bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymerization of propene with enantiomorphic site catalysts, 1. A statistical analysis
Authors: Di Silvestro Giuseppe , Sozzani Piero , Terragni Alberto 
Published: April 2003

AbstractRecently we proposed a stereochemical classification of stereorigid metallocene catalysts according to their symmetry; statistical models of increasing complexity for the polymerization of propene based on the alternating mechanism have been developed. The general model agrees with the alternating mechanism and accounts for the most important stereochemical error (skipped insertion) and for the effect of the solvent and of polymerization temperature. Analysis of literature data of pentad concentrations for syndiotactic polypropylenes shows that the skipped insertion is more probable at high polymerization temperature, at low monomer pressure and in polar solvents.
Influence of the stretching rate on the transition front structure of uniaxially deformed isotactic poly(propylene)
Authors: Alonso Matilde , Rodríguez‐Cabello José Carlos , Merino Juan Carlos , Pastor José Maria 
Published: April 2003

AbstractRecent models on the melting process of polymer crystals allow the study of semicrystalline polymer structures by calorimetric (DSC) measurements. In particular, this work is devoted to the study of those changes occurring during the deformation process of isotactic poly(propylene) samples along the transition front. By observing the evolution of the parameter of intrachain melting cooperativity in comparison with lamellar thickness, it has been possible to characterise the birth and further evolution of double fold molecules, totally extended polymer chains connecting two adjacent crystallites in the fibrillar structure, “taut tie molecules”. Furthermore, those structural changes depend on the stretching conditions. In general, low rate promotes high lamellar fragmentation and the presence of a small number of taut tie molecules. On the contrary, at higher rates crystallites coming from the original lamella show bigger size and a higher number of tie molecules are achieved.
MALDI‐TOF mass spectrometry in polymer analytics, 2. Molecular weight analysis of rigid‐rod polymers
Authors: Räder Hans Joachim , Spickermann Jochen , Kreyenschmidt Martin , Müllen Klaus 
Published: April 2003

AbstractMolecular weight analysis of rigid‐rod polymers by gel permeation chromatography (GPC) is known to give overestimated values if polystyrene is used for calibration. In this work matrix‐assisted laser desorption/ionisation time of flight (MALDI‐TOF) mass spectrometry was applied for the first time toward direct molecular weight determination of a rigid‐rod type tetrahydropyrene (THP) polymer. The obtained results were supported by investigation of a homologous series of GPC‐separated oligomers with the respective structure. As opposed to common MALDI‐TOF mass spectra, monodisperse THP oligomers reveal two unusual facts: (i) Beside the formation of molecular ions fragmentation also takes place. (ii) The radical ions are detected instead of cationised species. The fully characterised THP oligomers were also used to calibrate the GPC measurements of the THP polymers. The number‐average molecular weight (M̄n), weight‐average molecular weight (M̄w) and polydispersity (M̄w/M̄n) data obtained from the oligomer‐calibrated GPC compare well to those values measured by MALDI‐TOF mass spectrometry.
Thermal behavior and spherulitic superstructures of SBC triblock copolymers based on polystyrene (S), polybutadiene (B) and a crystallizable poly(ε‐caprolactone) (C) block
Authors: Balsamo Vittoria , von Gyldenfeldt Friederike , Stadler Reimund 
Published: April 2003

AbstractThe dynamic crystallization and the melting behavior of polystyrene‐block‐poly(ε‐caprolactone) (PS‐b‐PCL, short notation SC), polybutadiene‐block‐poly(ε‐caprolactone) (PB‐b‐PCL, BC) and polystyrene‐block‐polybutadiene‐block‐poly(ε‐caprolactone) (PS‐b‐PB‐b‐PCL, SBC) have been studied using differential scanning calorimetry. The copolymers with high molecular weight exhibit microphase separation into microphases consisting of polystyrene, polybutadiene and poly(ε‐caprolactone) and partial crystallization of the corresponding PCL block. The crystallization occurs at temperatures below the PS glass transition. Depending on the block copolymer composition, crystallization takes place through a combination of heterogeneous and homogeneous nucleation. Isothermal crystallization was studied in order to determine the equilibrium melting point, Tm0, of the PCL block, which depends on the weight ratio wPB: wPCL. The crystallization kinetics was analyzed in terms of Avrami equation. A general decrease in the overall crystallization rate in the block copolymers relative to the equivalent PCL homopolymer was found. Additionally, the growth rate of the spherulites was followed using polarized optical microscopy. Depending on the composition and flexibility of the block connected to PCL, some copolymers showed ring‐banded spherulites.
Synthesis and thermal stability of oligourethanes based on the cycloaliphatic diisocyanate trans,trans‐4,4′‐methylenebis(cyclohexylisocyanate)
Authors: Steinlein Christian , Hernandez Laurie , Eisenbach Claus D. 
Published: April 2003

