bluuebunny/crossref_metadata_2025_split huggingface dataset:
Negative pressure effects during the isothermal crystallization of isotactic poly(propylene) studied by light and atomic force microscopy
Authors: Thomann Ralf , Wang Chun , Kressler Jörg , Mülhaupt Rolf 
Published: April 2003

AbstractThe formation of holes during the late stage of the isothermal crystallization in thin films of isotactic poly(propylene) between two cover glasses was observed by light microscopy and atomic force microscopy. This behavior can be described consistently by the well‐known negative pressure effect. Light microscopy reveals the simultaneous and sudden occurrence of a large number of small holes at the liquid‐solid interface after the liquid in front of the spherulites is completely confined by other spherulites for a certain time interval. In exceptional cases only a few holes appear and finally large cavities are formed. Atomic force microscopy measurements carried out in the height mode are able to prove the hole formation in front of the spherulites. Furthermore, a substantial thinning of the two‐dimensional spherulites in thin films can be observed prior to the hole formation.
Kinetic study of free‐radical copolymerization of methyl acrylate and methyl methacrylate in benzene
Authors: Madruga Enrique López , Fernández‐García Marta 
Published: April 2003

AbstractThe variation of copolymerization rate with composition obtained for the system methyl acrylate (1)/methyl methacrylate (2)/benzene/2,2′‐azoisobutyronitrile using standard techniques of polymerization rate measurements has been interpreted on the basis of a penultimate effect upon the propagation reaction, giving values of s1 = 0.547 and s2 = 1.668 for the chain‐end reactivity ratios.
Mechanical and thermal behaviour of networks with “flexible” and “rigid” chains
Authors: Müller Andrea , Stadler Reimund 
Published: April 2003

Abstract“Rigid‐rod” telechelics were synthesized via repetitive Diels‐Alder reaction of biscyclohexadienes and bis(1,2,4‐triazoline‐3,5‐diones). The bistriazolinediones were used in slight excess. The rigidity of the building blocks and the molecular weight were varied. Various amounts of these reactive telechelics are used to crosslink cis‐1,4‐polybutadiene. The mechanical and the thermal properties of these two‐component networks were investigated by stress‐strain, differential scanning calorimetry and dynamic‐mechanical measurements. The occurrence of microphase separation between the “rigid” and the “flexible” components is discussed to explain the properties of these materials.
Telechelic diols from poly[(R)‐3‐hydroxybutyric acid] and poly{[(R)‐3‐hydroxybutyric acid]‐co‐[(R)‐3‐hydroxyvaleric acid]}
Authors: Hirt Thomas D. , Neuenschwander Peter , Suter Ulrich W. 
Published: April 2003

AbstractWe describe the preparation of telechelic OH‐terminated poly[(R)‐3‐hydroxybutyric acid] (PHB) and poly{[(R)‐3‐hydroxybutyric acid]‐co‐[(R)‐3‐hydroxyvaleric acid]} (PHB/HV), on a semi‐preparative scale, by a transesterification procedure from the high‐molecular weight polymers. The oligomers have well‐defined reactive end groups and are well suited for the preparation of high‐molecular‐weight block copolymers by chain extension.
Supported catalysts for ethylene polymerization: studies with the magnesium diethoxide‐tin tetrachloride‐titanium tetrachloride/tetraisobutylalumoxane catalyst system
Authors: Gupta Virendra K. , Ravindranathan Marayil 
Published: April 2003

AbstractSupported titanium catalysts are prepared by the reaction of magnesium diethoxide with tin tetrachloride followed by treatment with titanium tetrachloride. The catalysts are characterized by compositional analysis and measurements of the specific surface area. The performance of the catalysts is evaluated for the polymerization of ethylene using tetraisobutylalumoxane as cocatalyst. The rate of polymerization decreases with increasing reaction time indicating a decay‐type kinetic profile. Catalyst composition and concentration of cocatalyst govern the performance of the system.
Determination of the optical anisotropy of atactic polystyrene using a grating monochromator
Authors: da Silveira Nádya Pesce , Samios Dimitrios , Strehle Frank , Dorfmüller Thomas 
Published: April 2003

