bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solid‐state 13C NMR studies of vulcanized elastomers, 4. Sulfur‐vulcanized polybutadiene
Authors: Zaper A. Marie , Koenig Jack L. 
Published: April 2003

AbstractThe sulfur vulcanization of cis‐1,4‐polybutadiene was studied by solid‐state 13C NMR spectroscopy. Polybutadiene is cured with several different formulations including sulfur and accelerators in order to determine the network structure of the resulting vulcanizates. Polysulfidic crosslinks bound to the methylene carbons of the polybutadiene repeating unit were observed in the rubber network. Cyclic sulfide structures were detected in the network structure in addition to cis‐to‐trans chain isomerization. Two different pulse sequences were used for the NMR experiments of the sulfur‐vulcanized cis‐polybutadiene. The gated high power decoupling NMR experiment reflects the mobile regions of the vulcanizate sample while the cross polarization pulse sequence reflects the regions of the sample which are inherently more rigid. The cross polarization spectra of the samples cured with high sulfur levels showed that a considerable amount of rigidity is found in the vulcanized cis‐polybutadiene network. It was also possible to obtain cross polarization spectra of the lightly crosslinked polybutadiene vulcanizates. This is in contrast to the NMR results of the vulcanized natural rubber systems which generally tended to have considerably more mobility.
Synthesis and characterization of styrene‐based polymer supports
Authors: Arshady Reza 
Published: April 2003

AbstractA number of reactive styrene derivatives 3a – h was synthesized and copolymerized in suspension with styrene and divinylbenzene to produce beaded styrene‐based resins 5a – h, carrying bromo, methoxy, chloromethyl, hydroxymethyl, hydroxyethyl, or α‐hydroxy‐4‐methoxybenzyl groups. The swelling behaviour of selected samples of these resins was studied in tetrahydrofuran, toluene, dichloromethane, dioxane, ethyl acetate, dimethylformamide, and methanol. Swellability data are given for resin samples having different percentages of crosslinking and for those produced in the presence of chlorobenzene as a monomer diluent (or polymerization solvent). The significance of the swellability data are briefly discussed in terms of the nature of solvent, the degree of crosslinking and the effect of the monomer diluent on the matrix structure. Details of a series of model reactions of the resin‐bound functional groups are also given, and the results are discussed on the basis of resin swellability and polymer‐substrate compatibility.
Sulfur‐containing polymers, 4. Polymers with thiocarbonate and dithiocarbonate moieties from aliphatic dithiols. Syntheses and characterization
Authors: Berti Corrado , Marianucci Elisabetta , Pilati Francesco 
Published: April 2003

AbstractSeveral polycarbonate analogues with sulfur atoms replacing all or part of the oxygen atoms in the carbonate units of the polymer, were prepared by interfacial synthesis from aliphatic dithiols and phosgene or bisphenol‐A bischloroformate or bisphenol‐A polycarbonate oligomers. That way, polydithiocarbonates (containing SCOS groups) (2a – c), polythiocarbonates (containing OCOS groups) (4a – c) and block copolymers 6a – c (containing OCOO groups, mainly, and OCOS groups randomly distributed along the chain) were prepared. The expected chemical structures were confirmed by 1H NMR, 13C NMR and FT‐IR spectroscopy. Their thermal transitions were investigated by DSC, and the effects of replacing oxygen atoms for sulfur atoms are discussed.
Rheological properties of moderately concentrated solutions of polystyrene‐block‐polybutadiene‐block‐polystyrene in different selective solvents and at different temperatures
Authors: Baloch Musa Kaleem , Rauf Abdur 
Published: April 2003

AbstractThe shear viscosity of a moderately concentrated solution of the triblock copolymer polystyrene‐block‐polybutadiene‐block‐polystyrene is studied in a common solvent (1,4‐dioxane) and in so‐called selective solvents (mixtures of 1,4‐dioxane with different alcohols). In the latter, which dissolve only the styrene blocks and precipitate the butadiene blocks, the block copolymer molecules aggregate and form micelles with the precipitated blocks as the core and the dissolved blocks as the cilia. The micelle solutions exhibit non‐Newtonian behaviour over certain concentration ranges. The viscosity of the micellar solutions in the dilute regime is found to be lower than that of their unimer solutions (i. e., the viscosity measured in 1,4‐dioxane) at the same concentration, whereas at higher concentrations the situation is opposite. The viscosity of micellar solutions is first increasing and then decreasing with temperature for all selective solvents used. These variations with concentration and temperature are explained in terms of micelle structure, intermicellar entanglement, swelling of the inner core and coiling of the micelle cilia.
Polyurethane ionomers: Order in 4,4′‐methylenedi(phenyl isocyanate)‐ and hexamethylene diisocyanate‐based poly(ether‐urethane) cationomers
Authors: Chen Show‐An , Chan Wu‐Chung 
Published: April 2003