AbstractThe synthesis of molecularly uniform and isomerically pure oligourethanes is described. The compounds are models for the hard segments in polyurethane elastomers based on the aliphatic trans,trans‐4,4′‐methylenebis(cyclohexylisocyanate) (ttHMDI)/butanediol system. The thermostability of the urethanes was determined by differential scanning calorimetry (DSC), gel permeation chromatography (GPC) and temperature‐dependent FT‐IR spectroscopy. The aliphatic urethane group was found to be more stable than urethanes based on the corresponding aromatic 4,4′‐methylenebis(phenylisocyanate) (MDI). The stability also depends on the physical properties and morphology of the oligourethane. The ttHMDI urethane group does not decompose up to the individual melting point of the oligomer, whereas in aromatic MDI diisocyanate systems decomposition occurs already significantly below the melting; the MDI‐specific transurethanization is not observed in the ttHMDI‐based urethanes.
Formation of macrocyclic polymers by intramolecular coupling of α,ω‐difunctional precursors. Numerical evaluations
Authors: Dong Dahai , Hogen‐Esch Thieo E. , Shaffer J. Scott 
Published: April 2003

AbstractThe end‐to‐end cyclization reaction of living monodisperse α,ω‐dianion precursors with difunctional electrophiles (EX2) in the presence of partial anion termination is described. A computer simulation was developed to establish the relationship among the initial concentration, the molecular weight of the dianion precursor, the extent of anion termination, and the yield distribution for all of the cyclic and linear polymer species. A master curve is calculated allowing the determination of the macrocycle yield as a function of MW and concentration of the dianion precursor, and degree of anion termination.
Dilute solution properties of polybutadiene modified by 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione
Authors: Bica Clara I. D. , Burchard Walther , Stadler Reimund 
Published: April 2003

AbstractThe dilute solution properties of 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione‐modified polybutadienes were studied in tetrahydrofuran by static and dynamic light scattering and compared with those from unmodified polybutadiene chains. For the unmodified polymer, the scaling laws were established and the coil interpenetration parameter k was determined in the thermodynamically good solvent tetrahydrofuran; the chains exhibited common flexible chain behavior. For the modified polybutadiene, the results indicate at infinite dilution a weak extent of intermolecular crosslinking via the urazole groups, coupled with a very high extent of intramolecular ring formation. In order to evaluate the fraction of rings, an analysis of the association equilibrium by Fourier‐transform infrared spectroscopy (FTIR) was performed in the absorption region of the carbonyl stretching vibration of the urazole ring.
Polynorbornene: synthesis, properties and simulations
Authors: Haselwander Thomas F. A. , Heitz Walter , Krügel Stefan A. , Wendorff Joachim H. 
Published: April 2003

AbstractThe vinylic polymerization of norbornenes upon catalysis with Pd2+ complexes with norbornylnitrile as ligands is reported. The polynorbornenes (M̄w = 106) display a set of unique properties including a dense packing in the amorphous state, high glass transition temperatures, large refractive index, low birefringence and significant brittleness. To test the concept that these properties can be traced back to the conformational constraints of the polymer chains, we performed ab initio calculations, semi‐empirical quantum mechanical calculations and force‐field calculations employing a force field developed by us for polynorbornenes.
Poly(methyl methacrylate)‐supported isoxazolinium permanganates: preparation and application as oxidising reagents
Authors: Shiney Abraham , Rajan Padinjare Kochampilly , Sreekumar Krishna Pillai 
Published: April 2003

AbstractDivinylbenzene (DVB), ethylene glycol dimethacrylate (EGDMA) and N,N′‐methylenebis(acrylamide) (N,N′MBA) crosslinked poly(methyl methacrylate) (PMMA) was functionalised to generate isoxazolinium permanganate resins. These resins were found to selectively oxidise alcohols to the corresponding carbonyl compounds in appreciable yields. These reagents were found to possess the characteristics of polymeric reagents including operational simplicity.
New polyurethanes based on 4,4′‐diphenylmethane diisocyanate and 1,4:3,6 dianhydrosorbitol, 2. Synthesis and properties of segmented polyurethane elastomers
Authors: Cognet‐Georjon Estelle , Méchin Francoise , Pascault Jean‐Pierre 
Published: April 2003

