bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymers of carbonic acid, 4. Crystalline smectic polyurethanes derived from piperazine or 4,4′‐bipiperidine and diphenols containing aliphatic spacers
Authors: Kricheldorf Hans R. , Awe Jens 
Published: April 2003

Abstract4,4′‐Alkylenedioxydiphenols (3a–e), prepared from α,ω‐dibromoalkanes and hydroquinone, were converted with phosgen to the corresponding dichloroformates 4a–e, which were reacted with piperazine, trans‐2,5‐dimethylpiperazine or 4,4′‐bipiperidine under the conditions of interfacial condensation. The DSC measurements of polyurethanes derived from 2,5‐dimethylpiperazine displayed one endotherm indicating a normal melting process, whereas the polyurethanes derived from piperazine or 4,4′‐bipiperidine showed a reversible first order phase transition below the melting point. WAXS powder patterns indicate a change between two different smectic modifications. Thermomechanical analyses (penetration method) proved that also the high‐temperature smectic modification is a solid state and not a liquid‐crystalline one.
Polymers of carbonic acid, 5. Nematic polyurethanes derived from 4,4′‐dihydroxybiphenyl and 4,4′‐bipiperidine, ethylene‐4,4′‐bipiperidine or trimethylene‐4,4′‐bipiperidine
Authors: Kricheldorf Hans R. , Awe Jens 
Published: April 2003

Abstract4,4′‐Bipiperidine (3a), 1,2‐bis(4‐piperidinyl)ethane (3b) and 1,3‐bis(4‐piperidinyl)propane (3c) were condensed with the dichloroformates of p‐phenylene, 2‐methyl‐1,4‐phenylene or 2,5‐biphenylylene. Furthermore, two copolyurethanes were prepared either by mixing 3a and 3c or by mixing the dichloroformates for p‐phenylene and 2,5‐biphenylylene. Inherent viscosities between of 0,6 and 1,7 dl/g were found for the polyurethanes of 3c, but only values below 0,86 dl/g for those of 3a and 3b. The polyurethanes derived from hydroquinone or methylhydroquinone are semicrystalline polymers with a short‐term thermostability up to 310°C. The polyurethanes deriving from phenylhydroquinone are amorphous with a thermostability up to 360°C. The homo‐and copolyurethanes containing 4,4′‐biphenylylene units form a smectic layer structure in the solid state and a nematic melt above the melting point.
Characteristics of rectifying devices with thin films of polyphthalocyanine
Authors: Abe Katsuya , Saito Hiroshi , Kimura Takeshi , Ohkatsu Yasukazu , Kusano Toru 
Published: April 2003

AbstractChemically and thermally stable thin films of polyphthalocyanine were prepared by a simple evaporation‐polymerization method. The rectifying characteristics of metal/semiconductor/metal (MSM) type sandwich devices with the film were studied. A Schottky type device metal (Cu, Al, Ti)/polyphthalocyanine/Cu shows reproducible rectifying characteristics when Ti is selected as a counter electrode. The reproducibility is improved by pre‐oxidation treatment of the surface of Cu substrate. Best electric parameters for the device are as follows: rectifying ratio = 14; threshold potential difference = 0,61 V; saturation current = 2,5 · 10−6 A · cm−2; barrier height = 0,75 eV; diode ideality parameter = 4,23. Doping of five kinds of quinones [p‐benzoquinone (p‐BQ), tetrabromo‐p‐benzoquinone (p‐TBBQ) tetrachloro‐p‐benzoquinone (p‐TCBQ) tetrachloro‐o‐benzoquinone (o‐TCBQ) 2,3‐dichloro‐5,6‐dicyanobenzoquinone (DDQ)] and 2,5‐cyclohexadien‐1,4‐diylidenedimalodinitrile (TNCR) in thin films of polyphthalocyanine affected electrocharacteristics in some cases. The diode ideality parameter decreases to 2,17 at 0,90 · 10−6 mol · cm−1 of p‐TBBQ, and the rectifying ratio increases to about fourteen times by doping p‐TBBQ and p‐TCBQ. The doped device shows a rectifying response up to 1 kHz.
Molecular structure of 1,7‐dichlorotetradecaphenylheptasilane as a model of poly(diphenylsilane)
Authors: Ovchinnikov Yuri E. , Dement'ev Vyacheslav V. , Shklover Valery E. , Frunze Tat'yana M. , Struchkov Yuri T. , Antipova Bella A. , Igonin Vladimir A. 
Published: April 2003

