bluuebunny/crossref_metadata_2025_split huggingface dataset:
Novel synthetic approach to poly(p‐benzenesulfonamide): Self‐polycondensation of active p‐aminobenzenesulfonic acid derivatives under mild conditions
Authors: Saegusa Yasuo , Ogawa Takeshi , Kondo Hiromune , Nakamura Shigeo , Chau Nguyen , Iwakura Yoshio 
Published: April 2003

AbstractThree active p‐aminobenzenesulfonic acid derivatives, 1‐(p‐aminobenzenesulfonyl)imidazole (4a), 1‐(p‐aminobenzenesulfonyloxy)benzotriazole (4b), and 2‐phenyl‐4‐(p‐aminobenzenesulfonyl)‐1,3,4‐oxadiazoline‐5‐thione (4c) were synthesized by reacting p‐isocyanatobenzenesulfonyl chloride (1) with stoichiometrical quantities of water in the presence of dibutyltin didodecanoate and subsequently with imidazole, 1‐hydroxybenzotriazole and 2‐phenyl‐1,3,4‐oxadiazoline‐5‐thione, respectively. The self‐polycondensation of 4a–c, leading to poly(p‐benzenesulfonamide) (7), was carried out in solution using polar aprotic solvents, N‐methyl‐2‐pyrrolidone (NMP) and hexamethylphosphoric triamide (HMPA), and acidic media, dimethyl sulfoxide (DMSO) and m‐cresol, with or without an appropriate acid catalyst or acid acceptor under mild conditions. Poly(p‐benzenesulfonamide) having the highest reduced viscosity of 0,14 dl·−1 was obtained almost quantitatively from 4c by using m‐cresol as a solvent without any acid catalyst and acid acceptor at 25°C. The polymers are soluble in polar aprotic solvents such as NMP, HMPA and DMSO and in aqueous sodium hydroxide. These poly(p‐benzenesulfonamide)s are less thermally stable than completely aromatic polyamides, because the initial weight‐loss started at 250–350°C. Aminolysis of three benzenesulfonic acid derivatives, 1‐benzenesulfonylimidazole (5a), 1‐benzenesulfonyloxybenzotriazole (5b), and 2‐phenyl‐4‐benzenesulfonyl‐1,3,4‐oxadiazoline‐5‐thione (5c), with the same leaving groups was also carried out as a model reaction of self‐polycondensation to determine the reaction conditions.
Oligomerization and cyclization of 1‐phenoxy‐2,3‐epoxypropane induced by magnesium perchlorate
Authors: Tänzer Wolfram , Müller Heike , Wintzer Jana , Fedtke Manfred 
Published: April 2003

AbstractDuring the reaction of 1‐phenoxy‐2,3‐epoxypropane (1) with catalytic amounts of Mg(ClO4)2 a variety of reaction products are formed which do not correpond to a normally distributed oligomer range. Essentially, three reaction paths can be distinguished which lead to oligo‐(hydroxyether)s of similar structure (6 and 8) and to cyclic, isomeric dimers (9 and 10) of very low reactivity. During the reaction of bifunctional 2,3‐epoxypropyl ethers, cyclic products act as nonreactive diluents decreasing the network density of the final crosslinked product.
Rigid rod polymers with flexible side chains, 4. Synthesis, structure and phase behaviour of polyimides prepared from pyromellitic anhydride and 2,5‐di‐n‐alkoxy‐1,4‐phenylene diisocyantes
Authors: Wenzel Markus , Ballauff Matthias , Wegner Gerhard 
Published: April 2003

