bluuebunny/crossref_metadata_2025_split huggingface dataset:
The backbone conformation of liquid‐crystalline side‐chain polymers in the mesophases and in the isotropic phase determined by scattering methods
Authors: Ohm Hubertus G. , Kirste Rudolf G. , Oberthür Radulf C. 
Published: April 2003

AbstractLight scattering, neutron scattering and viscosity measurements on a nematic and a smectic polymethacrylate demonstrate the presence of molecularly disperse coils in solution. For the nematic polymer, toluene is a theta solvent, the behaviour familiar from conventional polymers (unperturbed coil conformation) being exhibited at the theta point. The isotropic melts likewise contain unperturbed coils; in the case of the nematic polymers, however, the coils in the melt have a radius of gyration which is about 30% smaller than that in solution at the theta point. In the liquid‐crystalline phase, the mean radii of gyration in both cases are identical to the corresponding parameters in the isotropic melt. In the nematic material, however, the coils can be shown to have a substantial anisotropy, the radius of gyration parallel to the director being about 20% smaller than that at right angles to this direction. On the basis of a theoretical chain simulation, a model for the main‐chain conformation has been developed which takes into account both short‐range interactions along the main chains and three‐dimensional interactions by the oriented side groups. This model indicates the degree of orientation from which a change in the mean radius of gyration can be expected. Wide‐angle neutron scattering experiments on smectic polymer provide information about the main‐chain distribution in the smectic phase. The main chains are present in a substantially higher concentration between the smectic layers, but there are hints that they do not have a true two‐dimensional arrangement.
Polymerization of 1‐alkynes initiated by μ‐alkylidene complexes of tungsten, 3. Kinetics and mechanism of the propagation reaction
Authors: Meziane Driss , Soum Alain , Fontanille Michel 
Published: April 2003

AbstractA comprehensive study of the propagation step of 1‐heptyne polymerization initiated by a dinuclear μ‐alkylidene complex of tungsten, was carried out. Kinetic orders, apparent rate constants and thermodynamic parameters were determined. The structure of the active species and that of the organic side‐products appearing during this step, were analyzed by NMR and mass spectroscopy. According to the experimental data, a mechanism of the propagation reaction is proposed: the propagating species could derive from inactive metalated oligomers by loss of a carbonyl ligand; the monomer then coordinates at the free site of the transition metal of the μ‐alkylidene active species and inserts into the CW bond. In competition with the normal insertion of the monomer molecule, termination and transfer reactions occur (including or not the monomer and/or the polymeric chain).
Electroinitiated cationic polymerization by anodic dissolution
Authors: Pierre Gérard , Limosin Danièle , Cheradame Hervé 
Published: April 2003

AbstractThe polymerization of several monomers, such as styrene, α‐methylstyrene, lactones, isobutyl vinyl ether, and hexamethylcyclotrisiloxane, was carried out in H‐shaped cells equipped with sacrificial anodes. The solvents, dichloromethane or nitromethane, contained tetrabutylammonium perchlorate playing the role of supporting electrolyte. Among the different metals tested (Cu, Ag, Hg, Al, Pb, Sn), only mercury and aluminium anodes gave initiation. The conditions of the electrolysis, the nature of the monomers, and the results of special experiments carried out in the presence of a hindered pyridine demonstrate that the polymerization involves the electrophilic addition of the active species to the monomer followed by cationic chain growth.
Influence of internal and external donors on activity and stereospecificity of ziegler‐natta catalysts
Authors: Soga Kazuo , Shiono Takeshi , Doi Yoshiharu 
Published: April 2003

