bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stereosequencing in poly(leucine) obtained from stereoselective polymerization of racemic leucine N‐carboxy anhydride
Authors: Semen John , Elias Hans‐Georg 
Published: April 2003

AbstractPolymerization of mixtures of D‐ and L‐isomers of α‐amino acid N‐carboxy anhydrides follow normal copolymerization behavior, and sometimes even ideal copolymerization, which is conventionally interpreted as leading to a random distribution of monomer units along the polymer chains. Equations are dereived which relate the fraction of isotactic L‐diads to experimental data from the previously reported methods involving sequential and stereospecific cleavage with enzymes. The application of these equations to poly(D,L‐leucines), which were prepared by polymerization of racemic leucine N‐carboxy anhydride with chiral and achiral primary amines as initiators, indicated that the polymers contain between 94 and 98% isotactic diads. The poly(leucines) thus consist of long stereoblocks despite the observed ideal copolymerization behavior.
A bifunctional anionic initiator soluble in non‐polar solvents
Authors: Beinert Gérard , Lutz Pierre , Franta Emile , Rempp Paul 
Published: April 2003

AbstractAddition of two molecules of sec‐butyllithium to one molecule of m‐diisopropenylbenzene produces a bifunctional initiator which is soluble in non‐polar solvents. This initiator is quite efficient for the polymerization of isoprene and butadiene and allows the preparation of samples of particular interest: bifunctional polydienes with high 1,4‐cis and 1,4 contents, respectively, and by using a cross‐linking agent elastomeric gels even after removal of the solvent.
Advances in etherification reaction mechanism of poly(oxymethylene)diol[α‐hydro‐ω‐hydroxypoly(oxymethylene)] with triethyl orthoformate
Authors: Colombo Paolo , Custro Sergio , Ermoni Mario , Radici Pierino 
Published: April 2003

AbstractThe etherification of poly(oxymethylene)diol[α‐hydro‐ω‐hydroxypoly(oxymethylene)] with orthoesters in the presence of Lewis acids leads to the simultaneous formation of various types of end groups: orthoformyl [bis(alkoxy)methoxy] groups (A), formyl (oxyformyl)(B), and ether (alkoxy) groups (C). It was elucidated theoretically and experimentally that the orthoformyl end groups are intermediates of formyl end groups, and partially of ether end groups. The kinetics of the reactions was also evaluated at various temperatures.
Copolymerization of carbon dioxide with propylene oxide catalyzed by poly(p‐hydroxystyrene)/diethylzinc system
Authors: Nishimura Masatoshi , Kasai Masanori , Tsuchida Eishun 
Published: April 2003

AbstractA polymeric catalyst prepared from poly[1‐(4‐hydroxyphenyl)etylene] (1), and Zn(C2H5)2 was found to be effective for the copolymerization of carbon dioxide and 1,2‐epoxypropane. The highest activity was observed when a mole ratio of phenolic hydrogen in 1 to Zn(C2H5)2 equal to unity was applied in contrast to the catalysts so far reported. The structure of the catalyst after the copolymerization was determined by IR and H1 NMR spectroscopy. A Zn—C2H5 bond in this system was confirmed to be the active center. A possible inactivation process of the catalyst is proposed.
13C NMR spectra of poly(alkyl α‐chloroacrylate)s
Authors: Hatada Koichi , Kitayama Tatsuki , Lenz Robert W. 
Published: April 2003

Abstract13C NMR spectra of isotactic and syndiotactic poly(ethyl α‐chloroacrylate)s and poly(isopropyl α‐chloroacrylate)s were measured in toluene‐d8 at 25 MHz. The spectra were analyzed for triad, tetrad and pentad tacticities comparing the spectra with the results previously obtained by 1H NMR spectroscopy. Tetrad tacticities of the polymers were measured from the resonance of the backbone methylene carbon and favorably compared with tetrad values obtained by 1H NMR. The resonance of the carbonyl carbon showed the peaks corresponding to the tactic triad with a pentad splitting in mm resonance. The triad values obtained from the carbonyl carbon resonance were in good agreement with those calculated from the tetrad values as well as the triad tacticities obtained by 1H NMR. The quaternary carbon reconances were very complicated because the chemical shift differences for the different tactic triads were of the comparable magnitude with those for the pentads, and a tentative peak assignment was made with the aid of the statistical calculation of pentad values assuming first‐order Markovian statistics for the isotactic polymer and Bernoullian statistics for the syndiotactic polymer.
Macroion‐pairs and macroions in the kinetics of polymerization of hexamethylene oxide (oxepane)
Authors: Brzezińska Krystyna , Matyjaszewski Krzysztof , Penczek Stanisław 
Published: April 2003

