bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polypyridine‐based catalysts: Epoxidation of olefins with supported peroxotungstic complexes
Authors: Gelbard Georges , Breton François , Charreyre Marie‐Thérèse , Dong Doan 
Published: March 2011

AbstractEpoxidation of cyclohexene with hydrogen peroxide was performed with tungsten‐based catalysts in the form of polymer supported pyridinium peroxotungstate salts and betaines. These catalysts were obtained from copolymers of 4‐vinylpyridine and divinylbenzene or from aminomethylpyridines alkylated with chloromethylpolystyrene. The free bases and the corresponding N‐oxides were reacted with peroxotungstic acid to give the catalytic species.
Thermal characterization of macromolecular metal complexes of mo(VI) as heterogeneous oxidation catalysts
Authors: Ferruti P. , Ranucci E. , Tempesti E. , Casolaro Mario 
Published: March 2011

AbstractTwo multifunctional carboxylic resins were synthesized and characterized in terms of their CO2H content. The thermal stability of the resins was investigated by DTA and TG analysis before and after Mo(VI) complexation. Simultaneous IR analyses at various stages of the heating processes were also performed.
Structure and properties of superconducting and nonsuperconducting alkali‐metal fullerides axc60 (A = Na, K, Rb, or Cs)
Authors: Wiley John B. , Huang Shiou‐Mei , Cho Shinho , Diederich François , Whetten Robert L. , Holczer Károly , Kaner Richard B. 
Published: March 2011

AbstractShielding diamagnetism and X‐ray powder diffraction were used to characterize alkali‐metal fullerides of sodium, potassium, rubidium, and cesium. The superconducting phase in both the potassium and rubidium systems has the composition A3C60 and a face centered cubic structure with alkali metal filling all octahedral and tetrahedral sites of close packed C60, layers. High pressure magnetic susceptibility measurements on K3C60 showed a negative pressure dependence on the superconducting transition temperature of −0.78 K/kbar. No evidence for superconductivity was observed in either the sodium or cesium systems, even though Na3C60 appears isostructural with K3C60 and Rb3C60.
Tailored macromolecules by living carbocationic techniques
Authors: Kennedy Joseph P. 
Published: March 2011

AbstractThis presentation concerns our latest results for the controlled synthesis of various homopolymers, blocks, random copolymers, networks, by living carbocationic polymerization (LC⊕ Pzn). We start with an analysis of the Winstein ionicity spectrum, a roadsign toward LC⊕ Pzn systems. Living isobutylene (IB) homopolymerization can be effected by the addition of common anion salts to conventional polymerization charges, e.g., by adding nBu4NCl to a 2‐chloro‐2,4,4‐trimethylpentane (TMPCl)/TiCl4/IB system. Various AB diblocks have been prepared by sequential monomer addition. The first clean svnthesis of an AB poly(olefin‐b‐alkyl vinyl ether) diblock, ie., poly(isobutylene‐b‐methyl vinyl ether), by sequential monomer addition was accomplished. These novel amphiphilic diblocks promise to be excellent nonionic detergents. The field of linear A‐B‐A triblocks and three‐arm star blocks where A = glassy and B = rubbery (polyisobutylene) segment, is vigorously expanding. Several new thermoplastic elastomers (TPEs) have been prepared, characterized and tested, e.g., poly‐(indene‐b‐isobutylene‐b‐indene). The synthesis of random copolymers, e.g., isobutylene/2,4,4‐dimethyl‐1,3‐pentadiene, by living reactivity leveling has been demonstrated. Transformation of the polyisobutylene cations PIB⊕ and ⊕PIB⊕ yielded the corresponding anions PIB⊖ and ⊖PIB⊖, which upon block polymerization of butadiene (Bd) and methyl methacrylate (MMA), respectively, gave rise to the new diblock PIB‐PBd and triblock PMMA‐PIB‐PMMA. In the latter, the largely syndiotactic sPMMA endblocks were stereocomplexed with isotactic iPMMA and thus the upper use‐temperature of these novel TPEs was enhanced. Novel amphiphilic networks comprising hydrophilic polymethacrylates (e.g., dimethylaminoethyl methacrylate (DMAEMA) or hydroxyethyl methacrylate (HEMA)) crosslinked by methacrylate‐telechelic PIBs were prepared and their potential usefulness for biomedical applications has been studied.
The carbenium ion ‐ oxonium ion exchange processes related to vinyl and ring‐opening polymerization
Authors: Penczek Stanislaw , Szymanski Ryszard 
Published: March 2011