AbstractThree kinds of MgCl2‐supported TiCl4 catalysts (ester‐free, ethyl benzoate (EB, monoester) and dibutyl phthalate (DNBP, diester) as internal donors) were prepared. Polymerization of propylene was carried out using these catalysts with and without phenyltriethoxysilane (PTES) as an external donor. Significant differences were observed in the kinetic behavior of polymerization among ester‐free, monoester, and diester systems. Addition of PTES, however, did not change the kinetic behavior. The polymers produced were separated into three fractions by extraction with boiling heptane and octane, and the molar mass distribution (MMD) curves were measured for these three fractions. The heptane‐insoluble, isotactic polymer obtained in the absence of PTES was found to consist of two fractions, octane‐soluble and ‐insoluble. The octane‐soluble polymer having lower molar mass contained appreciable amounts of syndiotactic stereoblocks in the chains, whereas the octane‐insoluble polymer did not contain such stereoblocks. Addition of PTES drastically increased the octane‐insoluble fraction without changing the average molar mass. On the other hand, the MMD curve for the heptane‐soluble, atactic polymer gradually shifted to the lower molar mass range with an increase in the concentration of PTES. From these results, the effects of internal and external donors on catalyst activity and stereospecificity were discussed putting emphasis on the differences between monoesters and diesters.
Thermodynamic properties in the liquid state of high melting polymers containing phenylene and naphthylene groups
Authors: Cheng Stephen Z. D. , Pan Robert , Bu Hai Shan , Cao Miao‐ Yong , Wunderlich Bernhard 
Published: April 2003

AbstractHigh melting polymers of three different types of crystallization behavior were analyzed as to their thermal properties. The heat capacity at constant pressure of liquid poly(butylene terephthalate) (PBT) from 490 to 540 K was measured by scanning calorimetry. Combining with prior measured liquid heat capacity data of poly(oxy‐1,4‐phenylene) (PO) (358 – 620 K), poly‐(thio‐1,4‐phenylene) (PPS) (540 – 600 K), poly(ethylene 2,6‐naphthalenedicarboxylate) (PEN) (400 – 450 K, 530 – 600 K), an addition scheme for liquid heat capacities was constructed. In addition, the thermodynamic functions H and S have been calculated for those five polymers. The absolute, molar, residual entropy for the glassy state at zero kelvin is estimated to be 6,6,15,2, 7,48, 5,70, and 19,9 J/(K · mol) for PPS, PEN, PPO, PO, and PBT, respectively. Another two polymers with similar structure, poly(1,4‐oxybenzoic acid) (POB) and poly(2,6‐oxynaphthoic acid) (PON), were also studied in their high temperature mesophase states. A test of the addition scheme has been made to predict their heat capacities.
Cross polarization/magic angle spinning 13C solid state nuclear magnetic resonance of model compounds related to supported ziegler‐natta catalysts
Authors: Abis Luigi , Albizzati Enrico , Giannini Umberto , Giunchi Giovanni , Santoro Ettore , Noristi Luciano 
Published: April 2003

AbstractCross polarization/magic angle spinning 13C NMR has been applied to the investigation of some solid organometallic compounds of the general formulae TiCl4 · n RCOOR′, MgCl2 · n RCOOR′ (RCOOR′ = p‐CH3C6H4COOCH3 and C6H5COOC2H5, n = 1; 2; and 0,15). Compounds with n = 1 and 2 show narrow resonance lines indicative of crystalline regular structures while for MgCl2 · 0,15 RCOOR′ a disordered structure is found with the organic ligands strongly bonded to the surface of MgCl2 crystallites. For n = 2 splitting into a doublet is found for some resonances due to the spatial non‐equivalence of the two ligands induced by crystalline packing. A shift has been found for some resonances in going from Mg to Ti complexes which reflects the different Lewis acidity of the two metal atoms.
Influence of shear on the demixing of polymer solutions, 2. Stored energy and theoretical calculations
Authors: Krämer‐Lucas Helga , Schenck Heiko , Wolf B. A. 
Published: April 2003

