bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anion Effects on the Activity and Stereoselectivity in Propene Polymerisations Catalyzed by C2‐Symmetric and “Oscillating” Catalysts
Authors: Rodriguez‐Delgado Antonio , Hannant Mark D. , Lancaster Simon J. , Bochmann Manfred 
Published: February 2004

AbstractSummary: The influence of perfluoroborate anions on catalyst activity and stereospecificity has been determined for propene polymerisations at 20–60 °C. For C2‐symmetric ansa‐zirconocenes, activities were strongly ligand‐dependent, with systems activated by TIBA/Ph3C+X−, where TIBA = AliBu3, X = {Z[B(C6F5)3]2}, and Z = CN or NH2, giving significantly higher activities than methylaluminoxane under comparable conditions. For high‐activity catalysts at 60 °C, {H2N[B(C6F5)3]2}− proved superior to {CN[B(C6F5)3]2}−, presumably due to the higher thermal stability of the amidoborate. The influence of counteranions on PP stereospecificity for these catalysts is negligible. On the other hand, the conformationally flexible catalyst, (2‐PhInd)2ZrCl2/TIBA/Ph3C+X−, shows not only a strong anion dependence of its activity, but also significant variation in poly(propylene) isotacticity, mainly due to the formation of small fractions of highly isotactic (mmmm > 70%) PP. This effect was particularly pronounced for {CN[B(C6F5)3]2}− and the dianion, {Ni[CNB(C6F5)3]4}2−.Effect of {CN[B(C6F5)3]2}− and {H2N[B(C6F5)3]2}− on propene polymerisation productivities for zirconocenes 1–8 at 20 °C.imageEffect of {CN[B(C6F5)3]2}− and {H2N[B(C6F5)3]2}− on propene polymerisation productivities for zirconocenes 1–8 at 20 °C.
Syndiotactic‐ and Isotactic Specific Bridged Cyclopentadienyl‐Fluorenyl Based Metallocenes; Structural Features, Catalytic Behavior
Authors: Razavi Abbas , Bellia Vincenzo , De Brauwer Yves , Hortmann Kai , Peters Liliane , Sirole Sabine , Van Belle Stephan , Thewalt Ulf 
Published: February 2004

AbstractSummary: The stereochemistry of propylene insertion/propagation reactions with a variety of Cs and C1 symmetric, bridged cyclopentadienyl‐fluorenyl ligand containing metallocene catalysts are investigated. It is shown that active species with a local Cs symmetry and enantiotopic coordination positions, in the general contest of the chain migratory insertion, behave syndioselective. However, the bilateral symmetry rule, “central dogma” of syndioselectivity, is not a catholic prerequisite and may be ignored by the Cs systems whenever symmetric “excess” in steric bulk is present. An asymmetric “excess” of steric forces, on the other hand, will perturb the migratory insertion process completely and induce a full tactic inversion in resulting C1 symmetric catalysts. The findings also reveal that C2 symmetry and helicity of homotopic catalysts, conditions thought to be essential for high isoselectivity, can be lifted in light of recent developments in high performance centrally chiral, C1 symmetric enantiotopic catalysts.Ligand outline, chain orientation, and monomer coordination mode with enantiomorphous active species.imageLigand outline, chain orientation, and monomer coordination mode with enantiomorphous active species.
Synthesis and Properties of Poly(ketone‐co‐alcohol) Materials: Shape Memory Thermoplastic Elastomers by Control of the Glass Transition Process
Authors: Pérez‐Foullerat David , Hild Sabine , Mücke Angela , Rieger Bernhard 
Published: February 2004

