bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ein neuartiges Verfahren zur Bestimmung der Molmassen Breit verteilter polymerer mit Hilfe der Gelpermeations‐Chromatographie und der viskosimetrie am Beispiel Hämoglobin‐hyperpolymerer
Authors: Pötzschke Harald , Barnikol Wolfgang K. R. , Domack Ulrike , Kirste Rudolf G. 
Published: April 2003

AbstractAn iterative, approximative procedure is presented, to calibrate the determination of molar masses of polymers with gel‐permeation chromatography, additionally using viscometry, and transformations, according to Benoit's concept of universal calibration, even if only polymers with broad molar mass distribution are available. The calculated (intermediate) values of the average molar masses from each step of iteration converge to final values. With at least two fractions of the polymers to be analyzed, and with measured intrinsic viscosities of the fractions, a calibration curve of gel‐permeation chromatography and Mark‐Houwink's constants can be determined. Assumptions for the use of the calibration procedure are the existence of linear calibration curves for gel‐permeation chromatography, constant Mark‐Houwink's exponents, and a common universal calibration curve according to Benoit, of the polymers of interest, and of another polymer for comparison. From this second polymer the Mark‐Houwink equation must be known (or measurable with acceptable expense), and sufficient uniform fractions for chromatography must be available. In aqueous saline the assumptions are fulfilled by hyperpolymers of human haemoglobin, and by native proteins, as shown in a previous paper. The new procedure was applied to fractions of those hyperpolymers, it was evaluated, and variants of the procedure were compared. The evaluation was done by comparison of the number‐and mass‐averages of the molar masses of the fractions of haemoglobin hyperpolymers, determined with gel‐permeation chromatography calibrated with the new procedure, with the values obtained from osmometry and light scattering. The goodness of the new procedure, especially the power of correction of molar masses, can be demonstrated with the application to fractions of haemoglobin hyperpolymers, it changes with their uniformity. Furthermore, the new procedure shows its efficiency, when three steps of iteration are enough to reach the final values. At last, with a Benoit transformation of the averages of molar masses, obtained by a theoretical consideration within the given marginal conditions, a rectification of the new procedure is given.
Coordination polymerization of lactides, 5. Influence of lactide structure on the transesterification processes in the copolymerization with ε‐caprolactone
Authors: Bero Maciej , Kasperczyk Janusz 
Published: April 2003

AbstractThe influence of lactide configuration on the chain microstructure of lactide/ε‐caprolactone copolymer was investigated. The copolymerization was carried out in the presence of Al(acac)3, AlEt3 and ZnEt2 as initiators. The chain microstructure analysis of the copolymers was performed by means of 13C NMR spectroscopy. The effect of lactide configuration on the transesterification and randomization of the copolymer chain was determined. The contribution of transesterification processes in the case of D,L‐lactide was found to be considerably higher than that observed when L,L‐lactide was used.
Liquid crystalline main‐chain polymers containing the ferrocene unit as a side group
Authors: Wilbert Götz , Zentel Rudolf 
Published: April 2003

AbstractWe have incorporated three new diethyl ω‐ferrocenylalkylmalonates into a smectic liquid crystalline main‐chain polymer in contents of about 10 mol‐%. As mesogenic unit 4,4′‐bis(6‐hydroxyhexyloxy)azoxybenzene was used as diol component and diethyl phenylmalonate as diacid component. Three ferrocene‐containing polymers were investigated in the oxidized and non‐oxidized state of the ferrocene unit varying the counterion. DSC data show a shift toward higher phase transition temperatures after oxidation, which increases with the length of the alkyl spacer between main chain and ferrocene unit. X‐ray measurements of the non‐oxidized species show an unusual increase of the smectic layer thickness with increasing length of the alkyl spacer.
Molecular structure of some model compounds for poly(aryl ether ketone)s
Authors: Shibata Mitsuhiro , Yosomiya Ryutoku , Zheng Yu‐Bin , Ke Yang‐Chuan 
Published: April 2003

AbstractThe molecular structure of a series of model compounds for poly(aryl ether ketone)s was investigated by means of 13C NMR spectroscopy, quantum chemical calculation, and wide‐angle X‐ray scattering. The comparison of the chemical shifts for the model compounds dissolved in 98% H2SO4 and CDCl3 (or CDCl3 + DMSO‐d6) suggested that their carbonyl groups are partially protonated by sulfuric acid and the induced positive charges are delocalized in their aromatic rings. This result was supported by the charge distribution obtained by quantum chemical calculations. The model compounds were also used to characterize the molecular structure of poly(aryl ether ketone)s. The length of the repeating unit of the polymer chain, which was calculated based on the whole chain length or fragment chain length of the model compounds obtained by semiempirical PM3 method, is compared with the c‐axis of the crystal unit cell of the polymer. For poly(aryl ether ketone)s containing biphenyl moieties, the length of the c‐axis of the unit cell is approximately twice that of the repeating unit of the macromolecule.
Electrosynthesis of poly(3‐methylthiophene) films with high strength and stabile conductive properties
Authors: Zhou Liang , Jin Shi , Xue Gi 
Published: April 2003

