bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nuclear magnetic resonance study on the relationship between the helicity and L‐alanine content of L‐alanine/β‐alanine random copolypeptides in connection with silk fibroin conformation
Authors: Kashiba Hitoshi , Asakura Tetsuo , Komoto Tadashi 
Published: April 2003

AbstractThe helicities of six kinds of L‐alanine/β‐alanine random copolypeptides having different L‐alanine contents were determined using 1H NMR. Next, the theoretical helicities of these copolypeptides were calculated on the basis of a statistical thermodynamic analysis of the helixcoil transition of the random copolypeptide — using Monte Carlo methods — as a function of the L‐alanine content. The statistical weight parameters used in the model were determined from a comparison of the observed and calculated results. The experimental and theoretical results are in agreement with the fact that Bombyx mori silk fibroin with 30,0 mol‐% L‐alanine content assumes exclusively a random‐coil conformation and that Philosamia cynthia ricini silk fibroin with 48,8 mol‐% L‐alanine content locally assumes an α‐helical conformation in the sequence of the L‐alanine residues, both in aqueous solution.
Role of polymer matrix on the conductivity of polymers doped with tetracyanoquinodimethane (TCNQ) salts of polycations
Authors: Pecherz Janusz , Kryszewski Marian 
Published: April 2003

AbstractThe influence of interactions with polymer matrix on the critical concentration and stability of heterogeneous conductive polymer films was investigated. These films were obtained by reticulate doping of polyacrylonitrile (PAN), poly(methyl methacrylate) (PMMA) and polycarbonate (PC) with complex salts of tetracyanoquinodimethane (TCNQ) with polycations having sulfonium groups in the main chain, Ks[4,6]. It was found that the chemical structure of the matrix influences the conductivity of such systems. The PMMA matrix is most suitable for obtaining conducting systems at low concentration of the dopant. In PMMA the absorption spectra of moleculary dispersed Ks[4,6] do not change with time. The strong influence of PAN matrix was confirmed by the study of absorbance changes of Ks[4,6] with time in this matrix and particularly by investigation of absorption of this salt in solutions containing acrylonitrile/methyl methacrylate copolymers of various composition.
Structural investigations and phase behaviour of a ternary lyotropic liquid‐crystalline cellulosic system: Cellulose tricarbanilate/3‐chlorophenylurethane of cellulose/triethylene glycol monomethyl ether
Authors: Siekmeyer Maria , Steinmeier Hans , Zugenmaier Peter 
Published: April 2003

AbstractTwo similar, fully substituted cellulose derivatives, phenylurethane and 3‐chlorophenylurethane of cellulose, and mixtures of various ratios thereof in a common solvent were investigated in the lyotropic liquid‐crystalline phase. Helicoidal structures of different handedness were found with regard to the two binary liquid‐crystalline systems. Compatibility of the considered ternary system may be concluded from a structural investigation in the high and low composition range with regard to one cellulose derivative component and incompatibility of the lyotropic liquid‐crystalline system in the medium composition range. Structural features of the ternary system at elevated temperatures were evaluated by a turbidimetric study.
Phase transitions and structure changes in poly[bis(phenoxy)‐λ5‐phosphazene]
Authors: Kojima Morio , Sun Del C. , Magill Joseph H. 
Published: April 2003

AbstractPhase transition behavior in poly[bis(phenoxy)‐λ5‐phosphazene] (PBPP) was studied by electron microscopy, X‐ray diffraction techniques and differential scanning calorimetry. Several polymorphic forms were detected. Relative changes in enthalpy associated with the thermotropic transition, T(1), are examined as a function of heat treatment. Correspondingly, structural and morphological changes have been established in line with enthalpy results.
Preferential solvation of polystyrene by an excimer‐forming fluorophore in the system polystyrene/cyclohexane
Authors: Fuhrmann Jürgen , Wadle Armin , Krampitz Gerhard , Hennecke Manfred 
Published: April 2003

AbstractFluorescence spectroscopy is used to study the preferential solvation of the polymer and the mobility of the fluorophore in the highly diluted ternary system polystyrene/ethyl 1‐naphthoate/cyclohexane under theta‐conditions. The ratio of the excimer to monomer fluorescence intensity Iexc/Imon of the fluorophore is correlated with the concentration and the mobility of the fluorophore in the two phases, inside and outside the polymer coil; the limits of this model are discussed in detail. In the selected system preferential solvation increases the Iexc/Imon ratio whereas the reduced mobility of the fluorophore inside the coil acts in the opposite manner. The model allows to calculate the distribution coefficient K for the distribution of the fluorophore between the two phases and the ratio q of the mobilities for the fluorophore in the two phases. The values of K obtained indicate a strong preferential solvation of polystyrene by the ethyl 1‐naphthoate fluorophore. The mobility ratio q depends on the molar mass of the polymer in such a way that it reflects segmental density.
ABA triblock comb copolymers with oligo(oxyethylene) side chains as matrix for ion transport
Authors: Khan Ishrat M. , Fish Daryle , Delaviz Yadollah , Smid Johannes 
Published: April 2003

