bluuebunny/crossref_metadata_2025_split huggingface dataset:
Siloxane networks swollen in chloroform/diethyl ether. Divergent preferential adsorption
Authors: Gomez‐Anton Maria Rosa , Masegosa Rosa Maria , Horta Arturo 
Published: April 2003

AbstractTotal solvent sorption and preferential adsorption by networks of poly(methylphenylsiloxane) (PMPS) and of poly(dimethylsiloxane) (PDMS) were determined in the mixture chloroform/diethyl ether. This liquid mixture has a negative GE. The swelling degree of the networks was found to vary linearly with mixed solvent composition (Cl3CH volume fraction ϕ), contrary to what is expected in view of GE < 0. The preferential adsorption by PDMS shows an inversion which is of the divergent type (preferential adsorption of the liquid in major proportion in the mixture). With PMPS no inversion was observed, Cl3CH is always preferentially adsorbed, but the trend is also divergent (with the inversion point displaced to ϕ = 0). The unexpected behaviour of the swelling degree and the displacement of the inversion in preferential adsorption are attributed to strong attractive interactions of the siloxane backbone with the two solvents, and of phenyl groups (in PMPS) with Cl3CH. The intrinsic viscosity of linear PMPS at infinite dilution was determined in the same mixed solvent, in order to check the possible influence of the polymer concentration. Comparison with network swelling shows a similar behaviour.
Photo‐crosslinking of polymers containing pendant epoxy groups
Authors: Tomoi Masao , Oda Hidehiro , Kakiuchi Hiroshi 
Published: April 2003

AbstractThe photo‐crosslinking of polymers containing pendant epoxy groups was carried out at room temp. in the presence of a photosensitive sulfonium salt which is an initiator of cationic polymerization. The crosslinking reactivity of the epoxide‐containing polymers was found to depend on the mobilities of both the backbone of the polymers and the pendant epoxy groups, and on the epoxide structure. The introduction of spacer chains between the polymer backbone and the epoxy groups increases the mobilities of the backbone and the epoxides, resulting in an increases crosslinking reactivity. The introduction of a methyl group at the epoxy ring of the polymers with glass transition temp. (Tg) lower than room temp. enhances the crosslinking reactivity, whereas it diminishes the reactivity for the polymers with Tg higher than room temp. This result can be explained by assuming that the presence of the methyl group results not only in an increase of the epoxide reactivity due to both the inductive effect of the methyl group and the increased ring strain, but also the decreased mobility of the epoxy groups. Thus, the reactivity of the rubbery polymers is principally controlled by the intrinsic reactivity of the epoxides, and the reactivity of the rigid polymers is mainly controlled by the mobility of the reactive sites.
Emulsion copolymerization of acrylonitrile and butyl acrylate, 7. Effect of concentration and type of emulsifier on polymerization kinetics
Authors: Capek Ignác , Mlynárová Márie , Bartoň Jaroslav 
Published: April 2003

AbstractThe emulsion copolymerization of acrylonitrile and butyl acrylate initiated by potassium peroxodisulfate (K2S2O8) in the presence of an anionic, cationic, or nonionic emulsifier has been kinetically investigated at 60°C under batch conditions by gas chromatography (GLC) and gravimetric methods. It is found convenient to define three stages of emulsion polymerization. In the range of low conversion (interval 1) are generated particles and the rate of polymerization increases with increasing polymer particle concentration. In interval 2 (ca. from 15 to 70% conversion) the number of polymer particles and the rate of polymerization (maximum) are constant. At very high conversion (above ca. 70% conversion) the monomer concentration within polymer particles decreases abruptly and the polymerization rate slows down (interval 3). The rate of polymerization in interval 2 was found to be proportional to the 0,41, 0,48, and −0,42 power of the emulsifier concentration for the anionic, nonionic, and cationic emulsifier, respectively. The dependence of the final particle number on the emulsifier concentration deviates from simple micellar theory predictions. The exponent of the emulsifier concentration decreases with increasing emulsifier concentration (for the anionic and nonionic emulsifiers). These results were explained by a coagulative nucleation mechanism. The unexpected polymerization behaviour in the presence of the cationic emulsifier was explained by the formation of a product (due to interaction of the initiator with the emulsifier).
Poly(2,4‐hexadiynylene di‐p‐toluenesulfonate)/polyethylene crystallographic interactions: A polymer decoration study
Authors: Moigne Jacques Le , Graff Sabine , Wittmann Jean‐Claude 
Published: April 2003