AbstractIt has previously been proposed (Ref. 1) that in the cationic vinyl polymerizations, proceeding with termination due to the collapse of ion pairs, addition of bases increases “livingness”, because of the fast convertion of the otherwise dead (within the time of polymerization) covalent species into the onium ions; these, in turn, fast convert into carbenium ions, the actually propagating species.Equilibria between carbenium ions (CH3OCH2+A− has been used as a model) and their onium counterparts ((CH3)2O taken as a model base) as well as between covalent species (CH3OCH2OSO2CF3) and the corresponding oxonium ion (with a (CH3)2O ligand) have been studied by dynamic 1H and 19F NMR. Total ionization of methoxymethyl triflate (CH3OCH2OSO2CF3) has been shown to increase indeed from 104 (‐10°C) to 106 (‐70°C) times when 1,0 mol·L−1 of (CH3)2O is added.Although this model system better describes polymerization of cyclic acetals than that of vinyl ethers, it shows at least qualitatively the importance of bases in ionization of covalent species, which may be responsible for reinitiation in the cationic polymerization of vinyl ethers.
Synthesis of functionalized poly(1,3‐dioxolane)
Authors: Franta E. , Kubisa P. , Kada S. Ould , Reibel L. 
Published: March 2011

AbstractClassical initiation induces polymerization through cyclic tertiary oxonium ions which are responsible for the formation of an important quantity of cyclic oligomers. The activated monomer mechanism, i.e. polymerization in the presence of a diol, has been successful in the case of some substituted oxiranes such as epichlorohydrine and propylene oxide. It has also been used in the case of cyclic acetals [1,3‐dioxolane (DXL) and 1,3‐dioxepane (DXP)] and allows the preparation of dihydroxylated homopolymers as well as that of triblock copolymers. It was nevertheless shown that transacetalization leads to complications at the onset of the reaction. In order to shed some light on the reactions involved, we used a monoalcohol ‐ methanol ‐ instead of a diol. The products were separated and characterized: a monoadduct (methanol‐DXL) was observed, confirming the occurence of the active monomer mechanism, but dimethoxymethane was also observed, evidence of transacetalization between methanol and DXL. It was shown that fast equilibration takes place between the following compounds: (methanol + DXL), (monoadduct of methanol and DXL), (dimethoxymethane + ethyleneglycol).When p‐isopropenylbenzyl alcohol was used, it was possible to prepare macromonomers, i.e. poly(DXL) chains carrying polymerizable double bonds at their ends. Nevertheless because of the transacetalization reaction described above, a mixture of products was obtained.
Furan chemistry and ionic polymerization: Mechanisms and structures
Authors: Gandini Alessandro , Salon Marie Christine , Choura Mekki , El Gharbi Rachid , Amri Hilmi , Hui Zuen 
Published: March 2011

AbstractThe polymerization of furanic monomers using cationic and anionic initiators often leads to peculiar responses due to the specific chemistry of the heterocycle. The understanding of these mechanisms can help minimizing the problems encountered or, better still, exploiting them to synthesize novel macromolecular structures. The examples given here comprise the preparation of block copolymers and functionalized, polyconjugated or telechelic oligomers, the investigation of colour‐forming and branching reactions and the elaboration of powerful Lewis‐base resins.
Cationic polymerization of ϵ‐caprolactone in the presence of diols via activated monomer mechanism
Authors: Rozenberg B. A. 
Published: March 2011

AbstractThe kinetics of noncatalytic and catalytic interaction of ϵ‐caprolactone (ϵ‐CL) with a variety of diols in the presence of onium‐type catalysts as well as the resulting products structure were investigated. The phenomenon of the direction change of the lactone ring opening during the interaction with hydroxyl‐containing compounds of different functionality was discovered. The features of the reactions investigated were discussed and their kinetic parameters were determined.
Copolymerization of β‐butyrolactone and β‐benzyl malolactone with aluminoxane catalysts
Authors: Zhang Yan , Lenz Robert W. 
Published: March 2011

