bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ring‐opening metathesis polymerization of norbornenes with organosilicon substituents. Gas permeability of polymers obtained
Authors: Finkelshtein E. Sh. , Makovetskii K. L. , Yampol'skii Yu. P. , Portnykh E. B. , Ostrovskaya I. Ya. , Kaliuzhnyi N. E. , Pritula N. A. , Gol'berg A. I. , Yatsenko M. S. , Platé N. A. 
Published: April 2003

AbstractPolymers of norbornenes with SiMe3 and Si(Me2)CH2SiMe3 groups were synthesized and mass transfer properties of the polymers were studied. Ring‐opening polymerizations of these monomers were realized in the presence of homogeneous WCl6‐based and heterogeneous Re2O7‐based metathesis catalysts. Introduction of silicon‐containing groups in the polynorbornene main chain results in a drastic increase of the permeability (P) and diffusion (D) coefficients for different biatomic and multiatomic gases. Comparison of polymers having SiMe3 and Si(Me2)CH2SiMe3 substituents shows lower permeability and diffusion coefficients in the latter case. The combination of transport properties (Pi values) and separation factors aij = Pi/Pj of the two new silicon‐containing polynorbornenes permits one to consider them as representatives of the most permeable and sufficiently permselective group of polymers. Transport properties of the polymers studied were analysed on the basis of the free volume approach.
Haloaldehyde polymers, 43.. Structure of 2‐bornyloxy‐terminated chloral oligomers
Authors: Ute Koichi , Oka Ken‐ichi , Kashiyama Masaharu , Hatada Koichi , Xi Fu , Vogl Otto 
Published: April 2003

AbstractOligomerization of trichloroacetaldehyde (chloral) was carried out with the lithium salt of (1 S, 2 R, 4 S)‐(–)‐borneol as the initiator. The unimer and dimer fractions consisted of two and four diastereomers, respectively; the individual isomers were isolated from the fractions by crystallization from methanol or by high performance liquid chromatography. The X‐ray single‐crystal analysis showed that the major isomer in the unimer fraction is the (R)‐form which has the acetal carbon in (R)‐configuration. The diastereomeric ratios were determined by 1H NMR as R/S = 57/43 for the unimers and RS/SR/RR/SS = 34/25/23/18 for the dimers. The conformations of the meso‐dimers [(R,R)‐ and (S,S)‐isomers] in the crystalline form corresponded to a half turn of the 41‐helix of isotactic polychloral, whereas the conformations of the racemo‐dimers (the (R,S)‐ and (S,R)‐isomers) were different from the helical structure in the crystal and in solution. The trimer fraction consisted of six of the eight possible diastereomers; among these isomers, the mm isomers (the (R,R,R)‐ and (S,S,S)‐isomers) were highly predominant. The amount of the (R,R,R)‐trimer formed was only slightly larger than that of the (S,S,S)‐isomer. (a) Part 42, cf. G. D. Jaycox, O. Vogl, J. Am. Chem. Soc., submitted.
Partiell acetylierte cellulose — synthese und bestimmung der substituentenverteilung mit hilfe der 1H NMR‐spektroskopie
Authors: Deus Carsten , Friebolin Horst , Siefert Egon 
Published: April 2003

AbstractPartially acetylated cellulose was synthesized by homogeneous acidic and basic saponification of cellulose triacetate (fully acetylated cellulose) and by homogeneous acetylation of cellulose dissolved in molten N‐ethyl‐pyridinium chloride. The result of 1H NMR spectroscopic investigations was that acetylation and acid saponification lead to products with different esterification of the hydroxy groups at C2, C3 and C6 whilst basic saponification leads to uniform acetylation. Furthermore, the solubility of the cellulose acetates depends on the method of preparation.
Synthesis of SH‐ and NCO‐terminated thiocarbamate prepolymers
Authors: Klemm Elisabeth , Stöckl Cornelia 
Published: April 2003