AbstractCationic polymerization of oxepane (hexamethylene oxide) (1) in CH2Cl2 and C6H5NO2 as solvents was initiated with 1,3‐dioxolan‐2‐ylium hexafluoroantimonate (2). Dissociation constants (KD) of the ion‐pairs of polyoxepane into ions were measured: KD (in CH2Cl2, T = 25°C) = 2,8·10−5 mol·l−1 [ΔHD = −3,8 kJ·mol−1 (−0,9 kcal·mol−1), ΔSD = −98 J·mol−1·K−1 (−23,4 cal·mol−1·K−1)]; KD (in C6H5NO2, T = 25°C) = 1,6·10−3 mol·l−1 [ΔHD = −7,1 kJ·mol−1 (−1,7 kcal·mol−1), ΔSD = −78 J·mol−1·K−1 (−18,7 cal·mol−1·K−1)]; these values are close to those of the ion‐pairs of polytetrahydrofuran. Rate constants kp+ and kp±, determined from the kinetic measurements for degrees of dissociation of macroion‐paris ranging from 0,02 to 0,21 (in CH2Cl2) and from 0,09 to 0,7 (in C6H5NO2), were found to be identical within an experimental error of kinetic measurements. The activation parameters of propagation were measured and their dependences on the polarity of the polymerization mixtures are discussed.
Streulichtmessungen an polymerlösungen zur bestimmung der verteilungsbreite des molekulargewichtes
Authors: Hack Hrabanus , Meyerhoff Günther 
Published: April 2003

AbstractBy increasing the experimental accuracy of the classical light scattering technique it became possible to determine the width U = Mw/Mn − 1 of the molecular weight distribution of polymers. For this purpose a very stable laser and a lock‐in‐amplifier were used allowing an accuracy of 0,2–0,3% in the scattering intensity. The numerical evaluation of the polydispersity is done by a Gauß‐Newton procedure analysing the small curvature of the reciprocal scattering function. In an appropriate molecular weight range U is obtained with an error between 0,01 and 0,1 depending on the width of the molecular weight distribution of the sample tested.
Higher aliphatic aldehyde polymers, 8. Poly(undecanal)
Authors: Starr J. , Vogl O. 
Published: April 2003

AbstractCrystalline poly(undecanal) (2) was prepared by anionic polymerization of undecanal (1) with lithium tert‐butanolate in methylcyclohexane. As the aliphatic side chain length of the monomeric aldehyde increases, the polymerization becomes increasingly difficult and 2 could only be obtained if the temperature profile during the polymerization was carefully controlled. 2 of reasonable molecular weight was obtained in nearly 50% yield and was identified by IR and NMR spectroscopy. X‐ray diffraction measurements showed the polymer to be highly crystalline. The paraffinic side chains of 2 were found to be primarily responsible for the polymer crystallization and the polymer side chain transitions were found between 40 and 60°C. Normally, more than one endothermic peak was found by DSC in this region. 2 could be extended through an orifice to a coherent filament whose x‐ray diffraction pattern showed negligible orientation. In contrast, other aldehyde polymers with shorter side chains gave good fiber patterns on extrusion.
Metal compounds in free radical processes, 4. polymerization of vinyl monomers initiated by the system nickel(II) chloride/N,N‐dimethylaniline
Authors: Barton̆ Jaroslav , Leboc Ivan , Capek Ignác 
Published: April 2003

AbstractThe system nickel(II) chloride (NiCl2)/N,N‐dimethylaniline (DMA) initiates the polymerization of methyl methacrylate and acrylonitrile. The thermal polymerization of styrene is not affected. From the polymerization and copolymerization studies as well as from spectral measurements in the UV and visible region it is concluded that this polymerization exhibits free radical character. Neither NiCl2 nor DMA used separately initiate the polymerization. The initiating species are assumed to be formed as a result of interaction between the vinyl monomer/NiCl2 complex {e.g. in the case of MMA, [Ni(CH3OH)6–x(MMA)x]2+2Cl−, (2)} and DMA. Possible causes for the different initiating efficiency of the system NiCl2/DMA for various vinyl monomers are also discussed.
Anthracene sensitized photooxidation of polystyrene, 2. Anthracene photochemistry in polystyrene films
Authors: Nowakowska Maria 
Published: April 2003