AbstractThe electrochemical polymerization of 3‐methylthiophene was significantly facilitated by the presence of freshly distilled boron fluoride‐ethyl ether as supporting electrolyte and stainless steel as electrode during the polymerization. The lower oxidation potential of the monomer led to high overall stereoregularity and stacking order of poly(3‐methylthiophene) chains. A current density of 1 mA/cm2 and a monomer concentration of 35–70 mmol/L turned out to be optimal electrosynthesis conditions. Poly(3‐methylthiophene) films had high tensile strength (73 MPa) and flexibility. The high stereoregularity of poly(3‐methylthiophene) resulted in high conductivity with improved environmental stability.
Reactive groups on polymer covered electrodes, 4. Lactate‐oxidase‐biosensor based on electrodes modified by polythiophene
Authors: Welzel Hans‐Peter , Kossmehl Gerhard , Engelmann Gunnar , Neumann Barbara , Wollenberger Ulla , Scheller Frieder , Schröder Werner 
Published: April 2003

AbstractElectrocopolymerization of 3‐thiopheneacetic acid (1) and 3‐methylthiophene (2) under various conditions produces poly{(3‐methylthiophene‐2,5‐diyl)‐co‐[3‐(carboxymethyl)thiophene‐2,5‐diyl]} (3). By activation of the carboxy groups with dicyclohexylcarbodiimide (DCC) lactate oxidase (LOD) is covalently bonded to the surface of the electrode. In this way a lactate sensor was formed which is applicable for the determination of lactate in micromolar concentrations.
Liquid crystalline networks of polymethacrylates
Authors: Pfaffernoschke Matthias , Wolff Dietmar , Rübner Joachim , Springer Jürgen 
Published: April 2003

AbstractLC networks on the basis of methacrylate and dimethacrylate components were synthesized via bulk and precipitation copolymerization. Up to an amount of crosslinking component of 1 mol‐% a smetic A phase is observed. The networks with 3 and 5 mol‐% only show a nematic phase. From X‐ray diffraction an orientation of the smectic phase was observed that derives from surface effects or biaxial swelling. It was found that the orientation can be increased by multiple swelling/deswelling cycles.
Crystallization from the melt of poly(lactide)s with different optical purities and their blends
Authors: Tsuji Hideto , Ikada Yoshito 
Published: April 2003

AbstractPoly(lactide)s (PLA) with different optical purities (OP) were synthesized by copolymerization of D‐lactide and L‐lactide. Crystallization of D‐ and L‐lactide‐rich copolymers before and after 1 : 1 blending was studied from the melt over a wide range of annealing temperatures (Ta) using differential scanning calorimetry and polarizing microscopy. Melting temperature and crystallinity increased with an increase in OP for both the non‐blended and the 1 : 1 blended PLAs and they lost their crystallizability when their OP became smaller than 76%, suggesting that the critical isotactic sequence length of PLA for crystallization was approximately 15 isotactic lactate units. Normal spherulite formation was observed for both the non‐blended and the blended PLAs even when the OP of PLAs decreased to 76%, whereas the spherulitic size of the non‐blended PLAs was larger than that of the 1 : 1 blended PLAs when compared at the same OP and Ta. The highest Ta for crystallization increased with increasing OP and was higher for the 1 : 1 blended PLAs than for the non‐blended PLAs at a fixed OP, indicating that the crystallizable Ta range was extended to higher temperature by blending D‐ and L‐lactide‐rich PLAs. This is ascribed to stereocomplex (racemic crystallites) formation at high Ta from the 1 : 1 blended PLAs. Based on these results, the phase diagram for crystallization was depicted for the non‐blended and the 1 : 1 blended PLAs.
Polymerizations of butadiene with Ni(acac)2‐methylaluminoxane catalysts
Authors: Endo Kiyoshi , Uchida Yoshiki , Matsuda Yuichi 
Published: April 2003