AbstractSummary: The well‐controlled reduction of polyketone carbonyl functional group was performed without chain degradation by using NaBH4 in tetrahydrofuran (THF)/MeOH solvent mixtures. Three different families of flexible polyketones (alternating propene/CO “PCO”, hex‐1‐ene/CO “HxCO” copolymers, and “pulse feed” alternating olefin/CO terpolymers from ethene and propene “EPCO”) were investigated to achieve either a partial reduction, leading to poly(ketone‐co‐alcohol)s of corresponding composition, or a complete conversion into polyalcohols. Increasing the ratio of [OH]/[CO] functions allows continuous change of the Tg of the resulting polymers from below room temperature to about 75 °C. Properties of the synthesized materials, like thermal decomposition, glass transition temperature, surface tension, and mechanical performance, are described depending on the degree of reduction. Thermoplastic elastomers with an interesting “shape memory” effect result from the partially reduced, elastic EPCO terpolymers.Stress‐strain curves for ethylene‐propylene/CO copolymers reduced to different extents.imageStress‐strain curves for ethylene‐propylene/CO copolymers reduced to different extents.
Syndiospecific Polymerization of Styrene with Aryl Substituted Indenyl Halfsandwich Titanocenes
Authors: Stojković Olivera , Kaminsky Walter 
Published: February 2004

AbstractSummary: A series of 1‐ and 2‐aryl substituted indenyl titanium trichlorides (ArIndTiCl3, Ar = Ph, α‐Naph, β‐Naph) were synthesized and tested as catalyst precursors for the syndiospecific polymerization of styrene with methylaluminoxane (MAO) as a cocatalyst. The polymerization characteristics at varying Al:Ti ratios and the kinetic behavior of these systems were investigated at 30 and 50 °C. The optimal Al:Ti ratio for these compounds lies in the range of 750–1500 at 30 °C, while the optimum shifts to higher values of about 2000–5000 at 50 °C. The activity of the investigated catalysts decreases in the order 2‐PhInd > Ind > Cp > 1‐(β‐Naph)Ind > 1‐PhInd > 2‐(β‐Naph)Ind > 2‐(α‐Naph)Ind > 1‐(α‐Naph)Ind with an activity up to 6700 kg sPS/[(mol Ti) · h] for 2‐PhIndTiCl3/MAO as the most active catalyst. Compared with CpTiCl3/MAO, the indenyl substituted compounds show, as catalysts, increased long‐term stability, which was determined by variation of the polymerization time. Especially 2‐PhIndTiCl3, 1‐(β‐Naph)IndTiCl3 and 2‐(β‐Naph)IndTiCl3 show a good performance. Syndiotactic polystyrenes with extremely high molar masses up to 1.3 × 106 g/mol can be obtained by the catalytic system 2‐(β‐Naph)IndTiCl3/MAO.Dependence of the polymerization rate on polymerization time. Polymerization conditions: Tp = 30 °C, V = 150 ml, c(styrene) = 1.04 M, Al:Ti = 1500, m(MAO) = 0.145 g, solvent = toluene.imageDependence of the polymerization rate on polymerization time. Polymerization conditions: Tp = 30 °C, V = 150 ml, c(styrene) = 1.04 M, Al:Ti = 1500, m(MAO) = 0.145 g, solvent = toluene.
Ethene Copolymerization with Trialkylsilyl Protected Polar Norbornene Derivates
Authors: Wendt Ralf Alexander , Angermund Klaus , Jensen Vidar , Thiel Walter , Fink Gerhard 
Published: February 2004

AbstractSummary: The influence of the protecting group of polar norbornene derivatives and the structure of homogenous metallocene/MAO catalyst systems on the activity and the incorporation rates during ethene copolymerization reactions were studied. By varying the structure of the protecting group a relationship between the catalyst activity and the steric demand of the protecting group could be established. For the catalyst systems tested analogous relationships between the bulkiness of the protecting groups and the polymerization activity were found. Kinetic investigations point to a reversible deactivation reaction, during which a bond between the oxygen atom of the polar norbornene derivative and the center of the active catalyst is formed, competing with the olefin coordination and the subsequent insertion. The degree of polymerization deactivation can be qualitatively judged based on a correlation between calculated structural parameters of the trialkylsilyl protected norbornene derivatives and the experimentally determined polymerization activity.image
Stereoblock Isotactic‐Hemiisotactic Poly(propylene)s and Ethylene/Propylene Copolymers Obtained with ansa‐Cyclopenta[1,2‐b;4,3‐b′]dithiophene Catalysts
Authors: Ewen John A. , Jones Robert L. , Elder Michael J. , Camurati Isabella , Pritzkow Hans 
Published: February 2004