AbstractA series of rigid rod polyimides 1a–f derived from pyromellitic anhydride (PMDA) and 2,5‐di‐n‐alkoxy‐1,4‐phenylenediamine containing flexible alkoxy side chains with 4 to 16 carbon atoms was prepared by solution polycondensation. As demonstrated by model experiments full conversion to the imide structure is achieved by reaction of PMDA with 2,5‐dialkoxyphenylene diisocyanate, the latter compound being blocked by imidazole. The best solvent for the polycondensation, found in the course of the model reaction, is 1,3‐dimethyl‐2‐oxo‐perhydro‐pyrimidine together with 4‐dimethylaminopyridine as an accelerator. Wide‐angle X‐ray diffractograms showed that all polyimides under consideration here are highly crystalline at room temperature. The occurrence of a sharp reflection at the region of low angles together with its higher orders demonstrates the presence of a layered structure. The layer spacing was found to increase linearly with the length of the alkyl side chains. Polyimides bearing long side chains (n ≥ 10) exhibit two broad endotherms in the DSC analysis. As is revealed by wide‐angle X‐ray analysis the first transition is related to a disordering process of the side chains. The second transition leads to a layered high‐temperature phase akin to the modification (B) found in a recent study of a similar rigid polyester bearing flexible side chains.
Anodic polymerization of acrylamide in aqueous nitrate solution using an activated iridium electrode
Authors: Otero Toribio Fernández , Mugarza Maria Antonia 
Published: April 2003

AbstractThe flow of an electric current through an aqueous solution of acrylamide and NaNO3, using an activated iridium electrode as anode, induces the polymerization of the monomer in solution. The influence of the chemical and electrochemical variables on monomer conversion was studied. The experimental results point to the production of initiating radicals by charge transfer between the electrolyte and the electrode, followed by desorption of these radicals from the electrode into the solution. The electrode process is a mixed process in which all the species present take part. Electrode activation depolarizes the NO discharge and increases the polymerization rate.
Comportement au voisinage des conditions «théta» des solutions semidiluées et concentrées de poly(diméthylsiloxane) dans le styrène
Authors: Lapp Alain , Strazielle Claude 
Published: April 2003

AbstractThe thermodynamical properties of poly(dimethylsiloxane) (PDMS) were studied in the theta‐solvent styrene. Moderately diluted and semidiluted solutions of three PDMS samples with weight‐average molecular weights M̄w = 23 500, 160 000, and 860 000 were investigated by means of light scattering near the theta‐temperature. The dependency of the interaction parameter X on temperature and concentration was established for the three samples. The study of the third virial coefficient A3 showed that A3 is independent of molecular weight and temperature as predicted by theory. However, the experimental value of A3/(AM) was higher than expected. The critical properties, i.e., critical point and spinodal, were considered.
Electrochemical polymerization of derivatives from N‐methylpyrrole and thiophene to heteroarylenevinylene polymers
Authors: Berlin Anna , Wernet Wolfgang , Wegner Gerhard 
Published: April 2003

AbstractThe heteroaryl‐ and heteroarylenevinylene compounds 1, 2, 3, and 4 were investigated by means of cyclic voltammetry and submitted to oxidative electropolymerization under galvanostatic conditions; the products obtained were further characterized by means of elemental analysis, optical absorption spectroscopy and conductivity measurements. (E)‐1,2‐bis(N‐methyl‐2‐pyrrolyl)ethylene (1), 2,5‐bis[(E)‐2‐(N‐methyl‐2‐pyrrolyl)vinyl]thiophene (2) and N‐methyl2,5‐bis[(E)‐2‐(N‐methyl‐2‐pyrrolyl)vinyl]pyrrole (3) gave brittle to spongy films on electropolymerization with perchlorate as the counterion balancing the positive charge on the polymer backbone units. The d. c. conductivity of all three polymers (as perchlorates) was of the order of 10−3 Ω−1·cm−1. N‐methyl‐2,5‐bis[(E)‐2‐(2‐thienyl)vinyl]pyrrole (4) did not give a solid polymer.
Photosensitive polymers with pendent p‐dialkylaminobenzylideneacetophenone residues as photoinduced radical polymerization initiators
Authors: Ichimura Kunihiro , Kameyama Atsushi 
Published: April 2003

