bluuebunny/crossref_metadata_2025_split huggingface dataset:
Morphology and properties of polybutadiene‐ and polyether‐polyurethane zwitterionomers
Authors: Yang Chang‐Zheng , Hwang Kirk K. S. , Cooper Stuart L. 
Published: April 2003

AbstractTwo series of polyurethane zwitterionomers based on 4,4′‐methylene‐di(phenyl isocyanate) (MDI), N‐methyl diethanolamine (MDEA)Systematic IUPAC name: 2,2′‐(methylimino)diethanol.
, and either 1350 molecular weight hydroxyl terminated polybutadiene or 1000 molecular weight poly(tetramethylene oxide)Systematic IUPAC name: poly(oxytetramethylene).
were synthesized. Zwitterionization was accomplished by quaternizing the tertiary amine of MDEA with 1,3‐pro‐panesultone. In Both series, IR analysis suggests that the sulfonate ion SO3− associates with the counter ion on the chain extender and the acidic hydrogen of the urethane linkage. Ammonium sulfonation shifts the soft segment Tg of polyether‐based material to lower temperatures suggesting that ionization improves microphase separation. The soft segment Tg of the polybutadiene system is unaffected by ionization. IR dichroism measurements show that with increasing ammonium sulfonation both the hard and soft segments in the polyether‐polyurethane zwitterionomers orient to a greater extent with deformation. In contrast, in the poly‐butadiene‐based zwitterionomers the orientability of the hard segment decreased with ionization while the soft segment showed significant chain alignment. Coupling the dichroism measurements to stress‐strain results suggests that the hard segment domains of the polyether‐polyurethane system possess more of an interconnected structure, while the polybutadiene‐poly‐urethane system contains hard segment domains which are largely isolated. The formation of different morphologies in the two systems of zwitterionomers may be due to the different interdomain surface tensions.
Structural studies on molecular complexes of polyethers, 1. Urea‐ethylene oxide oligomer complexes
Authors: Suehiro Kazuaki , Nagano Yoshiaki 
Published: April 2003

AbstractComplexes of urea with ethylene oxide oligomeric mixtures were investigated by X‐ray diffraction, IR‐absorption, and differential scanning calorimetry. A new crystal modification (Form II) was found for the complexes of urea with ethylene oxide oligomers whose number average molecular weights ranged from 400 to 1000. The Form II complex has a tetragonal unit cell (a = 7,30 Å, c = 19,51 Å), containing eight molecules of urea and eight ethylene oxide units. This modification is metastable. A solid‐solid transition to the conventional Form I crystal occurs on heating up to a temperature between the melting points of both forms. The dependence of the melting points of these complexes on the molecular weight of the oligomers was also studied.
Synthèse et caractérisation de réticulats‐modèle de polyisoprène
Authors: Lutz Pierre , Herz Jean E. , Rempp Paul 
Published: April 2003

AbstractPolyisoprene model‐networks were synthesized by an “endlinking” process: an efficient bifunctional initiator, developped recently, was used to polymerize isoprene to a bifunctional “living” precursor polymer. The living sites were subsequently used to initiate the polymerization of a small amount of divinylbenzene, whereby a model network is formed, the elastic chains of which are of known length and low polydispersity. Equilibrium swelling data and stretching moduli were measured. Unfortunately no reproducible results could be obtained on unswollen networks. Qualitative experience was obtained on the degree of association of lithium organic sites in benzene solution: the value of 2 is to be considered as plausible.
Crystallinity of methylene‐oxyethylene‐methylene triblock oligomers derived from pentadeca(ethylene glycol)
Authors: Teo Hoon Hong , Swales Timothy G. E. , Domszy Roman C. , Heatley Frank , Booth Colin 
Published: April 2003