AbstractTo extract the intrinsic molecular scattering from unwanted collision‐induced contributions as much as possible we propose a simple useful method recording the depolarized Rayleigh spectra using a double grating monochromator and correcting the spectra for the high‐frequency wings. For this purpose we tested the system polystyrene/CCl4 for which an asymptotic value of the optical anisotropy 〈γ2〉/x ≅ 30 Å6 with degree of polymerization x > 20 was found. The depolarized Rayleigh intensity of 2,4‐diphenylpentane and anionically polymerized atactic polystyrene standards was also measured in dilute solutions in the θ‐solvent bicyclohexyl (θ = 61°C). From the absolute depolarized Rayleigh ratio we obtained the configurational average optical anisotropy per number of monomer units, 〈γ2〉/x. We have chosen cumene as a model compound estimating that its optical anisotropy is similar to that of a quasi monomer unit. No significant temperature dependence of 〈γ2〉/x and of the static internal pair correlation in the temperature range from 25°C up to 80°C was found.
Side‐chain liquid crystal polymers of 2,3‐disubstituted norbornenes via ring‐opening metathesis polymerization, 2. Methoxybiphenyl as mesogenic group, influence of flexible spacer length m = 4 to 10 on the thermotropic behaviour
Authors: Winkler Berthold , Ungerank Markus , Stelzer Franz 
Published: April 2003

AbstractWe report the synthesis and ring‐opening metathesis polymerization of (±)‐exo,endo‐bis[ω‐(4′‐methoxybiphenyl‐4‐yloxy)alkyl] bicyclo[2.2.1]‐hept‐5‐ene‐2,3‐dicarboxylates using the molybdenum‐carben initiator Mo(CH‐t‐Bu)(NAr)(OCCH3)(CF3)(2)2 with NAr = 2,6‐diisopropylaniline. The spacer length was varied from m = 4 to 10 methylene groups. All monomers and polymers show mesophases of the smectic type. Independently of the spacer length no glass transition was detected. An odd‐even effect of transition temperatures was observed for both the monomers and polymers. The monomers with m > 5 showed more phase transitions in the DSC‐heating runs. Dependency of liquid crystalline transition temperatures on molecular weight is shown for one polymer (m = 6). Transition temperatures are roughly constant for polymers consisting of more than 30 repeating units. In contrast, the enthalpy changes of these transitions are nearly independent of the molecular weights once the polymers contain more than 10 repeating units, but they are strongly dependent on spacer length, with a minimum at m = 6.
Thermosets obtained by chemical modification of poly(epichlorohydrin) with vinyl‐terminated aromatic carboxylates
Authors: Reina Jose Antonio , Serra Angels , Cádiz Virginia 
Published: April 2003

AbstractPoly(epichlorohydrin) was modified in a high extent with several vinyl‐terminated aromatic potassium carboxylates (4‐(2‐propenyloxy)benzoate, 4‐(5‐hexenyloxy)benzoate, 3‐(2‐propenyloxy)‐2‐naphthoate, 3‐(5‐hexenyloxy)‐2‐naphthoate and 2‐(thioallyl)nicotinate) under solid‐liquid phase‐transfer conditions. Simultaneously with this substitution reaction, cleavage and crosslinking side reactions occurred. The polymers obtained were characterized by NMR, IR, elemental analysis, viscosimetry, size exclusion chromatography (SEC), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Then, crosslinked materials were obtained by curing mixtures of these linear polymers with 10% w/w of a radical initiator (dicumyl peroxide or 2,2′‐azoisobutyronitrile) on a DSC device. Finally, the thermal stability of the thermosetting materials was tested by TGA, and the Arrhenius kinetic parameters were determined for dicumyl peroxide initiated crosslinking processes by calorimetric measurements.
Polymers made from cholic acid derivatives: selected properties
Authors: Zhang Y. H. , Zhu X. X. 
Published: April 2003

