bluuebunny/crossref_metadata_2025_split huggingface dataset:
Configurational double bond selectivity in the epoxidation of hydroxy‐terminated polybutadiene with m‐chloroperbenzoic acid
Authors: Aguiar Marcelo , de Menezes Sonia Cabral , Akcelrud Leni 
Published: April 2003

AbstractThe selectivity of the three different double bonds (CIS, TRANS and VINYL) of hydroxyterminated polybutadiene regarding epoxidation was evaluated, using m‐chloroperbenzoic acid in toluene below room temperature (−10°C, −5°C, 0°C and 5°C). To determine the kinetic constants for the three configuratons (k1,cis = (2,59–0,6) × 10−2 L · mol−1 · min−1; k2, trans = (5,35–0,82) × 10−2 L · mol−1 · min−1; k3, vinyl = (0,97–0,01) × 10−2 L · mol−1 min−1), 1H and 13C NMR was used along with a system of three parallel equations. The activation energy values were also evaluated (Ea, cis = 53,9 kJ · mol−1; Ea, trans = 70,7 kJ · mol−1 and Ea, vinyl = 261,1 kJ · mol−1) for the three double bond types.
Ultrathin crosslinked membranes at the interface between oil and water
Authors: Burger Andreas , Leonhard Herbert , Rehage Heinz , Wagner Ronald , Schwoerer Markus 
Published: April 2003

AbstractThe tensio‐active properties of different types of diesters can be used to synthesize two‐dimensional model networks at the interface between oil and water. We have systematically studied rubber‐elastic, glass‐like and transient membranes, which are stabilized and crosslinked by physical or chemical contacts. The kinetics of surface gelation and the mechanical properties of the crosslinked membranes were investigated by measuring two‐dimensional rheological parameters, such as the shear modulus or the surface viscosity. The experimental data of these investigations are in fairly good agreement with the theoretical predictions of percolation theories. Further informations on the molecular structure of the crosslinked membranes can be obtained from electron spin resonance (ESR) measurements. Using spin labels of significantly different sizes, which are diffusing from the aqueous environment into the oil phase, it is possible to determine the average mesh size of the interfacial network structure. The systematic study of these ultrathin membranes offers new insights into aspects of current research, and opens interesting new technical applications.
Rheo‐optical characterization (flow‐birefringence and flow‐dichroism) of the Tobacco Mosaic Virus
Authors: Reinhardt Ulf T. , de Groot Eleanor L. Meyer , Fuller Gerald G. , Kulicke Werner‐Michael 
Published: April 2003

AbstractRheo‐optical techniques of determining flow‐birefringence Δn′ and flow‐dichroism Δn″ were employed to investigate a Tobacco Mosaic Virus (TMV) solution under steady‐state and relaxation conditions to obtain further information about molecular dynamics in terms of local and global orientation and flexibility. These effects were investigated in a concentration range of 0,5 g/L ⩽ c ≦ 2,89 g/L, i.e. below and above the critical overlap concentration c* = 2,45 g/L. Although some aggregation was unavoidable it was determined that in the region of c* the dynamic behaviour was not influenced by varying the concentration. Furthermore it was shown that these aggregates naturally appearing in TMV are sensitive to shear force and dissolve at shear rates above 1 s−1. Beyond the critical shear rate this rodlike molecule should show a good agreement of the orientation angles determined through dichroism and birefringence and a constant ratio Δn″/Δn′ which in fact was found. This reveals experimentally that in spite of the sensitivity to different length scales dichroism and birefringence exhibit similar responses to shear forces for rigid and monodisperse macromolecules.
Poly(methyl methacrylate) containing pyrrole moieties in the side chains
Authors: Hallensleben Manfred L. , Stanke Dietmar , Toppare Levent 
Published: April 2003

AbstractTwo synthetic routes to copolymers 7 of methyl methacrylate (MMA) with 2‐(N‐pyrrolyl)ethyl methacrylate (PEMA, 11) are compared. Copolymerization of MMA (4) with 2‐bromoethyl methacrylate (BEMA, 3) leads to a precursor copolymer 5. The reactivity ratios are close to unity (rMMA = 0,90, rBEMA = 0,92). The polymer‐analogous reaction of 5 with N‐pyrrolylpotassium (6) runs to 99% conversion of the BEMA units. The synthesis of PEMA (11) is presented. The reactivity ratios of copolymerization of this monomer (11) with MMA (4) are determined to rMMA = 1.05 and rPEMA = 1,65. Copolymers 7 are further characterized by 1H nuclear magnetic resonance, infrared spectroscopy, gel‐permeation chromatography and differential scanning calorimetry.
Hexa‐n‐alkylcyclotrisiloxanes — synthesis, melting behaviour and polymerization
Authors: Out Gerhardus J. J. , Klok Harm‐Anton , Möller Martin , Oelfin Dieter 
Published: April 2003