AbstractPolymers with pendent p‐dialkylaminobenzylideneracetophenone (PABA) groups were prepared by copolymerization of 4‐(4‐dimethylaminobenzylidenemethylcarbonyl)phenyl methacrylate (1) with alkyl methacrylates and by the substitution reaction of poly(chloromethylstyrene‐co‐methyl methacrylate) with sodium 4‐(4‐dimethylaminobenzylidenemethylcarbonyl)phenolate (3). The polymers having PABA groups become insoluble upon photodimerization of PABA. Furthermore, the photosensitivity of the polymers increases considerably when mixed with vinyl monomers and diphenyliodonium hexafluorophosphate (DPI) during irradiation. The photocrosslinking may involve graft polymerization initiated by PABA which sensitizes the decomposition of DPI to form radicals. Introduction of unsaturated groups like maleate or crotonyl groups into the PABA polymer depresses the shrinkage of the photocured polymer film when the polymer was mixed with DPI. Sensitivity characteristics of PABA polymers toward Ar laser emitting 488 nm light are mentioned.
Spezifische Adsorbentien für das Peptidantibiotika synthetisierende Enzymsystem Gramicidin S Synthetase, 1. Darstellung niedermolekularer Spacer‐Ligand‐Verbindungen
Authors: Schlünsen Jürgen , Manecke Georg 
Published: April 2003

AbstractSeveral amide derivatives of phenylalanin and prolin were prepared as spacer/ligand compounds by reaction of unprotected or monoprotected aliphatic and aromatic diamines and monoamines with the succinimido esters of the corresponding N‐protected amino acids. The formation of diacylated aliphatic diamines was fast under normal conditions. In the case of aromatic diamines the presence of a bases is necessary. For the preparation of monoacylated diamines best results were obtained with monoprotected diamines. The acylated diamines were purified by column chromatography or by extraction.
Poly(epichlorohydrin)s obtained by means of a new calcium complex as catalyst
Authors: Lamot Ryszard 
Published: April 2003

AbstractA new catalytic complex was developed by reacting 1,1‐diphenylethylene with metallic calcium and submitting the resulting derivative [designated as (Ar)2Ca] to chemical modifications with 1‐chloro‐2,3‐epoxypropane (epichlorohydrin; ECh). From these reactions a series of (Ar)2Ca · x ECh catalysts resulted differing by the mole ratio ECh/Ca. A value of 0,7 was found to be the optimal one with regard to the catalytic efficiency of polymerizing epichlorohydrin. The poly(epichlorohydrin)s (PECh), obtained with yields of 46, 5 to 82, 4%, are distinguished by their chlorine content and cover a range of molar masses from 0,35 · 105 to 2,23 · 105 g/mol. The catalysts were characterized by elemental analyses and thermogravimetry. According to X‐ray patterns, PECh obtained by means of (Ar)2Ca · 0,7 ECh as catalyst displayes no crystallinity like PECh prepared in the presence of appropriate aluminium systems.
Study of the initiation mechanism of the vinyl polymerization with the system persulfate/N,N,N′,N′‐tetramethylethylenediamine
Authors: Feng Xin De , Guo Xin Qiu , Qiu Kun Yuan 
Published: April 2003

AbstractThe reaction mechanism of the redox initiation system persulfate/N,N,N′,N′‐tetramethyl‐ethylenediamine (TMEDA) was studied by spin trapping technique and ESR spectra. The free radical (CH3)2NCH2CH2(CH3)NCH (1) is one of the initial free radicals responsible for the initiation of the vinyl polymerization in addition to the sulfate free radical (HO3SO˙). The result of amino end group analysis confirmed the fact that the free radical 1 initiates vinyl polymerization and becomes the end group of the resulting polymers. The effect of TMEDA concentration on the final percentage of conversion of acrylamide polymerization and on the molecular weights of the resulting polymer were also studied. An initiation mechanism was proposed.
Synthesis of monomers and polymers by the Heck reaction
Authors: Heitz Walter , Brügging Wilhelm , Freund Lothar , Gailberger Michael , Greiner Andreas , Jung Holger , Kampschulte Uwe , Nießner Norbert , Osan Frank , Schmidt Hans‐Werner , Wicker Michael 
Published: April 2003