AbstractThe molecular and crystal of 1,7‐dichlorotetradecaphenylheptasilane Cl(SiPh2)7ClDedicated to Prof. Dr. H. Sinn on the occasion of his 60th birthday
(I) was determined. The molecule has a helical conformation with the torsion angles SiSiSiSi in the range of 154°–162°. Crystal I is built of infinite polysilane chains extended along the [111] direction and separated by solvating benzene and toluene molecules.
Synthèse de polysiloxanes acyloxyméthylés par réaction des acides acétique, benzoïque et méthacrylique, en présence de triéthylamine, sur des polysiloxanes chlorométhylés, 1. Synthèse et identification de trisiloxanes et tétrasiloxanes modèles
Authors: Jazouli Talha , Reyx Danièle , Thomas Michel 
Published: April 2003

Abstract3‐(Acyloxymethyl)‐1,1,1,3,5,5,5‐heptamethyltrisiloxanes 7b1, 7c1, 7d1 and 3,5‐bis(acyloxymethyl)‐1,1,1,3,5,7,7,7‐octamethyltetrasiloxanes 7b2, 7c2, 7d2 (7b: acetoxymethyl, 7c: benzoyloxymethyl and 7d: methacryloyloxyméthyl derivatives) were synthesized from 3‐(chloromethyl)‐1,1,1,3,5,5,5‐heptamethyltrisiloxane (7a1) or from 3,5‐bis(chloromethyl)‐1,1,1,3,5,7,7,7‐octamethyltetrasiloxane (7a2), respectively. Spectroscopic (1H NMR) and chromatographic (GPC and CG) characteristics of the isolated products were defined in order to standardize the analytical tools used for the study of the carboxylic acid reaction with chloromethylated polysiloxanes in the presence of triethylamine.
Synthèse de polysiloxanes acyloxyméthylés par réaction des acides acétique, benzoïque et méthacrylique, en présence de triéthylamine, sur des polysiloxanes chlorométhylés, 2. Etude de la réaction sur trisiloxane et tétrasiloxane modèles
Authors: Jazouli Talha , Reyx Danièle , Thomas Michel 
Published: April 2003

AbstractThe reaction of acetic, benzoic and methacrylic acids with 3‐chloromethylheptamethyltrisiloxane and 3,5‐bis(chloromethyl)octamethyltetrasiloxane in toluene in the presence of triethylamine was studied. Beside the expected transformation of oxy(chloromethyl)methylsilanediyle (A) units into oxy(acyloxymethyl)methylsilanediyle (C) units, redistributions of A, C and trimethylsilyl/oxytrimethylsilyl (M) were observed. The conversion versus time curves of distribution of the former oligomers (mole fractions of trisiloxanes: F1 = mM‐X‐M = mM‐A‐M + mM‐C‐M and tetrasiloxanes: F2 = mM‐X‐X‐M = mM‐A‐A‐M + mM‐A‐C‐M + mM‐C‐C‐M) were followed. The reaction rates were not only controlled by the acid used but also by the starting oligosiloxane (trisiloxane or tetrasiloxane). The distributions of the homogeneous and heterogeneous oligomers seem to result from controlled combinations of A, C and M according to orientations of cleavages and to relative affinities of RCOOH/NEt3 towards various siloxanes. For the total conversions the mole fractions F1 and F2 fit with those calculated by a law based on a hazard combination of C and M. This result may be explained by the compensation of electronic and steric factors.
On the distribution of the degree of polymerization occurring in the third kinetic stage of dilute‐acid‐catalyzed degradation of cellulose
Authors: Soubelet Oscar , Presta Mario A. , Marx‐Figini Marianne 
Published: April 2003