AbstractPhase diagrams were calculated for flowing solutions of polystyrene in trans‐decahydronaphthalene assuming that the energy (Es) stored in the sheared state has to be added to the Gibbs energy of mixing; Es is computed from viscometric data (flow curves). The resulting phase diagrams exhibit two maxima in most of the cases instead of only one for the stagnant solutions. A comparison with experimental data (Part 1) shows that the calculated demixing behaviour agrees well for moderate shear rates and concentrations of the polymer. Deviations in the semidilute region, particularly for higher values, are a consequence of the fact that so far no reliable theoretical relation has been given for these conditions to calculate Es from viscometric data. In all cases, however, the present attempt describes the characteristics of the phase diagrams very well, namely the eulytic points and the inversion of shear dissolution into shear demixing.
The glass transition temperatures of homogeneous blends of polystyrene, poly(methyl methacrylate), and copolymers of styrene and methyl methacrylate
Authors: Braun Dietrich , Kohl Paul R. , Hellmann Goetz P. 
Published: April 2003

AbstractThe glass transition temperatures Tg of homogeneous binary blends of the homo‐ and the statistical copolymers of the system poly(styrene‐co‐methyl methacrylate) were studied. Some of the blends, which are in the equilibrium phase separated, were forced into homogeneity. Tg (ϕ) of the homopolymer blends (PS/PMMA)ϕ follows the Fox equation, while Tg (x) of the pure copolymers P(SxMMA1 − x) exhibits a minimum. This minimum can be effectively removed by blending the copolymers with small fractions (ϕ ≈ 0,2) of one of the two homopolymers or a differently composed copolymer P(SyMMA1 − y).
Experimental verification of a model describing the occupied volume by polymers in solution
Authors: Dondos Anastasios , Pierri Evgenia , Skartsis Labros , Economou Christos 
Published: April 2003

AbstractA relation is proposed which yields the occupied volume by macromolecular chains in solution. The experimental verification of the model is carried out by a viscometric study of the ternary system polymer A/polymer B/solvent. More precisely the viscometric study permits the determination of the critical concentration c** corresponding to the incipient overlap of spherical coils.
Electrochemical preparation of poly(di(2‐thienyl)benzene)s and poly(4,4′‐di(2‐thienyl)biphenyl)
Authors: Mitsuhara Toshio , Tanaka Susumu , Kaeriyama Kyoji 
Published: April 2003

Abstract1,3‐Di(2‐thienyl)benzene (T13B), 4,4′‐di(2‐thienyl)biphenyl (TBP), and 3,5‐di(2‐thienyl)‐pyridine (T35P) were prepared. Films were deposited on the electrode in the anodic oxidative polymerization of T13B, 1,4‐di(2‐thienyl)benzene (T14B) and TBP, but the oxidation product of T35P did not cover the entire surface of the electrode. The infrared spectra of the films indicated oxidative coupling to occur at the 5 and 5′ positions of the thiophene rings. While the cyclic voltammograms of poly‐T14B were well‐defined, those of poly‐T13B and poly‐TBP had complex shapes with two or three anodic peaks. When the absorption spectra were measured during electrochemical oxidation, new peaks appeared at 2,0 and 1,9 eV for poly‐T13B and poly‐TBP, respectively. The films looked green in the oxidized state and faintly yellow in the neutral state. The green colour was retained without applied voltage in the cell and in the dry state. It was concluded that conjugation along the main chain is insufficient in these polymers.
Combined liquid‐crystalline polymers with chiral phases, 2. Lateral substituents
Authors: Kapitza Heinrich , Zentel Rudolf 
Published: April 2003

AbstractChiral combined liquid‐crystalline polymers (i. e. polymers with the mesogenic groups in the main chain as well as in the side groups) with dipole moments perpendicular to the mesogenic groups were synthesized and characterized. These dipole moments were introduced by lateral substituents, which were located at different parts of the mesogen or directly at the chiral centre. The polymers, thus prepared, show crystalline or glassy phases at room temperature and smectic A, chiral smectic C* or cholesteric phases at higher temperatures. Since the lateral substituents decrease the melting temperature more strongly than the clearing temperature, the liquid‐crystalline phases are broadened compared to the unsubstituted polymers. Often glassy liquid‐crystalline phases are obtained. The dipole moments perpendicular to the mesogenic groups or at the chiral centre may help to obtain a high spontaneous polarisation in the chiral smectic C* phase (ferroelectricity).
Computer simulation of the steady state in reversible polymer‐analogous reactions, 3. Flows and statistics in detailed balance
Authors: Krieger Dorit , Klesper Ernst 
Published: April 2003