AbstractPolymers of methacrylate and methacrylamide derivatives of cholic acid were prepared by free radical polymerization in solution. To verify the stereoisomeric effect of the monomeric units, certain properties of the resulting polymers were compared, including conversion rate, molecular weight, and glass transition temperature. The 3β‐epimers of the methacrylates and methacrylamides are to polymerize more easily than the 3α‐epimers. Water absorption experiments showed that the methacrylamide polymers are more hydrophilic than the methacrylate polymers and that the polymers from the 3β‐epimers have higher hydrophilicity than those made from the 3α‐epimers. The free acid forms of the polymers were also prepared by selective hydrolysis of the methyl ester group of the cholic acid moiety which resulted in improved hydrophilicity of the polymers.
Fixation of pharmacologically active amines on polyphosphonates, 3. Synthesis and preliminary in vitro cytotoxic studies of bis(2‐chloroethyl)amino group containing polyphosphonates
Authors: Fontaine Laurent , Marbœuf Céline , Brosse Jean‐Claude , Maingault Martine , Dehaut Frédéric 
Published: April 2003

AbstractHydrosoluble poly(3,6,9‐trioxaundecamethylene phosphonate) with attached cytotoxic bis(2‐chloroethyl)amine in the side chain was synthesized by chemical modification of the corresponding polyphosphonate via the Atherton‐Todd reaction. The structure of the product was confirmed by 1H, 13C and 31P NMR spectroscopy. Preliminary in vitro cytotoxic studies revealed that the polymeric derivative exhibited an eight fold more cytotoxic potency against human hepatocellular carcinoma cell line HepG2 than against murine leukemia cell line L1210.
Interpolymer complexes of a graft copolymer with polyelectrolytes and equivalent blends of binary homopolymer complexes: A comparative study of their stability and thermodynamic parameters
Authors: Chatterjee S. K. , Misra Neeti 
Published: April 2003

AbstractInterpolymer complexes of acrylamide/vinyl alcohol graft copolymers (AAm/VA) were prepared with two typical polyelectrolytes, e. g. poly(methacrylic acid) (PMA) and poly(ethyleneimine) (PEI). The equivalent blends of the same composition as the graft copolymer complexes were also prepared by mixing stoichiometric portions of binary homopolymer complexes. The stability constant (K), degree of linkage (θ) and related thermodynamic parameters (e. g. standard free energy change ΔG0, standard enthalpy change ΔH0 and standard entropy change ΔS0) were determined for each system by using Osada's method. The comparative study between graft copolymer complexes and equivalent blends indicated a considerable difference in these parameters. An interpretation of this discrepancy was sought in terms of copolymer effect, neighbouring group influence, and the nature of secondary binding forces upon interpolymer complexation.
Polymerization of cyclotrisiloxanes by organolithium compounds and P2‐Et base
Authors: Molenberg Aart , Möller Martin 
Published: April 2003

AbstractThe use of the phosphazene base P2‐Et(a) as a promoter for the anionic polymerization of hexamethylcyclotrisiloxane (D3Me) or hexaethylcyclotrisiloxane (D3Et) initiated by an organolithium compound leads to well‐defined polysiloxanes. At low conversion (< ca. 9%) the polymerization of D3Me behaves like a living polymerization, however, polymers with a narrow molecular weight distribution (M̄w/M̄n < 1.1) are obtained up to much higher conversions (ca. 70%). Kinetic data and NMR spectroscopy revealed the existence of a dynamic equilibrium between complexed and uncomplexed lithium silanolates. Below ambient temperature several different types of aggregates were indicated. The occurrence of an acceleration was observed after ca. 9% conversion.
Temperature rising elution fractionation of a random ethene/styrene copolymer
Authors: Thomann Yi , Sernetz Friedrich G. , Thomann Ralf , Kressler Jörg , Mülhaupt Rolf 
Published: April 2003

