bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymeric prodrugs, 8. Synthesis and hydrolytic behaviour of dextran‐bound anticancer agents
Authors: Móra Melinda , Pató János 
Published: April 2003

Abstract3‐Chloro‐2‐hydroxypropyl ether of dextran (3a) and succinyldextran (4a) were prepared and used for coupling the anticancer agents 6‐purinethiol and 5‐fluorouracil. The “in vitro” drug liberation was measured at pH 7,2 and 8,8. The release rate from the dextran conjugates was compared with that of the poly(1‐vinyl‐2‐pyrrolidone‐co‐maleic acid) derivatives of these drugs. The effect of the macromolecular chain on the hydrolytic behaviour of the polymer‐bound drugs was clearly detected.
Polylactones, 19. Anionic polymerization of L‐lactide in solution
Authors: Kricheldorf Hans R. , Kreiser‐Saunders Ingrid 
Published: April 2003

AbstractThe anionic polymerization of L‐lactide was studied with four potential initiators of different basicity: potassium benzoate, potassium phenoxide, potassium tert‐butoxide and butyllithium. Regardless of the solvent, only the two most basic initiators proved to be reactive enough to initiate and maintain the polymerization. This result and the formation of benzyloxy end‐groups upon addition of benzyl bromide prove that the polymerizations proceed via alkoxide chain ends. Absence of initiator fragments in the isolated polylactide chains suggests that initiation mainly involves deprotonation of L‐lactide, whereas nucleophilic substitution only occurs to a minor extent. Furthermore, optical rotation measurements indicate that both the initiator and the alkoxide chain end cause partial racemization regardless of solvent and temperature. Furthermore, it was found that reagents such as triethylamine, pyridine or potassium benzoate which are not reactive enough to initiate polymerization, are basic enough to cause partial racemization of L‐lactide by deprotonation.
Alkoxy substituted liquid‐crystalline aromatic copolyesters
Authors: Schleeh Thomas , Kßmehl Gerhard , Hinrichsen Georg 
Published: April 2003

AbstractThe increasing exchange of 2,5‐dipentyloxyterephthaloyl units by terephthaloyl units, studied up to 60 mole‐%, influences the chemical and physical behaviour of the corresponding copolyesters. The copolyesters with an exchange of 30 mole‐% and more become insoluble in chloroform and dichloromethane. The decomposition temperatures increase and the copolyesters show a better long‐time thermal stability. The melting and clearing intervals shift to higher temperatures. The low temperature liquid‐crystalline (LC) phase, which can be seen very well in the HT05‐100 samples, disappears continuously with the increase of the terephthaloyl content. The solid to LC (high temperature phase) transition enthalpies decrease linearly with increasing terephthaloyl content.
Die ermittlung der protonierungsgleichgewichtskonstanten von ankergruppen komplexbildender ionenaustauscherharze
Authors: Huhn Gernot , Müller Helmut , Krauß Dieter , Schwachula Gerhard , Szabadka Ödön 
Published: April 2003

AbstractA previously derived equation for the calculation of the protonation constants of immobilized ligands is used for a description of the protonation equilibria of chelating resins containing iminodiacetic acid groups. The equilibrium protonation constants of technical and of pure ion exchange resins were determined. Data obtained from the pH titration curve, and measurements of counter ion and water uptake were used to calculate the three steps of protonation at 298 K. The obtained values of the equilibrium protonation constants were correlated with properties of the investigated resins like composition and degree of crosslinking.
Reversible immobilization of drugs on a hydrogel matrix, 2. Diffusion of free chloramphenicol from poly(2‐hydroxyethyl methacrylate) hydrogels
Authors: Yean Leanirith , Bunel Claude , Vairon Jean‐Pierre 
Published: April 2003

AbstractThe diffusional behaviour of chloramphenicolD‐(–)‐threo‐N‐[2‐hydroxyl‐1‐hydroxymethyl‐2‐(4‐nitrophenyl)ethyl]dichloroacetamide.
(1) from poly(2‐hydroxyethyl methacrylate) (pHEMA) hydrogels is reported. The drug was trapped in the matrix cross‐linked with various amounts of ethylene dimethacrylate (0,5–18 mol‐%), and the diffusion was followed from disc‐shaped slabs at swelling equilibrium in water (phosphate buffer, pH 7) at 37°C. The diffusion obeys the second Fick law and is rapid (D ≈ 10−8 cm2 s−1) in the case of the slightly crosslinked hydrogels used for corneal lenses. The diffusion coefficients decrease almost exponentially with increasing cross‐linking ratio, and the process appears predominantly controlled by the free volume contribution of the diluent rather than by the sieving of the network.
Multiple melting temperatures of poly(3,3‐diethylthietane)
Authors: Marco Carlos , Lazcano Silvia , Fatou José G. 
Published: April 2003