AbstractThe Heck reaction allows the synthesis of monomers in a one‐step reaction. Catalyzed by Pd, bromoarenes are reacted with ethylene to form substituted styrenes and symmetrical stilbenes. Unsymmetrical stilbenes are obtained from substituted bromoarenes and styrenes. Substituted hydroquinones and terephthalic acids are also available in high yields. Poly(1,4‐phenylenevinylene) is obtained starting from 4‐bromostyrene.
Conformational analysis of ß(1→4)‐linked polysaccharides in aprotic solvent solutions
Authors: Nardin Robert , Vincendon Marc 
Published: April 2003

AbstractThe 1H NMR parameters (chemical shift and coupling constant) of ß(1→4)‐linked polysaccharides xylan, cellulose, and chitin are compared in solutions of aprotic solvents. The following NMR parameters are analyzed: (1) Chemical shifts of labile protons, (2) their variation with temperature, (3) coupling constants through the HCOH moiety — for monomers, dimers, and the corresponding polymers. It is observed that the OH‐3 hydroxyl group for cellulose and chitin oligomers and polymers present a particular behaviour, which is in agreement with the existence of an intramolecular hydrogen bond between this hydroxyl of one monomeric unit, and the heterocyclic oxygen atom of the adjacent monomeric unit. This kind of intramolecular hydrogen bond is not observed in case of the xylan series. It can be concluded that substitution of an equatorial hydrogen atom at the C‐5 position of the sugar ring by a CH2OH group — when passing from xylan to cellulose and chitin — induces a rotation restriction around the glycosidic bond. This places the OH‐3 hydroxyl group in a favourable position to be hydrogen‐bonded. The consequent implication on the respective conformations of the chains in solution is discussed.
Synthesis and reactivity of 1,4‐disubstituted butadienes in the solide state
Authors: Augenstein Michael , Wegner Gerhard 
Published: April 2003

AbstractA novel synthetic route to (2E,4E)‐6‐amino‐2,4‐hexadienoic acid (1) and related ω‐aminodiene compounds is reported. These substances form layer perovskites, CdCl4(NH3—R)2, that furnish stereoregular 1,4‐polybutadienes upon γ‐irradiation in a topochemical solid state reaction. The synthesis of a chiral derivative is also described, that can be crystallized in a perovskite structure and polymerized by γ‐rays. An ambivalent solid state reactivity is observed for the hydrochloride of 1: γ‐rays induce a chain reaction leading to a polymer of identical chemical structure and stereochemistry as reported for the perovskite, but with higher molecular weight. Upon UV‐irradiation, however, the hydrochloride undergoes a stereoselective (2+2)‐cycloaddition to a cyclobutanoic dimer as main product and oligomers after prolonged irradiation. In the case of γ‐irradiation at 273 or 300K significant contributions from postpolymerization are found both for the hydrochloride and the perovskite of 1.
Evaluation of the viscometric constants for chitosan
Authors: Maghami Ghobad G. , Roberts George A. F. 
Published: April 2003

AbstractViscosity‐average relative molecular masses have been determined for a series of chitosans having the same relative molecular mass and relative molecular mass distribution but differing extents of N‐acetylation. The results obtained show that the same viscometric constants in the Mark‐Houwink equation [η] = Km ·Ma are applicable to chitosans over the range between 0 and 40% N‐acetylation Comparison of literature values for number‐ and weight‐avepge rela‐tive molecular masses Mn, and Mw, with the viscosity‐average relative molecular mass M, values calculated using the related viscosity data and each of the three sets of viscometric constants that have been proposed for chitosan, confirms that the most accurate values currently available are km = 1,81 · cm−3 · 10−1 and a = 0,93, using 0,l M acetic acid/0,2M NaCl as solvent.
Temperature dependence of the pitch of the cholesteric helix of poly(γ‐benzyl‐L‐glutamate) in N,N‐dimethylformamide and N‐methyl‐2‐pyrrolidone
Authors: Sikora Antonín , Siromyatnikova Tatyana A. , Ginzburg Boris M. , Alumyan Yurii A. , Shepelevskii Andrei A. , Frenkel Sergei Ya. 
Published: April 2003