AbstractThe distributions of the degree of polymerization (DP) of cellulose degraded in the third kinetic stage, i.e. in the second stage of decreasing reaction rate, obey throughout the most probable (Schulz‐Flory) type, and consequently cellulose specimens degraded at different conditions but with coinciding average DP coincide also with their DP distributions.
Liquid‐crystalline polyethers and copolyethers based on conformational isomerism, 5. Thermotropic copolyethers based on 1‐(4‐hydroxyphenyl)‐2‐(2‐methyl‐4‐hydroxyphenyl)ethane and flexible spacers containing odd and even numbers of methylene units
Authors: Percec Virgil , Yourd Raymond 
Published: April 2003

AbstractThe synthesis and characterization of thermotropic main‐chain liquid‐crystalline copolyethers based on 3‐methyl‐4,4′‐ethylenediphenol [1‐(4‐hydroxyphenyl)‐2‐(2‐methyl‐4‐hydroxyhenyl)‐ethane (MBPE)], which is a flexible rod‐like mesogenic unit or a rod‐like mesogenic unit based on conformational isomerism, and pairs of flexible spacers containing odd and even numbers of methylene units, X, Y, i.e., MBPE‐X/Y, where X/Y = 5/12, 5/10, 5/8, 6/11, 6/9, 4/11 and 4/9, are described. Copolymerization decreases the rate of crystallization and subsequently transforms virtual or monotropic mesophases of homopolymers into monotropic or even enantiotropic mesophases. Both liquid‐crystalline transition temperatures and enthalpy changes of the identical mesophases displayed by copolymers represent weight‐averaged values of the similar parameters of the parent homopolymers. Their extrapolation leads to the determination of the virtual mesomorphic transition temperatures and enthalpy changes of the parent homopolymers.
Functionalized polyacetals, 1. Copolymerization of trioxane with 1,3‐dioxep‐5‐ene and properties of the resulting copolymer
Authors: Pesce‐Rodriguez Rose Ann , Wang Shiang , Yang Nan‐Loh , Auerbach Andrew , Paul James 
Published: April 2003

Abstract1,3,5‐Trioxane (1) and 1,3‐dioxep‐5‐ene (2) were copolymerized with BF3OEt2 at 65°C. The products, after base hydrolysis, were characterized by 13C and 1H NMR and were found to assume the chemical structure 4 of a copolymer containing oxymethylene and oxy‐2‐butenylene units with 4‐hydroxy‐2‐butenyl and methoxy end groups, with the ratio of hydroxy‐2‐butenylene to methoxy end groups varying with experimental conditions. The copolymer demonstrates crystallinity and thermal stability comparable to poly(trioxane‐co‐ethylene oxide)s. Copolymer melting point was observed to decrease with increasing comonomer incorporation. The upper limit for incorporation of the comonomer 2 was found to be ca. 4 mol per cent. Viscosity and end group analysis (by 1H NMR) indicate molecular weights in the range of 104 to 105. The comonomeric unit demonstrates the ability to act as both a stopper against unzipping and as a trap for certain degrading agents.
Studies on elementary reactions in the polymerization of 1,2‐epoxycyclohexane with organozinc compounds as initiators
Authors: Hasebe Yoshihiro , Izumitani Keiko , Torii Masao , Tsuruta Teiji 
Published: April 2003

Abstract1,2‐Epoxycyclohexane (1) was found to behave differently from propylene oxide (PO) in polymerization reactions with organozinc compounds as initiators. A chair‐type complex, [Zn‐MP]2,2, is the only compound that shows high catalytic activity for both polymerization of 1 and PO, following an anionic coordination mechanism. On the other hand, the polymerization of 1 with ZnEt2 or (EtZnOMe)4 as initiator proceeds according to a cationic mechanism. Cationic polymerization of 1 with ZnEt2 has two modes of termination reaction resulting in the formation of terminal units containing vinyl ether and allyl ether moieties. The initiation and propagation mechanism of 1 by [Zn‐MP]2;2 is similar to that of PO, but chain transfer reaction takes place in the polymerization of 1 owing to the low stability of the growing chain end. By using [Zn‐MP]2,2 as initiator, it was possible to prepare a block copolymer consisting of an isotactic sequence of monomeric units of PO and a syndiotactic sequence of monomeric units of 1.
Synthèse de polymères α,ω‐bifonctionnels par réaction de métathèse. Méthodologie d'approche des différences de réactivité des sites carbéniques en présence
Authors: Reyx Danièle , Campistron Irène 
Published: April 2003