AbstractABA triblock copolymers consisting of two terminal blocks (A) of comb‐like polymethacrylate with oligo(oxyethylene) side chains (on the average eight oxyethylene units per side chain) and a middle block B of polystyrene were synthesized by anionic polymerization. The ratios A/B were varied, and the respective polymers characterized by 1H and 13C NMR, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The polymers were then solution‐cast from tetrahydrofuran solutions of lithium perchlorate, and the homogeneous, solvent‐free polymer electrolyte systems tested for their thermal characteristics (DSC) and conductivity. The inclusion of a polystyrene block in the comb‐like polymethacrylate electrolyte vastly improves their film‐forming and mechanical properties, but also lowers the conductivity. Addition of dimethyltetraethyleneglycol (2,5,8,11,14‐pentaoxapentadecane) enhances the ion conduction which can reach values of 10−4 Ω−1 · cm−1 at 70°C, depending on salt and styrene content.
Photon correlation spectroscopy of dilute polymer solutions: Dynamic zimm plots and scaling of molar‐mass‐dependent properties
Authors: Vancsó Gyula 
Published: April 2003

AbstractResults of photon correlation spectroscopy measurements on polystyrene (PS) standards in dilute tetrahydrofuran (THF) solutions are presented. The experiments were performed at 45°C on eight different samples covering the molar mass range between 5·105 and 1,6·107 g/mol. The first cumulant of the measured dynamic structure factor of the scattered light is discussed as a function of the scattering angle and of the solution concentration. The scaling constants of the centre‐of‐mass diffusion coefficient and of the Stokes effective hydrodynamic radius with molar mass are determined. The relationship between the concentration dependence of the centre‐of‐mass diffusion coefficient and the molar mass is derived. The values of the reduced first cumulants are presented by dynamic Zimm plots. The shape of the Zimm plots shows a deviation from the theoretically predicted form. This deviation is explained by applying the results of dynamic scaling considerations.
Radikalpolymerisation von methylmethacrylat im gesamten umsatzbereich. Stationäre und instationäre experimente zur bestimmung von wachstums‐ und abbruchsgeschwindigkeit
Authors: Sack‐Kouloumbris Regina , Meyerhoff Günther 
Published: April 2003

AbstractFree‐radical polymerization of methyl methacrylate in bulk at 0°C over the full range of conversion is reported. Details for stationary and non‐stationary experiments are described allowing to measure both kinetically relevant ratios fk/ka and kw/ka, f representing radical efficiency, kw rate constants of propagation and ka rate constant of termination. From these ratios the absolute rate constants kw and ka are available. The photochemical decay of the initiator 1,1′‐azodicyclohexanenitrile in connection with the rotating‐sector technique and observation of the post‐effect after stopping the initiator decay were used. The rate of polymerization and the number‐ and weight‐average molar masses were measured. Both, kw and ka, showed a strong dependence on conversion which is well known for ka but is reported here for the first time for kw since Hayden and Melville's determination of kw from measurements of the temperature increase during polymerization were reported.
Poly(2‐vinylpyridine) block copolymers. Phase separation and electric conductivity of iodine complexes
Authors: Möller Martin , Lenz Robert W. 
Published: April 2003

AbstractA series of AB diblock copolymers of poly(2‐vinylpyridine) (P‐2VP) and either polybutadiene or polystyrene were prepared in a nonpolar solvent at low temperature. Well‐defined polymers with narrow molecular weight distributions were obtained and electron micrographs showed that these block copolymers form a well‐separated two‐phase morphology. Percolation of P‐2VP domains could be achieved for samples with 40 and with 60 mol‐% of P‐2VP blocks. These samples were modified by addition of various amounts of iodine in solution and in the melt. Electric conductivities of the doped composites were determined by the four‐probe method. The conductivities of the two phase systems were, in general, lower than that of P‐2VP doped with I2.
Investigation of electrical conduction of thermally treated nylon‐6 films
Authors: Bhat Narendra V. , Kelkar Deepali S. 
Published: April 2003

