bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ligand‐exchange chromatography of racemates, 9. Ligand‐exchange chromatography of amino acid enantiomers on asymmetric sorbents with polydentate sulfur containing groupings
Authors: Yamskov Igor A. , Berezin Boris B. , Davankov Vadim A. 
Published: April 2003

AbstractThe paper describes the syntheses of four asymmetric sorbents, which contain S‐(2‐aminoethyl)‐L‐cysteine (1a), S‐(carboxymethyl)‐L‐cysteine (1c), S,S′‐(ethylene)‐bis(L‐cysteine) (2a), and N,N′‐(ethylene)‐bis(D‐methionine) (3a) groupings as the chiral fixed ligands in a cross‐linked polystyrene matrix. The sorbents were used for ligand‐exchange chromatography of amino acid enantiomers in the presence of Cu(II) and Ni(II) ions. Enantioselective effects in the formation of mixed‐ligand complexes consisting of a fixed ligand, a metal ion, and an amino acid enantiomer were determined. The highest values of enantioselectivity reaching 1 300 to 1 890J/mol were found in mixed‐ligand complexes containing histidine or β‐phenyl‐α‐alanine.
Solution properties and unperturbed dimensions of poly(pentachlorophenyl methacrylate)
Authors: Becerra Melvyn , Radic Deodato , Gargallo Ligia 
Published: April 2003

AbstractThe properties of dilute solutions of poly(pentachlorophenyl methacrylate) in various solvents are studied by measurements of viscosity and osmotic pressure.The unperturbed dimensions are determined in two Θ‐solvents: benzene at 40°C, ethylbenzene at 25°C, and several other solvents such as toluene, chlorobenzene, o‐xylene and o‐dichlorobenzene at 25°C.The results show a variation of the unperturbed dimensions with the solvent nature in good solvents. The flexibility factor, σ, calculated on the basis on the unperturbed dimensions in a Θ‐solvent and the dimensions of a freely rotating chain is higher than that of other polymethacrylates with chlorinated aromatic side groups. The polymer‐solvent interactions are discussed in relation to some other polymethacrylates.
Temperature changes of poly(oxymethylene) structures studied by infrared spectroscopy
Authors: Terlemezyan Levon , Mihailov Marin , Schmidt Pavel , Schneider Bohdan 
Published: April 2003

AbstractTemperature changes of infrared spectra of poly(oxymethylene) samples in the hexagonal crystalline form were measured; in the nascent state, these samples contained either long (type A) or short (type B) sequences of monomeric units in the G conformation. It was found that up to the temperature of “solid crystal‐plastic crystal” transition, the original structure of both types remains essentially unchanged. Only in the melt the original structure is completely destroyed. The composition of the melt is the same for both cases.
Polymeric phospholipid analogs, 11. Synthesis and polymerization of 2‐aminoethyl 2‐(p‐methacryloyloxybenzoyloxy)ethyl hydrogen phosphate
Authors: Nakai Shiro , Nakaya Tadao , Imoto Minoru 
Published: April 2003

AbstractThe preparation and characterization of 2‐aminoethyl 2‐(p‐methacryloyloxybenzoyloxy)ethyl hydrogen phosphate (7) are described. This monomer was polymerized with 2,2′‐azoisobutyronitrile (AIBN) and the properties of the resultant polymer are described.
Circular dichroism of poly{γ‐[2‐(9‐carbazolyl)ethyl] L‐glutamate} in dilute solution and in solid state
Authors: Yoshikawa Masao , Nomori Hiroiyuki , Hatano Masahiro 
Published: April 2003