AbstractThe addition reaction of 3,6‐dioxaoctane‐1,8‐dithiol with various diisocyanates, proceeding by addition of 1,4‐diazabicyclo[2.2.2.]octane as basic catalyst, was investigated. That way, NCO‐and SH‐terminated linear thiocarbamate telechelics (containing NHCOS‐groups) were synthesized. The structures were evaluated by IR and 13C NMR spectroscopy. Results show that side reactions of the NH protons with isocyanate (forming allophanates) can be excluded. The NCO‐terminated prepolymers are suitable to be used as participants in common isocyanate reactions. Thus, by treating with allyl alcohol, 2‐hydroxyethyl methacrylate or diallylamine, they can be transformed into telechelics with olefinic end‐groups (5, 6, 7). The products were characterized by their number‐average mol. wts. (VPO) and elemental analysis, and the expected chemical structures were confirmed by characteristic absorption bands.
Phase transitions in Nylons 8, 10 and 12 crystallized from solutions
Authors: Cojazzi Gianna , Fichera Anna Maria , Malta Viscardo , Zannetti Roberto 
Published: April 2003

AbstractThe peculiar structural modifications of Nylons 8, 10 and 12 prepared by crystallization from solutions and reported as α*, were studied by differential scanning calorimetry (DSC) and thermomicroscopy, supported also by some X‐ray diffraction (XRD) measurements. The results indicate that the phase transition shown by the α*‐forms of the Nylon 8–12 series exhibits the characteristics of a melting immediately followed by crystallization into γ‐form, rather than of a α* → γ solid‐solid transition. When the γ‐crystallization is concluded, the melting of this form takes place. DSC and XRD data demonstrate that the α* → γ transition is irreversible. The changes in the DSC traces of the Nylon 8 – 12 series were interpreted as indicative of a gradual stability increase of the α‐form in comparison with the corresponding α*‐form, depending on the increase of the number of methylene groups in the repeating unit.
Polymérisation induite sous irradiation laser visible, 4. Le système éosine/photoamorceur ultra‐violet/amine
Authors: Fouassier Jean P. , Chesneau Eliane 
Published: April 2003

AbstractA study of the photoinitiating system eosin/UV‐photoinitiator/amine has been carried out through time resolved laser spectroscopy. Rates of polymerization of methyl methacrylate have been determined. A model for the photoinitiation step is proposed: the efficient role played by the UV‐photoinitiator is mainly explained in terms of interactions in the excited states; a small contribution to a decrease of the termination reactions of the growing polymer chains by eosinderived radicals is also shown.
Boundary between acceleration and suppression effects of α‐substituent on polymerization and copolymerization of ethyl α‐(halomethyl)acrylates
Authors: Yamada Bunichiro , Otsu Takayuki 
Published: April 2003

AbstractRadical polymerization and copolymerization behaviour of ethyl α‐(halomethyl)acrylates was examined. Among them the bromomethylacrylate did not yield a homopolymer nor a copolymer because of fast chain transfer to the monomer. The chloromethylacrylate (ECMA) polymerized slower to form a lower molecular weight polymer than the fluoromethylacrylate (EFMA). In the copolymerizations with styrene and methyl methacrylate, ECMA was less reactive than EFMA owing to the steric effect of the slightly larger chloromethyl group. The reactivity of EFMA in the copolymerization was enhanced by the polar and resonance effects of the α‐substituent, prevailing over the steric effect. Characterization of the polymers by NMR spectroscopy and thermogravimetric analysis revealed the existence of steric congestion caused by the halomethyl groups in both polymers.
Anionic polymerization of fluorine‐containing vinyl monomers, 10. Studies on anionic polymerization reactivity of hexafluoro‐1,3‐butadiene
Authors: Narita Tadashi , Hagiwara Tokio , Hamana Hiroshi , Sezaki Mahito , Kezuka Namie , Nakagawa Kazuyuki , Nagai Akira , Nishimura Shin , Takahashi Akio 
Published: April 2003