AbstractPolyurethane cationomers from poly(oxytetramethylene) of molecular weight 2000 as soft segments, 2,2′‐methyliminodiethanol as chain extender, glycolic acid as quaternization agent, and 4,4′‐methylenedi(phenyl isocyanate) (MDI) and hexamethylene diisocyanate (HDI) as diisocyanates are synthesized and characterized by using wide‐angle X‐ray diffraction, dynamic mechanical analysis, differential scanning calorimetry and tensile‐elongation testing. It is found that, in the unionized and ionized cases, the hard segments exhibit a disorder and short‐ and long‐range order, but no crystallinity. The ordered hard segments in the hard domains aggregate so tightly as to act as crosslinks, such that crystallization of soft segments occurs during elongation. Such disorder and order are also found to exist in the solutions of ethyl methyl ketone as reflected in variations of conductivity and viscosity during addition of water at 20°C. Ionization by insertion of the acid can disrupt the order in MDI and HDI systems, but can increase the cohesion between the neighbouring hard segments, the latter being predominant over the former. Dispersion is apt to disrupt the long‐range order in HDI systems but has only an insignificant effect on the order in MDI systems.
Intrapolymeric interactions of bile pigments covalently anchored to an insoluble polystyrene‐based resin, as determined by gel‐phase 13c NMR
Authors: Feliz Miguel , Giralt Ernest , Ribó Josep M. , Trull Francesc R. 
Published: April 2003

AbstractBile pigments covalently anchored to beads of a polystyrene‐based resin show in gel‐phase 13C NMR spectroscopy hydrogen‐bond interactions between the anchored groups. Such interactions are similar to those observed in homogeneous solution: attached 5(1 H)‐pyrromethenones in aprotic solvents show dimer formation analogously to what happens in homogeneous solution.
Temperature dependence of the polymorphous phases of nylon 6
Authors: Fichera Annamaria , Malta Viscardo , Marega Carla , Zannetti Roberto 
Published: April 2003

AbstractThe α, γ, γ* polymorphous forms and the physical mixtures of the α and γ‐like forms of Nylon 6 were examined from room temperature up to the melting point by X‐ray diffraction techniques. The α‐ and γ*‐forms evinced a more evident structural change as a function of temperature than the γ‐form. The study carried out on the polymorphous forms of Nylon 6 at temperatures higher than room temperature furnished new insights in comparison to usual annealing. The level of structural order and the specific aspects of the structure were found to be largely determinant for the equilibrium state in the polymorphous forms of Nylon 6 from room temperature up to the melting point.
A real‐time drawing study of melt‐crystallized ultra‐high molecular weight polyethylene. Comparison with conventional X‐ray results
Authors: van Aerle Nick A. J. M. , Braam Ad W. M. 
Published: April 2003

AbstractIn the past morphological changes, caused by uni‐axial drawing of flexible polymers have been studied mostly under conditions, quite different from the drawing conditions. This could give rise to certain artefacts, leading to mis‐interpretations. Up to now very little was known about this possibility. Therefore, X‐ray patterns obtained by conventional drawing studies and by real‐time X‐ray drawing studies are compared in this paper. It will be shown, that although some results on melt‐crystallized polyethylene discussed here show indeed small differences, conventional X‐ray studies can be used without any problem for qualitative studies. However, studies of deformation phenomena in elastic deformable regions as well as quantitative X‐ray studies require real‐time measurements.
Influence of shear on the demixing of polymer solutions, 1 apparatus and experimental results
Authors: Krämer‐Lucas Helga , Schenck Heiko , Wolf B. A. 
Published: April 2003