AbstractCircular dichroism (CD) and ultraviolet absorption (UV) spectra were measured for poly{γ‐[2‐(9‐carbazolyl)ethyl] L‐glutamate} (PCLG), whose side chain chromophore has three π – π* transitions in a wavelength region not overlapping with the n – π* transition of the main chain peptide group. For the dilute solution in any given helicogenic solvent, the observed CD sign had a good correlation to the polarization direction of the π – π* transitions. On the other hand, a concentrated solution with a concentration of ca. 15 wt.‐% was found to form a liquid crystalline phase, which was probably nematic at room temperature. The CD spectral profiles of the cast film of the polypeptide were quite different from that of the dilute solution. Origins of the optical activity are discussed.
Cationic polymerization of anethole by triphenylmethyl hexafluoroantimonate
Authors: Rooney John M. 
Published: April 2003

AbstractCationic polymerizations of anethole in methylene dichloride initiated by triphenylmethyl hexafluoroantimonate were studied by dilatometry and UV‐visible spectroscopy at temperatures between 0 and 35°C. Initiator consumption continued throughout polymerization, reaching 85–95%. Monomer conversion ranged from 75 to 98%. Reaction half‐lives were on the order of 15 to 60 min at 25°C. Polymer molecular weights were bimodal with some evidence of branching and cross‐linking. The principal termination reaction appeared to involve formation of a chromophore absorbing at 501 nm. Rate constants on the order of 10−3 dm3·mol−1·s−1 for initiation and 1 dm3·mol−1·s−1 for propagation at 25°C were estimated.
Zur theoretischen deutung der temperaturabhängigkeit der relaxationszeiten von polymeren
Authors: Havlíček Ivan , Vojta Vladimír , Kästner Siegfried , Schlosser Eckard 
Published: April 2003

AbstractThe free volume theory of Cohen and Turnbull, the results of which are identical with the empirical relationship of Williams, Landel and Ferry (WLF), was compared with the theory of conformational entropy of Adam and Gibbs (AG) using experimental results of measurements of the temperature dependence of the relaxation times of poly(vinyl acetate). In spite of being different in their mathematical form, both theories were found to describe the experiment with similar adequacy. A procedure was also suggested permitting to obtain the AG parameters if the WLF parameters are known. The procedure was applied to 59 compounds, the WLF parameters of which were found in the literature. The results are tabulated.
Temperature effect of 1H NMR chemical shifts of poly(vinyl chloride)
Authors: Ando Isao 
Published: April 2003

AbstractThe 1H NMR chemical shift difference of the CH2 protons of meso and racemic dyads in poly(vinyl chloride) was measured as a function of temperature and was found to decrease linearly with increasing temperature. On the other hand, the temperature dependence of the chemical shift difference was calculated by taking into account the statistical weights of the preferred conformations of any specified stereochemical configuration. The experimental behavior could be verified by this calculation by considering the four‐bond interaction.
Conformational studies on polypeptides containing L‐alanine and ω‐amino acids
Authors: Pra Antonio Del , Spadon Paola , Boni Renzo , Bonora Gian Maria , Scatturin Angelo 
Published: April 2003

AbstractThe synthesis and the conformational studies of the following sequential polypeptides are reported: poly(alanyl‐3‐aminopropanoic acid), poly(alanyl‐4‐aminobutanoic acid), poly(alanyl‐5‐aminopentanoic acid), and poly(alanyl‐6‐aminohexanoic acid). These compounds were examined in the solid state by X‐ray diffraction and in solution by circular dichroism spectroscopy. X‐ray diffraction patterns indicate that all copolymers assume an antiparallel pleated‐sheet conformation. The results in solution suggest that the synthetic polypeptides, in 2,2,2‐trifluoroethanol (TFE)/methanol exhibit a β‐conformation. The addition of water to a solution of copolymers in TFE destabilize this ordered structure except in the case of poly(alanyl‐6‐aminohexanoic acid).
Über die Eigenschaften einiger wasserlöslicher Azo‐Initiatoren
Authors: Nuyken Oskar , Kerber Robert 
Published: April 2003