AbstractThe results of studies of co‐metathesis reactions of 1,5‐cyclooctadiene (1) with dimethyl 3‐hexenedioate (2a) and for comparison, with 4‐octene (2b) and 1,5‐hexadiene (2c) are analyzed in order to approximate the relative reactivities of the carbene species and of the different types of double bonds. To this end, the experimental distributions of the first telomers are compared with theoretical ones calculated on the one hand allowing equal probability of arrangement of alkylidene groups and on the other hand allowing a kinetic control of propagation and transfer reactions. In other respects, the possibilities of mass control of the products obtained by the same co‐metathesis or by degradation of 1,4‐polybutadiene are studied. The results show that the reactivity of the 1,5‐cyclooctadiene double bonds is higher than that of the other types of double bonds, this being in agreement with the hypothesis of stabilization of the β‐carbomethoxycarbene species by carbene/ester complexation. This stabilization allows us to explain the distribution of α,β‐difunctional oligomers in agreement with the hypothesis of kinetic control. The distribution of non‐functional oligomers agrees with a random combination of alkylidene groups. This stabilization is compatible with the controlling method of molecular weights in the products obtained by polymerization of cyclooctadiene and also by degradation of 1,4‐polybutadiene in the presence of 2a.
Simulation of coupled modification reactions of polymers, 4. Mono‐ and disubstitution of 1,4‐polybutadiene, coupled with partial double‐bond shift
Authors: Martl Michael G. , Hummel Klaus 
Published: April 2003

AbstractMonte Carlo calculations for a modification reaction of 1,4‐polybutadiene were carried out. The simulated process consisted in the substitution in α‐position to the double bond, partially coupled with double‐bond shift. The reaction model included mono‐ and disubstitution (one or two substituents at a carbon atom) and the formation of substituted double bonds in shift reactions. The number of molecules, the degree of polymerization and the degree of substitution were varied. The resulting multicomponent copolymers were evaluated with respect to different units (considered from one double bond to the next) and to their mole fractions. For example, more than 800 different units resulted for a mean of two substituents per unit. Units with up to 10 carbon atoms of the chain were found. Small molecule collectives gave representative results if only units above a minimum mole fraction were considered. The constitution of the products depended on the molecular size in the oligomer range. The distribution of the length of the units and of the number of substituents in a unit were determined.
The key to successful acyclic diene metathesis polymerization chemistry
Authors: Wagener Kenneth B. , Boncella James M. , Nel Jan G. , Duttweiler Robert P. , Hillmyer Marc A. 
Published: April 2003

AbstractThis paper describes the key to successful metathesis polycondensation chemistry. Model compound reactions with styrene and styrene derivatives show that metathesis chemistry can occur exclusively if carbocation formation can be obviated through the proper choice of a Lewis acid free catalyst. Vinyl terminated oligo(octenylene)s were synthesized in this manner, which in turn were converted to polymers of high molecular weight.
Intramolecular charge transfer complexes, 28. Poly[ω‐(N‐carbazolyl)alkyl methacrylate‐co‐2‐(methacryloyloxy)ethyl 3,5‐dinitrobenzoate]s
Authors: Simionescu Cristofor I. , David Geta , Grigoras Mircea 
Published: April 2003

