)ethyl hexanoate by FeCl3 in nitromethane. Structural characterization using elemental analysis, FT‐IR and NMR spectroscopy shows that a partial nucleophilic substitution of the hydroxy group by chlorine and a partial cleavage of the ester function take place during polymerization. The presence of the ester function with a long aliphatic chain makes the polymers soluble and allows them to be processed into films. The polymers can be doped using a solution of FeCl3 to the maximum electrical conductivity of 10−3 Ω−1 cm−1.
Voltammetric study of some macromolecule ‐ metal complexes
Authors: Esteban M. , Díaz‐Cruz J. M. , Ariño C. , Casassas E. 
Published: March 2011

AbstractThe usefulness of a voltammetric model for studying macromolecule ‐ metal complex systems is verified. Complexes formed by a metal ion (Zn(II), Cd(II), Pb(II) or Cu(II)) and a macromolecule (polymethacrylic (PMA), polyacrylic (PAA), alginic (AA) or polygalacturonic (PGA) acids) are investigated. Several voltammetric techniques have been used: sampled direct current polarography (DCP), normal pulse polarography (NPP), differential pulse polarography (DPP), reverse pulse polarography (RPP), cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DPASV). Results confirm the validity of the model, in determining not only formation constants but also diffusion coefficients of the complexes. The behaviour of some systems agrees with that predicted by the model. Nonetheless, other systems only partially fulfil the predictions for different reasons, which are discussed.
Amidoxime polymers ‐ copper complexes
Authors: Boudakgi Amer , Jezierska Julia , Kolarz Bozena N. 
Published: March 2011

AbstractThe aminolysis of nitrile groups in macroporous acrylonitrile‐divinylbenzene copolymers leads to amphoteric ion exchange resins with 1.0 ‐ 3.3 mmol/g amidoxime groups content. The starting copolymers were synthesized from the same monomer mixture, but the composition of diluents used were different. The resulting polymers with amidoxime groups have different sorption of Cu(II) ions, the highest values between 1.3 and 3.5 mmol/g at pH 5. EPR and IR spectra were used to indicate the formation of the complexes between Cu(II) ions and amidoxime polymers. On the basis of the EPR parameters structure of complexes formed at different pH and Cu(II) concentration was postulated.
Structural macromolecular parameters determining electroconductivity of oxidized poly‐n‐vinylpyrrole
Authors: Ciardelli Francesco , Mori Stefano , Ruggeri Giacomo , Colligiani Arturo , Cagnolati Roberto , Campani Enzo , Rolla Pier Angelo , Lucchesi Mauro 
Published: March 2011

AbstractThe dependence of electroconductivity on conjugation length as well as the related basic mechanism was investigated by chemical (FeCl3) oxidation of insulating polymers from N‐vinylpyrrole (NVP) starting with different Fe/NVP ratios and different molecular weights. The results allow to establish that oxidation occurs mainly intrachain and that electroconductivity has a sharp increase for a conjugation length higher than ∼15 NVP‐units.
Structural features of 4‐methyl‐1‐pentene polymers prepared with different transition metal catalysts
Authors: Altomare Angelina , Solaro Roberto , Ciardelli Francesco , Barazzoni Lia , Menconi Francesco , Masi Francesco 
Published: March 2011

AbstractHomopolymerization of 4‐methyl‐1‐pentene carried out in the presence of catalysts containing variable relative amounts of Ti, Hf and Mg indicates that molecular weight and stereoregularity can be varied to an appreciable extent depending on catalyst nature and composition. A distinct behaviour of the various catalytic systems is also observed during the copolymerization of 4‐methyl‐1‐pentene with monoalkenes such as propylene, 1‐butene and 1‐hexene. These data are discussed by underlining the important role of the transition metal in determining the features of polyolefins materials.
Effect of the mixture t ‐ BuCl/SnCl4 on the cationic polymerization of isobutylene
Authors: Lukáš Rudolf , Toman Ludêk 
Published: March 2011

AbstractThe polymerizations of isobutylene initiated with the system tert‐butyl chloride (t‐BuCl)/SnCl4 and carried out in CH2Cl2 at −20°C and −78°C were investigated. The results obtained demonstrate that the presence of t‐BuCl in the polymerizing system gives rise to a PIB product with a distinctly bimodal MWD. The higher‐molecular weight (HMW) PIB, M̄n = 20000, I=M̄w/M̄n ∼ 2.5, is the result of existence of the protogenic initiation with residual water in the reaction system. The lower‐molecular weight (LMW) PIB, M̄n < 600, M̄w/M̄n ≤ 1.4, is the product of polymerization initiated presumably with a complex t‐BuCl‐SnCl4‐H2O. To elucidate the reaction mechanism of the polymerization initiated with the complex, a series of similar isobutylene polymerizations using the initiation system 2,5‐dichloro‐2,5‐dimethylhexane (DDH)/SnCl4 was run and the oily LMW PIB samples were investigated by 1H‐NMR. A new polymerization mechanism describing the role of DDH and t‐BuCl is suggested.
Living cationic polymerization of vinyl ethers and styrene derivatives: Design of initiating systems based on added salts with halogen anions
Authors: Sawamoto Mitsuo , Higashimura Toshinobu 
Published: March 2011