AbstractThe photooxidation of polystyrene films sensitized by anthracene was investigated. The quantum yield of singlet oxygen generation in the polystyrene‐anthracene system, irradiated with light at λ = 365 nm in the presence of oxygen was determined. A kinetic scheme of the photophysical and photochemical processes in the system was proposed and the rate constant of anthracene dimer formation in polystyrene was estimated.
Stereochemical structure and molecular weight distribution of polypropylenes prepared with vanadium‐based catalyst systems
Authors: Doi Yoshiharu , Takada Morio , Keii Tominaga 
Published: April 2003

AbstractVanadium tetrachloride combined with alkylaluminium could be shown to produce two types of polypropylenes, the syndiotactic and the isotactic ones, depending on both the kind of alkylaluminium component and polymerization temperature. It was found that the syndiotactic polypropylenes always have narrow molecular weight distributions (1,5≤M̄w/M̄n≤2,5), whereas the isotactic polypropylenes always have wide distributions (16≤M̄w/M̄n≤19), suggesting that the isotactic polymerizations are not induced by homogeneous but by heterogeneous catalysis. With the aid of ESR analysis for catalyst systems it was concluded that the syndiotactic polymerizations take place in a soluble complex of trivalent vanadium, whereas the isotactic polymerizations proceed on the insoluble vanadium dichlorides formed from the catalyst mixture.
Functional monomers and polymers, 54. Synthesis of poly‐β‐alanine from β‐alanine 4‐acyl‐2‐nitrophenyl esters
Authors: Hanabusa Kenji , Kondo Koichi , Takemoto Kiichi 
Published: April 2003

AbstractA series of active β‐alanine 4‐acyl‐2‐nitrophenyl esters with different lengths of alkyl groups was prepared, and their polycondensation was studied in various solvents. The results of the polycondensation of these esters with triethylamine at room temperature show that the conversion and the degree of polycondensation of the resulting poly(β‐alanine)s depend on the chain length of the alkyl groups. No polymer was obtained in both protic and dipolar aprotic solvents such as methanol and DMSO, whereas nonpolar solvents such as diethyl ether, carbon tetrachloride, or benzene were found to be suitable for the polycondensation. The effect of a variety of amines on the polycondensation was examined for β‐alanine 4‐dodecanoyl‐2‐nitrophenyl ester (4e) in diethyl ether solution.
Thermische zersetzung von benzpinakol und benzpinakolbis(trimethylsilyl)ethern in UP‐harzen
Authors: Wolfers Heinrich , Rudolph Hans , Rosenkranz Hans‐Jürgen 
Published: April 2003

AbstractDuring thermal cleavage of benzpinacol (1) in unsaturated polyester resins only 20–40% of the produced semibenzpinacol radicals (2) react via hydrogen transfer. The other radicals disproportionate into benzophenone and benzhydrol or add directly to the double bonds of the unsaturated polyester resin or to the growing polymer radicals. As during thermal cleavage of benzpinacol bis(trimethylsilyl) ether (5) in unsaturated polyester resins only up to 10% of the diphenyltrimethylsiloxymethyl radicals (6) undergo secondary fragmentation, we suppose that the curing of unsaturated polyester resins with 5 is initiated mainly by the relatively stable primary radicals 6. The different activity of the two compounds 1 and 5 in initiating radical polymerisation is explained by different mechanisms in the initiation process.
Heat capacities of water swollen hydrophilic polymers above and below 0°C
Authors: Pouchlý Julius , Biroš Ján , Beneš Svatopluk 
Published: April 2003

AbstractThe heat capacities of water swollen poly[2‐(2‐hydroxyethoxy)ethyl methacrylate] were determined in a DSC‐2 calorimeter within the temperature range 220–350K for concentrations from 0 to 1,2g of water per 1g of the polymer. At temperatures above 0°C the partial specific heat capacity of water in gel is concentration independent and equal to the specific heat capacity of pure liquid water. It seems, therefore, that water does not form stable icelike structures near polymer chains. To analyze phase transformations of water in gel below 0°C, general thermodynamic equations were derived and used as a basis for suggesting criteria which allow to decide whether in a given experiment the phase transformation proceeded in an equilibrium way. In measurements below the melting point of ice the conditions for an equilibrium process consist in the preceding heating of the frozen sample to a temperature close to the melting point, followed by cooling to 220K. The assessed composition dependence of the melting point depression is consistent with the dependence of activity on concentration obtained from measurements of water vapour sorption at 35°C. Analysis of data on the heat capacity below 0°C led to the conclusion that at a water content of 0,4g/g and lower, or at temperatures below 250K the crystallization of water from gel was inhibited by kinetic factors originating probably in the reduced diffusivity of water in gel, due to the reduced mobility of polymer chains. Hence, non‐freezing water need not be identical with “strongly bound” water; in the study of water structure in polymers based on heat capacities, preference should be given to data obtained at usual and elevated temperatures.
The model of specific volume of amorphous vinyl polymers
Authors: Roszkowski Zbigniew 
Published: April 2003