AbstractHexafluoro‐1,3‐butadiene (HFBD), which can be hardly polymerized under radical polymerization conditions, was polymerized with caesium and rubidium compounds as initiators. Among the initiators examined, caesium fluoride, tert‐C4H9OCs, Cs+ (α‐methylstyrene)n2− Cs +, caesium naphthalene (C10H8°Cs+), tert‐C4H9ORb, Rb+ (α‐methylstyrene)n2−Rb+ and rubidium naphthalene (C10H8°Rb+) show surprisingly high activity. Polymerization of HFBD with typical anionic polymerization initiators possessing lithium and sodium as counter cations failed. The ionic radius of the counter cations may thus be important in the anionic polymerization of HFBD. The investigation of the initiation reaction supported the anionic polymerization mechanism. Poly(HFBD) obtained is a white powdery substance which is insoluble in any solvent. Poly(HFBD) possesses a 1,4 microstructure in the main chain as derived from solid‐state 13C NMR and infrared spectra. High thermostability of poly(HFBD) was confirmed by differential scanning calorimetric analysis.
Calculation of average molecular properties during nonlinear, living copolymerization
Authors: Macosko Christopher W. , Miller Douglas R. 
Published: April 2003

AbstractDescribing network formation during chainwise polymerization is more complex than for stepwise (condensation) systems. The kinetics of chain growth must be combined with probability laws for random linking between chains. This approach is used to derive molecular weight averages, gel point and sol fraction during living, anionic copolymerization of vinyl with divinyl monomers. Comparison of predicted molecular weight and gel point to experimental values from Worsfold (1970), Lutz, Beinert and Rempp (1982) and others indicate that a significant amount of intramolecular linking or cyclization occurs in this system.
Star polymers and block copolymers of 2‐oxazolines using chloroformates as initiators
Authors: Dworak Andrzej , Schulz Rolf C. 
Published: April 2003

AbstractPolyfunctional chloroformates were applied to the polymerization of 2‐phenyl‐2‐oxazoline and 2‐methyl‐2‐oxazoline. The use of a trifunctional initiator, viz. the chloroformate of 2,2‐bis(hydroxymethyl)‐1‐butanol, led to three‐arm star polymers of 2‐oxazolines. Two macromolecular initiators, viz. poly(ethylene oxide) with two chloroformate end groups (α‐chloroformyl‐ω‐chloroformyloxypoly(oxyethylene)) with number‐average molar masses 350 g/mol ≤ M̄n ≤ 6000 g/mol and α‐chloroformyl‐ω‐methoxypoly(oxyethylene) with M̄n = 350 and 750 g/mol were applied for the synthesis of poly(2‐oxazoline)‐block‐poly(ethylene oxide)‐block‐poly(2‐oxazoline) and poly(2‐oxazoline)‐block‐poly(ethylene oxide) copolymers, respectively.
Oligomerization of oxiranes in the presence of phosphoric acid. Kinetics of model reaction
Authors: Biela Tadeusz , Kubisa Przemysław 
Published: April 2003

AbstractThe kinetics of the reaction between ethylene oxide and diethyl phosphoric acid (diethyl hydrogen phosphate) was studied in order to elucidate the mechanism of addition of oxiranes to phosphoric acid, the first reaction leading to phosphorus‐containing polyols. It was shown that the reaction proceeds by addition of the activated ethylene oxide molecule to the POH bond. Due to the low ionisation constant of the acid, activation via formation of the secondary oxonium ion plays a minor role, and the reaction proceeds mainly with participation of hydrogen‐bonded complexes.
Thermal transition and frequency response of the dielectric behaviour of some cellulosic substances
Authors: Abdel‐Moteleb Mohamed Magdy 
Published: April 2003