AbstractPoly (β‐hydroxylbutyrate‐co‐benzyl β‐malolactonate), (P‐HB‐co‐BML) copolymers, were prepared by the ring‐opening copolymerizations of β‐butyrolactone (BL) and benzyl β‐malolactone (BML) with several alkyl aluminoxane catalysts, including ethylaluminoxane (EAO), methylaluminoxane (MAO), and isobutylaluminoxane (IBAO). The copolymers had very broad molecular weight distributions with weight average molecular weights, M̄w, greater than 200,000. The products were fractionated by solubility into acetone‐soluble and insoluble copolymers. The former were random, atactic copolymers while the latter were stereoblock copolymers. Random, atactic copolyesters of these two monomers were also obtained with the diethylzinc‐water, ZnEt2‐H2O (0.6:1), and the (5,10,15,20‐tetraphenylporphinato)aluminium chloride, TPPAlCl, catalysts. The copolymerization reactions with the latter two catalysts gave much higher yields (up to 98%) and better control of both the copolymer compositions and the molecular weight distributions, but these copolymers had M̄w values of only 20,000 or less. The copolymer tacticities and comonomer sequences were determined by 13C NMR spectroscopy.
Anionic polymerization of arylbismuth, lead and tin derivatives of styrene and α‐methylstyrene
Authors: Ignatious Francis , Delaviz Yadollah , Cabasso Israel , Smid Johannes 
Published: March 2011

AbstractStyryl‐ and α‐methylstyryldiphenylbismuth (I and II, respectively), and styryl and α‐methylstyryltriphenyllead and the two corresponding tin‐containing monomers (III, IV, V and VI, respectively) were synthesized. Compounds III through VI were obtained pure, but I and II contain substantial quantities of Ph3Bi and di‐ and tri‐vinyl derivatives. Homopolymers of I, III and V, as well as copolymers with methyl acrylate were synthesized radically. Monomers III, V, and VI yielded narrow MWD polymers with anionic initiators such as the potassium salt of the α‐methylstyrene dimer carbanion in THF at −80°C, while I gave a broad, bimodal MWD. Monomers II and IV did not polymerize under these conditions due to side reactions with the initiator. Glass transition temperatures, thermal stabilities and radiopacities of a number of the polymers were determined.
Functionalization during anionic polymerization of heterocycles
Authors: Kazanskii Konstantin 
Published: March 2011

AbstractGeneral approaches to the synthesis of functional polymers based on heterocycles are considered. Most attention is paid to the living anionic polymerization with functionalization through initiation or deactivation. It is shown that demands of both high molecular weight and quantitative functionalization cannot be completely satisfied. Some examples of preparing functional polyethers and polyesters are given, namely dinitrophenyl derivatives and vinyl ether macromonomers of poly(ethylene oxide) as well as methacrylate macromonomers of β‐propiolactone. Some of perspective applications of these polymers are also touched upon.
Active centre structure and the stereoregulation process in anionic polymerization
Authors: Bywater Stanley 
Published: March 2011

AbstractThe mechanism of stereoregulation in the anionic polymerization of butadiene and isoprene is discussed in terms of what is known about the structure of the active centres. This includes the effect of the presence of cis and trans isomers and the dynamics of their interconversion and in the isoprene case, the effect of two distinct types having 1,4 and 4,1 structures.
Quasielastic light scattering as a method for determining the distribution of relaxation times in a polymer system
Authors: Burchard Walther , Lang Peter , Bauer Jörg 
Published: March 2011

AbstractAmongst other techniques, dynamic light scattering may be used to obtain molar mass distributions. The first step in this process consists in the Laplace inversion of the time correlation function that was measured by dynamic light scattering. This inversion gives a distribution of diffusion coefficients. In order to convert this distribution into the corresponding molar mass distribution, a relationship between diffusion coefficient and molar mass of monodisperse fractions has to be known. Such a relationship can be derived for linear and star‐branched macromolecules from measurements of polydisperse systems, since the polydispersity of the distributions does not change with the molar mass. The problem is more involved with randomly branched materials, since in these cases the polydispersity increases strongly as the point of gelation is approached. A procedure is suggested for deriving the diffusion‐molar mass dependence of monodisperse samples from polydisperse systems.After an outline of this background the method is applied to the three selected systems (i) radically polymerized linear PMMA, (ii) a star‐branched microgel where monodisperse arms are attached to a microgel center and (iii) a randomly branched poly(dicyanate) sample based on bisphenol A. The results are compared with the combined column chromatography SEC/LALLS/VISC. Good agreement was found up to molar masses of about 10 millions g/mol, but systematic deviations occured in the high molar mass region. These differences result from the limitations of size permeation chromatography. Finally it is shown that the size distribution can be determind by this method, even for associates.
Dynamic light scattering for characterization of latices
Authors: Killmann Erwin , Sapuntzjis Perikles , Maier Herbert 
Published: March 2011