AbstractA random ethene/styrene copolymer containing 13.8 mol‐% styrene was prepared with the Ziegler‐Natta catalyst system Me2Si(Me4Cp)(N‐t‐butyl)TiCl2/methylaluminoxane and characterized by means of preparative temperature rising elution fractionation (TREF) combined with size exclusion chromatography, NMR, differential scanning calorimetry and wide‐angle X‐ray scattering analyses of the copolymer fractions. Efforts are made to describe the distribution of the styrene content of the copolymers using the Stockmayer‐Tacx distribution function. Both, comonomer distribution and molar mass distribution strongly support the presence of a single type of catalytically active center.
Radically initiated polymerization of a methacryloylamido‐terminated saccharide, 2. Copolymerization with 2‐hydroxyethyl methacrylate
Authors: Badey Bérangère , Boullanger Paul , Domard Alain , Cros Philippe , Delair Thierry , Pichot Christian 
Published: April 2003

AbstractKinetics of radically initiated copolymerization of 6‐deoxy‐6‐methacryloylamido‐D‐glucopyranose (MAG) with 2‐hydroxyethyl methacrylate (HEMA) was investigated at 60°C in water using 4,4′‐azobis(4‐cyanopentanoic acid) as initiator. Reactivity ratios of the binary system were determined to be rHEMA = 3.50 and rMAG = 0.60, indicating a strong copolymerization drift as polymerization proceeds. Copolymers with homogeneous composition were prepared using a simple and easy method based on the knowledge of the consumption rate of each monomer. These copolymers were then characterized with regard to composition (by 1H NMR) and physicochemical properties in aqueous media (using SEC with MALLS and refractometry detection and viscosimetric measurements).
Polyketone materials: control of glass transition temperature and surface polarity by co‐ and terpolymerization of carbon monoxide with higher 1‐olefins
Authors: Abu‐Surrah Adnan S. , Wursche Roland , Rieger Bernhard 
Published: April 2003

AbstractHighly soluble alternating 1‐olefin/carbon monoxide copolymers with olefin monomers (H2CCHR) containing 4, 5, 6, 10, 14, 16 and 18 C‐atoms in the R‐substituents were prepared by the use of dicationic palladium(II) phosphine catalysts and an optimized amount of methanol as activator. In terpolymerization experiments the influence of icosene‐CO or octadecene‐CO units, distributed randomly along a propene‐CO or ethene‐CO copolymer backbone, on molecular weight, glass transition temperature and on the surface polarity of films casted from solution has been investigated. As the length of the α‐olefin side chain increases, the glass transition temperature (Tg) of the copolymer is reduced from room temperature to almost −60°C. For octadecene‐CO and icosene‐CO copolymers side chain crystallization occurs, leading to elastic materials. Contact angle measurements, performed on water drops located on the surface of selected co‐ and terpolymer films demonstrate the wide range of surface polarity which can be covered by simple copolymerization of polar CO groups with apolar alkenes.
Synthesis and properties of (D)‐ and (L)‐lactide stereocopolymers using the system achiral Schiff's base/aluminium methoxide as initiator
Authors: Wisniewski Muriel , Borgne Alain Le , Spassky Nicolas 
Published: April 2003