AbstractA homologous series of hexa‐n‐alkylcyclotrisiloxanes and poly(di‐n‐alkylsiloxane)s has been prepared with alkyl side groups varying in length between 4 and 10 carbon atoms. Melting transition enthalpies of the hexa‐n‐alkylcyclotrisiloxanes indicated a reversed odd‐even effect, showing higher melting enthalpies for cyclotrisiloxanes with n‐alkyl side groups with an odd number of carbon atoms. The melting behaviour of the heptyl‐ and octyl‐substituted cyclotrisiloxanes was rather complex. Multiple melting transitions could be observed, which are presumably due to formation of a kinetically favoured crystalline phase next to the thermodynamically stable crystal modification. All hexa‐n‐alkylcyclotrisiloxanes could be polymerized by anionic or cationic ringopening polymerization. The observation of longer polymerization times and formation of relatively larger amounts of cyclic byproducts in the case of hexadecylcyclotrisiloxane compared to hexaethylcyclotrisiloxane indicated that with increasing side group length, the anionic polymerization propagation rate constants kp decreased, whereas the rate constants of depolymerization kdx increased. Cationic polymerization with trifluoromethanesulfonic acid as the initiator, offered a way to enhance kp relative to kdx, which allowed the preparation of high molecular‐weight polymeric products in good yields even in case of cyclotrisiloxanes substituted with long n‐alkyl groups. Apart from poly(dimethylsiloxane), poly(diheptylsiloxane) and poly(dinonylsiloxane), all poly(di‐n‐alkylsiloxane)s showed two crystalline phases which were separated by a crystal‐crystal transition signifying melting of the side groups. Starting from poly(diethylsiloxane), poly(di‐n‐alkylsiloxane)s up to poly(dihexylsiloxane) displayed a hexagonal columnar mesophase as well, the stability of which increased with longer alkyl side groups. However, further elongation of the n‐alkyl side groups to decyl appeared to destabilize the columnar mesophase. Poly(didecylsiloxane) only exhibited a metastable columnar mesophase in combination with the high‐temperature crystalline phase.
Poly(cycloalkyl[c]thiophene)s — syntheses, electrical properties and charge transport mechanism
Authors: Rühe Jürgen , Berlin Anna , Wegner Gerhard 
Published: April 2003

AbstractPoly(cycloalkyl[c]thiophene)s were synthesized by electrochemical or chemical oxidation of bicyclic, α,α′‐unsubstituted thiophenes. NMR measurements on neutral, soluble poly(cyclododeca[c]thiophene) indicate that the polymers have the expected linear structure. The optical spectra and the electrochemical properties of the films are reported. The electrical conductivity σ of salts of the polymers varies from 50 S/cm to 8 · 10−5 S/cm depending on the ring size of the substituent and degree of oxidation of the polymer backbone. A linear correlation between log σ and the diameter of the alkyl substituent demonstrates that interchain contacts play a dominant role in the conductivity of these polymers. The temperature dependence of the conductivity was measured in the range of 300 to 5 K and its frequency dependence in the range of 1–107 Hz at 300 to 120 K. The conductivity data were analyzed in terms of hopping of localized charge carriers and the localization length of the charge carriers was calculated.
Morphology and structure of organosilicon polymer‐modified epoxy resins
Authors: Zheng Sixun , Wang Haiqian , Dai Qizhou , Luo Xiaolie , Ma Dezhu , Wang Ke 
Published: April 2003

AbstractAn epoxy‐terminated organosilicon polymer (denoted as ETOP) was used as modifier to blend with bisphenol A type epoxy resins. For uncured epoxy resins/ETOP blends, the miscibility is mainly the contribution of entropy. The phase boundary was investigated. The turbidity points were determined on the basis of optical microscopic observation. While the aromatic amine curing agents were added to the systems, curing at higher temperature, an obvious phase separation between cured bisphenol A type epoxy resins (DGEBA) and ETOP was observed. The structure of the resulting cured products was investigated by differential scanning calorimetry (DSC), dynamic mechanical property analysis (DMA) and scanning electron microscopy (SEM). It is the very elastomeric phase (0,1–5 μm) that enhances the toughness of epoxy resins. Another significant phenomenon is that the crosslinked epoxy‐rich phase (matrix) possesses a higher glass transition temperature (Tg) than pure epoxy resins cured with an aromatic amine, particularly at a higher content of ETOP. This may be considered as participation of epoxide groups on ETOP molecules in the crosslinking reaction of matrix and enhancing the crosslinking density of the matrix (i.e., increasing the Tgs). The results provide ones a larger choice to improve the toughness of the epoxy resin without loss of substantial modulus and thermal resistance.
Copolymers of N‐vinyl‐2‐pyrrolidone and 2‐(dimethylamino)ethyl methacrylate, 1. Synthesis, characterization, quaternization
Authors: Deboudt Karine , Delporte Michèle , Loucheux Claude 
Published: April 2003