AbstractWater soluble azo compounds of the structure 1a, b, 2a, b, 3, 4, and 5 decompose, depending on the substitution of the aromatic ring, in water already at room temperature. Therefore, they are useful initiators for solution and emulsion polymerisations in this temperature region. Reactions competing with thermolysis, as the formation of a hydrazone (pH>8) and ionic reactions with suitable reagents (phenols) are described.
Anthracene sensitized photooxidation of polystyrene, 1. Photochemical reactivity of anthracene in hexane solution
Authors: Nowakowska Maria 
Published: April 2003

AbstractThe photochemical reactivity of anthracene in hexane solution was investigated. A kinetic scheme of photochemical and photophysical processes occurring in the system irradiated with light at λ = 365 nm was proposed. The quantum yield of singlet oxygen generation in the system was estimated.
Absorption and luminescence spectra of halogen derivatives of poly(N‐vinylcarbazole)
Authors: Janowski Andrzej , Rzeszotarska Jadwiga , Pielichowski Jan , Ranachowski Jerzy 
Published: April 2003

AbstractAbsorption and luminescence spectra of halogen derivatives of poly(N‐vinylcarbazole) have been investigated in solution and solid films. The emission spectra in solution exhibit excimer phosphorescence only, whereas solid film spectra show excimer fluorescence only. Changes in the character of emission spectra on passing from solution to solid film are discussed.
Polymérisation et copolymérisation d'acétoxy‐2 alcadiènes‐1,3 – l'acétate de (cyclopentène‐1 yle)‐1 vinyle et l'acétate de (méthyl‐3 butadiène‐1,3) yle‐ 2 – formation des polycétones correspondantes
Authors: Bonnans‐Plaisance Chantal , Casals Pierre‐François , Levesque Guy 
Published: April 2003

AbstractThe polymerization of 1‐(1‐cyclopentenyl)vinyl acetate (1) and (3‐methyl‐1,3‐butadien‐2‐yl) acetate (7) under radical conditions, leading to 1,4‐polymers, and the copolymerization with vinyl monomers were studied. The reactivity ratios are compared with those previously described for some acetoxydienes. Polyketones and copolyketones were obtained by alkaline hydrolysis of the polymers of 1 and 7 and copolymers of 1 and 7 with styrene.
Synthèse et caractérisation de copolymères coordinés par des sels métalliques
Authors: Rietsch François , Bottiglione Vincent , Morcellet Joëlle 
Published: April 2003

AbstractThe anionic block copolymerisation of isoprene and 2‐vinylpyridine (2VP) followed by a coordination with iron (III) chloride, leads to thermoreversibly crosslinked copolymers. These copolymers are character+ed by a low polydispersity (M̄w/M̄w≈1,1) between the coordination nodules of poly(2‐vinylpyridine). The study of the swelling ratio at the equilibrium in benzene shows that such a polymeric network does not reach the equilibrium state expected from the thermodynamic analysis of the system. The presence of 2VP in the copolymer induces a screening effect which prevents the solvent diffusion through the polyisoprene network.
Influence of the nature of the blocks on the ordered structures of block copolymers
Authors: Douy André , Gallot Bernard 
Published: April 2003

AbstractThe structure of AB block copolymers with a polydiene block (polybutadiene or polyisoprene) and another block (polystyrene, poly(α‐methylstyrene)), poly(2‐vinylnaphthalene), poly(2‐vinylpyridine) or poly(4‐vinylpyridine) was studied by low angle X‐ray diffraction and electron microscopy. The influence of the nature of the non‐diene block (styrene, α‐methylstyrene, 2‐vinylnaphthalene), the nature and the microstructure of the diene block and the isomery of the vinylpyridine block on the parameters of the lamellar structure and the conformation of the macromolecular chains was established.
Polybutadiènes hydroxytéléchéliques, 2 Microstructure et fonctionnalité des polyméres obtenus par voie anionique. Etude par résonance magnétique nucléaire du proton et du carbon 13
Authors: Camberlin Yves , Pascault Jean Pierre , Pham Quang Tho 
Published: April 2003