AbstractThe polymerization of lactides with various D/L enantiomeric compositions using achiral Schiff's base/aluminium methoxide as initiator (SALENAlOCH3) in dichloromethane solution at 70°C is reported. The conversion was kept below 70% in order to limit transesterification reactions. The polymers obtained after precipitation show a narrow molecular weight distribution (ratio of weight‐ to number‐average molecular weights Mw/Mn = 1,1–1,2) and an optical rotation higher than that expected from the optical purity of the starting monomers. The examination of the thermal properties reveals that whatever their enantiomeric composition all the prepared polymers are crystalline. This unusual behavior is explained by an end‐chain propagation mechanism producing stereocopolymers with long enantiomeric sequences, i.e., increased isotacticity as substantiated by an examination of the microstructure of the polymers by means of 13C nuclear magnetic resonance. A stereocomplex formation was observed for stereocopolymers with optical purities below 40%.
Polyelectrolyte complexes from poly(N‐ethyl‐4‐vinylpyridinium bromide) and poly(sodium methacrylate). A stopped‐flow/light scattering investigation
Authors: Trinh Cam Khon , Schnabel Wolfram 
Published: April 2003

AbstractTime‐resolved light scattering measurements performed in conjunction with the stopped‐flow method revealed information on the formation of polyelectrolyte complexes (PECs) of the weak polyelectrolyte (PE) couple poly(N‐ethyl‐4‐vinylpyridinium bromide) and poly(sodium methacrylate). The stability of the PECs depends, apart from other parameters, on the total ionic strength of the solution [I], the PE concentration and the concentration ratio (Φ) = [PVPE]/[PMA]. On the basis of Φ‐[I] diagrams, obtained for three PE combinations differing in average molar mass, the stability of PECs is characterized by the regimes A, B and C referring to conditions, where PECs are quite stable and water‐insoluble (A), PECs are not very stable and water‐soluble (B) and PECs are instable (not formed). The course of the curves separating regime A from regime B reflects the action of two competing effects regarding the stability of PECs, namely the increase in charge density and the increase in ion condensation with growing total ionic strength: Kinetic measurements revealed that, at low ionic strength right upon mixing, supramolecular complexes and later large aggregates are formed. The aggregates undergo rearrangements leading eventually to smaller complexes. At high ionic strength aggregates are formed rather slowly after mixing. This behavior is related to ion condensation. PECs can form only after the small ions occupying the charged sites at the PE chains are removed. Detachment of small ions from PE chains is a relatively slow process and is the rate‐determining step in PEC formation at moderately high ionic strength of the solution.
Studies of lyotropic liquid crystalline mesophases of some novel regioselective substituted cellulose derivatives, 1. Synthesis and characterization
Authors: Aust Nicolai , Derleth Christina , Zugenmaier Peter 
Published: April 2003

AbstractNovel regioselective substituted cellulose derivatives, suitable for investigations of their liquid crystalline phase behaviour, were synthesized. The derivatives, tricarbanilates with varying substituents at the phenolic residue, were characterized according to their molecular weight and molecular weight distribution by means of size exclusion chromatography coupled with low angle laser light scattering (SEC/LALLS). A simple new method is presented, which allows the calculation of the constants K and a of the Staudinger‐Mark‐Houwink (SMH) equation, the viscosity‐average molecular weight Mη as well as the intrinsic viscosity [η] from the light scattering calibration curve of an SEC experiment. The calculated values of the intrinsic viscosity are in good agreement with those derived from measurements with a low‐shear viscometer. A plot [η] vs. weight‐average molecular weight Mw shows, that a substitution at the C‐2 and C‐3 position of the glucosic unit with 3‐chlorocarbanilate leads to a well pronounced enlargement of the polymer dimensions which is mirrored by larger values of [η] at the same Mw as compared with other cellulose derivatives.
A study on the effect of Cu2+ ions on the stability of triple helix poly[(riboadenylic acid):2 poly(riboinosinic acid)]
Authors: Yang Pin , Hua Erbing , Yang Binsheng 
Published: April 2003