AbstractThe crystallographic interactions between the toluenesulfonate‐substituted diacetylene 2,4‐hexadiynylene di‐p‐toluenesulfonate (TS), its corresponding polymer (PTS) and polyethylene (PE) have been established in detail with the help of the polymer decoration technique. Although monomer and polymer are known to be isomorphous, the decoration patterns observed on their (100) crystal surface differ significantly, revealing some subtle structural changes on solid‐state polymerization. The single and twofold orientations obtained on TS and PTS, respectively, are discussed and shown to be of epitaxial character. The PE contact planes for the two decoration orientations are however, significantly different, since the chain packing distances at play are 5,26 Å (or 4,94 Å) and 7,47 Å, respectively. From the very close similarity in crystal structures, it is anticipated that favourable interactions may also exist in many other polydiacetylene/polymer binary systems.
Crystalline morphology of block‐copoly(oxypropylene/oxyethylene/oxypropylene) by small‐angle X‐ray and Raman scattering
Authors: Viras Fotini , Luo Yun‐Zhu , Viras Kyriakos , Mobbs Richard H. , King Terence A. , Booth Colin 
Published: April 2003

AbstractBlock‐copoly(oxypropylene/oxyethylene/oxypropylene)s, with central‐block lengths of 39 and 75 oxyethylene units and end‐block lengths in the range 1 to 13 oxypropylene units, were investigated in their solid states by small‐angle X‐ray diffraction and low‐frequency Raman spectroscopy, supplemented by differential scanning calorimetry. Low‐frequency Raman transitions were assigned to longitudinal modes (LAM) of either unfolded or once‐folded chains. The solid state comprised stacked monolayer lamellae in which the chains were usually tilted with respect to the lamellar end plane.
Schwefelhaltige telechele mit SH bzw. CCH‐endgruppen
Authors: Nuyken Oskar , Siebzehnrübl Florian 
Published: April 2003

AbstractThe reaction of 1,3‐benzenedithiol (1) with 1,4‐diethinyl‐benzene (2) at room temperature yields polymers with thio‐1,3‐phenylenethiovinylene‐1,4‐phenylenevinylene repeating units. The polymerization proceeds without addition of an initiator and without UV‐irridiation. Because of the resulting structure a radical mechanism is suggested. However, the molar mass/conversion relation shows similarities with a step‐growth polymerization. Because of this behaviour this reaction was successfully used for the preparation of telechelics in which molar mass and end groups are controlled simply by the unstoichiometric ratio of the educts.
Supported Ziegler‐Natta catalysts for propene polymerization: Grinding and co‐grinding effects on catalyst improvement
Authors: Spitz Roger , Duranel Laurent , Guyot Alain 
Published: April 2003

AbstractSolid ternary MgCl2/aromatic ester (A. E.)/TiCl4 catalysts are obtained by grinding MgCl2 followed by co‐grinding MgCl2 and A. E. and then by TiCl4 impregnation. The productivity increases with grinding time up to a maximum value and the stereospecificity decreases continuously. A convenient choice of the A. E. improves the results. The productivity seems to be correlated with details of the pore size distribution. Infrared analysis of the catalyst reveals different ways of Ti‐fixation but without clear relation to the catalytic properties.
Dependence of glass‐transition temperature Tg on tacticity of poly(vinyl chloride). A preliminary study by differential scanning calorimetry
Authors: Mijangos Carmen , Martínez Gerardo , Millán José‐Luis 
Published: April 2003

AbstractThe glass‐transition temperature, Tg, of poly(vinyl chloride) (PVC) has been found to depend linearly on both the overall isotactic triad content and a small fraction of isotactic triads. It was previously demonstrated, that the latter react with sodium benzenethiolate at temperatures as low as −30°C, probably because they adopt a definite local conformation. In general, it was believed before that the tacticity effect on Tg occurs only for disubstituted CC‐polymers, the results obtained in this work for PVC would suggest that specific conformations of isotactic triads can also enhance the motion of chain segments in the polymer.
The gel degradation theory, 2. An experimental verification with model networks formed by the random crosslinking of monodisperse primary chains
Authors: Argyropoulos Dimitris S. , Bolker Henry I. 
Published: April 2003