AbstractThe steady state of reversible polymer‐analogous reactions was simulated by Monte Carlo calculations. The length of the simulated copolymer chains was chosen large enough to yield data with an acceptable degree of statistical fluctuation. Two types of sets of relative rate constants K were investigated, first K1 = K2 = K3, and second K1 ≠ K2, K1 ≠ K3, K2 ≠ K3, with K1 · K3 = K22. The relative rate constants K are defined as K1 = k(AAA)/k(ABA), K2 = k(AAB+)/k(ABB+), and K3 = k(BAB)/k(BBB), where k is the ordinary rate constant pertaining to the reaction of the central monomeric unit in the triad given in parentheses, with two different types of monomeric units A and B in the binary copolymer. For both types of sets of relative rate constants the simulation showed a detailed balance to prevail for the kinetics in the steady state. It was also shown that the same kinetics and statistics were obtained in the steady state when starting the simulation first from a homopolymer consisting of A‐monomeric units, and then from a homopolymer of B‐monomeric units. Based on the finding of a detailed balance and on the definition of K, it could be shown by analysis that the first type of the sets of K leads to a Bernoullian statistics of the copolymers in the steady state, while the second type leads to a first‐order Markov statistics. Correspondingly, equations are given which allow to calculate the relative rate constants from statistics and vice versa. The equations have also been confirmed by Monte Carlo simulation. In addition, the equations for the interrelations between the standard Gibbs free energies of the individual reactions for the central units in the triads are given.
Analysis of hydrodynamic data on linear poly(dimethylsiloxane) under theta‐conditions in terms of the bead‐chain and the continuous worm‐like cylinder models
Authors: Bohdanecký Miloslav , Petrus Vladimír , Horská Jitka , Edwards Christopher J. C. , Stepto Robert F. T. 
Published: April 2003

AbstractHydrodynamic data for linear poly(dimethylsiloxane)s (103 ≦ molecular weight ≦ 106) under theta‐conditions (intrinsic viscosity [η]Θ, intrinsic translational friction coefficient [f]Θ) are compiled and discussed in terms of theories developed for the bead‐chain model and the continuous worm‐like cylinder. While the former as applied fits the [f]Θ data only, the latter is found to describe consistently the molecular‐weight dependences of both [η]Θ and [f]Θ. Parameters of the worm‐like cylinder are estimated. The Kuhn statistical length, AK, agrees well with the theoretical value of the rotational isomeric state model. The effective diameter, 1,1 cm ≦ d · 108 ≦ 1,6 cm, is very low as compared with the diameter of the cross‐sectional area obtained from crystallographic data or the partial specific volume. Factors which may account for this discrepancy and the shortcomings of the interpretations using the bead‐chain model are discussed.
Mechanism of stereoselective polymerization of propylene oxide with [{MeOCH2CH(Me)OZnOCH(Me)CH2OMe}2 · {EtZnOCH(Me)CH2OMe}2] as initiator
Authors: Hasebe Yoshihiro , Tsuruta Teiji 
Published: April 2003