AbstractBlock oligomers of the general formula CH3(CH2)nO[CH2CH2O]15(CH2)nCH3 where n + 1 = nc = 1 to 18 and 21 have been prepared. Both the oxyethylene and the methylene blocks are monodisperse. Examination of their crystallinity (by differential scanning calorimetry (DSC); X‐ray scattering; IR, Raman, and 1H NMR spectroscopy) shows two important structures I and II.I: 3 ⩽ nc ⩽ 6: oxyethylene blocks crystalline, methylene blocks non‐crystalline;II: 13 ⩽ nc ⩽ 18: oxyethylene and methylene blocks crystalline.Samples with nc = 1 or 2 crystallise essentially as poly(oxyethylene). Samples with 7 ⩽ nc ⩽ 12 are intermediate in structure between I and II. Structure II has 7/2 helical oxyethylene blocks in high density crystalline layers, with a structure closely related to that of monoclinic poly(oxyethylene), and planar zig‐zag methylene blocks in low density crystalline layers. The oxyethylene helices are normal to the lamella end‐planes, or almost so, and the methylene planar zig‐zags are tilted. The enthalpies of fusion of the type II block oligomers show an even‐odd effect. There is evidence of chain folding in the block oligomer with nc = 21.
Viscosity and intrinsic viscosity/temperature relationships for dilute solutions of poly(2‐biphenylyl methacrylate) and poly(4‐biphenylyl methacrylate)
Authors: Hadjichristidis Nikos 
Published: April 2003

AbstractThe actual viscosity η and the intrinsic viscosity [η] of six fractions of poly(2‐biphenylyl methacrylate) {poly[1‐(2‐biphenylyloxycarbonyl)‐1‐methylethylene], (POB); weight average molecular weight M̄w: 4,0 · 104 to 1,42 · 106, polydispersity ratio M̄w/M̄n ≈ 1,4} and of three fractions of poly(4‐biphenylyl methacrylate) {poly[1‐(4‐biphenylyloxycarbonyl)‐1‐methyl‐ethylene], (PPB); M̄w : 8,1 · 104 to 5,3 · 105, M̄w/M̄n ∼ 1,4} in benzene have been determined at different temperatures between 20 and 60°C. Values of the apparent activation energy of the viscous flow Q and the pre‐exponential term A in the expression η = A · exp[Q/(RT)] have been obtained. Q varies with M̄w and concentration c according to Moore's equation: Q = Q0 + Ke · M · c, where Q0 refers to the solvent and Ke depends on polymer and solvent. The numerical value of Ke for POB and PPB is 1,6 · 10−4 (6,7 · 10−4) and ‐8,1 · 10−4 cal · dl · g−1 (‐3,4 · 10−3 J · dl · g−1), resp. From all polymethacrylates studied POB is the only polymer with a positive Ke value. The positive value of Ke for POB may possibly be related to the more extended form of POB in benzene and also may be connected, at least partly, with its low flexibility. The temperature coefficient of the unperturbed dimensions dln〈r02〉/dT for POB estimated from the viscosity data using the Burchard‐Stockmayer‐Fixman relation, is 0,14 · 10−3, much lower than for PPB (2,3 · 10−3 between 22 and 40°C and 1,2 · 10−3 between 40 and 60°C). The positive values of dln〈r02〉/dT indicate that extended conformations of these polymers in benzene must be associated with higher energies.
New experiments concerning the mechanism of solid‐state photopolymerization of 2,5‐distyrylpyrazine
Authors: Braun Hans‐Georg , Wegner Gerhard 
Published: April 2003

AbstractThe photoinduced formation of oligomers in single crystals of 2,5‐distyrylpyrazine (DSP) was investigated by X‐ray and electron diffraction techniques and also by gel permeation chromatography (GPC). The DSP crystals were characterized for the presence and nature of dislocations by dark‐field images and etch‐pit studies. Small angle grain boundaries were identified to be the prominent feature, but in general the crystals were highly perfect. A correlation between the sites of the defects and the formation of the photoproduct could not be detected. The oligomers formed in a solid‐solution under appropriate irradiation conditions. Thus, DSP oligomer of number average degree of polymerization P̄n = 3,2 in macroscopic single crystal texture was obtained for the first time using a laser light source at 478 nm. Deterioration of the single crystal texture of DSP usually observed during photopolymerization is explained as being caused by inhomogeneous light distribution which in turn causes an inhomogeneous product distribution with accumulation of large strain fields. These can be made visible by the multiplication of etch pits. Phase separation between oligomer and polymer is observed on further irradiation of the oligomer single crystals. The oligomer phase seems to play the role of an intermediate in the photopolymerization of DSP at wavelengths λ < 400 nm. The molecular weight distribution of the oligomers was studied by GPC. The data are only compatible with the assumption that the rate constant of dimerization is higher than that for the addition of a monomer to an already existing oligomer.
Synthèses de polysiloxanes organofonctionnels, 2. Les poly[(halométhylméthyl)siloxane]s et leurs modèles
Authors: Reyx Danièle , Guillaume Pierre 
Published: April 2003