AbstractModel networks formed by the crosslinking of monodisperse carboxylated polystyrene chains with decamethylene glycol, were degraded by random cleavage of the crosslinks. The weight‐average molecular weights (M̄w) of the resulting soluble fractions quantitatively correlated with the gel degradation theory which is essentially the Flory‐Stockmayer gelation theory applied in reverse. As such, this paper furnishes support for the universal applicability of the gel degradation theory.
13C NMR study of the tacticity of poly(propylene oxide)s prepared by polymerization with α,β,γ,δ‐tetraphenylporphyrin/AlEt2Cl as initiator system: An example of first‐order markovian statistics in ring‐opening polymerization
Authors: Borgne Alain Le , Spassky Nicolas , Jun Chang Lim , Momtaz Ardéchir 
Published: April 2003

AbstractRacemic and enantiomerically enriched poly(propylene oxide)s were prepared using α, β, γ, δ‐tetraphenylporphyrin/AlEt2Cl as initiator system. Triad tacticity of the polymers was analyzed by 13C NMR spectroscopy (62,89 MHz). A predominance of isotactic triads was observed in the case of the racemic polymer, corresponding to a non‐random distribution of configurational units in the polymer chain. A model correlating tacticity with enantiomeric excess of starting monomer in the case of a first‐order Markovian distribution was established. Good agreement between experimental results and calculated triad contents (according to the model previously described) was observed for enantiomerically enriched polymers. This indicates a steric control by the last unit of the growing chain end. The influence of the size of the substituent was examined for the case of poly(1,2‐epoxybutane). The origin of the chain‐end effect is discussed.
Modelization of the photocatalyzed oxidation of polyolefins, 3. Oxidation of model hydrocarbons with ZnO
Authors: Lacoste Jacques , Arnaud René , Singh Raj Pal , Lemaire Jacques 
Published: April 2003

AbstractThe present paper reports on analytical aspects of the ZnO photocatalyzed oxidation of linear and cyclic alkanes. Normal and branched hydrocarbons were examined as models in the photoageing of both polyethylene and polypropylene, respectively. IR, GC‐MS and chemical analyses confirm the formation of hydroxyl and carbonyl groups and ascertain the presence of γ‐lactones in the photooxidation of polyolefins. In the presence of ZnO as pigment, ketone groups accumulate and no acidic groups are observed. The formation of γ‐lactones is favoured in substituted aliphatic alkanes like 2,4‐dimethylpentane and 2,2,4‐trimethylpentane, i.e. in molecules where methyl groups are in β‐position of a tertiary carbon atom. A mechanism of the formation of γ‐lactones in photooxidation of both model alkanes and polyolefines is proposed.
2H NMR study of correlated spin‐lattice relaxation in solid polyelectrolyte complexes of poly(dimethyliminioalkylenes) (α,ω‐ionenes) and polystyrenesulfonate
Authors: Westermark Bertel , Spiess Hans Wolfgang 
Published: April 2003

AbstractSpin‐lattice relaxation rates (1/T1) have been used to study the correlation between the molecular motions in the polyion components of polyelectrolyte complexes from poly(dimethyliminioalkylenes) (α,ω‐ionenes) and polystyrenesulfonate. The length of the alkyl chains in the α,ω‐ionenes has been varied studying the complexes with 3,3‐ionene, 6,6‐ionene, and 10,10‐ionene, respectively. In the latter, three different positions in the alkylene chains were deuterated selectively. The relaxation rate curves show that the more rigid polystyrenesulfonate component of the complexes is relaxed through the rapid large‐angle motions in the alkylene chains of the α,ω‐ionenes. In the complex with 10,10‐ionene coupling is stronger with the mobility of the CH2 groups adjacent to the quaternary ammonium ion.
Synthesis of polystyrene macromonomers for use in polycondensation reactions
Authors: Heitz Thomas , Höcker Hartwig 
Published: April 2003

AbstractThe preparation of aromatic macromonomers with hydroxyl functions was achieved by termination of living polystyrene (PSLi) upon addition of 2,5‐dimethoxybenzyl bromide (2) or 1,1‐bis(4‐methoxyphenyl)ethylene (16). Ether cleavage with boron tribromide resulted in the formation of the de‐protected macromonomers 15 and 17. Side reactions occurring in the functionalisation reaction with 2 were investigated by means of a respective model reaction. The formation of side products could be suppressed by reacting PSLi with 1,1‐diphenylethylene prior to functionalisation with 2. The macromonomers were characterized by GPC, UV, and FT‐IR spectroscopy.
Crosslinkable liquid‐crystalline combined main‐chain/side‐group polymers with low glass transition temperatures
Authors: Bualek Sauvarop , Zentel Rudolf 
Published: April 2003