AbstractA series of studies on molecular level elucidation of stereospecific polymerizations of propylene oxide (PO) were carried out with a well‐defined organozinc complex of ‘chair’ type structure, [{CH3OCH2CH(Me)OZnOCH(Me)CH2OCH3}2 · {EtZnOCH(Me)CH2OCH3}2] ([Zn‐MP]2,2), which contains two four‐coordinated Zn and two six‐coordinated Zn atoms, the latter being surrounded, respectively, by three types (endo‐coordinated, exo‐coordinated and non‐coordinated) of D‐ and L‐methoxypropoxy groups. An experiment using a partly deuterated [Zn‐MP]2,2 and PO‐α‐d showed the initiation reaction to be caused by an attack of the non‐coordinated methoxypropoxy (MP) group on a monomer molecule. Another experiment using (L)‐PO as monomer showed that the (D)‐MP group was preferentially transferred to (L)‐monomer to break its OCH2 bond. A molecular model study of [Zn‐MP]2,2 complex suggested that there may be chiral holes which can accomodate only one sense of enantiomeric PO molecule. The chiral structure of the hole around the six‐coordinated zinc atom is presumably determined by the chair type ZnO framework together with the coordinated MP groups.
Lineare und sternförmige hybrid‐polymere, 4 Ein neuer weg zur synthese von cellulose und amylose enthaltenden blockcopolymeren
Authors: Pfannemüller Beate , Dengler Thomas 
Published: April 2003

Abstract(A‐B)n‐Block copolymers containing oligosaccharide blocks (A) and synthetic polymer blocks (B) coupled by amide linkages were synthesized. As starting material fully substituted cellulose and amylose derivatives with protecting groups of variable stability were used: triacetates, tricarbanilates and trimethyl ethers. The reaction steps were as follows: (i) trisubstituted oligosaccharides in the range of 2 < P̄n < 20 with OH endgroups at C‐1 and C‐4 were obtained by acidolysis or alcoholysis of the polysaccharide derivatives. (ii) By reaction of the OH endgroups with isocyanatoacetic ethyl or methyl ester, ester endgroups were introduced. (iii) Condensation with diamines [dodecamethylenediamine, NH2‐terminated poly(oxyethylene)] could be achieved by direct amidation of the ester endgroups in the case of the tricarbanilates and trimethyl ethers. As an alternative route, saponification of the ester endgroups and conversion into the more reactive p‐nitrophenyl ester was investigated. While condensation of the p‐nitrophenyl ester with diamines proceeds under mild conditions, difficulties arise in the quantitative p‐nitrophenylation of the COOH groups. In the case of the triacetates acetyl and ester endgroups were cleaved simultaneously by saponification, leading to unsubstituted oligosaccharides with COOH or lactone groups at both ends, a building block suitable for various reactions.
Syntheses of thermotropic copolyesters and their minimum needed fraction of mesogenic units
Authors: Zhang Hongzhi , Ning Xin , Wang Pingping , Zhang Zhibin , Guan Zhibin 
Published: April 2003

AbstractSeveral series of thermotropic copolyesters with different spacers, containing the moieties of 1,4‐butanediol (4a or 4b), 1,6‐hexanediol (6a or 6b), bisphenol‐A (10a), bisphenol‐S (10b) or a telechelic polysulfone (12a or 12b) were synthesized. The mesomorphic properties of the resulting copolyesters were examined by visual observation of stir‐opalescence and birefringence under a polarizing microscope. Copolyesters 4a, 4b, 6a or 6b with mole fractions of mesogenic units over a broad extent (≥0,2) being thermotropic within wide mesomorphic temperature ranges, regardless of the spacers based on 1,4‐butanediol or 1,6‐hexanediol, have microstructures of block sequence distribution and do not retain liquid‐crystallinity if the mean lenghts of mesogenic segments are shorter than that of the triad with three phenyl rings. For the thermotropic copolyesters 10a, 10b, 12a or 12b the minimum mole fraction of mesogenic units needed is not higher than 0,10, despite of the different varieties and lengths of rigid spacers.
Synthesis of difunctional poly(dimethylsiloxane)s: Application to macromonomer synthesis
Authors: Gnanou Yves , Rempp Paul 
Published: April 2003