AbstractWith photon correlation spectrometry the diffusion coefficients of colloid particles in highly diluted aqueous suspensions can be measured and average diameters and polydispersities of the samples can be determined. Electrokinetic and electroviscous effects caused by polarization of the electrostatic double layer influence the diffusion of the particles. The adsorption of macromolecules at the interfaces of the particles results in an increase of the hydrodynamic diameter and a decrease of the diffusion and sedimentation coefficients. The hydrodynamic thicknesses of the polymer layers can be evaluated. The thickness values and their dependences on adsorbed amount and molar mass can only be interpreted by the existence of long tails of the adsorbed macromolecules dangling from the interface into the solution. The resulting conformation model is supported by the new theory of Scheutjens‐Fleer. Special importance have those tails for the interaction of particles and their stability and flocculation in disperse systems.
Characterization of ultrahigh molar mass, water‐soluble, cationic polyelectrolytes
Authors: Kulicke W.‐M. , Jacobs A. 
Published: March 2011

AbstractFour different cationic polyelectrolytes were investigated, which are used as flocculating agents in the dewatering of sediments from Hamburg harbour. The chemical structures of these polyelectrolytes were characterized by means of IR and 13C NMR spectroscopy. The substances concerned are the two copolymers of acrylamide formed with acrylate and methacrylate esters, and the homopolymers of these esters. The charge density was determined with the aid of titrimetric methods and quantitative evaluation of IGATED 13C NMR spectra. Determination of the molar mass and steric characterization were carried out by multi‐angle laser light scattering. In order to resolve the experimental problems which arise especially during light scattering in water‐soluble cationic systems, a special method of sample preparation has been devised to remove impurities, which will be described in detail. This method involves the combination of filtration and ultracentrifugation. Evaluation of the light scattering data provided the values for the molar mass Mw′ the second virial coefficient A2 and the radius of gyration <R2G>0,5Z, which also gives information about the solution structure. By comparing the curve of the scattering function extrapolated to zero concentration with model curves and with the aid of the a exponent of the [η]‐M‐relationship, it can be seen that the polyelectrolyte has a highly expanded coil structure in salt solution. This can be primarily attributed to the steric influence of the side groups.
Counterion binding by poly(styrenesulfonate)
Authors: Nordmeier Eckhard 
Published: March 2011

AbstractBinding isotherms of poly(styrenesulfonate) with hydrogen and selected alkali ions have been determined by dialysis equilibrium and dye spectroscopy, employing Pb2+, Mg2+, and Ca2+ as the competing divalent ions. The observed degrees of counterion binding, Θz, defined as the number of bound counterfoils of valence z per poly ion site‐group, agree quite well with those predicted by Manning's two variable theory. The binding preference follows the order Cs+ > Rb+ > K+ > Na+ > H+ >Li+, indicating that the binding process is of a territorial nature. Independently performed light scattering measurements show that a plot of the radius of gyration, >S z>, against the actual polyion charge gives a sigmoidal curve. This result is taken to indicate that (1) a polyion is, in general, not completely neutralized in the Θ‐state and that (2) a polyion may be not fully stretched when the polyion charge density is largest.
Characterization of star polymers in solution by small angle neutron scattering
Authors: Willner L. , Jucknischke O. , Richter D. , Fetters L.J. , Huang J.S. , Farago B. 
Published: March 2011

AbstractIn this paper we present the small angle neutron scattering characterization of two polyisoprene and one poly(ethylenepropylene) star polymers in solution. In the limit of low scattering vector, Q, and low concentration, φ, the molecular characteristics were determined. The molecular weights obtained are in good agreement with light scattering data. Deviations in second virial coefficients are due to a difference in solvent quality. Radii of gyration of the stars are well determined by the use of Kratky plots as is shown by the good agreement with average values of Zimm and Guinier analysis. Additionally, some thermodynamic properties were investigated in dilute and semidilute solutions. We have found that the concentration dependence of the osmotic compressibility is influenced by an expected step at the overlap concentration in both concentration regions.
Modern methods for determining the molar mass distribution of polymers. General considerations and application to sedimentation equilibrium
Authors: Lechner M. Dieter , Mächtle Walter 
Published: March 2011