Abstract1,4:3,6‐Dianhydrosorbitol (DAS) was used as chain extender in the preparation of new segmented polyurethane elastomers, based on polyoxytetramethylene or hydrogenated polybutadiene soft segments and 4,4′‐diphenylmethane diisocyanate (MDI). These materials exhibit a two‐phase microstructure, due to the thermodynamic immiscibility between hard and soft segments, which results in an elastomeric behavior over a wide temperature range. The thermal and dynamic mechanical properties of various formulations were then examined and related to the complex morphology of the corresponding (often semi‐crystalline) materials. DAS leads to particularly stiff hard segments and provides longer rubbery plateaux, compared with a classical diol such as 1,4‐butanediol. Phase separation is favored by longer and less polar soft segments. In any case, the structure of the materials strongly depends on the composition and synthesis procedure (bulk polycondensation leads to more heterogeneous samples), and most of all on the thermal history of the samples. This latter behavior is related to the existence of a possible order‐disorder transition (ODT) which explains the change‐over from a two‐phase to a one‐phase system after specific annealing experiments.
Synthesis and characterization of new polyamides and polyimides derived from (E)‐9‐[β‐(2,4‐diaminophenyl)vinyl]anthracene
Authors: Fomine Sergei , Sànchez Carlos , Fomina L. , Alonso J. C. , Ogawa Takeshi 
Published: April 2003

AbstractA new anthracene‐containing diamine, (E)‐9‐[β‐(2,4‐diaminophenyl)vinyl]anthracene, was prepared and used for the synthesis of a series of polyamides and polyimides by low temperature solution polycondensation. The polymers were highly amorphous, soluble in aprotic solvents and gave films with good optical quality on spin‐casting. The polymers showed 10% weight loss at a temperature of 415–460°C under nitrogen. The polymers exhibited an intense luminescence in the region of 450–500 nm due the emission from the excited state of the diamine moiety. It was shown that charge‐transfer (CT) interactions in polyimides were negligibly small in both the ground and the excited state, probably due to the bulky diamine fragment together with the rigid polymer backbone.
Anionic graft copolymerization of methyl methacrylate with lithium diisopropylamide‐treated poly(methacrylate)s
Authors: Akutsu Fumihiko , Inoki Mari , Takahagi Atsuko , Kasashima Yoshio , Naruchi Kiyoshi 
Published: April 2003

AbstractThe anionic grafting of methyl methacrylate onto several lithium diisopropylamide (LDA)‐treated polymers of methacrylates, such as 2‐acetoxyethyl methacrylate (1), 2‐propionyloxyethyl methacrylate (2), 2‐isobutyryloxyethyl methacrylate (3), 1‐methoxy‐carbonylethyl methacrylate (4), and methoxycarbonylmethyl methacrylate (5), or onto the LDA‐treated copolymers of the methacrylates with styrene was investigated. Graftings onto homopolymethacrylates and onto the copolymers of 1 and 2 with styrene did not occur due to the deactivation of the macromolecular lithium enolate by side reactions. Graftings onto copolymers P‐3, P‐4 and P‐5, from methacrylates 3, 4 and 5 with styrene, however, proceeded. The relative grafting efficiency decreases in the following order: P‐3 > P‐4 > P‐5. The grafting is highly influenced by the aggregation behavior of the macromolecular lithium enolates and the side reactions deactivating the lithium enolate. The aggregation behavior decreases the number of the activated points on the feed polymer, lowers the inititiation rate and the polymerization rate of the grafting, and causes a large polydispersity value (M̄w/M̄n) of the side‐chain poly(MMA).
The substitution effects of donor and acceptor on properties of poly(1,4‐phenylenevinylene) derivatives. Syntheses of poly(2‐methoxy‐5‐methylsulfinyl‐1,4‐phenylenevinylene) and its copolymers
Authors: Yoon Chong‐Bok , Shim Hong‐Ku 
Published: April 2003