AbstractSummary: Stereoblock, isotactic‐hemiisotactic poly(propylene) is produced with C1‐symmetric Me2C(η5‐3‐(2‐adamantyl)‐C5H3)(η5‐C9H4S2)ZrCl2 (1). Ethylene/propylene copolymerization data with the Cs‐symmetric Me2C(η5‐C5H4)(η5‐C9H4S2)ZrCl2 (2) metallocene reveals that it is highly propylene‐specific and that it produces more random ethylene/propylene copolymers than its fluorenyl analog.image
Supporting Effects of Methylaluminoxane on the Living Polymerization of Propylene with a Chelating (Diamide)dimethyltitanium Complex
Authors: Hagimoto Hitoshi , Shiono Takeshi , Ikeda Tomiki 
Published: February 2004

AbstractSummary: Modified methylaluminoxane (MMAO), from which free AlMe3 and Al(iBu)3 were reduced to ca. 0.1 mol‐%, was supported on metal oxides, such as anhydrous silica gel, alumina, or magnesia; the metal oxide‐supported MMAO prepared were used as cocatalysts for propylene polymerization combined with a chelating (diamide)dimethyltitanium complex. The systems conducted living polymerization of propylene at 0 °C regardless of the support for MMAO. The propagation rate constants (kp) of these systems and the molecular weight distribution ($\overline M _{\rm w} {\rm /}\overline M _{\rm n}$) of the produced polymer depended on the metal oxide employed. The XPS analysis of the supported MMAOs suggested that the kp value increased with the Lewis acidity of MMAO on the support and the broadening $\overline M _{\rm w} {\rm /}\overline M _{\rm n}$ was ascribed to the distribution of kp caused by the heterogeneity of the supported cocatalyst.Plots of \overline M _{\rm n} and \overline M _{\rm w} {\rm /}\overline M _{\rm n} against polymerization time in propylene polymerization with [ArN(CH2)3NAr]TiMe2: MMAO/SiO2 system, \overline M _{\rm n} (•), \overline M _{\rm w} {\rm /}\overline M _{\rm n} (○); MMAO/Al2O3 system, \overline M _{\rm n} (▴), \overline M _{\rm w} {\rm /}\overline M _{\rm n} (▵); MMAO/MgO system, \overline M _{\rm n} (▪), \overline M _{\rm w} {\rm /}\overline M _{\rm n} (□); corresponding homogeneous system, \overline M _{\rm n} (▾), \overline M _{\rm w} {\rm /}\overline M _{\rm n} (▿).imagePlots of \overline M _{\rm n} and \overline M _{\rm w} {\rm /}\overline M _{\rm n} against polymerization time in propylene polymerization with [ArN(CH2)3NAr]TiMe2: MMAO/SiO2 system, \overline M _{\rm n} (•), \overline M _{\rm w} {\rm /}\overline M _{\rm n} (○); MMAO/Al2O3 system, \overline M _{\rm n} (▴), \overline M _{\rm w} {\rm /}\overline M _{\rm n} (▵); MMAO/MgO system, \overline M _{\rm n} (▪), \overline M _{\rm w} {\rm /}\overline M _{\rm n} (□); corresponding homogeneous system, \overline M _{\rm n} (▾), \overline M _{\rm w} {\rm /}\overline M _{\rm n} (▿).
Preparation and Characterization of Novel Temperature Sensitive Poly(N‐isopropylacrylamide‐co‐acryloyl beta‐cyclodextrin) Hydrogels with Fast Shrinking Kinetics
Authors: Zhang Jian‐Tao , Huang Shi‐Wen , Zhuo Ren‐Xi 
Published: February 2004