AbstractCrosslinkable and crosslinked liquid‐crystalline polymers with elastic properties were prepared from main‐chain and combined main‐chain/side‐group polymers. These polymers exhibit nematic, smectic A, and smectic C phases. Polymers of these types with azoxybenzene as mesogen do not crystallize upon cooling. As a consequence, the liquid‐crystalline phases are frozen in glassy around room temperature.
Characterization of cellulose nitrate with gel permeation chromatography ‐ low angle laser light scattering (GPC‐LALLS), GPC‐infrared, and membrane osmometry
Authors: Wirsén Anders 
Published: April 2003

AbstractCellulose nitrates with nitrogen contents in the range 11,2 to 13,3 mol‐% are characterized with gel permeation chromatography (GPC) using various detectors, membrane osmometry, static low angle laser light scattering (LALLS) and solution viscosity measurements. The molecular weight data from GPC‐LALLS are generally in good agreement with those obtained by static LALLS and membrane osmometry. GPC‐infrared is used to analyze the nitrogen content. These techniques are also used to characterize cellulose nitrate in propellants. A comparison between two different column packings in GPC‐LALLS analysis is integrated into this study.
Electron transfer from carbanionic salts to linear sequences of conjugated double bonds, 1. Mechanism of n doping of polyacetylene
Authors: Rudatsikira Alphonse , Mathis Claude , Francois Bernard 
Published: April 2003

AbstractIt is shown that the mechanism of polyacetylene (PA) reduction (or n “doping”) by alkaline carbanionic salts and butyllithium is a simple electron transfer without addition. In this reduction reaction the dicarbanionic dimer of 1,1‐diphenylethylene (DD2– Na2+) is quantitatively converted to 1,1‐diphenylethylene. The reduction by 3‐methyl‐1,1‐diphenylpentyllithium produces free radicals which deactivate in solution by coupling and disproportionation. But the strong dependence of the ratio of disproportionation to coupling of these radicals on solvent polarity is unusual: no coupling is observed in diethyl ether or pentane, while it is the most important reaction in THF. sec‐Butyllithium in pentane also reduces PA by a simple electron transfer process. The “doping” levels can be deduced accurately from the quantitive analysis of the by‐products by gas chromatography.
Composite model for the thermal expansivity of polymers
Authors: Biswas Prabir K. , Sengupta Shyamal , Basu Ashok N. 
Published: April 2003

AbstractThe thermal expansivity of semicrystalline polymers is interpreted within the framework of the composite model which has already been found useful in describing mechanical and optical properties as well as the thermal conductivity of a large number of polymers. The model assumes the polymers to be an aggregate of units composed of crystalline and amorphous phases. The thermal expansivities of the unit are calculated in terms of those of the constituents. In the undrawn state the units are distributed randomly, and the isotropic thermal expansivity of the bulk results. The development of strong anisotropy in thermal expansivity on drawing is explained in terms of preferred orientation of the units. The orientational changes on drawing have been directly calculated from the birefringence versus draw ratio data. The results of these investigations indicate that the present model is quite successful in interpreting thermal expansivity data for poly(oxymethylene) and poly(propylene) over the entire draw ratio and temperature range.
Polymeric bound porphyrins and their precursors, 7. Synthesis of water‐soluble, positively charged polymers with covalently bound moieties of porphyrin derivatives
Authors: Wöhrle Dieter , Krawczyk Gerhard , Paliuras Mihail 
Published: April 2003

AbstractPositively charged polymers 6–13 containing covalently bound moieties of tetraphenylporphyrin (1), phthalocyanine 2 and naphthocyanine 3 were obtained by reaction of poly(chloromethylstyrene) with low‐molecular weight substituted porphyrins (1 b, 2 b, 2 d, 3 c) in the presence of triethylamine. The water‐soluble polymers contain moieties of one or of two or three different porphyrin derivatives.
Regioselectively modified stereoregular polysaccharides, 12. Synthesis of (1→6)‐α‐linked polysaccharides consisting of D‐glucose and 2,3,4‐tri‐O‐octadecyl‐D‐glucose units
Authors: Ichikawa Haruo , Kobayashi Kazukiyo , Sumitomo Hiroshi 
Published: April 2003