AbstractA new procedure for the determination of the molar mass means Mn, Mw and Mz and of the molar mass distribution W(M) = f(M) of polymers is proposed and applied on measurements of the sedimentation equilibrium. The procedure includes the extrapolation of the experimentally determined polydisperse measurable quantity at different concentrations to zero concentration. From these values the molar mass distribution is calculated by nonlinear least squares routines of the integral equation. This method of calculation is, contrary to the inverse transformation of the integral equation, which has been used up to now, well conditioned and stable.The proposed method has been applied to sedimentation equilibrium. In this case the reduced concentration profiles (interference optic, absorption optic) or reduced concentration gradient profiles (schlieren optic) measured at different concentrations must be extrapolated to zero concentration and followed by nonlinear regression of the integral equation Uw(X) = ∫ W(M) U(X,M) dM. Measurements on polystyrenes with different polydispersities and modalities (e.g. bimodal molar mass distributions), and on the polyelectrolytes sodium polystyrene sulfonate and polyethylene imine exhibit resonable results. The result of the investigation is, that the proposed procedure is a suitable and reasonable possibility for the determination of molar mass distribution of polymers by sedimentation equilibrium. For polyelectrolytes in particular this method is better than gel permeation or size exclusion chromatography.
Determination of molar mass distributions of poly(methacrylates) in the analytical ultracentrifuge with schlieren and UV optics
Authors: Ortlepp Bernhard , Panke Dietrich 
Published: March 2011

AbstractThe significance of the analytical ultracentrifuge (AUC) for industrial research has not decreased during the last decades and seems to be growing. The AUC is used for the development and for controlling the production of emulsion polymers (via measurement of particle size distributions) as well as for the determination of molar masses and molar mass distributions of polymers which cause difficulties with conventional methods like light scattering or size exclusion chromatography.In order to speed up the principally very time‐consuming AUC measurements, our machines were equipped with multiplexers for multiple place rotors and with video systems for digital recording and processing of the schlieren images. Furthermore for measurements with the UV scanner the optical system had to be considerably improved in order to assess wavelengths down to 210 nm because of the unfavourable UV absorption of the poly(methacrylates).The experimental methods and the data evaluation will be explained and discussed using a very high‐molecular‐weight poly(methylmethacrylate) and a cationic polyelectrolyte, viz. poly(trimethylammoniumethylmethacrylate hydrochloride), as examples.
Characterization of polyelectrolyte solutions by analytical ultracentrifugation
Authors: Ebert G. 
Published: March 2011

AbstractIn this paper some applications of ultracentrifugation on characterizing cationic polypeptides are reviewed. Especially the influence of α‐helix favoring, water‐structure breaking (chaotropic) anions (e.g. ClO4−) as well as that of strongly hydrated, water structure‐making anions (e.g. sulfate) on the sedimentation behaviour of (Lys)n and (Arg)n is considered. Moreover ultracentrifuge studies on the interaction between DNA and strong basic nucleoproteins (protamines) and on the solubilisation of the basic polypeptides mentioned before in reverse micelles are presented.
Molar‐mass distribution of celluloses
Authors: Saake Bodo , Patt Rudolf , Puis Jürgen , Linow K.‐J. , Philipp Burkhard 
Published: March 2011

AbstractThe investigation of polymers by gel permeation chromatography has become a standard method for the determination of the molecular weight distribution. In case of cellulose and pulps the samples are mostly carbanilated or nitrated in order to get them soluble in organic solvents. In this context it is important that the derivatives obtained represent the composition of the starting material. High molecular wood pulps were carbanilated and further prepared for chromatographic separation using different methods. For bleached and unbleached pulps, the influence of the refining conditions on the molecular weight distribution and on the percentage of the soluble portion of the derivatives was investigated. It could be shown that low‐molecular portions of the cellulose samples were lost applying those refining methods which included precipitation steps. For unbleached pulps, the risk existed that part of the derivatives remained insoluble and formed gel‐like particles. For some pulp samples better results could be obtained by elongation of the derivatization time. Some selected pulps were carbanilated and nitrated, and the corresponding results were compared.