AbstractSummary: Novel temperature sensitive poly(N‐isopropylacrylamide‐co‐acryloyl beta‐cyclodextrin) (P(NIPA‐co‐A‐CD)) hydrogels with fast shrinking rates were prepared by radical polymerization of NIPA, A‐CD and crosslinker in a mixture of water/1,4‐dioxane as solvent. Because the mixed solvent was a poor solvent for the copolymers, phase separation occurred during the polymerization, which resulted in a heterogeneous, porous structure of the hydrogels. In contrast to the normal PNIPA hydrogel and the homo P(NIPA‐co‐A‐CD) gel prepared in water, the P(NIPA‐co‐A‐CD) hydrogels synthesized in water/1,4‐dioxane as solvent exhibited higher swelling ratios at the temperature below the lower critical solution temperature (LCST) and shrunk rapidly to equilibrium within shorter time when the temperature was increased above LCST. Increasing the acryloyl beta‐cyclodextrin content in the gels led to a slight decrease of the swelling ratio at lower temperature and had no marked influence on the shrinking kinetics. The gels prepared in water/1,4‐dioxane, at different v/v ratios of 1.0/0.2, 0.8/0.4 and 0.6/0.6, showed similar properties.SEM photos of the heterogeneous P(NIPA‐co‐A‐CD) hydrogel prepared in water/1,4‐dioxane.imageSEM photos of the heterogeneous P(NIPA‐co‐A‐CD) hydrogel prepared in water/1,4‐dioxane.
New Zinc Dicarboxylate Catalysts for the CO2/Propylene Oxide Copolymerization Reaction: Activity Enhancement Through Zn(II)‐Ethylsulfinate Initiating Groups
Authors: Eberhardt Robert , Allmendinger Markus , Zintl Manuela , Troll Carsten , Luinstra Gerrit A. , Rieger Bernhard 
Published: February 2004

AbstractSummary: A series of zinc dicarboxylates were synthesized by the reaction of diethylzinc with dicarboxylic acids. Zinc monocarboxylate monoalkyl intermediates were obtained by using a defined excess of diethylzinc over dicarboxylic acid. A subsequent insertion reaction of SO2 into these zinc alkyl bonds resulted in a defined number of Zn‐ethylsulfinate groups, which act as active centers for the copolymerization reaction of CO2 and propylene oxide. Corresponding ethylsulfinic acid ester end groups were detected in the poly(propylene carbonate) (PPC) products. The polymerization activity depended strongly on the number of sulfinate groups incorporated and has been significantly increased compared to conventional zinc dicarboxylates. The obtained PPCs have molecular weights ($\overline M _{\rm w}$) exceeding 80 000 g · mol−1 and polydispersities in the range of 2.3 to 3.3.Formation of poly(propylene carbonate).imageFormation of poly(propylene carbonate).
Saccharide Polymers, 5
Authors: Glümer Anke , Skeries Bernhard David , Buchholz Klaus 
Published: February 2004

AbstractSummary: New “saccharide polymers” were synthesized via free radical polymerization. The saccharide compounds in copolymerisation reactions were 2,4,6‐tri‐O‐acetyl‐3‐deoxy‐D‐erythro‐hex‐2‐enono‐1,5‐lactone (1), (Ac‐GEL 1) and 2,4,6‐tri‐O‐benzoyl‐3‐deoxy‐D‐erythro‐hex‐2‐enono‐1,5‐lactone (2), (Bz‐GEL 2). These sugar monomers are easily obtained with high yield in a one step reaction from glucono‐δ‐lactone. They have a pyranoid structure containing an endocyclic double bond and they are electron acceptor compounds. Copolymerization reactions were carried out in solution and in substance. Copolymers with different sugar contents and low as well as high molecular weights were obtained. The structures and the compositions of the soluble saccharide polymers were established by elemental analysis, polarimetry, FTIR spectroscopy, 1H and 13C NMR spectroscopy. Some characteristic properties, e.g., molecular weight, optical rotation and copolymerization parameters are reported.Schematic conversion of glucono‐δ‐lactone to saccharide monomers.imageSchematic conversion of glucono‐δ‐lactone to saccharide monomers.
Response of Polyelectrolyte Complexes to Subsequent Addition of Sodium Chloride: Time‐Dependent Static Light Scattering Studies
Authors: Dautzenberg Herbert , Rother Gudrun 
Published: February 2004