AbstractElectron donor and acceptor substituted poly(2‐methoxy‐5‐methylsulfinyl‐1,4‐phenylenevinylene) (PMMSPV) and a series of copolymers containing 1,4‐phenylenevinylene (PV) units were synthesized via the water‐soluble precursor pathway and cast into films. The electrical conductivity of FeCl3‐doped PMMSPV was 1.5 × 10−4 S ċ cm−1 and the copolymers showed conductivities in the range of 10−4 ∼ 10−1 S ċ cm−1 depending on the copolymer compositions. The second‐order nonlinear optical coefficient of PMMSPV was obtained with second harmonic generation method. The measured d33 value was 1.5 pm/V and gave no decay at 100°C over 40 d.
Structure of polystyrene‐block‐poly(ethylene oxide) diblock copolymer micelles in water
Authors: Jada Amane , Hurtrez Guy , Siffert Bernard , Riess Gérard 
Published: April 2003

AbstractMicellization in water of two homologous series of AB‐type diblock copolymers, composed of polystyrene (PS) as the A block and poly(ethylene oxide) (PEO) as the B block, were investigated by small‐angle X‐ray scattering (SAXS) and dynamic light scattering (DLS). The copolymers have molecular weights Mn in the range 2 000—34 800, and have in a given series, the same number of repeating units of the PS block, (NPS = 10 and 38), and a variable number of repeating units of the PEO block (NPEO values in the range 23–704). In order to avoid secondary association of micelles, a dialysis technique was used to prepare the micellar systems, in the case of copolymers having high Mn values of the PS block. The experimental micelle properties such as the core radius Rc and the aggregation number N of non‐equilibrium structures, so called “frozen micelles”, obtained by dialysis, were found to be independent of the copolymer characteristics. However, for equilibrium structures, obtained by direct solubilization of the copolymers (NPS = 10) in water, Rc and N were found to decrease with increasing NPEO for the homologous series.
Radically initiated polymerization of a methacryloylamido‐terminated saccharide, 1. Monomer synthesis, homopolymerization and characterizations
Authors: Badey Bérangère , Boullanger Paul , Domard Alain , Cros Philippe , Delair Thierry , Pichot Christian 
Published: April 2003

AbstractA methacrylamido‐terminated saccharide, 6‐deoxy‐6‐methacryloylamido‐D‐glucopyranose (MAG), was synthesized using a new and easy pathway. Kinetics of the radically initiated solution homopolymerization of this monomer was investigated at 50°C using 4,4′‐azobis(4‐cyanopentanoic acid); the obtained kp/kt1/2 value around 1.0 mol−1/2 ċ L1/2 ċ s−1/2 is indicative of the strong ability of MAG to polymerize (kp and kt being the rate constants of propagation and termination, respectively). The chemical structure of the homopolymer, as analyzed by 13C NMR spectroscopy shows a tacticity which is in favor of a syndiotactic configuration resulting from the bulkiness of the side group. The dimensional characteristics of the polymers were studied by light scattering as an on‐line detection in size exclusion chromatography (SEC). As expected from the kp/kt1/2 value, high weight‐average molecular weights were obtained. The small average radii of gyration were found to reflect a relatively compact structure in water due to inter‐ and intramolecular interactions; viscosity studies in various solvents as well as values of the second virial coefficient corroborate such a behavior which reflects that water is a poor solvent for poly(MAG).
Structure investigations of a crosslinkable main chain liquid crystalline copolyester by infrared spectroscopy, differential scanning calorimetry and wide‐angle X‐ray scattering
Authors: Eichhorn Klaus‐J. , Sahre Karin , Jehnichen Dieter , Tobisch Josef , Häußler Liane 
Published: April 2003

AbstractFTIR spectroscopy, differential scanning calorimetry (DSC) and wide‐angle X‐ray scattering (WAXS) were used for the characterization of structural properties of a cross‐linkable ternary liquid crystalline (lc) copolyester and its binary model copolyesters. The copolyesters based on itaconoylbis(4‐oxybenzoic acid), sebacoylbis(4‐oxybenzoic acid) and 2‐methylhydroquinone were annealed at different temperatures to analyse the structural changes of mesogenic and spacer segments due to their phase transitions. The results of the DSC and WAXS measurements are useful to explain the small effects in the IR spectra connected with polymer morphology. FTIR spectroscopy is able to provide information about the molecular structure along the polymer chains and also about the interactions between these chains. Micro‐ and macromolecular structures influence the orientation and crosslinking processes in dependence on temperature and time. It was shown that an increase in the ordered state and quality of crystallinity was obtained using different annealing procedures.
Heat capacities of solid, globular proteins
Authors: Zhang Ge , Gerdes Stina , Wunderlich Bernhard 
Published: April 2003