AbstractThe melting behaviour of semicrystalline poly(3,3‐diethylthiethane) (PDET), was studied by differential scanning calorimetry (DSC), wide‐angle X‐ray scattering (WAXS), small‐angle light scattering (SALS), and thermooptical analysis (TOA). Two samples of number‐average molecular weights 6,0 · 104 and 1,8 · 105 and rather narrow molecular weight distributions (ratio of weight‐to number‐average molecular weights M̄w/M̄n = 1,3) were analyzed. When PDET is isothermally crystallized from the molten state in the range 275–333 K, the calorimetric curves show one or two melting endotherms, depending on crystallization temperature (Tc) and heating rate. WAXS analysis shows conclusively that polymorphism is absent. It was shown that the melting behaviour of PDET is being dictated by processes of melting and recrystallization occurring during the experimental analysis.
Polyanion‐polykation‐komplexe mit saccharid‐substituierten polyacrylsäuren und polyvinylaminen
Authors: Kötz Joachim , Philipp Burkart , Pfannemüller Beate 
Published: April 2003

AbstractSamples of saccharide‐substituted poly(acrylic acid) and polyvinylamine varying in DS and length of the saccharide side chains were investigated with regard to their polyelectrolyte character by determining their pK0a values and by a potentiometric, conductometric and turbidimetric titration with an oppositely charged polyelectrolyte. Criteria employed for the evaluation of these “symplex titrations” were the ratio of cationic to anionic groups at the endpoint and the course of the turbidimetric curve classified according to several schematized curve types. From the results obtained it can be concluded that substitution by saccharide side chains in the case of poly(acrylic acid) impedes Coulombic interaction to some extent only by steric hindrance, while in the case of the substituted polyvinylamines also intermolecular H‐bonds between the amino groups and the saccharide side chains have to be taken into account.
Asymmetric induction polymerization of monomer salts prepared from 1,3‐butadiene‐1‐carboxylic acid and optically active amines
Authors: Yamaguchi Hidemasa , Iwama Tetsuroh , Hayashi Toshio , Doiuchi Tohru 
Published: April 2003

AbstractChiral monomer salts, prepared from 1,3‐butadiene‐1‐carboxylic acid (BuCOOH) and optically active 1‐cyclohexylethyl‐ or bornylamines (CyA, BoA), were polymerized in methanol with AIBN. The obtained optically active polymer salts (Poly‐1(BoA) and Poly‐1(CyA)) were deaminated by repeated reprecipitation. The deaminated polymers (Poly‐2(BoA) and Poly‐2(CyA)) were optically inactive. In the case of the salt from optically active 1‐phenylethylamine (PhA) and BuCOOH (PhA/BuCOOH), Poly‐2(PhA) was still optically active even after the removal of PhA from Poly‐1 (PhA). Furthermore, PhA/BuCOOH was polymerized in the mixed solvent of methanol/benzene of methanol/chloroform. From the optical behavior of Poly‐2 and the 1H NMR spectra of the monomer salts, the role of the phenyl ring in the monomer salt on the asymmetric induction polymerization is discussed.
Soft‐segment crystallization and properties of copoly(ether‐ester) elastomers
Authors: Lembicz Franciszek , Slonecki Jerzy 
Published: April 2003

AbstractDifferential scanning calorimetry, dynamical mechanical, and spin probe measurements were conducted to study relaxation and soft‐segment crystallization phenomena in block copoly(ether‐ester) elastomers obtained through transesterification and melt polycondensation of dimethyl terephthalate, 1,4‐butanediol and poly(ethylene oxide). The elastomers investigated differed both in molecular weight of the poly(ethylene oxide) used as well as in their ratio of hard to soft segments. It was found that a crystallization process of the soft‐segment phase does not occur for oligoethers with a molecular weight lower than 1000. The spin probe method can be used to monitor the melting process and additionally it supplies information on the relaxation processes taking place in the amorphous part of the soft phase. Some data on the crystallization of the rigid phase are also given.
Observation of the conformation and structure of some liquid‐crystal polymers by small‐angle neutron scattering
Authors: Pépy Gérard , Noirez Laurence , Keller Patrick , Lambert Marianne , Moussa Fernande , Cotton Jean‐Pierre , Strazielle Claude , Lapp Alain , Hardouin Francis , Mauzac Monique , Richard Hélène 
Published: April 2003