AbstractPolymerizations of butadiene (BD) with transition metals (MtX) and methylaluminoxane (MAO) catalysts were studied. Among the catalysts examined, nicke(II) acetylacetonate [Ni(acac)2] in combination with MAO revealed the highest catalytic activities for the polymerization of BD, giving high molecular weight polymers consisting of mainly cis‐1,4‐units in the microstructure. With Ni(acac)2‐MAO catalyst, the overall activation energy for the polymerization of BD between 0°C and 60°C was estimated to be 18 kJ/mol. From a kinetic study, the rate equation for the polymerization of BD with the Ni(acac)2‐MAO catalyst at 30°C can be expressed as follows: Rp = [BD]1.8 [Ni(acac)2‐MAO]0.9. The polymerization mechanism of the polymerization of BD with the Ni(acac)2‐MAO catalyst is discussed.
Anionic polymerization of 2‐vinylpyridine: a computational study of solvent effects on polymerization stereochemistry.
Authors: Pratt Lawrence M. , Khan Ishrat M. , Hogen‐Esch Thieo E. 
Published: April 2003

AbstractAnionic polymerization of 2‐vinylpyridine shows significant solvent effects on the polymer stereochemistry. Polymerization with butyllithium in tetrahydrofuran (THF) yields a largely isotactic polymer, while polymerization with butyllithium in tetramethyl‐ethylenediamine (TMEDA) results in a material with nearly the same stereochemistry as radical polymerization. Semiempirical molecular orbital calculations were used to explain these solvent effects.
Enzyme‐catalyzed synthesis of poly(1,6‐hexanediyl maleate‐co‐fumarate) in organic medium. Study of macrolactone formation in relation to the composition of the initial monomer mixture
Authors: Mezoul Gilles , Lalot Thierry , Brigodiot Maryvonne , Maréchal Ernest 
Published: April 2003

AbstractThe lipase‐catalyzed synthesis of poly(1,6‐hexanediyl maleate‐co‐fumarate) from 1,6‐hexanediol, dimethyl maleate and dimethyl fumarate is described. No secondary reaction involving the double bounds takes place, so that the copolyester composition can be well defined by adjusting the mole fraction of the dimethyl esters in the initial monomer mixture. The average molar masses of the non‐fractionated copolyesters depend on the mole fraction of the dimethyl maleate and are correlated with the amount of macrocycles formed. The possibility that the reaction system obeys a ring‐linear chain equilibrium is discussed. Linear polyester chains and macrolactones are characterized by 1H NMR spectroscopy, steric exclusion chromatography and tonometry. A comparison is made with the homopolyester syntheses which were described in previous works.
Synthesis and characterization of polyoxetanes containing 4‐cyanobiphenyl‐based side groups for nonlinear optical applications, 2. Synthesis, characterization and polymerization of 3,3‐bis(4‐cyano‐4′‐biphenylyloxymethyl)oxetane
Authors: Guichard Bertrand , Poirier Véronique , Noël Claudine , Reyx Danièle , Le Borgne Alain , Leblanc Marc , Large Maryanne , Kajzar François 
Published: April 2003

Abstract3,3‐Bis(4‐cyano‐4′‐biphenylyloxymethyl)oxetane was prepared by reaction of 3,3‐bis‐(chloromethyl)oxetane with the sodium salt of 4‐cyano‐4′‐hydroxybiphenyl. With highly purified dichloromethane, single crystals could be prepared. The X‐ray patterns could be indexed in terms of a monoclinic cell a = 13,87 Å, b = 14,74 Å, c = 13,91 Å and β = 118,68°. Some experiments were carried out to determine the cationic polymerization behavior of this oxetane. The initiating system BF3 ċ Et2O/dichloromethane was used and it was shown that unusually high initiator concentrations were necessary to observe polymerization. By means of steric exclusion chromatography and NMR spectroscopy, the formation of cyclic oligomers was evidenced. Upon heating, all the polymers showed a nematic phase. Some preliminary Corona poling experiments were performed and the second harmonic generation coefficients d31 and d33 were measured. It was shown that one can gain in net polar ordering by starting with a liquid crystalline system. The ratio d33/d31 was found to be much larger than 3 in agreement with the molecular statistical models for electric field poling of liquid crystals.
Thermodynamics of 5,5‐dimethylperhydro‐1,3‐oxazin‐2‐one, its polymerization in bulk and poly(5,5‐dimethyl‐2‐oxo‐1‐oxa‐3‐azahexamethylene) between 0 K and 500 K
Authors: Lebedev Boris , Smirnova Natal'ya , Telnoy Vadim 
Published: April 2003