AbstractBy ring‐opening copolymerization of 1,6‐anhydro‐2,3,4‐tri‐O‐octadecyl‐β‐D‐glucopyranose (1) with 1,6‐anhydro‐2,3,4‐tri‐O‐benzyl‐β‐D‐glucopyranose (2) using phosphorus pentafluoride as initiator in dichloromethane at 0°C, stereoregular copolymers 3, with M̄n = 6 · 103 to 24 · 103 were obtained. For debenzylation of copolymers 3, either the reduction with sodium in liquid ammonia or radical bromination‐hydrolysis was applied, depending on solubility and copolymer composition. Poly[2,3,4‐tri‐O‐octadecyl‐α‐D‐glucopyranosyl‐(1→6)‐stat‐α‐D‐glucopyranosyl‐(1→6)] (4,) exhibits characteristic solution properties arising from its amphiphilic structure. Polysaccharide 4, with mole fractions of trioctadecylated unit (x) below 0,03, are water‐soluble and interact with magnesium 1‐anilino‐8‐naphthalenesulfonate (ANS) in water. The polysaccharide 4 (x = 0,29), which is soluble in chloroform, was found to solubilize an aqueous methyl orange solution in chloroform. Formation of micelles in water and reversed micelles in chloroform is suggested.
Propene polymerization with MgCl2 supported Ziegler catalysts: Activation by hydrogen and ethylene
Authors: Spitz Roger , Masson Patrick , Bobichon Charles , Guyot Alain 
Published: April 2003

AbstractComplementary experiments confirm the recent findings that the rate of propene polymerization is temporary enhanced if a small amount of ethylene is introduced during the polymerization, normalizing after consumption of ethylene by copolymerization. In addition, the study of the sequence distribution of propene monomeric units in the copolymerization carried out under various conditions revealed that the activation by ethylene does not involve the propagation steps, but the re‐initiation after deactivation. A similar temporary activation effect was observed after the addition of small amounts of hydrogen. In this case, however, hydrogen is not consumed. Thus, the deactivation observed after the initial rate enhancement is due to another reason. The deactivation could be shown to be reversible after removal of the adsorbed hydrogen when either ethylene or hydrogen was added again to allow re‐initiation of the polymerization. One of the important reasons of the continuous decrease of the propene homopolymerization rate may be due to the fact, that, after a transfer step, the re‐initiation of polymerization does not take place spontaneously. Small amounts of ethylene or hydrogen allow the reinitiation to take place, at least for some kind of active sites.
New developments in star polymer synthesis. Star‐shaped polystyrenes and star‐block copolymers
Authors: Lutz Pierre , Rempp Paul 
Published: April 2003

AbstractA new method for the synthesis of compact, multifunctional star‐shaped polystyrenes was designed. A plurifunctional metalorganic initiator is obtained upon reaction of potassium naphthalene with commercial divinylbenzene. The resulting polymeric “core” exhibits a number of metalorganic sites. In a subsequent step, these sites initiate the polymerization of styrene to yield a star‐shaped polymer. High numbers of branches can be obtained, thus rendering these molecules extremely compact. However, the major advantage of the “core first” method is that it allows functionalization of the branches at their outer end, thus providing the possibility of further reaction or selective adsorption. This “core first” method was also applied to the preparation of star‐block copolymers formed of a polystyrene block and a poly(ethylene oxide) block.
Configurational statistics of polymers obtained by ring‐opening polymerization of heterocyclic monomers
Authors: Sepulchre Maurice 
Published: April 2003

AbstractA general reexamination of the configurational statistics of polymers obtained by ringopening polymerization of heterocyclic monomers is presented. The polymers under study involve one or two asymmetric centres in the main chain per monomeric unit. Sequence probabilities are calculated for Bernoullian, and first‐ and second‐order Markov propagation models. The analyses of two polymers [poly(styrene oxide) and poly(tert‐butyloxirane)] for which tacticity data are available in the literature are given as examples.
Polymeric phthalocyanines and their precursors, 14. Synthesis and analytical characterization of polymers from oxy‐ and arylenedioxy‐bridged diphthalonitriles
Authors: Wöhrle Dieter , Schulte Bernd 
Published: April 2003

AbstractPhthalocyanine moieties containing polymers 3 a – e were prepared by the reaction of several oxy‐ and arylenedioxy‐bridged diphthalonitriles 2 a – e in the absence or the presence of metal salts or metals. The structure of the polymers was thoroughly discussed on the basis of their IR and UV/VIS spectra. According to the nitrile end groups determined by IR spectroscopy, the structurally uniform polymers consist of phthalocyanine moieties. Saponification of the nitrile end groups of 3 a – e leads to polymeric phthalocyanines with carboxylic acid end groups with a lower degree of annulation than that of the polymers before saponification. The low‐molecular‐weight phthalocyanines 5a, b were prepared as model compounds for the polymers.