AbstractThe effect of Cu2+ on the stability of the triple‐stranded helical structure of poly[(riboadenylic acid): 2 poly(riboinosinic acid)] poly(A : 21) was studied by means of circular dichroism spectroscopy and ultraviolet spectroscopy. The experimental results show that Cu2+ induces the hyperchromicity of poly(A : 2I) and causes the melting temperature Tm of poly(A : 2I) to decrease with increasing Cu2+ concentration. At the ratio of the concentration of Cu2+ to that of phosphate in poly(A : 2I), rt = 0, poly(A : 2I) is stable, is stable, at rt = 0.27, poly(A : 2I) decays in poly(A) and 2 poly(I), and at rt = 1.6, there is a racemate.
Polyhalide derivatives of poly[N‐(2‐aminoethyl)‐acrylamido]triethylammonium resins as iodinating reagents
Authors: Mitra Sudha Sumi , Sreekumar Krishnapillai 
Published: April 2003

AbstractPoly[N‐(2‐aminoethyl)acrylamido]triethylammonium dichloroiodate, tetrachloroiodate and dibromoiodate resins have been developed as a new class of heterogeneous reagents. The use of the polyhalide derivatives for the selective iodination of aromatic amines and phenols is described. The influence of the various reaction parameters including nature of the solvent, effective molar concentration of the reagent and temperature were investigated to find out the optimum reaction conditions for achiveing selectivity for monoiodination.
Kinetic studies of the injection of comonomers during polymerization of ethene and propene with MgCl2‐supported Ziegler‐Natta catalysts
Authors: Wester Thale Sofie , Ystenes Martin 
Published: April 2003

AbstractThe effects of injecting ethene, propene, 1‐hexene, 2‐methylpropene, 3,3‐dimethyl‐1‐butene, cis‐2‐butene, trans‐2‐butene, 2,3‐dimethyl‐2‐butene, cyclopentene, styrene, 1,3‐butadiene and 1,4‐pentadiene during polymerizations of ethene and propene have been investigated. Catalysts used were a supported MgCl2/EB/TiCl4 ballmilled catalyst and precipitated MgCl2/2‐EH/TiCl4/DIBP catalysts activated with triethylaluminium in presence of EB. (EB = ethyl benzoate, 2‐EH = 2‐ethylhexanol, DIBP = diisobutyl phthalate). The polymerizations were performed at 50°C, in a heptane slurry at 1 atm (1.00 · 105 Pa) total pressure.The instantaneous polymerization rate was observed by continuous monitoring of the monomer consumption, the time resolution of the measurements being less than one second. Two different kinetic effects can be observed after injection of the comonomer. First there is an immediate rate change, usually a rate reduction. Then a secondary effect may follow, which is a slow, and sometimes significant and persistent, activation. The two effects obviously have different causes, and for none of these we found single causes that can explain all the observations. The strongest immediate effect was observed after addition of dienes and indicates a direct association of the comonomer to the active center. A marked nonlinearity in the response may hint to inhomogeneity in the structural environment of the active centers. Addition of α‐olefins during ethene polymerization gave the strongest secondary effect. In general the immediate effects were stronger during propene polymerization than during the polymerization of ethene. A significant difference in the effects of cis‐2‐butene and trans‐2‐butene in the polymerization of propene indicates that steric effects may be important.
Monomolecular and bimolecular termination in the polymerization of di(meth)acrylates
Authors: Andrzejewska Ewa , Bogacki Mariusz B. 
Published: April 2003

AbstractThe termination mechanism in the polymerization of a series of analogous di(meth)‐acrylates differing only by the type of the heteroatom (S or O) in the ester group was investigated. The experimental method was based on differential scanning calorimetry measurements of photochemically initiated polymerization. The ratio of the bimolecular termination and propagation rate constants k/kp and/or the monomolecular termination rate constant k were determined according to three termination models (monomolecular, bimolecular, and mixed). Statistical techniques were used for choosing between the models to find out by which mechanism (monomolecular, bimolecular or mixed) the termination occurs. The results obtained prove than monomolecular reaction is an important termination way in the polymerization of multifunctional monomers and must be taken into account when kinetic constants are determined, even at low degree of conversion. The sulfur‐containing monomers are characterized by much lower k values than the analogous sulfur‐free monomers.