AbstractIn an ongoing effort to understand the thermodynamic properties of proteins, solid‐state heat capacities of poly(amino acid)s of all 20 naturally occurring amino acids and 4 copoly(amino acid)s were previously determined using our Advance Thermal Analysis System (ATHAS). Recently, poly(L‐methionine) and poly(L‐phenylalanine) were further studied with new low‐temperature measurements from 10 to 340 K. In addition, an analysis was performed on literature data of a first protein, zinc bovine insulin dimer C508H752O150N130S12Zn. Good agreement was found between experiment and calculation. In the present work, we have investigated four additional anhydrous globular proteins, α‐chymotrypsinogen, β‐lactoglobulin, ovalbumin, and ribonuclease A. The heat capacity of each protein was measured from 130 to 420 K with differential scanning calorimetry, and the data were analyzed with both the ATHAS empirical addition scheme and a fitting to computations using an approximate vibrational spectrum. For the solid state, agreement between measurement and computation scheme could be accomplished to an average and root mean square percentage error of 0.5 ± 3.2% for α‐chymotrypsinogen, −0.8 ± 2.5% for β‐lactoglobulin, −0.4 ± 1.8% for ovalbumin, and −0.7 ± 2.2% for ribonuclease A. With these calculations, it was possible to link the macroscopic heat capacities to their macroscopic causes, the group and skeletal vibrational motion. For each protein one set of parameters of the Tarasov function, Θ1 and Θ3, represent the skeletal vibrational contributions to the heat capacity. They are obtained from a new optimization procedure [α‐chymotrypsinogen: 631 K and 79 K (number of skeletal vibrators Ns = 3005); β‐lactoglobulin: 582 K and (79 K) (Ns = 2188); ovalbumin: 651 K and (79 K) (Ns = 5008) and ribonuclease A: 717 K and (79 K) (Ns = 1574), respectively]. Enthalpy, entropy, and Gibbs free energy can be derived for the solid state.
New synthesis of a highly active δ‐MgCl2 for MgCl2/TiCl4/AlEt3 catalytic systems
Authors: Di Noto Vito , Bresadola Silvano 
Published: April 2003

AbstractA good supporting material for Ziegler‐Natta type catalysts was obtained by reaction between powdered metallic magnesium and 1‐chloro‐n‐CmH2m+1 (m = 3–9). This reaction affords a highly disordered form of MgCl2 which was characterized by FT‐IR spectroscopy and powder X‐ray diffraction (XRD) analysis. This MgCl2 form shows a crystallographic disorder much higher than that exhibited by the products obtained following the commercial activation procedures of α‐MgCl2, either mechanical or chemical. As shown by the XRD spectra, the synthetized MgCl2 is characterized by the typical structure of the δ‐form. Therefore, this MgCl2 form, in view of its highly disordered structure, appears as a promising material for the preparation of active supported Ziegler‐Natta type catalysts. Thus, by titanation of the obtained δ‐MgCl2 we have prepared some supported catalysts which have been tested in the slurry propene polymerizations, showing high activity (136000–138000 gPP/gTi) and good stereoselectivity (82–88% I.I.).
Ordering fractal aggregates of liquid mixtures
Authors: Zhu Peng Wei 
Published: April 2003

AbstractMixtures of liquid paraffin and polydimethylsiloxane (PDMS) were studied by small angle X‐ray scattering. The scattering patterns exhibited a single peak in finite angles and deviated from Porod's law in larger angles. The fractal dimension of mixtures was determined by power‐law analysis. The whole scattering curves were fitted well by a scattering formula. The average size and correlation distance of the aggregates were calculated from a correlation function. The fractal dimension and the static parameters were found to decrease with increasing the temperature and PDMS concentration.
Concise synthesis and characterization of 30‐membered macrocyclic monomer for poly(ether ether ketone)
Authors: Chen Mingfei , Fronczek Frank , Gibson Harry W. 
Published: April 2003

AbstractA 30‐membered macrocyclic arylene ether ketone monomer for poly(ether ether ketone) was synthesized by a two‐step method. The first step involves synthesis of a long bisphenol from hydroquinone and 4,4′‐difluorobenzophenone. The second step is the cyclization of the bisphenol with 4,4′‐difluorobenzophenone. The pure macrocycle was isolated and characterized by IR, NMR, MS, TGA and DSC techniques. The X‐ray structure of the macrocycle was also determined.