AbstractAn apparatus for turbidimetric measurements of demixing temperatures under shear flow is presented, and the results of experiments with trans‐decahydronaphthalene/polystyrene (TD/PS) solutions, investigating molecular weights ranging from 100 kg/mol to 1770 kg/mol, are compared with viscometric data. It is found that the sign and magnitude of shear effects depend on molecular weight (Mw), polymer concentration (c2), and shear rate (). For the first time, it was possible to study a solution which exhibits shear dissolution at low shear rates but shear demixing at high shear rates.
Polyuréthannes à propriétés emulsifiantes et électrolytiques, 2. Cinétique de polycondensation en solution des alkylimino‐2,2′ diéthanols avec le diisocyanate d'isophorone. Etude par 1H et 13C NMR
Authors: Gerard Jean‐Francois , Perchec Pierre Le , Pham Quang Tho 
Published: April 2003

Abstract13C NMR analysis of carbamates and substituted ureas as model compounds, derived from 5‐isocyanato‐1,3,3‐trimethylcyclohexylmethyl isocyanate (isophorone diisocyanate) (3), allowed the quantitative determination of global conversions of hydroxyl and NCO groups. The individual conversions of the two NCO groups, as observed in the polycondensations of 2,2′‐methylimino‐ and 2,2′‐dodecyliminodiethanol (1a and 1b) with 3 in toluene, were examined. The primary NCO group of 3 was found to be two times more reactive than the secondary one. The global kinetics of the polycondensations followed the 2nd and 3rd order for conversions lower than 50%. Beyond 50% of conversion, zero order kinetics were observed because of the decrease of the rate due to the steric hindrance of both cyclohexyl and alkyl residues. Alkyl radical length in 1 and hydroxyl auto‐association equilibria were found to have the same effect on polycondensation as on condensation.
The effect of active site composition and support structure in supported catalysts on the nascent morphology of polyethylene
Authors: Semikolenova Nina V. , Nesterov Gennadii A. , Zakharov Vladimir A. , Krjukova Galina N. , Ivanov Vyacheslav P. , Gol'denberg Grigorii I. 
Published: April 2003

AbstractThe formation process and morphology of polyethylene (PE) produced by the non‐porous catalyst species tufa‐ and kaoline‐supported Cr(C5H5)2, Zr(BH4)4 and TiCl4 were studied by scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS). The PE morphology was found to depend upon the catalyst active component composition, the polymer yield and the morphology of the support. A quantitative estimation of the PE coverage of the catalyst particles was made.
Polymerization of 2‐methoxy‐2‐oxo‐1,3,2‐dioxaphospholane. Kinetics and polymer microstructure
Authors: Penczek Stanislaw , Libiszowski Jan 
Published: April 2003

AbstractThe polymerization of 2‐methoxy‐2‐oxo‐1,3,2‐dioxaphospholane (1), initiated with aluminium triisopropanolate in CH2Cl2 as solvent, was studied. Under the chosen conditions one molecule of initiator produces one polymeric chain. At low conversion exclusively linear chains of poly[oxy(methoxyphosphoryl)oxyethylene] [poly(1)] are formed. Later, chain transfer to polymer leads to extensive branching. Kinetic studies strongly indicate propagation on covalent active species. Rate constants of initiation and propagation, found from non‐stationary kinetics at 25°C, are equal to 6,5 · 10−3 mol−1 · 1 · s−1 and 4,5 · 10−1 mol−1 · 1 · s−1, respectively.
Synthesis and characterization of a polyoxyethylene derivative for the affinity labeling of human hemoglobin
Authors: Leonard Michèle , Dellacherie Edith 
Published: April 2003

AbstractThe possibility of preparing a polyoxyethylene derivative containing only one active group per chain, and with a narrow distribution of molecular size, was investigated. The aim of this investigation was to obtain a polymeric derivative of benzenehexacarboxylate (BHC) capable of interacting specifically inside the polyphosphate binding site of human hemoglobin (Hb) and which, after covalent coupling with this protein, could lead to conjugates with well‐defined oxygen‐binding properties. Such conjugates could be of interest in the field of blood substitutes. To minimize the percentage of high‐molecular‐weight products resulting from the fact that, on one hand, commercial monomethoxypolyoxyethylene (MPOE 5000) contained a considerable amount of difunctional and high‐molecular‐weight species, and on the other hand that several reactions were likely to lead to cross‐linked products, fractionation steps and/or chromatographic steps were carried out. The final compound obtained under these conditions (83,5% of BHC‐mono substituted polyoxyethylene, 8,5% of BHC disubstituted and 8% MPOE) was found to interact with the polyphosphate binding site of Hb, as it was capable of lowering its affinity for oxygen. After covalent coupling with deoxy‐Hb under defined conditions, this effect was strengthened, which means that the binding was probably formed with an amine of the Hb polyphosphate binding site.
Study of miscibility of the system polystyrene/poly(methylvinyl ether) by inverse gas chromatography
Authors: Elorza José María , Fdez‐Berridi María José , Iruin Juan José , Uriarte Cristina 
Published: April 2003