AbstractThis paper reports the variation in electrical conduction of thermally treated nylon‐6 films. The conductivity measurements were performed in vacuum over the temperature range from room temperature to 80°C. The samples of the nylon‐6 films varying in form and degree of crystallinity were prepared by heat‐setting nylon‐6 films in nitrogen atmosphere at different temperatures for one hour. The results of the variation of conductivity with temperature and the current‐voltage characteristics are used to analyze the mechanism of electrical conduction in nylon‐6 as well as for the calculations of the activation energy of electrical conduction. A change in the structure of nylon‐6 was found to affect both the mechanism of electrical conduction and the activation energy.
Strictly alternating polyamides with stiff and flexible chain segments: Effects on thermotropic liquid crystallinity of the introduction of an ethylene unit into the mesogenic group
Authors: Schmucki Marcel , Jenkins Aubrey D. 
Published: April 2003

AbstractBipolyamides containing mesogenic groups were prepared by solution polycondensation from aromatic dicarbonyl dichlorides and novel diamines. Ortho‐substitution and the aliphatic chain length of α,ω‐bis(4‐aminophenyl)alkylenes affected the thermal transitions of the resulting polyamides profoundly. Introduction of an ethylene unit into the stiff biphenylene segment not only reduced the isotropization temperatures, but also depressed the tendency to form liquid crystals.
Properties of polyacetylene obtained with (η‐Cp)2Ti(PMe3)2
Authors: Martinez Jairo R. , Rausch Marvin D. , Chien James C. W. , Alt Helmut G. 
Published: April 2003

AbstractAcetylene was polymerized by (η‐Cp)2Ti(PMe3)2 at room temperature to give predominantly trans‐polyacetylene. All properties are within the ranges reported for polyacetylene produced with Ti(OBu)4/AlEt3 as catalyst.
Synthesis of polyamides by direct polycondensation with phenylphosphonic anhydride as an activating agent
Authors: Ueda Mitsuru , Honma Tsukasa 
Published: April 2003

AbstractA new activating agent for amide condensations, phenylphosphonic anhydride (1), was prepared by the reaction of phenylphosphonic dichloride with water. The new activating agent was found to be useful for the preparation of amides from carboxylic acids and amines. The direct polycondensation of dicarboxylic acids with aromatic diamines using the activating agent in the presence of pyridine proceeds at 60°C to produce polyamides with inherent viscosities up to 1,1 dl/g. Furthermore, the activating agent was used for chemoselective polyamidation; that is, polyamides from dicarboxylic acids and diamines containing various functional groups were prepared without special protection of acylating‐sensitive groups.
Polymeric phthalocyanines and their precursors, 16. A structure model for polymeric phthalocyanines
Authors: Knothe Gerhard , Wöhrle Dieter 
Published: April 2003

AbstractA model for describing the structural features such as degree of polymerization, size, and shape of polymeric phthalocyanines 2, 4, 6 is described. Analytical methods such as IR, titration of carboxylic end groups, and elemental analysis are used in the structure investigation. The results demonstrate that for polymeric phthalocyanines 2 with cyano end groups, prepared from 1,2,4,5‐benzenetetracarbonitrile (1), the number of macrocycles (n) in the polymer is not higher than 7–9, and that linear polymers as well as polymers with two rows are possible. Polymers 6, prepared from bridged diphthalonitriles 5, are considerably larger showing a more two‐dimensional structure. For polymeric phthalocyanines 4 with carboxylic end groups, prepared from 1,2,4,5‐benzenetetracarboxylic acid derivatives 3, a linear structure with n = 4–9 is favoured. Literature results are examined in the light of the described model.
Synthesis and properties of poly(peptide)‐wrapped unsubstituted metalophthalocyanines by polycondensation of micellar or reversed micellar aggregates
Authors: Hanabusa Kenji , Ye Xuanjing , Koyama Toshiki , Kurose Akio , Shirai Hirofusa , Hayakawa Tadao 
Published: April 2003

AbstractPoly(peptide)‐wrapped unsubstituted metalophthalocyanines (Mt‐Pc's, Mt = Fe, Co) were synthesized by polycondensation of amphiphilic bifunctional active esters of amino acids (1 and 2), which form micellar or reversed micellar aggregates and solubilize Mt‐Pc's. Though Mt‐Pc's are insoluble in most organic solvents, the obtained poly(peptide)‐wrapped Mt‐Pc's are soluble in protic solvents such as formic acid, dichloroacetic acid, and trifluoroacetic acid. The wrapped Mt‐Pc's are stable, and their leakage out of the poly(peptide)s is not observed. UV‐Vis spectra revealed that the wrapped Fe‐Pc is predominantly in the monomeric state. ESR spectra confirmed the poly(peptide)‐wrapped structure of Mt‐Pc's.
Enzyme‐analogue built polymers, 25. Synthesis of macroporous copolymers from α‐amino acid based vinyl compounds
Authors: Wulff Günter , Vietmeier Jürgen 
Published: April 2003