AbstractThe examination, by 1H NMR, of anionic hydroxytelechelic polybutadienes in conjunction with accurately measured Mn values allows the simultaneous determination of the number average functionality and the identification of the nature of the chain ends bearing the functional groups. The microstructure of the polymer chains has been studied by 13C NMR. A high proportion of isolated vinyl units has been found only if the percentage of vinyl is less than 70%, whereas the vinyl sequences are atactic. During the functionalization, if lithium is utilized as catalyst, only one molecule of ethylene oxide is added at each end of the polymer chain. With potassium, ethylene oxide polymerizes. Owing to the chain ends, reaction mechanisms of the addition of ethylene oxide onto the living polymer have been proposed.
Formaldehyde polymers, 25. Copolymerization of 6,8‐dimethyl‐4‐oxo‐5‐chromanylmethyl acrylate with styrene, methyl methacrylate, and vinyl chloride
Authors: Ninagawa Akira , Tokunaga Yukio , Matsuda Haruo 
Published: April 2003

AbstractThe free radical copolymerizations of 6,8‐dimethyl‐4‐oxo‐5‐chromanylmethyl acrylate (DCA) with styrene (St), methyl methacrylate (MMA), and vinyl chloride (VC) by the solution polymerization method were studied. For copolymerization of DCA(M1) with St(M2), the reactivity ratios were r1=0,32, r2=0,70; with MMA(M2) they were r1=0,43, r2=2,00; and with VC(M2) they were r1=4,00, r2=0,08. The Q and e values for DCA were 0,54 and 0,42, respectively. It was also shown that the chromanone skeleton acts as UV‐absorber, and inhibits photodegradation of the copolymers.
Radical copolymerisation of vinylidene chloride and methacrylonitrile, 2. Sequence microstructure measured by 13C NMR
Authors: Suggate John R. 
Published: April 2003

AbstractThe radical copolymerisation of vinylidene chloride and methacrylonitrile (M) was studied in bulk, in cyclohexanone, in DMF, and in hexane. From 13C NMR spectra of the copolymers, the dyad and triad monomer sequences and some tetrad and pentad sequences were obtained. Copolymerisation in homogeneous solution showed no dependence on the solvent used (DMF and cyclohexanone). The heterogeneous bulk copolymerisation kinetics were very similar to those of copolymerisation in homogeneous solution, but significantly different from heterogeneous copolymerisation in hexane. The triad sequence distributions could be shown to fit a kinetic scheme incorporating penultimate effects on radical reactivities for copolymerisation from vinylidene chloride rich feeds. However, for copolymerisations from methacrylonitrile rich feeds this model fails because of a dependence upon monomer feed of the reactivity ratio for the ∼︁MM· radical; this might possibly be explained by the involvement of a monomer‐monomer charge‐transfer complex in the copolymerisation.
Kinetische und morphologische untersuchungen zur polymerisation von oxacyclischen monomeren im festen zustand, 5. Zur morphologie der während der sublimation von trioxan‐ und tetroxankristallen wachsenden polyoxymethylene
Authors: Muñoz‐Escalona Antonio 
Published: April 2003

AbstractThe polymerization and crystallization of polyoxymethylene obtained by sublimation of trioxane (1,3,5‐trioxane) and tetroxane (1,3,5,7‐tetroxocane) crystals was investigated. Electron microscopy techniques and thermal analysis were used to characterize the polymer crystals as produced and after annealing. The polyoxymethylene crystals resulting from tetroxane show a regular lamellar folded chain macroconformation similar to those previously reported by polymerization of tetroxane crystals chemically initiated. The polymerization follows a crystallization succeeding polymerization mechanism. Trioxane gives mainly fibrous crystals, showing well oriented electron diffraction diagrams and higher melting points, consisting mostly of extended chains. A “pseudolamellar” morphology was also observed, being established by annealing, that the chain directions are parallel to the edges of the crystals. The strange growing habit seems to be produced by disruption of the electrical field of the trioxane crystals by a water effect. The polymerization seems to follow mainly a simultaneous polymerization and crystallization mechanism. The initiation of the polymerization is in both cases due to the gaseous formaldehyde formed during sublimation.
On the copolymerization of acrylonitrile with styrene in the presence of Lewis acid, 2. Regulation of molecular weight
Authors: Bartoň Jaroslav , Werner Peter 
Published: April 2003