AbstractThe real part of the relative permittivity ϵ′r of some cellulosic materials contaminated with commercial impurities and NaCl (determined as weight percent ash contents), and that of the purified fibres, as well as their hydrolysed residues, free of such contaminations, was measured in the frequency range 102 Hz ≤ f ≤ 105 Hz and in the temperature range 283,15 K ≤ T ≤ 333,15 K. Additional measurements of the imaginary part of relative permittivity ϵ″r have been carried out in the same frequency and temperature ranges for hydrocellulose samples free of inorganic impurities and contaminated with NaCl. The results obtained show that the variation with temperature of the relative permittivity of the samples examined exhibits a change in slope in the vicinity of 303,15 K except for hydrocellulose samples free of impurities. They further show that the presence of inorganic contaminations has a significant effect on the magnitude of the relative permittivity and its variation with temperature, particularly at low frequency. In the case of samples contaminated with inorganic impurities, interfacial polarization is responsible for the anomalous dielectric behaviour observed with the examined samples.
Characterization and detection of polyanions by direct polyelectrolyte titration
Authors: Wassmer Karl‐Heinz , Schroeder Ulrich , Horn Dieter 
Published: April 2003

AbstractA novel technique is described for the investigation of polyanions by direct polyelectrolyte titration. In connection with a specially developed phototitrator, an extremely high sensitivity can be reached using 3,6‐ionene bromide as cationic titrant and eriochrome black T as metachromatic indicator for end‐point detection. This enables both the determination of charge densities for polymer characterization as well as the detection of polymers in aqueous solution down to trace concentrations of 10 μg/L. Monovalent salt ions do not interfere with the titration up to concentrations of about 0,1 mol/L. Potential interference of divalent metal ions can be prevented by adding ethylenediaminetetraacetic acid (EDTA) as chelating agent. The applicability of the method was proved by measuring charge densities of poly(sodium acrylate) (NaPAA) in the concentration range of 0,01 to 10 mg/L and of poly(potassium vinyl sulfate) (KPVS). As expected, the charge density of NaPAA decreases with a pH decrease from 11 to 7, whereas the charge density of KPVS is independent of pH.
Triblock copolymers via thermal “macroiniferters”: Block copolymers of ethyl acrylate with methyl methacrylate or styrene
Authors: Nair Chethrappilly Reghunadhan , Richou Marie Christine , Clouet Gilbert 
Published: April 2003

AbstractThe concept of macro iniferter (MI) was applied to realize the synthesis of triblock copolymers of ethyl acrylate (EA) with styrene (St) or methyl methacrylate (MMA), with EA forming the end blocks. The syntheses involved 3 steps. Secondary amine terminated poly(ethyl acrylate) was synthesisted by polymerization of EA in presence of butyl‐(2‐mercaptoethyl)ammonium chloride as a functional chain‐transfer agent. The macroamine so obtained was converted to the macrothiuram disulfide by reaction with CS2 and I2. Thermal polymerization of MMA or St in presence of this macroiniferter led to the respective triblock copolymers. The kinetics of polymerization of MMA and styrene using MI and two different chain lengths was done in limited concentration ranges. The kinetic parameters indicated that the iniferter action was not affected by the incorporation of the thiuram disulfide groups in the polymer backbone. Triblock copolymers of differing block lengths of hard and soft segments could be prepared by varying the chain length of the macroamine and the concentration of the iniferter in the reaction system. The copolymers were characterized by GPC analysis and spectral or elemental analyses. In the case of St, analysis showed formation of perfect triblocks, whereas for MMA, tendencies to form diblocks were observed on increasing the chain length of the iniferter‐forming block. DSC analyses showed demixing of the soft EA block and the hard central blocks.
13C NMR characterization of ethylene oxide/propylene oxide adducts
Authors: Gronski Wolfram , Hellmann Günther , Wilsch‐Irrgang Anneliese 
Published: April 2003