AbstractTemperature depenences of the pitch of cholesteric helix in solutions of poly(y‐benzyl‐L‐glutamate) in N,N‐dimethylformamide and N‐methyl‐2‐pyrrolidone were measured for various molar masses of poly(γ‐benzyl‐L‐glutamate). It was found that in N‐methyl‐2‐pyrrolidone inversion of the cholesteric helix takes place, i. e., that the right‐handed helix changes to the lefthanded one. By using an equation derived by Kimura, the temperatures at which the system has a nematic order were determined. The results obtained allow the statement that an important role in the inversion of the cholesteric helix in poly(γ‐benzyl‐L‐glutamate) solutions is played by conformational changes in side chains of the polypeptide molecule.
Association of three‐block copolymers polycaprolactam‐block‐polystyrene‐block‐polycaprolactam
Authors: Tuzar Zdeněk , Stehlíček Jaroslav , Koňák Čestmír , Lednický František 
Published: April 2003

AbstractColloidal particles of three‐block copolymers polycaprolactam‐block‐polystyrene‐block‐polycaprolactam, formed in a solvent mixture toluene/2,2,3,3‐tetrafluoropropanol as a good solvent of polycaprolactam, were studied by static and dynamic light scattering and transmission electron microscopy. Two kinds of spherical multimolecular particles differing in size were found in the solution. The smaller particles containing tens of copolymer molecules were interpreted as regular copolymer micelles, and the larger particles formed from thousands of copolymer molecules were interpreted as associates of these micelles.
Eine erweiterung der gaußschen netzwerktheorie durch die berücksichtigung voll gestreckter netzbögen
Authors: Ortmann Reinhold , Dietrich Johann , Bonart Richard 
Published: April 2003

AbstractThe Gaussian network theory of Kuhn and Grün neglects the limited contour length of network chains connecting neighbouring crosslinking points. Therefore, in the unstrained material Treloar replaces Gaussian network chain statistics by a sperical shell distribution neglecting the random walk behaviour of chain segments. We try to overcome this discrepancy in the present paper. Starting from Gaussian end‐to‐end distance statistics in the unstrained material we calculate the strain dependent amount and orientation of fully extended chains in strained samples. Fully extended chains are supposed to behave as stiff rods during further elongation. Thus, we take into account randomly coiled and fully extended chains simultaneously. We, therefore, have to replace the conventional assumption of linear affine deformation by a more complex relation, i. e. by a geometrically averaged affine deformation. This is connected with a model strain ratio differing from the macroscopic strain. The model ratio refers to the orientation behaviour of the end‐to‐end vectors, which, in the case of already fully extended network chains, hardly contribute to the macroscopic elongation of the sample. The calculation leads to a bimodal orientation function. The orientation factor is similar to that which follows from the conventional theory, whereas the entropic retractive force deviates from the conventional result.
A convenient synthesis of functional monomers: Unsaturated spiroorthoesters using phase transfer catalysis
Authors: Isobe Naoki , Nishikubo Tadatomi , Tagoshi Hirotaka , Endo Takeshi 
Published: April 2003

AbstractUnsaturated spiroorthoesters, which undergo no shrinkage on polymerization, were synthesized in high yield by an elimination reaction of the corresponding halomethylated spiroorthoesters with potassium hydroxide (KOH) or potassium tert‐butoxide (t‐BuOK) using a phase transfer catalyst. It was found that tetrabutylammonium bromide exhibits a catalytic activity higher than that of the other quaternary ammonium salts, 18‐crown‐6 and poly(ethylene glycol) (M̄w = 300) under equal conditions. The elimination reaction of halomethylated spiroorthoesters proceeds easily in toluene or diglyme with t‐BuOK and in tert‐butyl alcohol with KOH leading to the corresponding unsaturated compounds in high yields. In addition, the bromomethylated spiroorthoesters showed higher reactivity than the chloromethylated spiroorthoesters under equal conditions.
Transformation of polyester chains into dicationically living ones and synthesis of telechelic co‐oligomers thereof
Authors: Zhang Hongzhi , Feng Xinde , Fu Jingguo , Yang Huichang 
Published: April 2003