AbstractThe suitability of a variety of newly prepared polymerizable a‐amino acid derivatives for the preparation of template‐imprinted polymers was investigated. The polymerizable binding sites were attached to the α‐amino acid template via azomethine, carboxylic ester or boronic ester linkages. Macroporous polymers containing these monomers were prepared. The extent to which the templates could be split off from the polymer, the degree of racemization of the a‐amino acids during polymerization and cleavage as well as the degree of rebinding to the polymers were studied.
Cationic polymerization of bis(1‐alkylvinyl)benzenes and related monomers, 1. Structure elucidation of 1,1,3‐trimethyl substituted polyindane
Authors: Dittmer Thomas , Gruber Freddy , Nuyken Oskar 
Published: April 2003

Abstract1,4‐Bis(1‐chloro‐1‐methylethyl)benzene (BINIFER)/borontrichloride is known to be a very efficient initiating system for cationic polymerization of e.g. isobutene at low temperature (< −60°C). However, at higher temperature this system polymerizes by its own. The obtained polymers show a remarkable, high thermal stability and are soluble in common solvents. The analytical results indicate a very uniform structure consisting exclusively of 1,1,3‐trimethyl indane‐3,5‐diyl units. Other possible structures could be excluded. A mechanism explaining the surprisingly selective polyindane formation is discussed.
Synthesis and structure of nitro‐substituted poly(phthalidylidenebiphenyl‐4,4′‐ylene)s
Authors: Shitikov Aleksander V. , Zolotukhin Mikhail G. , Sultanova Venera S. , Panasenko Anatoly A. , Salaskin Sergei N. , Rafikov Sagid R. 
Published: April 2003

AbstractNitro‐substituted derivatives of poly(phthalidylidenebiphenyl‐4,4′‐ylene) (l), containing a controlled amount of nitro groups within 0,3 and 3,0 per mol of repeating unit, were prepared by nitrations under various conditions. The nitration was carried out either in nitric acid or by potassium nitrate and nitric acid in sulfuric acid solution. 13C NMR spectroscopy was used to study the structure of the resulting nitroderivatives. The trinitroderivative was found to contain the nitro groups in position 6 of the phthalide moiety and in positions 2 and 2′ of the biphenylylene unit. At lower degrees of nitration, some di‐, tri‐ as well as unsubstituted units are present in the polymer.
Poly(alkylene phosphate)s by polycondensation of phosphonic diamides with diols
Authors: Baran Jolanta , Klosinski Pawel , Penczek Stanislaw 
Published: April 2003

AbstractPolycondensation of diols with phosphonic bis(dialkylamide)s leads to high‐molecular‐weight polyphosphites (M̄n up to 4 · 104). Model reactions of 1‐butanol, 2‐butanol and phenol with phosphonic bis(diethylamide) (1) were studied and it was established, that these reactions exhibit characteristic induction periods. Linearization of the kinetic curves after addition of amines prior to reaction enabled us to postulate the mechanism of esterification, involving activation of 1 by hydrogen‐bonding to amines. However, the major side reaction lowering the degree of polymerization was found to be dealkylation of the formed ester units by added and/or evolved amine. Therefore, in order to increase the rate of polycondensation and to prevent the formed polymer chain from breaking down by dealkylation, the process was conducted at increased temperature (90°C) in a nonsolvent for the polymer of higher molecular weight. Thus, the polymer separates from the major solution and becomes less prone to dealkylation.
Kinetic effect of radiation intensity and thermal after‐treatment in the photopolymerization of diallyl oxydiethylene dicarbonate
Authors: Bellobono Ignazio R. , Selli Elena , Righetto Luca , Rafellini Peppino , Trevisan Lucio 
Published: April 2003