AbstractAnalytical studies are essential if ethylene oxide (EO)/propylene oxide (PO) adducts are to be comprehensively characterized. Because hardly any detailed information on their structure has previously been available, studies were carried out to assess the value of the information obtained by 13C NMR spectroscopy. The complex identification of the signals undertaken permitted detailed conclusions to be drawn about the structure of these products. The following structure parameters can be determined: Differentiation between random and block copolymers, persistence ratio (measure of the deviation from a fully random statistics), mean sequence lengths of EO/PO sequences, number of blocks per 100 monomeric units, triad probabilities, and starter and end‐groups.
Lichtinduzierte polymer‐ und polymerisationsreaktionen, 44. Zur kinetik der radikalischen photopolymerisation mehrfunktioneller acrylate in polymeren bindemitteln
Authors: Timpe Hans‐Joachim , Strehmel Bernd 
Published: April 2003

AbstractWith calorimetric measurements the kinetics of the free‐radical polymerization of various diacrylates in several polymeric binders have been investigated. The reaction was initiated by radicals formed through photolysis of α‐isopropoxydeoxybenzoin. In each case, the polymerization rate depends on the conversion degree. Mainly, this fact results from changes in the termination mechanism of the polymerization chain reaction. By means of the light intensity exponent such mechanistical changes can be quantitatively followed. Both, the results obtained by stationary and non‐stationary irradiation experiments lead to the same conclusions. The properties of the polymeric binders possess a stronger influence on the kinetics compared with the structural changes of the diacrylates used.
Polymer‐bound porphyrins and their precursors, 10. Syntheses and photoredox properties of water‐soluble polymers with covalently bonded zinc tetraphenylporphyrin
Authors: Wöhrle Dieter , Paliuras Mihail , Okura Ichiro 
Published: April 2003

AbstractPositively or negatively charged as well as uncharged water‐soluble polymers 2a – d, 6a – c, 7a – e and positively charged crosslinked polymers 3a, b containing covalently bonded moieties of the substituted zinc tetraphenylporphyrin 1a were prepared. In addition, positively charged polymers 4a – c with covalently bonded viologen, and 5 with covalently bonded 1a and viologen at one and the same polymer chain were obtained. The triplet lifetimes in water of different 1a‐ bonded linear polymers 2a – d, 6a – c, and 7a – e are not influenced by the kind of polymer environment. The photoredox activites in water of the polymers containing moieties of 1a in the presence of methylviologen and 2‐mercaptoethanol under irradiation with visible light are higher as compared with low‐molecular‐weight, positively or negatively charged porphyrins 1b, c. The influence of the amount of polymer‐bonded porphyrin and the molecular weight of a polymer on the photoredox activity is exemplarily described. Polymers 4a – c with viologen moieties as acceptor are more efficient than the low‐moleular‐weight methylviologen. The highest photoredox activities were observed with polymer 5 containing moieties of 1a and viologen. In the presence of the enzyme hydrogenase formation of hydrogen occurs.
Structural modifications of poly(1,4‐phenylenevinylene) to soluble, fusible, liquid‐crystalline products
Authors: Martelock Heidi , Greiner Andreas , Heitz Walter 
Published: April 2003

AbstractThe synthesis, solubility, and thermal behavior of soluble, fusible, liquid‐crystalline derivatives of poly(1,4‐phenylenevinylene) (1) is described. The improved solubility and fusibility were accomplished by reducing interchain interactions without change of the rigid rod‐like character. The interchain interactions were lowered by decreasing the structural regularity of the repeating units. The synthesis of derivatives of 1 was accomplished by the palladium‐catalyzed coupling of dihalogenoarenes and ethylene to avoid cis‐vinylene units. Irreversible crosslinking was observed from fusible products on annealing above the softening point.
1H and 13C NMR sturctural investigation of some titanium alkoxide‐magnesium halide complexes as Ziegler‐Natta catalyst precursors
Authors: Abis Luigi , Bacchilega Giancarlo , Spera Silvia , Zucchini Umberto , Dall'Occo Tiziano 
Published: April 2003