AbstractUnliving chains of aliphatic polyester were transformed into dicationically living poly(THF)‐block‐polyester‐block‐poly(THF) chains, and four different telechelic triblock co‐oligomers with primary, secondary, tertiary amine, and hydroxyl end‐groups were synthesized. A novel approach to the exchange of hydroxyl or carbonyl ends of polyester for amino end‐groups is described. The primary amine‐terminated telechelic triblock was used to modify an epoxy resin to give a toughened product with high strength.
Preparation and characterization of unsymmetrical “liposomes in a net”
Authors: Ringsdorf Helmut , Schlarb Bernhard 
Published: April 2003

AbstractNegatively charged lipid molecules were converted into polymerizable lipids by introduction of polymerizable mono‐ or bifunctional counterions. As an attempt to mimic the cytoskeleton of biomembranes, unsymmetrical polymeric vesicles were prepared, where the polyelectrolyte is attached either only to the inner or to the outer bilayer surfaces. Polymerizable cations were introduced to the outer surface of preformed small unilamellar vesicles via ion‐exchange. The outer counterions of vesicles bearing polymerizable counterions at both sides of the membrane were replaced by Na+. Polymerization of these systems leads to unsymmetrical vesicles. The introduction, separation and polymerization of the organic counterions was monitored by UV‐spectroscopy. Due to polymerization of the counterions, the phase transition temperature of the membranes is shifted remarkably to higher temperatures. For a comparison of ionically attached and covalently bound polymers, two cationic lipids were synthesized, which have a bifunctional polymerizable headgroup. In contrast to the lipids with “ionic” spacers, the polymerization of the covalently bound methacrylic units resulted in a decrease of the phase transition temperature. Thus, by application of ionically bound polymerizable units, unsymmetrical polymerized vesicle membranes are readily available. These systems may serve as models for mimicking the cytoskeleton of living cells.
Polylactones, 15. Reactions of δ‐valerolactone and ϵ‐caprolactone with acidic metal bromides
Authors: Kricheldorf Hans R. , Sumbél Movita‐Verena 
Published: April 2003

Abstractδ Valerolactone and ϵ‐caprolactone were reacted with BBr3, AIBr3, TiBr4, SnBr4 or Bu2SnBr2 in dichloromethane or chloroform in a 1 : 1 mole ratio. When these exothermic reactions were conducted with cooling, complexation of the lactones at the exocyclic oxygen was detectable by means of IR and 1H NMR spectroscopy as the first reaction step. However, heating to 60°C causes in all cases ring cleavage, and after hydrolytic removal of the metal bromides ω‐bromocarboxylic acids or oligomers with ω‐bromoalkanoyl end groups were obtained. SnBr4, Bu2SnBr2 and ZnBr2 proved to be good initiators of the polymerization of both lactones. At low monomer/initiator (M/I)‐ratios (high initiator concentrations) most of the initiator remained unchanged, and the average degrees of polymerization of the resulting polylactones largely exceeded the value expected for the M/I‐ratio. By means of viscosity and GPC measurements weight‐average molecular weights up to 70 000 were found. All polylactones obtained by initiation with these three metal bromides contain ϵ‐bromoalkanoyl end groups. Furthermore, high‐molecular‐weight poly(ϵ‐caprolactone) could be prepared at polymerization temperatures up to 150°C. The results do not indicate a cationic polymerization mechanism, but an insertion mechanism involving the metal‐O bond formed after the first cleavage of the lactone rings.