AbstractThe conformation of the backbone and the structure of the mesogenic groups of some liquidcrystal polymethacrylates and polysiloxanes were determined by small‐ and low‐angle scattering of neutrons. A strong magnetic field aligned the mesomorphic monodomains. For most samples and phases the polymer backbone adopts an oblate shape versus the mesogenic director. The observation of several diffuse spots together with Bragg peaks allows to propose models for the structure of these samples.
Synthesis and characterisation of chiral nematic liquid‐crystalline copolymers with the chiral centre in the flexible spacer
Authors: Cowie John M. G. , Hunter Hugh W. 
Published: April 2003

AbstractThe synthesis and characterisation of a series of novel chiral nematic liquid‐crystalline combbranch copolymers having the chiral centre in the flexible spacer are described. The copolymers, prepared from the chiral monomer (S)‐2‐(4′‐cyano‐4‐biphenylyloxy)‐1‐methylethyl methacrylate (7) and the nematogenic monomer 4‐cyanophenyl 4‐(6‐acryloyloxyhexyloxy)benzoate (8), were found to form planar textures which display bright reflection colours at low chiral monomer feed values. These coloured textures could be stored reversibly by cooling below Tg.
Epoxy prepolymers cured with boron trifluoride‐amine complexes, 1. Influence of the amine on the curing window
Authors: Bouillon Nelly , Pascault Jean‐Pierre , Tighzert Lan 
Published: April 2003

AbstractDifferent pure complexes were synthesized by an interchange reaction of BF3‐etherate with amines in dichloromethane. All of the resulting complexes are solid, but they can be dissolved in a low‐molecular‐weight poly(ethylene oxide) to favour their use as initiators. DSC analysis demonstrated strong interactions between the BF3‐complex and the polyether. This is probably caused by the formation of hydrogen bonding between the hydrogens of the amine and the ether groups. The reactivity of amine complexes was characterized by reaction with the epoxy prepolymer. The reactivity increases with decreasing basicity of the amine, showing a relationship between the initiation and propagation of the expoxy homopolymerization and the stability of the complex. A slight influence on the reaction temperatures by the amount of polyether is observed, but the glass transition temperature of the epoxy network decreases when a large excess is used.
Epoxy prepolymers cured with boron trifluoride‐amine complexes, 2. Polymerization mechanisms
Authors: Bouillon Nelly , Pascault Jean‐Pierre , Tighzert Lan 
Published: April 2003

AbstractThe kinetics of the polymerization of phenoxymethyloxirane (6) initiated by the BF3 complex of 4‐chloroaniline (7) solubilized in oligo(ethylene oxide) of molecular weight 300 (PEO) is characterized by an initial induction period, followed by a propagation step with a rate Rp = k [6] · [7]0,32 · [PEO]−0,55. The length of the induction period decreases with [7] and increases with [PEO]. However, Rp increases with [7] and decreases with [PEO]. The reaction can be explained by the activated monomer mechanism.
Epoxy prepolymers cured with boron trifluoride‐amine complexes, 3. Polymerization mechanism of a prepolymer containing epoxy groups
Authors: Bouillon Nelly , Pascault Jean‐Pierre , Tighzert Lan 
Published: April 2003

AbstractThe reaction of a diepoxy prepolymer (2) initiated by the BF3‐complex of 4‐chloroaniline (3), solubilized in poly(ethylene oxide) (PEO) of molecular weight 300, was studied. An initial induction period was observed, followed by a pseudo‐stationary stage with decreasing reaction rate due to gelation. In the pseudo‐stationary stage, the homopolymerization rate is given by the expression: Rp = k[2]1 · [3]·−0,55 · [PEO]·0,57. In addition to 2, we also used a Novolac prepolymer 4. Different networks were prepared and analyzed by thermal and mechanical techniques, and their water‐absorption rates were measured.
Morphology and phase transition study of polymers with discotic mesogens
Authors: Hsu Tsuey‐Chen , Hüser Bernhard , Pakula Tadeusz , Spiess Hans Wolfgang , Stamm Manfred 
Published: April 2003

AbstractThe discotic liquid‐crystalline polymers poly[oxy(3,7,10,11‐tetrapentoxy‐2,6‐triphenylenediyl)‐oxycarbonyltetradecamethylenecarbonyl] (1), containing discotic mesogenic groups in the main chain and poly[methyl(3,6,7,10,11‐pentapentoxy‐2‐triphenylenyloxyundecyl)siloxane] (2) with disc‐like groups attached to the polymer chain by flexible spacers, are studied by X‐ray diffraction, solid‐state nuclear magnetic resonance, differential scanning calorimetry and dynamic mechanical measurements, in order to determine the dynamic and structural transitions. It is shown that low‐temperature softening in both polymers is caused by the mobility of short aliphatic side chains attached to the discotic units. Once formed, the columnar mesomorphic structure is stable up to the temperature of isotropization. For the main‐chain polymer, a third transition is observed in samples quenched from the melt. The transition is related to the mobility of the main chain in an amorphous structure, where the discotic units are not organized in columns.
Miscibility in blends of random copolymers of styrene and acrylontrile with block copolymers of styrene and methyl methacrylate
Authors: Kressler Jörg , Karasz Frank E. , Kammer Hans‐Werner , Morgenstern Ute 
Published: April 2003