AbstractInverse gas chromatography technique was applied to the study of the miscibility of the system polystyrene/poly(methyl vinyl ether) (PS/PMVE) over a temperature range (75 – 155°C) including the phase separation temperature. This temperature was measured taking into account the retention diagrams of the PS/PMVE system with several probes, the comparison of the probe retention volumes in the blend with the algebraic average retention volumes of the pure homopolymers, and the variation of interaction parameter χ′23 with temperature within the temperature range investigated. According to these criteria, the phase separation temperature of the PS/PMVE (50/50 by wt.) system is within the temperature range of 115 – 120°C.
The Gordon‐Taylor equation. Additivity and interaction in compatible polymer blends
Authors: Schneider Hans Adam 
Published: April 2003

AbstractAn analysis of the Gordon‐Taylor equation shows that its background is based on additivity. The corresponding parameter K = ρ1 Δα2 / (ρ2 Δα1), however, may include also an interaction contribution if the quadratic concentration term is neglected in a virial‐like extension of the glass transition temperature vs. composition expression. Then K becomes a real fitting parameter. It is shown that a distinction of the two cases is possible by using the corresponding linearized form of the respective equations. The discussion of data of polystyrene/poly(2,6‐dimethyl‐1,4‐phenylene oxide), styrene copolymers/poly(2,6‐dimethyl‐1,4‐phenylene oxide) and poly(methyl vinyl ether)/polystyrene blends gives evidence for the decisive influence of the stiffer component on the glass transition behaviour of compatible polymer blends.
Synthesis and properties of para‐linked aromatic polyesters containing 2,2′‐dimethylbiphenylylene units
Authors: Schmidt Hans‐Werner , Guo Dajian 
Published: April 2003

AbstractThe syntheses and properties of a series of para‐linked aromatic homopolyesters with 2,2′‐dimethylbiphenylylene units are described. In the 2,2′‐dimethyl‐substituted biphenylylene unit the phenyl rings are forced into a non‐coplanar conformation, which decreases the interchain interactions. The combination of such a biphenylylene unit with a monosubstituted unit further reduces the regularity of the substituents along the polyester backbone. As a result, soluble and completely amorphous liquid‐crystalline (LC) aromatic polyesters with low phase transition temperatures are obtainable. Ternary solutions, consisting of a soluble aromatic LC polyester, a conventional randomly coiled thermoplastic and chloroform as solvent, can be used for the preparation of films and fibers.
Mobility and 29Si NMR relaxation in some cyclic siloxanes
Authors: Kosfeld Robert , Kreuzburg Christa , Krause Rosemarie 
Published: April 2003

Abstract29Si NMR spin‐lattice relaxation time (T1) measurements were performed with asymmetrically substituted oligomeric cyclosiloxanes (MeRSiO2/2)n (with R = phenyl, n = 3 and R = H, n = 4 – 6). Temperature‐ and field‐dependend measurements allow separation into different relaxation mechanisms. Based on these results, molecular correlation times τc were calculated. The methyl‐H cycles were found to be more mobile than the methyl‐phenyl ones.
Approach to the composition dependence of the glass transition temperature of compatible polymer blends, 2 The effect of local chain orientation
Authors: Brekner Michael‐Joachim , Schneider Hans Adam , Cantow Hans‐Joachim 
Published: April 2003

AbstractIn a previous publication a new concept has been presented for the composition dependence of the glass transition in compatible polymer blends. The concept starts with the idea that besides conformational energy barriers, contacts due to interaction are responsible for both conformation and “free” volume distribution. In accordance with the Flory‐Huggins lattice theory, the contact probability has been related to the volume fraction of the components, corrected for the different volume expansion coefficients. The concept accounts for both chainspecific and interaction‐specific contributions. It is concluded that local chain orientation due to the increased hetero‐contact interaction may explain the observed molecular weight influences on the composition dependence of Tg of polymer blends. Using experimental data for poly(vinyl methyl ether)‐polystyrene (PVME‐PS) blends it is shown that this local chain orientation due to hetero‐interaction is extremely strong in blends of the low molecular weight PS with high MW PVME. Thus, apparently, the stiffer component is dominating the Tg behaviour of compatible polymer blends.
Chain mobility in solid polyelectrolyte complexes
Authors: Westermark Bertel , Spiess Hans Wolfgang 
Published: April 2003