AbstractThe influence of radiation intensity (from 1,08 · 10−7 to 2,48 · 10−4 einstein.s−1 · 1−1) on the photopolymerization of diallyl oxydiethylene dicarbonate was investigated systematically not only in the initial stages of reaction, but also at high monomer conversion (x), in order to detect possible variations in the polymerization mechanism. In some of the runs irradiation was stopped at x = 0,55–0,65 and thermal after‐treatments were carried out both in the presence and absence of air by following kinetically x‐values during the self‐decelerating cross‐linking. To rationalize experimental data a model is proposed which assumes two basically different mechanisms occurring simultaneously (bimolecular termination and radical trapping), but with different “weights” as a function of time. Long living radicals produced by irradiation continue to react in the dark. The rate of this reaction, which is enhanced in the presence of oxygen, is fitted by a relaxation model that considers double bonds, particularly of pendant groups, as traps, with increasing lifetimes, able to transfer to radical sites. The role of oxygen is also discussed.
Insoluble polymeric sulfoxides as liquid‐solid‐liquid and solid‐solid‐liquid triphase catalysts
Authors: Kondo Shuji , Yasui Haruhiko , Tsuda Kazuichi 
Published: April 2003

AbstractCrosslinked polymers containing sulfinyl groups were prepared by free‐radical terpolymerization of p‐methylsulfinylstyrene, styrene, and divinylbenzene. These polymers serve as phasetransfer catalysts for the reaction of 1‐bromooctane with sodium iodide in toluene‐water system. The catalytic reaction is affected by some experimental parameters, such as stirring speed, particle size, degree of crosslinking, and solvent. The catalytic activity also depends strongly on copolymer composition, which causes differences in the adsorption of alkali metal ions and in the microenvironment around the active site. On the basis of the results of reactions of benzyl bromide with phenoxide, and of an alkyl methanesulfonate with sodium halides, it is evident that phase‐transfer reactions catalyzed by insoluble polymeric sulfoxides take place in the organic phase where a small amount of water exists. Furthermore, these polymers work as catalysts even in the absence of water.
Copolymerization of styrene with acrylonitrile initiated by 2‐methyl‐2‐undecanethiol
Authors: Cheng Haitao , Yan Deyue , Xia Ping 
Published: April 2003

AbstractThe copolymerization of styrene (St) with acrylonitrile (AN) initiated with 2‐methyl‐2‐undecanethiol (RSH) was investigated. Kinetic studies revealed that the initial rate of the copolymerization, which does not occur spontaneously in the absence of RSH, obeys the following expression: Rp ∝︁ [RSH]x, where x is 0,5 when [RSH] ranges from 3,4.10−4 to 3,4.10−3 mol/l and 0 when [RSH] is larger than 3,4.10−3 mol/l. The initial copolymerization rate, Rp, increases with increasing percentage of AN in the monomer feed. From the slope of ln Rp vs. 1/T, the apparent activation energy, Eapp, was calculated to be 17 kJ/mol in the temperature range of 30°C to 50°C. RSH is the only initiating species, and it also plays a role as chain‐transfer agent. The value of Mw/Mn, which varies from 1,5 to 2,0, is typical of a free‐radical poymerization. The reactivity ratios were calculated to be rSt = 0,42 ± 0,04 and rAN = 0,02 ± 0,03. It seems to be unnecessary to introduce a penultimate effect for explaining the experimental data.
Behaviour of homogenous catalysts for propene polymerization in methylene chloride
Authors: Longo Pasquale , Oliva Leone , Grassi Alfonso , Pellecchia Claudio 
Published: April 2003

AbstractPropene polymerizations in the presence of the homogeneous catalytic system Cp2Ti(C6H5)2‐Al(CH3)3‐Al(CH3)2F were performed at different monomer concentrations in CH2Cl2. A relevant increase of the polymerization rate is observed, resulting in polymer productivities higher than those obtained with methylaluminoxane cocatalyst in toluene. The dependence of the monomer conversion on the propene concentration seems to support the hypothesis of a cationic catalytic site. Similar results were obtained with a homogeneous catalyst based on a chiral zirconocene and Al(CH3)3‐Al(CH3)2F.
Polymers of 1‐azabicyclo[4.2.0]octane, 2. Polystyrene‐block‐poly(1‐azabicyclo[4.2.0]octane) by mixed‐mechanism technique
Authors: Mühlbach Klaus , Schulz Rolf C. 
Published: April 2003

AbstractBy endcapping of living polystyrene with ethylene oxide and subsequent reaction with bromoacetyl bromide a polymer with a bromoacetoxy endgroup was obtained. This was used as a macroinitiator for the living cationic polymerization of 1‐azabicyclo[4.2.0]octane. The structure and composition of the so formed two‐block copolymer was elucidated by different methods. The ratio of the two block and their lengths were varied within broad limits.