AbstractThis paper overviews three living cationic polymerization systems (for styrene, p‐methoxystyrene, and isobutyl vinyl ether) that are, in common, featured by:(i) specifically in nonpolar solvents, the use of the hydrogen halide/metal halide initiating systems (HX/MXn; X: I, Br, Cl; MXn: ZnX2, SnCl4), which generate a living growing carbocation stabilized by a nucleophilic counteranion (X−…MXn);(ii) specifically in polar solvents, the use of externally added ammonium salts (nBu4N+Y−; Y−: I−, Br−, Cl−), which permit the generation of living species from HX/MXn by providing nucleophilic halogen anions Y−, either the same as or different from the halogen X− in HX.
Direct observation and stability of active species in cationic polymerization: A reexamination of the polymerization of styrene initiated by triflic acid
Authors: Vairon J.‐P. , Rives A. , Bunel C. 
Published: March 2011

AbstractPolymerization of styrene initiated by triflic acid in CH2Cl2 solution was reexamined, using a new stopped‐flow device working in high purity conditions over a wide temperature range. Monomer and styryl cation were followed simultaneously through their respective absorbances at 290 and 340 nm. Initiation is very rapid, and cations concentration reaches a plateau the duration of which is depending on temperature. In our conditions (I0 = 0.5 − 9.10−3M, M0/I0 = 1 to 20), cations concentration is so low at room temperature that it is almost unmeasurable. At −65°C, it is 100 times higher, remains constant for several seconds and complete termination takes place within a minute or more. Such a profile of cation evolution agrees with an equilibrium situation between initiation and a much more temperature‐dependent backward deprotonation. Apparent initial rate of initiation is first order with respect to monomer, but the order with respect to initiator was found very high and variable with temperature (from 4.5 at −65°C to 3 at −20°C). This supports the presence, even if they are in low concentration, of acid high agregates, the reactivity of which increases with size. A first order monomer consumption is observed during the plateau, which leads to kp values ranging from 103 at −65°C to 9.104 M−1.s−1 at −10°C (Ep# = 43 kJ.mol−1). The disappearance of cations, which follows the plateau, slows down and becomes unimolecular when monomer consumption is complete, and kt values range from 6.10−2s−1 at −65°C to 1.2s−1 at −23°C (Et# = 33 kJ.mol−1).
Recent advances in macromolecular engineering via ionic methods
Authors: Rempp Paul 
Published: March 2011

AbstractSelected recent developments in the field of macromolecular engineering via ionic methods are presented: ω‐functional polymers and macromonomers, ampholytic block copolymers and novel thermoplastic block copolymers, star shaped macromolecules of several kinds. Attention is called upon the absolute necessity of adequately characterizing the samples obtained, in order to check wether their structure meets with expectation.
A comparison of group transfer and anionic polymerization of acrylic monomers
Authors: Webster Owen W. 
Published: March 2011

AbstractThe living polymerization of acrylic monomers by a repeated silyl Michael addition reaction (GTP)a operates at temperatures as high as 100° C. The resulting polymers are, however, nearly identical to those produced by anionic polymerization at low temperatures. Is GTP merely a special form of anionic polymerization? A proposal is made that GTP catalyzed by weak nucleophiles proceeds by insertion of monomer in silylated chain ends and that GTP catalyzed by strong nucleophiles proceeds by reversible generation of free enolate.
Solvation effects in anionic polymerization of polar vinyl monomers
Authors: Tsvetanov Ch.B. , Dimov D.K. , Petrova E.B. , Dotcheva D.T. 
Published: March 2011

AbstractThe anionic polymerization (AP) of polar vinyl monomers (PVM) is strongly affected by additives with electron donor and electron acceptor properties. For the purpose of estimating the interactions of the active centers (AC) of chain growth with different ligands, the approach of studying a reference system was adopted, viz. lithium picrate (LiPi) in dioxane (DO). Three types of interaction were distinguished: with electron pair donors (EPD), with Li salts and alkoxides, and with Lewis acids. Spectral evidence was found of charge transfer complexation with Li alkoxides and enolates, leading to modified dianionic Meisenheimer adducts. The experimental procedure was employed in studies of competitive solvation of LiPi by two ligands. The results were related to reviewed literature data on the kinetics and stereochemistry of methyl methacrylate (MMA) and 2‐vinylpyridine (2VP) polymerizations by lithium initiators.
Determination of the microstructure of the fermentation polymer xanthan
Authors: Kulicke W:‐M. , van Eikeren A. 
Published: March 2011