AbstractSeveral [Ti2(OR)8MtX2]2 complexes were prepared from MtX2 (Mt = Mg, Zn; X = Cl, Br, I) and Ti(OR)4 (R = ethyl, propyl, butyl). 1H and 13C NMR in toluene‐d8 solution and cross‐polarization/magic‐angle spinning (CP/MAS) 13C NMR spectra were taken of some complexes. The obtained spectra allowed to deduce their molecular structure in solution and to compare them with that of [Ti2(OC2H5) 8Cl]2Mg2Cl2 obtained by single‐crystal X‐ray diffraction analysis.
Polymerization in inverse microemulsions, 2. Copolymerization of water‐ and oil‐soluble monomers initiated by 2,2′‐azoisobutyronitrile
Authors: Vas̆ková Viera , Juranic̆ová Viera , Barton̆ Jaroslav 
Published: April 2003

AbstractCopolymerization of the water‐soluble monomer acrylamide (AAM) with the oil‐soluble monomer methyl methacrylate (MMA) and/or styrene (St) in inverse microemulsion initiated with 2,2′‐azoisobutyronitrile was studied. It was found that the overall polymerization rate increases with increasing mole fraction of AAM in the comonomer mixture, while the composition of the product changes only slightly. The copolymerization process is a typical “dead‐end” polymerization where the limiting conversion corresponds to the AAM concentration in the comonomer mixture. The concentration of MMA, resp. St at the locus of copolymerization was calculated as a function of the AAM mole fraction in the comonomer mixture.
Thin film processing of nonlinear optical materials, 2. Comb‐like polymers containing nonlinear optical active pendant groups
Authors: Mandal Braja K. , Takahashi Toru , Maeda Mutsumi , Kumar Sai , Blumstein Alexandre , Tripathy Sukant 
Published: April 2003

AbstractThe synthesis and characterization of new homopolymers and copolymers containing π‐extended (azomethine) active moieties separated by flexible methylene spacers are reported. All synthesized monomers and polymers show spectroscopic properties (nuclear magnetic resonance, infrared, ultraviolet) in accordance with the proposed structures. The inherent solubility of the polymers in common organic solvents permits the determination of the molecular weight distribution from gel‐permeation chromatography. The thermal characteristics of the polymers are also described.
Polyimides derived from ether ketone diamines
Authors: Rao Vattikuti L. , Bijimol Jacob 
Published: April 2003

AbstractPolyimides were prepared from the reaction of two aromatic dianhydrides with two diamines containing carbonyl and ether connecting groups between the aromatic rings. The diamines were prepared from the reaction of 4‐aminophenol or (3‐aminophenol) with an activated aromatic difluoro compound (4,4′‐difluorobenzophenone) in the presence of potassium carbonate. Some of these polyimides were shown to be semicrystalline as evidenced by wide‐angle X‐ray diffraction. Glass transition temperatures were observed between 203 and 242°C. All polyimides were found to be thermally stable up to 400–450°C with a char yield of about 50–60% at 900°C. The effect of the structure on the properties of polyimides, such as crystallinity, glass transition temperature and thermal behaviour, is discussed.
Surface tensions of liquid‐crystalline and isotropic polymer melts
Authors: Uzman Mehmet , Song Bihai , Runke Thomas , Cackovic Hinko , Springer Jürgen 
Published: April 2003

AbstractThe surface tensions (γ) of a branched polyethylene and two side‐group liquid‐crystalline (lc) polyacrylates were measured in the isotropic, nematic and smectic states by the pendant‐drop method. The surface tension vs. Temperature characteristics of the lc polyacrylates studied show anomalous behaviour. The slope in the isotropic state is initially negative but changes its sign near the isotropic‐nematic transition. The increase of γ with decreasing temperature is regained in the nematic phase, until at the nematic‐smectic transition the surface tension of the lc polymers discontinuously jumps to higher values and shows a very low temperature coefficient. The observed features have been found to be partly in agreement with the results of surface tension measurements on low‐molar‐mass liquid crystals, which indicates that the surface properties of the lc polymers are governed by the mesogenic side groups.