AbstractHeterogeneous linear polysiloxanes containing oxy[chloromethyl (or iodométhyl)méthyl]silanediyle, oxy(diméthyl)silanediyle, and oxy(methylvinyl)silanediyle units were prepared. Heterogeneously chloromethylated polysiloxanes were obtained by rearrangement of siloxane linkages in corresponding mixtures of polysiloxanes and oligocyclosiloxanes. Heterogeneously iodomethylated polysiloxanes were obtained by chlorine displacement in the previously chloromethylated polysiloxanes. The preparation of heterogeneously bromomethylated polysiloxanes is more difficult than that of the chloro and iodo derivatives. Their properties intervene between those of the chloromethylated and the iodomethylated products. Chlorine displacement leading to the bromomethylated derivatives, was studied on the bis(chloromethylated) disiloxane.
Synthesis, characterization, and kinetics of thermal degradation of copolyesters
Authors: Ponnusamy Ettigounder , Balakrishnan Thaikannu , Kothandaraman Harimurthi 
Published: April 2003

AbstractRandom terephthalate copolyesters of ethylene glycol and propylene glycol (1,2‐propanediol) with various contents of monomeric units of the diols were prepared by transesterification. The actual content of each monomeric unit in the copolyester was determined by 1H NMR. The thermal behaviour of the copolyesters was studied by differential thermal analysis. Kinetic order, heat and entropy of fusion, and activation energy for the thermal degradation of the copolyesters, were obtained.
High conversion copolymerization, 1. Kinetics of the copolymerization of styrene and maleic anhydride
Authors: Bartoň Jaroslav , Vašková Viera , Juraničová Viera , Mlynárová Mária 
Published: April 2003

AbstractThe copolymerization of styrene (S) with maleic anhydride (MAn) in 1,4‐dioxane at 60, 70 and 80°C up to high conversion (≈ 98%) was followed by differential scanning calorimetry. The rate of copolymerization increases up to 20 – 40% conversion of both monomers and then gradually decreases to zero. The increase in the copolymerization rate is more pronounced for equimolar ratios [S]/[MAn] as compared to ratios with an excess of S. For a given mole ratio of S and MAn the copolymerization rate in 1,4‐dioxane is higher at higher total monomer concentrations and/or at higher temperatures. The heat of copolymerization is 81,6 kj · mol−1 for the equimolar [S]/[MAn] mixture. For mixtures with [S]/[MAn] > 1 the heat of reaction is between 70 and 80 kj · mol−1. The limitingconversion of styrene for [S]/[MAn] = 1 is about 98%, and for [S]/[MAn] > 1 it is a function of the [S]/[MAn] ratio. Assuming exclusively the formation of an alternating S/MAn copolymer the following relation is derived.

for the ratio of the apparent rate constants of propagation k̄p, and termination k̄</t.
Synthèse de macromères à base de chlorures de vinyle et de vinylidène au moyen de télomères
Authors: Boutevin Bernard , Piétrasanta Yves , Taha Mohamed , Sarraf Tarek El 
Published: April 2003

AbstractNew macromers 4, 8, and 10, containing ester, alcohol, or acid functions, were prepared starting with vinyl chloride (CV) or vinylidene dichloride (CV2). The telomer 1, resulting from CV2 and CCI4 was telomerized with allyl acetate and the product was transformed into the acrylate 4 by hydrolysis of the reaction product and subsequent esterification. Macromers 8 and 10 were prepared from CV by radical telomerization with thioglycolic acid (7) and 2‐mercaptoethanol (9), respectively. Reactive double bonds were introduced into these macromers by reaction with acrylic acid, Vinyl chloroformate, methacryloyl chloride, or 2,3‐epoxypropyle methacrylate, leading to new macromers 12, 13, 14, and 15, respectively.
Propylene polymerization on titanium‐magnesium catalysts, 2. Study of catalyst formation
Authors: Sergeev Sergei A. , Bukatov Gennadii D. , Zakharov Vladimir A. , Moroz Ella M. 
Published: April 2003