AbstractThe results of the study of the acrylonitrile (AN)‐sytrene (St) copolymerization in the presence of zinc chloride and various hydrogen donors (cyclohexane, octane, isooctane, and decahydronaphthalene) are reported. It was found that the rate of copolymerization (Rp) increases with concentration of the hydrogen donor at constant concentrations of comonomers in acetone in the presence as well as in the absence of a free‐radical source (AIBN). The dependence of the reciprocal value of limiting viscosity number (1/[η]) of the equimolar copolymers on Rp in the system StANZnCl2AIBN is not linear. The position of the minimum on this curve at a given ratio of comonomers depends on the concentration of both zinc chloride and AIBN. The reduction of [η] of the equimolar copolymer attained by the effect of hydrocarbon is relatively small provided the reaction system is homogeneous. On the basis of the results obtained, it may be stated that a change in molecular weight of the copolymer is to be achieved more easily by a change in the rate of copolymerization (effected by AIBN) than by the effect of hydrogen donor (chain transfer).
The terpolymerisation of styrene, methyl methacrylate and maleic anhydride
Authors: Dodgson Keith , Ebdon John R. 
Published: April 2003

AbstractApplication of the Alfrey‐Goldfinger equations to data from terpolymerisations of styrene, methyl methacrylate and maleic anhydride leads to values of the relative reactivity (R) of styrene and methyl methacrylate towards the maleic anhydride radical that are dependent upon the concentrations of the monomers in the feeds. It is shown that it is unlikely that this effect arises from the influence of maleic anhydride‐comonomer complexes but may indicate the importance of a penultimate group effect involving styryl radicals.
Differentialkalorimetrie (DSC) einiger monomerer und polymerer Azoverbindungen
Authors: Nuyken Oskar , Gerum Johannes , Steinhausen Rainer 
Published: April 2003

AbstractDifferential scanning calorimetry (DSC) was used for the determination of decomposition rate constants, activation energies, and reaction enthalpies of different monomeric azo compounds. In all cases, except for 2‐arylazo‐2‐nitropropanes the decomposition was found to follow first order kinetics. The amount of azo‐groups in polymeric azo compounds and their decomposition kinetics were determined by this method.
31P and 19F NMR spectroscopic studies on ring‐opening polymerization of 1,6‐anhydro‐2,3,4‐tri‐O‐benzyl‐β‐D‐glucopyranose by PF5 catalyst
Authors: Uryu Toshiyuki , Ito Katsuhiro , Kobayashi Ken‐Ichi , Matsuzaki Kei 
Published: April 2003