AbstractDifunctional poly(dimethylsiloxane) (PDMS) macromonomers were synthesized. Emphasis was put on the synthesis of short PDMS chains exhibiting a narrow molecular weight distribution. This was achieved by the selection of an efficient initiator and under polymerization conditions such as to minimize reshuffling reactions. The macromonomers were subsequently obtained by deactivation of the living sites with an electrophilic unsaturation. Accurate characterization of the macromonomers (GPC, end‐group analysis) was performed.
Polymeric chiral crown ethers, 3 Synthesis of polymers incorporating D‐mannitol moieties via cyclopolymerization, and chiral recognition towards α‐amino acids
Authors: Kakuchi Toyoji , Takaoka Tohru , Yokota Kazuaki 
Published: April 2003

AbstractA novel approach to the production of chiral, polymeric crown ethers incorporating D‐mannitol moieties was developed. Three optically active divinyl ethers (3, 6 and 9), derived from 1,3 : 4,6‐di‐O‐benzylidene‐, 1,2 : 5,6‐diisopropylidene‐ and 1,4 : 3,6‐dianhydro‐D‐mannitol (2, 5 and 8) were polymerized with cationic catalysts. The cyclopolymerization led to the chiral polymeric crown ethers 4, 7 and 10 consisting of only cyclic constitutional units. Both monomer 9 and polymer 10, containing 1,4 : 3,6‐dianhydro‐D‐mannitol moieties are amphiphilic compounds. Polymer 4 with 1,3 : 4,6‐di‐O‐benzylidene‐D‐mannitol moieties was found to exhibit chiral recognition in favour of the (S)‐isomer of racemic ester salts of phenylglycine, phenylalanine, valine and methionine. The ability of chiral recognition, which was estimated as enantiomer distribution constants (EDC), is comparable to that of polymeric crown ethers with (R)‐2,2′‐binaphthyl moieties.
Poly(propylene sulfoxide) — a first approach to a dipolar aprotic, water‐soluble and reactive polymer
Authors: Orgeret‐Ravanat Catherine , Galin Jean‐Claude 
Published: April 2003

AbstractThe oxidation of atactic poly(2‐methylthiirane) (PPS, M̄w ≈ 1 – 2 · 105) to its corresponding sulfoxide (PPSO) is studied under a variety of experimental conditions: m‐chloroperbenzoic acid in homogeneous chloroform solution ( − 7°C) and hydrogen peroxide or bromine in an interfacial chloroform‐water system (20°C) lead to selective and quantitative oxidation under stoichiometric conditions with simultaneous chain degradation (M̄w (PPSO) ≈ 0,5 – 3 · 104). The high density of sulfoxide functions affords to the PPSO chain a number of specific properties such as: (a) solubility in dipolar protic (CH3OH, CHCHl3 …) and aprotic (DMF, DMSO) solvents, the polymer coils being, however, strongly associated in aqueous solution, (b) strong polarity of the bulk polymer, as shown by an “apparent local dipole moment” of about 4,1 D, (c) poor thermal stability, degradation starting at about 130°C under nitrogen, with a weight loss of 50% at 160°C (apparent activation energy Ea = 100 kJ · mol−1).
Polymères porteurs de dérivés du glycérol, 9 Modification de polyacides par des esters d'époxy‐2,3 propyle
Authors: Brosse Jean‐Claude , Razermera Faly , Soutif Jean‐Claude 
Published: April 2003

AbstractPreviously synthesized 2,3‐epoxypropyl esters were used to modify polymethacrylic and alginic acids. This way of synthesis led to polymers whose structure can be compared to that of polymers obtained from the reaction of acids with polymers bearing the same type of oxirane rings, the active molecule being linked to the polymer backbone through a glycerol spacer. As for the preceding studies, the reaction was investigated from a chemical and kinetical point of view with epoxypropyl esters of acetic acid and 1‐(4‐chlorobenzoyl)‐5‐methoxy‐2‐methyl‐3‐indolacetic acid (indomethacin).