AbstractCopolymers with intramolecular charge transfer interactions were synthesized by radical copolymerization of ω‐(N‐carbazolyl)alkyl methacrylates (where alkyl is propyl and butyl) with 2‐(methacryloyloxy)ethyl 3,5‐dinitrobenzoate. These copolymers are characterized by a dependence of the electronic absorption, the solubility and the density on the composition. The intramolecular degree of complexation depends on spacer length and exerts a maximum for the spacer with three methylene groups.
Determination of substituent distribution in cellulose ethers by means of a 13C NMR study on their acetylated derivatives, 4. O‐methyl‐O‐hydroxyalkylcelluloses
Authors: Tezuka Yasuyuki , Imai Kiyokazu , Oshima Mitsuyoshi , Chiba Tohru 
Published: April 2003

AbstractA structural study on O‐methyl‐O‐hydroxypropylcellulose (MHPC) and on O‐methyl‐O‐hydroxyethylcellulose (MHEC) was performed by means of a 13C NMR analysis after acetylation of the unsubstituted hydroxyl groups at the anhydroglucose ring and those at the end of the substituents. The carbonyl signal of the acetyl group in acetylated MHPC and MHPC samples was found to be resolved into four peaks according to the location of the acetyl function either at the 2‐, 3‐ and 6‐position of an anhydroglucose unit or at the end of an oligo(oxyalkylene) substituent, allowing to determine the distribution of methyl and oligo(oxyalkylene) substituent groups. The methyl signal of the methoxy group in MHPC was also found to be sensitive to its position either at the anhydroglucose unit or at the end of the oligo(oxypropylene) substituent.
Reversible immobilization of drugs on a hydrogel matrix, 3. Hydrolysis of chloramphenicol precursors
Authors: Yean Leanirith , Meslard Jean‐Claude , Subira Franck , Bunel Claude , Vairon Jean‐Pierre 
Published: April 2003

AbstractKinetics of hydrolytic release of chloramphenicol (1) chemically immobilized on HEMA‐based ophthalmic hydrogels were examined. The rate constants of hydrolysis of the phenolic ester and acetal bonds of the spacer immobilizing the drug were determined at 37°C, and essentially at neutral pH, for the monomeric drug, the soluble copolymers and the cross‐linked hydrogels, respectively. A drastic decrease in reactivity of the ester bond was observed from the small monomeric molecule to the soluble chains and then to the swollen network (relative reactivities ≈ 1300/25/1), whereas the acetal bond is less reactive, with a rate constant apparently independent of the size of the carrier. It is suggested that in all cases the ester bond is cleaved at first, liberating a drug bearing acetal intermediate which is then slowly hydrolysed to free chloramphenicol. All reactions were observed to be first order with respect to the hydrolysable precursor. When the rate constants are low enough, which is the case when considering the hydrogels, a pseudo‐zero order is obtained and the release rate of chloramphenicol is constant over a long period of time and depends only on the initial concentration of immobilized, drug. Nevertheless, the too slow acetal hydrolysis in neutral physiological conditions limits the daily delivery to a few micrograms for a standard corneal lens with a 5 mol‐% drug loading.
Synthesis and characterization of new halogen‐containing poly(azomethine‐urethane)s
Authors: Tamareselvy Krishnan , Venkatarao Krishnan , Kothandaraman Harimurthi 
Published: April 2003

AbstractA series of fluorine‐ and chlorine‐containing bisphenols and their non‐halogenated analogues were synthesized from various hydroxyaldehydes (1) and diamines (2). The structures of the corresponding bisphenols (3) were confirmed by 1H NMR, 19F NMR and IR spectra. Poly(azomethine‐urethane)s were prepared by reacting these monomeric bisphenols (3) with diisocyanates such as 4,4′‐methylenedi(phenyl isocyanate) (4), 2,4‐toluylene diisocyanate (6) and hexamethylene diisocyanate (8). Poly(azomethine‐urethane)s (5, 7 and 9) thus obtained were characterized by IR, UV, solubility, viscosity and thermal analysis (TG).
A novel rearrangement in the syntheses of poly(3,3′‐phthalidylidene‐4,4′‐biphenylylene)s
Authors: Zolotukhin Mikhail G. , Sedova Elvira A. , Sorokina Yulia L. , Salazkin Sergei N. , Sangalov Yuri A. , Sultanova Venera S. , Panasenko Anatoly A. , Khalilov Leonard M. , Muslukhov Rinat M. 
Published: April 2003