AbstractSummary: The applications of polyelectrolyte complexes range from large‐scale industrial products to special uses in biotechnology and medicine, yet one significant problem is their instability against changes in their environmental conditions, particularly the addition of salts. This concerns the colloidal stability as well as the stability of ionic bindings. Previous work on the effect of sodium chloride revealed that not only additional aggregation, but also complete dissolution may occur, depending on the nature of the polyelectrolyte components used. In these studies, the systems required up to one hour to become stable. Multi‐angle static light scattering was used to investigate the processes taking place after the addition of NaCl to polyelectrolyte complexes (PEC) formed in pure water. PECs were prepared with polymethacrylate as polyanion and poly(diallyldimethylammonium chloride) and a copolymer of this polycation with 53 mol‐% of acrylamide. These systems were chosen because of their interesting behavior: secondary aggregation, swelling, and dissolution at a critical salt concentration. The time‐dependence of these effects was studied in detail by static light scattering.Aggregation and swelling demonstrated by changes in particle mass, radius, and structure density of the PEC.imageAggregation and swelling demonstrated by changes in particle mass, radius, and structure density of the PEC.
Effect of Additional Hydroxyl Functionalities on the Hydrolytic Stability of Oligoesters
Authors: Soucek Mark D. , Johnson Aaron H. , Meemken Leon E. 
Published: February 2004

AbstractSummary: The addition of a trifunctional polyol (trimethylolpropane) to oligoesters comprised of hexahydrophthalic anhydride, cyclohexane‐1,4‐dicarboxylic acid, cyclohexane‐1,3‐dicarboxylic acid, neopentyl glycol, and cyclohexane‐1,4‐dimethanol was investigated via an accelerated hydrolysis environment. The oligoesters were dissolved in an acetone/water solution, and the hydrolysis was evaluated by monitoring carboxylic acid formation and by measurement of the molecular weight shift by size exclusion chromatography. Aliquots of the oligoester solution were evaluated intermittently over a 36‐week period. Both the initial rate and the overall rates of hydrolysis were reported as hydrolysis velocities. The influence of hydroxyl concentration is apparent in the initial velocity of hydrolysis. After the induction period, steric effects appear to be the controlling factor for the retardation of main chain scission.A comparison of the initial and final rates of hydrolysis as a function of oligoester composition.imageA comparison of the initial and final rates of hydrolysis as a function of oligoester composition.
Multiple Melting Behavior of Poly(thiodiethylene terephthalate): Further Investigations by Means of X‐ray and Thermal Techniques
Authors: Fichera Anna Maria , Finelli Lara , Gazzano Massimo , Lotti Nadia , Munari Andrea 
Published: February 2004

AbstractSummary: The complex multiple melting behavior of poly(thiodiethylene terephthalate) (PSDET) was investigated by means of differential scanning calorimetry, X‐ray diffraction and hot‐stage optical microscopy. The phenomenon was ascribed to the existence of two different crystal structures (α and β), each of them being able to melt and recrystallize under the experimental conditions adopted. Linear and nonlinear treatments were applied in order to estimate the equilibrium melting temperature for α PSDET, by using the corrected values of Tm. The nonlinear estimation led to a higher value by about 25 °C. Isothermal crystallization kinetics of each crystalline form were analyzed according to Avrami's treatment. In both cases, values of Avrami's exponent, n, close to 3 were obtained, in agreement with a crystallization process originating from predeterminated nuclei and characterized by three dimensional spherulitic growth. The rate of crystallization of each crystalline structure was found to become lower as the crystallization temperature is increased, as usual at low undercooling, where the crystallization process is controlled by nucleation.XRD patterns of PSDET samples isothermally crystallized at the indicated Tcs.imageXRD patterns of PSDET samples isothermally crystallized at the indicated Tcs.
Direct Observation of Poly(propylene)‐block‐Poly(ethylene‐co‐propylene) Molecules by Atomic Force Microscopy
Authors: Prokhorov Valery V. , Nitta Koh‐hei , Terano Minoru 
Published: February 2004