AbstractPhase behavior in blends of random copolymers of styrene and acrylonitrile with block copolymers of styrene and methyl methacrylate was studied by light scattering, light microscopy and glass transition temperature measurements. The results are compared with those of respective blends containing random copolymers of styrene and methyl methacrylate. In terms of macrophase separation, the block copolymers display a more extended miscibility domain with styrene/acrylonitrile copolymers than the random copolymers. However, the extent of the miscibility domain varies as a function of temperature. Unlike the random copolymer blends, all blends containing block copolymers exhibit lower critical solution temperature behavior. Finally, it is established that the systems studied here undergo spinodal decomposition leading to macrophase separation.
Enantioselective hydro‐oligomerization (protio‐ or deuterio‐) of α‐olefins
Authors: Pino Piero , Galimberti Maurizio , Prada Paolo , Consiglio Giambattista 
Published: April 2003

AbstractThe enantioselective protio(deuterio)oligomerization of propene, 1‐pentene and 4‐methyl‐1‐pentene was carried out with the diastereomerically pure catalyst precursor (−)‐(R)‐ethylenebis [1–3a,7a‐η‐(4,5,6,7‐tetrahydro‐1‐indenyl)]zirconium (S)‐1,1′‐bis‐2‐naphtholate (3) and/or with (−)‐(R)‐ethylene [1–3a,7a‐η‐bis(4,5,6,7‐tetrahydro‐1‐indenyl]dimethylzirconium (1) in the presence of methylalumoxanes. The enantioselectivity of both reactions which take place (deuteration and oligomerization) is from fair to high and essentially independent of the catalyst precursor. In the hydrooligomerization the enantioface of the olefinic monomer which prevailingly reacts is from a geometric point of view the same for all three substrates. In the case of 1‐pentene and 4‐methyl‐1‐pentene the enantioface prevailing embedded in the oligomers is opposite to that prevailingly deuterated. The significance of the growing chain for enantioface selection during stereospecific polymerization is thus emphasized.
Model networks based on poly(1,3‐dioxolane)
Authors: Franta Emile , Gérard Eric , Gnanou Yves , Reibel Léonard , Rempp Paul 
Published: April 2003

AbstractPolyurethane networks whose elastic chains are constituted of hydrophilic poly(1,3‐dioxolane) of well‐defined molecular weight were synthesized using an end‐linking process. The poly(1,3‐dioxolane) (PDXL) precursor polymers, fitted with OH functions at both chain ends, were prepared cationically in the presence of ethylene glycol. The latter compound is involved in the initiation reaction and provides the OH functions at the chain ends. The end‐linking process, leading to the formation of the poly(1,3‐dioxolane) network, involves the reaction of the precursor with a stoichiometric amount of a plurifunctional isocyanate, under conditions that minimize defects. The swelling behavior of the poly(1,3‐dioxolane) networks is compared with that of poly(ethylene oxide) networks previously studied.
Evaluation of individual rate constants from the chain‐length distribution of polymer samples prepared by intermittent (rotating sector) photopolymerization, 3. Theoretical foundations for termination by disproportionation
Authors: Zifferer Gerhard , Olaj Oskar Friedrich 
Published: April 2003

AbstractThe chain‐length distribution and its moments were calculated for a periodically interrupted photopolymerization with termination by disproportionation and negligible chain transfer. For a wide range of experimental conditions, which are readily accessible in the overwhelming majority of cases, the position of the first point of inflection in the chain‐length distribution corresponds exactly to the quantity kp [M]t0, kp representing propagation rate constant, M monomer and t0 the period length. Thus kp can be directly evaluated from the chain‐length distribution of the polymer. Together with the ratio k/kt, kt being the termination rate constant, calculated from the rate and weight‐average degree of polymerization according to a universal relationship—the validity of which is also verified — resolution into the individual rate constants is easily accomplished. The dependence on experimental conditions of the ratio weight‐ to number‐average degrees of polymerization Pw/Pn, which is a measure of the width of the molecular weight distribution of the polymer formed, is discussed.
Synthesis and rheological study of some maleic acid and fumaric acid stereoregular polyesters, 5. Structural study by 1H and 13C NMR of random, multi‐block and alternating unsaturated copolyesters from fumaric, maleic and phthalic acid potassium salts and 1,4‐dibromobutane
Authors: Sepulchre Marie‐Odile , Moreau Michel , Sepulchre Maurice , Djonlagić Jasna , Jaćović Mihailo S. 
Published: April 2003