Abstract2‐(Dimethylamino)ethyl methacrylate (DMAEM) — N‐vinyl‐2‐pyrrolidone (VP) copolymers were synthesized and characterized. The copolymerization parameters were determined: rVP = 0,61, rDMAEM = 11,41. The tacticity of DMAEM sequences and the distribution of monomer units were estimated. Then, the experimental conditions for the quaternization of the copolymers with alkyl bromides were defined. The modified copolymers were characterized and the mechanism of the quaternization reaction was studied via potentiometry.
Calorimetric study of blends of low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) temperature rising elution fractionation (TREF) fractions
Authors: Joskowicz Pablo L. , Muñoz Alberto , Barrera Julio , Müller Alejandro J. 
Published: April 2003

AbstractPreparative temperature rising elution fractionation (TREF) on commercial linear low density polyethylene (LLDPE) and low density polyethylene (LDPE) samples has been performed. The resulting fractions exhibited a bimodal and a unimodal distribution, respectively. Two LLDPE fractions of low (5 CH3/1000 C) and high (21 CH3/1000 C) short‐chain branching content were solution‐mixed with the LDPE central fraction (16 CH3/1000 C). Indirect evidence based on differential scanning calorimetry results suggest that the fractions with similar branch contents are more miscible than those with dissimilar ones.
Synthesis and characterization of multiblock copolymers poly[poly(L‐lactide)‐block‐polydimethylsiloxane]
Authors: Bachari Abdelkrim , Bélorgey Georges , Hélary Gérard , Sauvet Georges 
Published: April 2003

AbstractThe preparation of multiblock copolymers poly[poly(L‐lactide)‐block‐polydimethylsiloxane] by polycondensation of bifunctional oligomers via hydrosilylation is described. The procedure consists first to synthesize the two bifunctional oligomers α,ω‐disilyl‐polydimethylsiloxane and α,ω‐diallyl‐poly(L‐lactide). The former is prepared in one step by cationic polymerization of octamethylcyclotetrasiloxane in the presence of 1,1,3,3‐tetramethyldisiloxane as end‐blocker. Two steps are necessary to prepare α,ω‐diallyl‐poly(L‐lactide). The first one is the polymerization of L‐lactide initiated by the system ethylene glycol/tin 2‐ethylhexanoate. In a second step, the hydroxyl end‐groups of the resulting α,ω‐dihydroxy‐poly(L‐lactide) are transformed, by reaction with allyl isocyanate, into terminal allylic functions. Different multiblock copolymers were prepared by hydrosilylation (catalyzed by hexachloroplatinic acid) using the same α,ω‐diallyl‐poly(L‐lactide) (M̄n = 2000 g · mol −1) and various α,ω‐disilyl‐polydimethylsiloxanes (M̄n from 1 750 to 9 000 g · mol −1). The influence of parameters such as temperature, stoichiometry of reactive end‐groups and catalyst concentration on the molecular weight of the copolymers was studied. High molecular weight copolymers were obtained (DPn > 12 by SEC). In addition to the biodegradability of the lactic acid units, the immiscibility of the polydimethylsiloxane and poly(L‐lactide) blocks imparts thermoplastic elastomer properties to these copolymers. The crystallinity of the poly(L‐lactide) phase is dependent on the molecular weight of the polydimethylsiloxane blocks.
A method for determining intrinsic diffusion coefficients in the pervaporation process
Authors: Walcher Tobias , Göritz Dietmar 
Published: April 2003