AbstractSummary: Atomic force microscopy (AFM) has been applied to get molecular images of diblock poly(propylene)‐block‐poly(ethylene‐co‐propylene) copolymers deposited on mica from diluted solutions at elevated temperatures. Both isolated molecules and their small aggregates have been visualized as compact particles of various sizes with outspreading poly(ethylene‐co‐propylene) chains. On the base of the height, volume and morphological analysis AFM images were divided into three groups. In the first group the compact particles are suggested to be small regular‐shaped crystallites formed by a few poly(propylene) blocks. Some isolated particles of this group were connected with single copolymer chains. In the second group the compact particles have larger dimensions and irregular or round shapes implying unordered packing of constituents. The third group were represented by isolated poly(ethylene‐co‐propylene) coils. The two‐dimensional expansion of coils on mica both isolated and included in aggregates exceeds several times their dimensions in a solution. The probable mechanism of such an expansion is proposed relying on the existence of van‐der‐Waals surface force field of a sufficient strength in the vicinity of the crystal surface.Enlarged AFM height images of block‐copolymer aggregates of group A with small compact particles of regular shapes (frames a, b, c) and group B (frame d) with a large globular compact particle.imageEnlarged AFM height images of block‐copolymer aggregates of group A with small compact particles of regular shapes (frames a, b, c) and group B (frame d) with a large globular compact particle.
Metal‐ and Metalloid‐Containing Macromolecules Symposium
Authors: Abd‐El‐Aziz A. S. , Zeldin M. 
Published: February 2004

AbstractConference Report: This section contains reports on topical conferences. Reports are usually written at the request of the editorial office, but unsolicited contributions are also welcome. Suggestions should be sent to the editorial office of the Macromolecular journals, preferably by E‐mail to macromol@wiley‐vch.de.
Cover Picture: Macromol. Chem. Phys. 1/2004
Authors: Eberhardt Robert , Allmendinger Markus , Zintl Manuela , Troll Carsten , Luinstra Gerrit A. , Rieger Bernhard 
Published: February 2004

Cover: The cover page shows the formation of polycarbonate formation on solid Zn‐gluterate.Further details can be found in the Full Paper by R. Eberhardt, M. Allmendinger, M. Zintl, C. Troll, G. A. Luinstra, and B. Rieger* on page 42.
Cover Picture: Macromol. Chem. Phys. 2/2004
Authors: Bolze Joerg , Ballauff Matthias , Rische Thorsten , Rudhardt Daniel , Meixner Jürgen 
Published: February 2004

Cover: The cover shows small angle X‐ray scattering data of semicrystalline PUR latex particles. A data decomposition procedure yields the scattering contribution due to the lamellar structure.Further details can be found in the Full Paper by J. Bolze, M. Ballauff,* T. Rische, D. Rudhardt, and J. Meixner on page 165.
Cover Picture: Macromol. Chem. Phys. 3/2004
Authors: Grassi Alfonso , Guerra Gaetano , Longo Pasquale , Oliva Leone , Pellecchia Claudio 
Published: February 2004

Cover: The picture on the cover shows the copolymerization studies on deuterated propenes published by A. Zambelli, M. G. Giongo and G. Natta (Makromol. Chem. 1968, 112, 183). These studies allowed the elucidation of the cis mechanism of addition to the double bond, for the propene polymerization to syndiotactic polymers.This special issue is dedicated to Prof. Adolfo Zambelli on the occasion of his 70th birthday.
Chemical Modification of Terephthalate Polyesters by Reaction with Bis(hydroxyethyl ether) of Bisphenol A
Authors: Berti Corrado , Colonna Martino , Fiorini Maurizio , Lorenzetti Cesare , Marchese Paola 
Published: February 2004

AbstractSummary: Copolyesters of terephthalic acid with bis(hydroxyethyl ether) of bisphenol A (BHEEB) in different molar ratios have been synthesized by reactive blending from terephthalate polyesters and by melt polycondensation from the monomers. By this way, bisphenol A groups were inserted in the polyester chains with the aim to obtain polyesters with improved mechanical properties. The insertion of the BHEEB into the polyester backbone is quantitative and does not give rise to side reactions. These copolyesters can be obtained by the chemical recycling of commercial polymers; indeed BHEEB can be synthesized by chemical recycling of bisphenol A polycarbonate and may be incorporated in the polyester by reactive blending with recycled terephthalate polyesters. A new method for BHEEB synthesis by chemical recycling of PC is also presented.Glass transition temperature (Tg) as function of BHEEB content for copolyesters prepared by reactive blending BHEEB with terephthalate polyesters.magnified imageGlass transition temperature (Tg) as function of BHEEB content for copolyesters prepared by reactive blending BHEEB with terephthalate polyesters.