AbstractFormation of a supported titanium‐magnesium catalyst for propylene polymerization was studied using highly dispersed magnesium chloride (surface area ca. 100 m2/g). By means of X‐ray diffraction, chemical analysis, and measurement of the surface area it was found that: i) interaction of ethyl benzoate (EB) with MgCl2 results in the formation of a compound EBEB·MgCl2 (1:1 by mole); ii) milling of products nEB · MgCl2 (n < 1) results in the decomposition of the lattice of the compound EB · MgCl2 and in the decrease of the size of MgCl2 crystallites; iii) treatment of the product nEB · MgCl2 with titanium tetrachloride results in the removal of a part of EB in the form of an EB·TiCl4, complex from the support, the decomposition of the lattice of the compound EB·MgCi2 an increase of the size of the MgCl2 crystallites, and a sharp increase of the surface area; iv) a small amount of EB (EB/MgCl2 = 0,1 to 0,2) considerably increases the isoptacticity of polypropylene. The high activity of catalysts prepared by milling is due to a higher surface area of these catalysts compared to unmilled samples.
Polyarylenealkenylenes and polyheteroarylenealkenylenes, 15. Syntheses and electrical conductivities of alkoxylated poly(2,5‐thiophenediylvinylene‐1,4‐phenylenevinylene)s
Authors: Koßmehl Gerhard , Samandari Massoud 
Published: April 2003

AbstractPoly(2,5‐thiophenediylvinylene‐1,4‐phenylenevinylene)s with one or two alkoxy groups as side chains of variable lenghts (8a, b and 9a – c) were prepared by Wittig‐reaction of 2,5‐thiophenedicarbaldehyde with the corresponding “bis(Wittig‐salt)s”. To establish the structure of the polymers, model compounds 10 and 11 were synthesized. Charge‐transfer (donor‐acceptor) complexes were prepared by iodine doping of the polyvinylenes 8 and 9. The room temperature conductivity, σ298K, of the original polymers was found to be increased by several orders of magnitude upon doping. It was not possible to remove all the iodine from the charge‐transfer complexes in vacuum.
Alternating copolymers of vinyl chloride and isobutylene with alkyl acrylates: Synthesis with an ethylaluminium dichloride catalyst and 13C NMR characterization
Authors: Florjańczyk Zbigniew , Kauran Witold , Langwald Norbert , Sitkowska Jadwiga 
Published: April 2003

AbstractCopolymerizations of alkyl acrylates (alkyl: ethyl, butyl, isobutyl, tert‐butyl, and 2‐ethylhexyl) with vinyl chloride and isobutylene in the presence of catalytic amounts of C2H5AlCl2 were studied. Depending on the inonomer feed, equimolar or acrylate‐rich copolymers were obtained in most of these reactions. Only tert‐butyl acrylate does not produce any copolymers, due to its decomposition under the action of C2H5AICI2. 2‐Ethylhexyl acrylate forms with isobutylene only acrylate‐rich copolymers. By 13C NMR spectroscopy it could be shown that equimolar copolymers have an alternation structure.
Kristallisation und schmelzverhalten von fraktionen verzweigten polyethylens, 1. Darstellung und charakterisierung der fraktionen
Authors: Maderek Eugeniusz , Strobl Gert R. 
Published: April 2003

AbstractA branched polyethylene with broad molecular weight distribution was separated into a series of fractions by fractional precipitation from dilute solution. The fractions were characterized by viscometric and density measurements, IR‐spectroscopy and calorimetry. The methyl group content and the density turned out as largely constant. Molecular weight effects show up in the melting behaviour. The main range of melting and the end of the melting curve shift to lower temperatures with decreasing molecular weight. Compared to the overall extension of the melting range these shifts are small. One has to conclude that polydispersity gives only a minor contribution to the broadening of the melting range, partial melting being mainly caused by the branches.
Aqueous gel permeation chromatography of electrolytes and polyelectrolytes, 2. Donnan salt exclusion effect
Authors: Kadokura Satoru , Miyamoto Takeaki , Inagaki Hiroshi 
Published: April 2003