AbstractAn apparatus based on a differential gas‐chromatographic detection system was designed in order to obtain information about the average permeation coefficient for pervaporation (PVAP) of pure liquids through isotactic poly(propylene) (i‐PP). The non‐ideal concentration dependence of diffusivity D prevents one from solving the diffusion equations exactly. Therefore, a method has been developed to obtain information on the intrinsic diffusion coefficient D0 and the plasticisation parameter γ for the two‐parameter function D(c) used. In additon, the concentration profile of the liquid in the membrane can be evaluated.
Struktur der aktiven Spezies und Erklärung des Wanderungsmechanismus bei der 2,ω‐polymerisation von α‐olefinen
Authors: Schubbe Regine , Angermund Klaus , Fink Gerhard , Goddard Richard 
Published: April 2003

AbstractThe catalytic system nickel(0) compound and bis(trimethylsilyl)amino‐bis(trimethylsilylimino)‐phosphoran polymerizes α‐olefins via 2,ω‐linkage. Therefore this reaction is called 2,ω‐polymerization. Using tris(ethylene)nickel as the nickel compound in these systems, it is possible to obtain catalytically active species. The X‐ray analysis of these crystals proves that the nickel atom is complexed by one of the imino nitrogen atoms and fixed over a C2 bridge at the phosphorus atom. The unusual 5‐membered ring for complexes of this type gives a view into the mechanism of the 2, ω‐polymerization. The phosphorus ligand shields the nickel atom at which the insertion takes place so effectively that the nickel is practically sitting in a “cave” with a very small entrance. Inside the cave NiC reacts to NiH and CC and also in reverse: this means the enthalpy change is zero and it is a question of statistics (entropy) which C atoms of the double bond will be attacked. Varying the phosphorus compound demonstrates the high sensitivity of the catalytic system with respect to this compound. Substituting the trimethylsilyl groups at the imino nitrogen atoms by the more voluminous dimethyl‐tert‐butyl groups, we obtained an absolutely inactive system. In contrast, nickel(II)‐bis(acetylacetonate) can be used in combination with the phosphoran and aluminium triethyl as cocatalyst to obtain a catalytically active system for the 2,ω‐polymerization. The structure of this complex was identified by X‐ray analysis. Because of the higher volume of the ligand, this system is unable to polymerize branched α‐olefins; only linear α‐olefins will be polymerized via 2, ω‐linkage.
Propene polymerization in the presence of MgCl2‐supported Ziegler‐Natta catalysts, 5. Microstructural characterization of the “isotactic” (heptane‐insoluble) polypropene fractions
Authors: Busico Vincenzo , Cipullo Roberta , Corradini Paolo , De Biasio Rosanna 
Published: April 2003

AbstractThe stereosequence distribution in the heptane‐insoluble fraction of polypropene samples prepared with a number of MgCl2‐supported catalysts was analyzed in detail by means of 13CNMR. The results indicate that what is conventionally taken as “isotactic” polypropene is normally a stereoblock polymer, in which at least part of the macromolecules contain long isotactic blocks spaced by much shorter “syndiotactoid” sequences. This implies that the active sites responsible for the formation of the two types of stereosequences are able to interconvert reversibly on the surface of the MgCl2 support in times which may be shorter than the average growth times of the polymer molecules. Possible models of active sites apt to explain the observed polymerization behavior are also briefly discussed.
Phase equilibria and interfacial tension between coexisting phases for the system water/2‐propanol/poly(acrylic acid)
Authors: Tong Zhen , Meissner Kristin , Wolf B. A. 
Published: April 2003

AbstractThe cloud point curve, tie‐lines and interfacial tensions were measured for solutions of 50 mol‐% neutralized (counter‐ion Na⊕) poly(arylic acid) (mass‐average molar mass M̄w = 9700 g/mol; polydispersity index M̄w/M̄n = 2,0) in the mixed solvent water/2‐propanol at 30°C. Due to the non‐uniformity of the polymer, the end‐points of the tie‐lines are not situated on the cloud‐point curve. The interfacial tension σ — determined by means of the spinning drop method — increases in sigmoidal manner with Rtl, the length of the tie‐line, expressed in terms of weight fractions. An evaluation of these data in a double‐logarithmic plot of σ · M−0,5 versus Rtl yields a critical exponent of 4,23 as compared with 3,85 in the case of binary systems. The dependence of σ on ww, the over‐all weight fraction of water in the mixture, can also be expressed as a power‐law choosing (wcw−ww)/wcw as the concentration variable (wcw: critical weight fraction of water); for the present system the exponent of the resulting equation amounts to 2,33 as compared with 2,0 for toluene/polyisobutylene/poly(dimethylsiloxane).
Catalytic properties of enzymes modified with temperature‐responsive polymer chains
Authors: Nagayama Hitomi , Maeda Yasushi , Shimasaki Choichiro , Kitano Hiromi 
Published: April 2003