AbstractThe thermodynamic properties of the six‐membered cyclic urethane, viz. 5,5‐dimethylperhydro‐1,3‐oxazin‐2‐one (DIO, 1) and the corresponding polymer, poly(5,5‐dimethyl‐2‐oxo‐1‐oxa‐3‐azahexamethylene) (PDIO, 2) were studied by calorimetry. The temperature dependence of the heat capacity at constant pressure Cp0 of the monomer and the polymer was studied between 5 K and 500 K. Temperatures and enthalpies of physical transitions were determined. The energies of combustion of the above compounds were measured. From the results the thermodynamic functions Cp0(T)–H0(O), S0(T) G0(T)–H0(O), were calculated for various physical states of the monomer and the polymer from 0 K to 500 K. The standard enthalpies of combustion ΔHcomb0 and the thermochemical parameters of formation of DIO and PDIO were estimated at temperature T = 298,15 K and pressure p = 101,325 kPa. The zero entropy Sgt0(O) and configurational entropy Sconf0 of PDIO in the glassy state were evaluated. The thermodynamic parameters of the bulk polymerization of DIO were calculated in the range of 0 K to 400 K at standard pressure. It was established that an equilibrium of the polymerization reaction of DIO to PDIO is shifted towards the formation of the monomer in the whole temperature range studied from 0 K to 450 K.
Bismaléimides et polybismaléimides à pont éther et thioéther—synthèse, réactivité et tenue thermique
Authors: Milano Jean Claude , Mekkid Said , Vernet Jean Louis 
Published: April 2003

AbstractThis paper describes the synthesis and characterization of six structurally different bismaleimides. They were prepared by reacting maleic anhydride with diamines containing ether and thioether bridges. Thermal polymerization of these monomers in the presence or absence of radical initiators was investigated by differential scanning calorimetry. Activation energy (E), kinetic order (n), rate constants (k) and heat of polymerization (ΔH) were determined. The cured resins are stable up to 334–418°C both in argon and air atmosphere.
Study on the enantioselective oligomerization of 1‐butene by chiral non‐racemic Ti complexes fixed on MgCl2
Authors: Fuhrmann Hans , Kortus Karin , Fuhrmann Christa 
Published: April 2003

AbstractA number of chiral non‐racemic titanium complexes of the type (R*O)2TiCl2 (R* being an enantiomerically pure monosaccharide derivative) was incorporated in a MgCl2 matrix by coprecipitation from a non‐solvated n/iso‐Bu2Mg solution with CCl4. The precatalysts formed were activated with different organoaluminium cocatalysts and used for the oligomerization of 1‐butene. In dependence of the cocatalyst and the temperature various reaction pathways were observed. In most cases saturated oligomers were isolated. At −20°C with i‐Bu3Al2OBuCl2 as cocatalyst 55–65% olefinic oligomers with 50–70% enantiomeric excess (ee) are formed. If the growing chain is terminated by chain transfer to the Al cocatalyst, epimerization of the last inserted monomer occurs, possibly due to a rearrangement which might be favoured by an agostic interaction. The fixation of TiCl4 to a chiral modified MgCl2 support does not lead to enantiomerically enriched oligomers under the same reaction conditions.
Molecular dynamics in liquid crystalline N‐acylated oligoethylenimines as studied by broadband dielectric spectroscopy
Authors: Groothues Herbert , Kremer Friedrich , Plesnivy Thomas , Ringsdorf Helmut 
Published: April 2003

AbstractThe molecular dynamics and the charge transport in six liquid crystalline N‐acylated oligoethylenimines were investigated by dielectric spectroscopy. The dielectric spectra in the temperature range from 125 K up to 400 K and in the frequency range between 10−2 Hz and 107 Hz could be described by a conductivity contribution and three relaxation processes. The molecular assignment of the α‐process is a relaxation of the rigid benzamide unit. Its mean relaxation time is influenced by the length of the alkoxy side chains, the spacer length (ethylene or propylene groups) and the neighboring repeating units. In the columnar mesophase this process is cooperative due to sterical hindrance. A normalized g‐factor expressing the intermolecular cooperativity was calculated. The cooperativity increases when approaching the glass transition temperature. The γ‐process is assigned to local librational motions of the alkoxy side chain involving the ether linkage. It has an Arrhenius‐like temperature dependence (activation energy ΔEa = 22–32 kJ/mol). The β‐process is presumably a libration at the end of the alkyl chains. The conductivity contribution to the imaginary part of the dielectric function ε″ is frequency independent except for very low frequencies where electrode polarization causes a decrease in the measured conductivity. The charge transport is strongly influenced by the phase transitions isotropic to columnar and columnar to crystalline, but not by the glass transition.
New polymers by metallocene catalysis
Authors: Kaminsky Walter 
Published: April 2003