AbstractThe salt exclusion of electrolytes and polyelectrolytes in aqueous GPC was investigated theoretically and experimentally, in order to elucidate the feasibility of GPC as a technique for measuring the Donnan salt exclusion parameter, Γ¯, of polyelectrolytes. Three simple salts different in the valency of the anion, i.e., sodium chloride, sodium sulfate and naphthalene‐1,3,6‐trisulfonic acid trisodium salt, were eluted with aqueous NaNO3 solution on a Sephadex G‐10 gel column. The experimental results were analyzed in terms of the Donnan equilibrium established on the gel, and the Γ¯ value of these simple salts was evaluated. It was found that the Γ¯ value from GPC was in good agreement with the theoretical value of 1/2 for an ideal case, showing that the colligative properties of electrolytes and polyelectrolytes such as Γ¯ can be accurately investigated by means of GPC. GPC experiments on the Donnan salt exclusion were further carried out for the heparin‐NaCl system by using a Sephadex G‐25 gel column. From the experimental data, the Γ¯ value of heparin was estimated.
Instantaneous shape and relative orientation of model chains as a function of their intermolecular separation
Authors: Olaj Oskar Friedrich , Zifferer Gerhard 
Published: April 2003

AbstractEnsembles of self avoiding five‐way cubic lattice chains consisting of 50 segments were generated for athermal and θ‐conditions, and the instantaneous shape and the orientation of each chain were characterized by evaluation of the squared three axes L, L, and L of its equivalent ellipsoid and their orientation in space; the variation of these quantities within allowed pair configurations (relative to their values in isolated chains) was studied as a function of the separation R between the two centers of gravity of the two members of all isolated chain pairs, which could be formed from the ensemble. For small R (when R is smaller than the average radius of gyration of isolated chains 〈s2〉1/20) L, the squared longest axis of the equivalent ellipsoid, is strongly expanded for athermal as well as for θ‐conditions, while the squared two shortes axes, L and L, are much less enlarged or even decreased in this range, thus emphasizing the prolate character of the ellipsoids on approaching R = 0. Furthermore the angle between the two L3‐axes of the two chains forming a compatible pair is remarkably increased at vanishing separation (by ca. 10° in athermal systems and by ca. 7° in θ‐systems). Thus, chains forming compatible pairs at R = 0 not only have to increase their dimensions (as already described earlier) but also have to change their instantaneous shape (towards a still higher anisotropy of the equivalent ellipsoids) and their relative orientation (the longest axes L3 tend towards orthogonal orientation) in order to relieve the thermodynamic stress which they impose on each other. By integration of the effects over all separations the concentration dependence of all quantities was determined in the limit of zero concentration. Most quantities are subject to an appreciable, non‐zero concentration dependence. Contrary to most theoretical predictions this is also true for θ‐conditions.
Perméabilité des matériaux copolymères: modélisation moléculaire, 1. Essai d'application d'un modèle de percolation
Authors: Guyot Alain , d'Auriac Jean‐Christian Angles 
Published: April 2003

AbstractThe diffusion of small molecules across a copolymer membrane is simulated as a site percolation problem, assuming that in copolymers consisting of A and B units, B are active sites and A are inactive sites. Molecular modeling is conducted in three steps: (i) generation of a copolymer by a Monte‐Carlo process, taking into account the sequence distribution of the copolymer, (ii) organization of the material through a slipping process of the linear chain towards maximization of the dipolar interactions between the A units, and (iii) the site percolation itself. A quantitative application is carried out for acrylonitrile/methyl acrylate copolymers. The results show that the influence of the slipping process upon the internal organization of the material is most important.
Strategic planning in a turbulent environment: evidence from the oil majors
Authors: Grant Robert M. 
Published: April 2003

AbstractThe long‐running debate between the ‘rational design’ and ‘emergent process’ schools of strategy formation has involved caricatures of firms' strategic planning processes, but little empirical evidence of whether and how companies plan. Despite the presumption that environmental turbulence renders conventional strategic planning all but impossible, the evidence from the corporate sector suggests that reports of the demise of strategic planning are greatly exaggerated. The goal of this paper is to fill this empirical gap by describing the characteristics of the strategic planning systems of multinational, multibusiness companies faced with volatile, unpredictable business environments. In‐depth case studies of the planning systems of eight of the world's largest oil companies identified fundamental changes in the nature and role of strategic planning since the end of the 1970s. The findings point to a possible reconciliation of ‘design’ and ‘process’ approaches to strategy formulation. The study pointed to a process of planned emergence in which strategic planning systems provided a mechanism for coordinating decentralized strategy formulation within a structure of demanding performance targets and clear corporate guidelines. The study shows that these planning systems fostered adaptation and responsiveness, but showed limited innovation and analytical sophistication. Copyright © 2003 John Wiley & Sons, Ltd.