AbstractAlthough xanthan has long been the subject of wide‐ranging investigations, it has not yet been possible to establish any clear link between the solution properties and the chemical and steric microstructure. This is due to the fact that large variations in the properties may occur between samples of different manufacturers. Hence more than fifty different samples in liquid and powder form were investigated. This involved the determination of pyruvate and acetate content for all the samples by means of enzymatic analysis and Comparison with results from 1H NMR spectroscopy. In addition, the contents of the side groups are for the first time given in mass and molar percentages.Low angle and multi‐angle laser light scattering as well as viscometry were employed for the determination of the steric microstructure. Here it was ascertained that preliminary treatment of the sample has a crucial influence on the results of light scattering. A method of sample preparation was therefore devised which is aimed at avoiding the formation of microgels and preserving the structure of the native. xanthan. In addition, xanthan is used to illustrate a novel procedure which enables very readily interpretable Zimm plots to be obtained from one individual reading over a few minutes. In a comparison of the scattering curve extrapolated to c=0 with calculated model curves for semiflexible rods, the structure of native xanthan was determined to be more rigid than corresponds with the exponents of previously published [η]‐Mw relationships.
Supermolecular structures in polymer solutions interpretation of static light scattering data
Authors: Dautzenberg Herbert , Rother Gudrun 
Published: March 2011

AbstractThe characterization of supermolecular structures in polymer solutions by static light scattering requires an improved analysis of the scattering curves. A comparison of the experimental curves with model calculations for various basic structure types in a scaled plot offers the possibility to extend the range of a reliable determination of the structural parameters to particle sizes up to 500 nm. The influence of the polydispersity and problems of an unambiguous interpretation are discussed. Especially, a closed analytical expression for the scattering function of polydisperse systems of spheres with a Schulz‐Zimm distribution of radii was derived.
Characterization of thermo‐reversible gels by means of sedimentation equilibria
Authors: Borchard Werner , Cölfen Helmut 
Published: March 2011

AbstractThis paper describes the deformation of gels in a centrifugal field leading to a continuous equilibrium. A gel is considered to be a binary mixture of cross‐linked polymer and solvent and is assumed to remain isotropic during the deformation. From the equation for the osmotically effective pressure, called swelling pressure, the thermodynamic properties of a gel can be calculated. For highly swollen gels the expression of Svedberg and Pedersen is obtained. It is shown that the complete concentration dependence of the swelling pressure in the concentration range of the maximally swollen gel up to that at the cell bottom can be measured in a single equilibrium experiment. The homogeneity of weakly cross‐linked gels can be examined by means of the method described. Soluble parts which are not incorporated into the polymer network can also be detected if they are present. From the swelling pressure‐concentration curves it is possible to derive the thermodynamic properties of the physically crosslinked gelatin/water gels that were investigated. These gels can be described by means of a slightly modified Flory‐Huggins equation with an interaction parameter χw in the weight fraction scale, which depends linearly on concentration. The interaction parameters show a dependence on concentration which is explained by an increased branching and crosslinking of the polymer with increasing initial polymer concentration of the gels. At low initial polymer concentration, the primary chains have to aggregate to build up relatively long chains between the network junctions. The static shear modulus G which can be calculated from the network term has the same order of magnitude as the real part of the complex shear modulus which is measured at low frequency.
Characterization of polysaccharide solutions by means of chromatography‐multidetection
Authors: Huber Anton 
Published: March 2011

AbstractSize exclusion chromatography (SEC) combined with double detection, utilizing a differential refractive index (DRI)‐ and a low angle laser light scattering (LALLS) ‐ detector represents a powerful experimental set‐up in the field of chromatography‐multidetection (C‐MD). By means of these techniques high‐quality information for profound polymer characterization is provided in a fast and semi‐automatical (autosampler/PC‐controlled) way. Molecular characteristics such as molecular weight distributions, molecular weight averages, tendencies for intermolecular interactions, can be obtained by these techniques. Successful handling of data from C‐MD‐techniques within reasonable time ranges requires adequate hardware and software. This is especially true if advanced data processing is applied, e.g. to yield polymer particle size/shape characteristics in terms of Staudinger/Mark/Houwink constants (K,a), distributions of sphere equivalent particle radii (RcD)‐, sphere equivalent mass density of solved polymer coils (ρcD)‐ and intrinsic viscosity ([η]D). For aqueous solutions of polysaccharide samples (waxy maize starch hydrolyzate, hydroxyethyl‐amylopectin from waxy maize hydrolyzate, dextran) data from SEC‐DRI/LALLS and universal calibration experiments are utilized for a comprehensive physico‐chemical characterization of these polymers.