AbstractThe sequence distribution in random, multi‐block and alternating copolyesters based on the reaction of fumaric, maleic and phthalic acid potassium salts with 1,4‐dibromobutane were examined by 1H and 13C NMR spectra. Quantitative sequence distibution results were obtained from the analysis of 13C NMR spectra. The different structures of synthesized copolyesters, expected from the experimental procedures used, were confirmed. In addition, it can be concluded that the esterification route used is irreversible and that no appreciable transesterification reaction between two different ester groups occurs in the course of the synthesis.
13C NMR studies on the relative reactivity of isocyanate groups of isophorone diisocyanate isomers
Authors: Bialas Norbert , Höcker Hartwig , Marschner Michael , Ritter Wolfgang 
Published: April 2003

AbstractModel reactions of isophorone diisocyanate (IPDI (1)) with ethanol were examined using 13C NMR technique to locate the chemical shift of different urethane and isocyanate groups in the products. The reactivity of the secondary and primary isocyanate group of the IPDI isomers is catalyst‐dependent. In the presence of Lewis acids (e.g., dibutyltin dilaurate) the secondary NCO group is more reactive, while in the presence of Lewis bases (e.g., triethylamine) it is the primary one. This effect allowed the chemical shift assignment of urethane‐ and isocyanate carbonyl C atoms in adducts formed by reaction of IPDI with ethanol in mole ratio NCO:OH = 2:1. In ethyl carbamates from the main isomer the chemical shift δ = 155,93 ppm is assigned to the carbonyl C atom of the urethane group at the secondary C atom, the signal at δ = 157,07 ppm to the primary urethane group. Furthermore, it was possible to assign the signal at δ = 122,12 ppm to the primary NCO group and the signal at δ = 122,98 ppm to the secondary NCO group of isophorone diisocyanate.
Hydrogels for site‐specific oral delivery. Poly[(acrylic acid)‐co‐(butyl acrylate)] crosslinked with 4,4′‐bis(methacryloylamino)azobenzene
Authors: Přádný Martin , Kopeček Jindřich 
Published: April 2003

AbstractCopolymers of acrylic acid and butyl acrylate crosslinked with 4,4′‐bis(methacryloylamino)‐azobenzene were synthesized by radical copolymerization with different amounts of acrylic acid and crosslinker. They were characterized by equilibrium degree of swelling, modulus of elasticity in compression at pH 2 and 7, and effective network density. The acido‐basic properties of crosslinked copolymers were compared with linear (soluble) ones of the same composition. The study of the dependence of the apparent dissociation constant (pKapp) on the degree of dissociation has shown that conformational transition from the compact to the random conformation of the polymeric chains occurs only in crosslinked copolymers. The high values of pKapp obtained indicate that strong Donnan effects and low polarity of environment of carboxy groups are operative in acido‐basic equilibria.
An unusual bacterial polyester with a phenyl pendant group
Authors: Fritzsche Katharina , Lenz Robert W. , Fuller R. Clinton 
Published: April 2003

AbstractThe microorganism Pseudomonas oleovorans is known to produce polyesters containing 3‐hydroxyalkanoate units when grown on n‐alkanes and n‐alkanoic acids under nutrient limiting conditions, but when 5‐phenylvaleric acid was supplied as the only carbon source, poly[3‐hydroxy‐5‐phenylpentanoate], a polyester with a phenyl pendant group, was produced. The optimum substrate concentrations and harvesting times were determined by measuring the change of cell growth and polymer yield during the growth. A 12‐L cell culture yielded 222,5 mg polymer/L and 25% polymer per cellular dry weight. This bacterial polymer showed an optical rotation of [α] = −24,5° ± 0,2°. The structure was corroborated by 1H NMR and 13C NMR spectroscopy. The composition of the polymer was also determined by methanolysis to the methyl ester of the repeating unit, which was subsequently analyzed by GC. By this procedure the polyester was found to be a homopolymer to the extent of at least 99%. The polyester has a glass transition at 13°C, a melting range from 54 to 69°C, and a weight‐average molecular weight of M̄w = 350000 with a polydispersity M̄w/M̄n of 3,5, as determined by GPC relative to polystyrene standards.