AbstractStudies were made on the synthesis of halide‐substituted poly(phthalidylidenearylene)s by Friedel‐Crafts polycondensations of 3‐aryl‐3‐chlorophthalides containing substituents in 4‐position of the phthalide cycle. As follows from the C13 NMR spectra, those monomers can afford polymers containing two types of isomeric units substituted in 4‐ or 7‐position. The possible routes of formation of the isomeric units are analyzed and a scheme is suggested for the monomer rearrangement in the synthetic course. The polymers containing those two types of units were shown to be highly thermostable and to contain about 30% of a crystalline phase.
Methyl labeling as a tool for investigating the regiochemistry of the electrochemical oxidative polymerization of 1H,8H‐pyrrolo[3,2‐g]indole
Authors: Berlin Anna , Pagani Giorgio , Schiavon Gilberto , Zotti Gianni 
Published: April 2003

AbstractThe preparation of the three isomeric dimethyl derivatives 4–6 of 1 H,8H‐pyrrolo[3,2‐g]indole (1), substituted at the nitrogen atoms or in the positions α and β to them, respectively, is described. These products were synthesized for investigating the regiochemistry of the electrochemical oxidative polymerization of the parent compound 1. Anodic coupling in acetonitrile of the dimethyl derivatives 4–6 produces polymeric films which are reversibly oxidized with a charge exchange of 0,5 electrons per repeating unit. For 5 and 6, coupling occurs in the free positions of the pyrrole rings, yielding a non‐conjugated and poorly conducting (5 · 10−6 Ω−1 · cm−1) polymer and a conjugated and conducting (1 Ω−1 · cm−1) polymer, respectively. The N‐substituted isomer 4 couples in the α‐positions and the resulting polymer shows a decrease in conductivity (10−2 Ω−1 · cm−1) relative to poly(1), analogous to that of poly(N‐methylpyrrole) relative to polypyrrole. Further comparisons of conductivity data and behaviour of the methyl substituted derivatives of 1 allow to conclude that the unsubstituted polymer couples in the position α to the nitrogen atom.
Synthesis and rheological study of some maleic acid and fumaric acid stereoregular polyesters, 4. Synthesis of random, multi‐block and alternating unsaturated copolyesters from fumaric, maleic and phthalic acid potassium salts and 1,4‐dibromobutane
Authors: Djonlagić Jasna , Sepulchre Marie‐Odile , Sepulchre Maurice , Spassky Nicolas , Dunjić Branco , Jaćović Mihailo S. 
Published: April 2003

AbstractThe reaction of dicarboxylic acid potassium salts with dibromo derivatives in 1‐methyl‐2‐pyrrolidone at moderate temperature was applied to the synthesis of high‐molecular‐weight co‐ and terpolyesters containing fumaric, maleic, phthalic and succinic ester residues and tetramethylene groups. Co‐ and terpolyesters with a random structure were obtained from the reaction of binary or ternary mixtures of salts with 1,4‐dibromobutane. While the composition in ester residues of the organic phase varies continuously during the first 6 h of the polycondensation reaction, that of the copolyesters obtained after 24 h is determined by the composition of the initial mixture of salts. The relative amounts of cyclic n‐mers produced in the course of the reaction and those of the different possible dimers were evaluated from GPC analyses of the reaction products. Multi‐block copolyesters were prepared either by the reaction of a potassium salt with a mixture of 1,4‐dibromobutane and a low‐molecular‐weight α‐ω‐dibromopolyester or by the coupling reaction of two low‐molecular‐weight α,ω‐dibromopolyesters with succinic acid potassium salt. The reaction of bis(4‐bromobutyl) phthalate and fumaric or maleic acid potassium salt produced the corresponding alternating copolyesters. Physico‐chemical and compositional data of the prepared unsaturated copolyesters are given.