Abstract2H NMR is used to study the mobility of the alkylene chain in solid poly[(dimethyliminio)‐alkylene]s (α,ω‐ionenes) complexed with poly(styrenesulfonate). In 10, 10‐ionene the alkylene chain motion was probed on samples selectively deuterated at the 1‐, 2‐, and 4‐position as well as in the methyl part of the quaternary ammonium groups. 2H NMR spectra show that all positions in the polymethylene chains are involved in conformational jumps between trans and gauche states. The mobility of the methylene units adjacent to charged centres was found to be significantly reduced compared with that of units in the inner part of the chain. The charged quaternary ammonium groups themselves, however, do not take part in trans‐gauche isomerization. An increase in mobility resulting from increasing the length of the alkylene chains between the charge centres was observed in 3,3‐, 6,6‐ and 10,10‐ionene complexes labelled in the 2‐position. The differences in chain dynamics were also detected via EPR line shapes of small spin probe molecules incorporated into the complexes.
Rheological properties of two‐dimensional model networks
Authors: Rehage Heinz , Schnabel Edith , Veyssié Madeleine 
Published: April 2003

AbstractWe measured the tensio‐active properties of octamethylene dimethacrylate (1), octamethylene diisobutyrate (2) and octamethylene isobutyrate methacrylate (3) at the oil‐water interface. The results indicate that these molecules are strongly adsorbed at the boundary between oil and water. The amphiphatic compounds in the monolayer can be polymerized and cross‐linked by UV irradiation. The kinetics of surface gelation was studied by measuring the two‐dimensional shear modulus as a function of the time of irradiation. A two‐dimensional sol‐gel transition was observed which is in fairly good agreement with percolation theories. The kinetics of the two‐dimensional polymerization can be completely interpreted in terms of a simple reaction scheme. The elasticity of the two‐dimensional films depends strongly on the surface concentration of the cross‐linking agent. The rheological properties of the polymerized films exhibit typical features of rubber‐elastic systems and there exists an interesting analogy to corresponding structures of three‐dimensional networks.
Rheologic properties of semi‐rigid polymers for the example of cellulose nitrate, 2. Influence of molecular weight distribution on the flow curves of semi‐dilute solutions
Authors: González Francisco Rex , Marx‐Figini Marianne , Figini Rubén V. 
Published: April 2003

AbstractThe apparent viscosity η of semi‐dilute solutions of cellulose nitrate in ethyl acetate was measured as a function of shear rate at 20°C by rotational viscometry. The mass concentration c of the solutions was chosen such that the product between c and the intrinsic viscosity was 8 < c · [η] < 22, lying in the range of viscosity‐average degrees of polymerization covered by the employed samples 550 < DPη < 7600. The experimental flow curves were interpreted in terms of Graessley's theory for non‐Newtonian flow of polydisperse polymers. The polydispersities derived for five individual samples according to the theory of Graessley were used for calculating the resulting theoretical curves belonging to four binary mixtures each between two of them. The reasonable good agreement between calculated and experimental reduced flow curves of blends indicates consistency of the theory when applied to the present system of a semi‐rigid polymer. This and other results point to a flow behaviour of semi‐rigid cellulose nitrate being similar to that of linear flexible polymers.
Small angle X‐ray studies on diffusion processes at the boundary between poly(methyl methacrylate) and poly(vinylidene difluoride)
Authors: Garbella Rüdiger Wilhelm , Wendorff Joachim Heinz 
Published: April 2003

AbstractDiffusion processes taking place across the boundary between the two compatible polymers poly(methyl methacrylate) (PMMA) and poly(vinylidene difluoride) (PVDF) were studied by means of small angle X‐ray scattering. The excess scattering resulting from thermal concentration fluctuations was used to monitor the diffusion process as a function of the molecular weight of the PMMA component and the diffusion geometry. The results obtained were analyzed on the basis of simplified versions of the interdiffusion theories proposed by Brochard (slow‐mode model) and by Kramer (fast‐mode model). This, however, required, the introduction of approximations with respect to the concentration dependences of monomer mobilities and interaction parameter and with respect to the role of molecular weight distribution. Using these approximations it is possible to account quantitatively for all experimental findings on the basis of the slow‐mode approach. Discrepancies between experimental results and theoretical predictions were found for the model based on the fast‐mode approach.