AbstractTemperature‐responsive changes in catalytic properties of enzymes modified with a temperature‐responsive polymer, poly(N‐isopropylacrylamide) (PIPA), were examined. PIPA with a carboxyl group at its end was prepared using 2,2′‐azoisobutyronitrile as initiator in the presence of 3‐mercaptopropionic acid as a chain transfer reagent. After being activated by the coupling with N‐hydroxysuccinimide, PIPA was directly bound to enzymes such as acid phosphatase and trypsin. The catalytic activities of the modified enzymes showed a bending point in their Arrhenius plots at about 33°C due to a coil‐globule transition of PIPA chains. The ratio of amidase‐ and esterase‐activities of trypsin modified with PIPA chains was largely affected by the changes in temperature. As for the semi‐enzymatic synthesis of N‐benzoyl‐L‐arginylglycinamide, secondary hydrolysis of the peptide product observed with free trypsin was effectively suppressed in modified trypsin at 45°C (above the transition temperature), and the peptide was obtained with higher conversion.
The 1H and 13C NMR spectra of an alternating ethene/maleic anhydride copolymer and the corresponding acid and sodium salt
Authors: Komber Hartmut 
Published: April 2003

AbstractThe 1H and 13C NMR spectra of an alternating ethene/maleic anhydride copolymer and the corresponding acid and sodium salt were reinvestigated with regard to the signals depending on the configuration of the succinyl unit. From these assignments a 85/15 ratio of threo‐and erythro‐ succinyl configurations was determined. Threo‐ and erythro‐units are statistically distributed. Furthermore, signal splittings were observed due to microtacticity. Explanations are given for the signal fine structure. The polymer chain is atactic but a small degree of stereoregularity can be proved. T1 values and nuclear Overhauser effect (NOE) factors were determined; they correspond to investigations on other polymers.
Synthesis and characterization of novel triazeno‐group containing photopolymers
Authors: Nuyken Oskar , Stebani Jürgen , Lippert Thomas , Wokaun Alexander , Stasko Andrej 
Published: April 2003

AbstractThe synthesis of novel triazeno‐group containing photopolymers is described including their characterization by spectroscopic methods, differential scanning calorimetry, and thermogravimetric analysis. Triazene polymers synthesized by a polycondensation reaction between a bisdizaonium salt and a bifunctional secondary amine are well soluble in usual organic solvents. Transparent, light yellow films of these photopolymers may be produced by simple spin‐coating and solution‐casting techniques. The effect of polymer structural elements on the photolytic decomposition is studied. Depending on the structure of the polymer, thermolysis proceeds either via a one‐step or two‐step mechanism.
Synthesis and molecular weight characterization of end‐functionalized N‐vinyl‐2‐pyrrolidone oligomers
Authors: Ranucci Elisabetta , Spagnoli Gloria , Sartore Luciana , Bignotti Fabio , Ferruti Paolo , Schiavon Oddone , Caliceti Paolo , Veronese Francesco M. 
Published: April 2003

AbstractNew oligomers of N‐vinyl‐2‐pyrrolidone, functionalized at one end with hydroxy functions, were obtained by radical polymerization in the presence of a hydroxylated compound, namely 2‐isopropoxyethanol, acting as chain‐transfer agent. The oligomeric samples obtained were characterized in terms of molecular weight and molecular weight distribution by means of analytical size exclusion chromatography (SEC). To this purpose, a calibration curve for a set of SEC columns had been determined, making use of poly(N‐vinyl‐2‐pyrrolidone) standards purposely prepared. The chain transfer constant CT of 2‐isopropoxyethanol towards N‐vinyl‐2‐pyrrolidone was determined from the knowledge of the cumulated number‐average degree of polymerization X̄n and monomer conversion Yt of the samples during the reaction.
Synthesis and properties of molecularly uniform oligourethanes with chain‐folding units in the center
Authors: Eisenbach Claus D. , Stadler Edmund , Enkelmann Volker 
Published: April 2003

AbstractThe study of a series of molecularly uniform poly(N‐alkylurethanes) with a systematically varied and tailored chain architecture has shown that the packing and superstructure can be controlled by the primary structure of the urethane chain and reversibly altered by the sample treatment, respectively. Depending on the conformation or the stereogeometry of the constitutive unit built in the middle of the otherwise symmetrical oligourethane, chain‐extended and/or chain‐folded crystallization of the urethane chain can occur. The packing order, i. e., adjacent recentry chain‐folding or chain‐extended crystallization, and the thermal properties of the oligourethanes are related to the chemical structure of the central constitutive unit.