AbstractWork in the field of application of metallocene‐based catalysis in olefin, diolefin and styrene polymerization has become a research topic of growing interest in recent years. A great number of symmetric and chiral zirconocenes have been synthesized, that give tailored polymers of totally different structures. Single site catalysts have the capability of permitting the user to control polymer tacticity, molecular weight and molecular weight distribution more efficiently. Beside the homopolymers of polyethylene and poly(propylene), new kinds of copolymers and elastomers can be synthesized.
Synthesis of thiol‐ and carboxyl‐terminated poly(p‐phenylene sulfide) oligomers
Authors: Yu Zili , Miao Guoxiang , Wu Qixian , Chen Yongrong 
Published: April 2003

AbstractPoly(p‐phenylene sulfide) (PPS) oligomers were synthesized from sodium sulfide (SS) and p‐dichlorobenzene (p‐DCB) in hexamethylphosphoramide (HMPA) under atmospheric pressure. The effects of reaction time, temperature, and monomer ratio on end groups and molecular weight of PPS oligomers were investigated. The results show that the molecular weight is controlled by the above parameters. Thiol‐terminated PPS oligomers were prepared by two routes. One was the polycondensation of p‐DCB with equimolar SS followed by the reaction with an extra amount of SS. The other was the depolymerization of high molecular weight PPS with SS in HMPA. The results show that the second route is the best one for preparation of thiol‐terminated PPS oligomers. Carboxylterminated PPS telechelic oligomers were produced through the reaction of thiol‐terminated PPS oligomers with p‐chlorobenzoic acid.
Synthesis of ferroelectric liquid‐crystalline polymethacrylates containing 1,2‐diphenylethane based mesogens
Authors: Hsu Chain‐Shu , Her Bin‐Sheng 
Published: April 2003

AbstractThe synthesis of side‐chain liquid‐crystalline polymethacrylates containing (2S)‐2‐chloro‐4‐methylvaleric acid end groups and 1,2‐diphenylethane based mesogenic units is presented. Differential scanning calorimetry, optical polarizing microscopy and X‐ray diffraction were used to determine the thermal transitions and to analyze the anisotropic phases. Among the methacrylate monomers prepared in this study, those without lateral chloro substituent show only a smetic A phase while those with a lateral chloro substituent display a cholesteric phase. All polymers exhibit smectic mesomorphism and do not undergo side‐chain crystallization. All four polymethacrylates without lateral chloro substituents reveal enantiotropic smectic A and smectic B phases while the other four polymethacrylates with lateral chloro substituents reveal enantiotropic smectic A and chiral smectic C phases. The results seem to demonstrate that incorporating a lateral chloro substituent into the mesogenic core enhances the formation of a tilted chiral smectic C phase.
Synthesis and electro‐optical properties of polyurethanes with nitrostilbene side chains
Authors: Jin Shengyu , Wübbenhorst Michael , Turnhout Jan Van , Mijs Wim 
Published: April 2003

AbstractTwo side‐chain polyurethanes, HMDI‐PU (2a) and TDI‐PU (2b), have been synthesized from 2,2′‐iminodiethanol (“diethanolamine”) N‐substituted with a nitrostilbene group on a hexamethylene spacer with, respectively, hexamethylene diisocyanate and 1‐methyl‐2,4‐phenylene diisocyanate (“2,4‐toluenediisocyanate”). 2a showed a smectic liquid‐crystalline phase; 2b proved to be amorphous. The phase behavior was characterized by means of differential scanning calorimetry, polarization microscopy and wide‐angle X‐ray scattering. Thermally stimulated discharge current measurements (TSD) revealed at least two strong relaxation processes above the glass transition temperature Tg which are related to the dynamic glass transition involving the backbone part (α) and the mesogenic units (λ). Non‐linear optical analysis of 2a showed that the Pockels coefficient r13 was low in the mesophase and high in the isotropic phase. Contrary to expectation, poling in the mesophase did not enhance the Pockels effect. The amorphous 2b gave both a high and a stable Pockels coefficient (r33 around 6.0 pm/V). The stability could be improved by ageing and prolonged poling at the ageing temperature. However, the Pockels coefficient proved to be dependent on the temperature: high above 85°C, low below 85°C (provided that the sample had been heated once before). This was attributed to an antiparallel association of the chromophores. The role of hydrogen bonds influencing poling has been assessed by temperature‐dependent infrared spectroscopy.