AbstractIn order to elucidate the catalytic behavior of phosphorus pentafluoride in the polymerization of anhydro sugars, 13P and 19F NMR spectra were measured on a reaction mixture of 1,6‐anhydro‐2,3,4‐tri‐O‐benzyl‐β‐D‐glucopyranose (LGTBE) and PF5 with different mole ratios in a temperature range of −40 to −80°C. In the 31P NMR spectrum measured at low temperatures, there was a total of 16 peaks, which consisted of a broad quintet, a septet, and a sharp quartet, being assigned to the PF4O‐group, to PF, and to POF3, respectively. These fluoro compounds were also determined by the 19F NMR spectrum of the reaction mixture. The concentration of PF ions was found to correspond to that of oxonium ions, which are assumed to be actual propagating species, by determining both the concentration of PF from 19F NMR spectrum and the degree of polymerization of 2,3,4‐tri‐O‐benzyl‐α‐D‐glucopyranan obtained. Formation of the PF5: LGTBE complex was observed from the 31P NMR spectrum of the polymerization system at −80°C, which exhibits a broad sextet as well as absorptions due to POF3, PF4O–, and PF. To confirm the PF5:LGTBE complex, the NMR measurement of the PF5: tetrahydropyran complex was carried out. A polymerization mechanism of LGTBE by PF5 catalyst is discussed on the basis of the NMR measurement of the polymerization system.
Darstellung von phenolischen verbindungen und phenol/formaldehyd‐polykondensaten mit ketoxim‐, aldoxim‐ oder 1‐methyl‐4‐hydroxyiminomethylpyridinium‐gruppen und deren wirkung auf parathion‐methyl® und verwandte verbindungen
Authors: Kämmerer Hermann , Hegemann Günter , Lotz Werner , Ritz Jürgen , Pachta Katharina , Müller Oskar 
Published: April 2003

AbstractThirteen low molecular weight oximes were prepared: one derivative of acetophenone (1), two derivatives of benzophenone (2 and 3), two derivatives of salicylaldehyde containing two phenolic nuclei (4c and 5c), and eight compounds in which a phenol unit is substituted by a 4‐hydroxyiminomethylpyridiniummethyl group (8a–f, 10c, and 11c). Besides these compounds polymeric phenol formaldehyde condensates were synthesized which contain units deriving from benzophenoneoxime (15b) or from salicylaldehyde (22b) and condensates containing 4‐hydroxyiminomethylpyridiniummethyl groups (23c). A series of low molecular weight and water soluble compounds (8a–f) were proved as antidotes on mice which were poisoned by paraoxon, sarin, soman, or tabun. These compounds showed a distinct but only a little antidote activity in the case of soman and tabun. Adsorption studies of parathion‐methyl in a solution of water and methanol (volume ratio 10:1) by the water insoluble polycondensates showed that the oximes adsorb better than the parent carbonyl products.
Calculation of macrocyclization equilibria for poly(ethylene terephthalate)
Authors: Suter Ulrich W. , Mutter Manfred 
Published: April 2003

AbstractThe cyclization equilibria constant Kx is evaluated for the formation of cyclic poly(ethylene terephthalate)s (PET) in the range of degree of polymerization 2 ≤ x ≤ 10 on the basis of an elaborated form of the Jacobson‐Stockmayer theory. According to this theory, Kx = W(0)·2Γ0(1)/(σcx NA), where W(r) is the probability density function for the chain vector r; Γ0(γ) is the probability distribution, when r = 0 of γ = cos Δθ; Δθ being the deviation of the bond angle formed by cyclization from its unconstrained value; σcx corresponds to the symmetry number of the ring; NA is Avogadro's number. The evaluation of W(r) is performed in different approximations. The required configurational averages for computing the density distribution W(r) and the angular correlation factor Γ0(1) are obtained by Monte Carlo techniques. The density W(0) of chain vectors at r = 0 is overestimated by the Gaussian approximation. Values of W(0) calculated in higher approximation lower Kx for x < 10.By taking into account the oriental correlation between terminal bonds of the x‐meric acyclic sequence, Kx is lowered additionally by factors of ca. 2,2, 1,3 and 1,1 for x = 4, 5 and 6, respectively. Similar to other polymer chains treated so far, Kx is lowered for medium sized chain lengths by taking into account the deviation from Gaussian distribution and angular correlations of chain ends. This result is in contradiction to experimental data, which yield even higher Kx‐values than expected by the classical Jacobson‐Stockmayer theory for medium sized chain lengths. The inclusion of cis‐ester residues into the all trans‐ester PET chain only slightly reduces this discrepancy. Structural modifications of the PET chain during cyclization experiments are discussed as a rationale for the deviations from the present theory.