AbstractA model of the specific volume of amorphous vinyl polymers, valid in the range of continuous expansion coefficients above and below the glass transition temperature is proposed. For the case of these polymers the volumetric criterion of the transition of an undercooled liquid in the glassy state, the parameters characterizing the chain and a rigorous definition of the free volume are formulated. The new terms inaccessible volume and nonequilibrium free volume are introduced. Moreover, the van der Waals volume of a substance from its properties is determined and a method is proposed to calculate the specific volume of a polymer in the rubbery state at 0 K, based on a consideration of molecular motions.
High pressure copolymerisation of maleic anhydride with cyclic olefins and substituted ethylenes
Authors: Kellou Mohamed , Jenner Gérard 
Published: April 2003

AbstractThe pressure effect on the rate of maleic anhydride copolymerisations with various substituted ethylenes was found to be considerable, leading to high negative values of the activation volume, especially when the comonomer is crowded with bulky substituents. No significant variation of the polymer composition was observed and the reactivity ratios were found to be less affected by pressure than rates and generally decrease slightly with increasing pressure. Pressure influences also the e‐value of the monomers.
Synthèse et étude de copolymères sequencés photochromiques
Authors: Goett Christian , Lambla Morand , Wippler Constant 
Published: April 2003

AbstractNew photochromic polymers were prepared by deactivating living homo or block copolymers with various 2H‐chromene‐2‐spiro‐2′‐indolines (3a–3d). Classical anionic polymerization was used throughout this work. By varying the chemical nature of the blocks as well as that of the photochromic units, a series of novel materials was obtained and their structure and behaviour were characterized.
N‐trifluoracetyl‐nylon 66 als polymeres reagenz
Authors: Günster Engelbert J. , Schulz Rolf C. 
Published: April 2003

AbstractN‐Trifluoroacetyl‐Nylon 66 (2) obtained by the reaction of Nylon 66 (1) with trifluoroacetic anhydride is very suitable as a polymeric reagent for the trifluoroacetylation of amines and alcohols. The advantages of 2 compared with low molecular trifluoroacetylating reagents are discussed. The selectivity against different substituted anilines and against structurally isomeric secondary amines was studied intensively by kinetic measurements.
Konstruktion eines vollautomatischen präzisionschromatographen auf der basis der phasendistributionschromatographie (PDC)
Authors: Greschner Georg S. 
Published: April 2003

AbstractThe design of a fully automatized chromatograph based on Phase Distribution Chromatography (PDC) is presented and some of the most important results of the measurements shown. PDC represents a dynamical phase separation as column method: the separation of the polymer components in a PDC‐column is based on thermodynamic‐kinetical interactions of the mobile phase (the polymer to be analyzed) below the theta temperature of the system by a gel of the same high polymer situated on the surface of small glass beads. The sigmoidal shape of the measured PDC calibration curves can be explained by introducing a dynamical flow‐equilibrium in the system sol/gel which highly differs from the thermodynamic equilibrium at low temperatures of the column.
Kombination und disproportionierung von modellradikalen für die wachsende polystyrolkette
Authors: Gleixner Günther , Olaj Oskar Friedrich , Breitenbach Johann Wolfgang 
Published: April 2003

AbstractThe mechanism of the bimolecular reaction between the model radicals for polystyryl: 1‐phenylethyl, 1‐phenylpropyl, and 1,3‐diphenylpropyl radical is investigated by means of gas chromatography. The radicals are generated either at 80°C by thermal or at 20°C by photochemical decomposition of the corresponding azoalkanes in benzene solution. At 80°C 7,5% of the 1‐phenylethyl radicals, 12,9% of the 1‐phenylpropyl radicals, and 13,5% of the 1,3‐diphenylpropyl radicals undergo disproportionation. Since the structure of these model radicals approaches that of the growing polystyrene chain in this order one may expect polystyryl radicals to disproportionate to about the same extent as 1,3‐diphenylpropyl radicals. In photolysis experiments evidence for ortho coupling of 1‐phenylalkyl radicals is found. Photoisomerisation of this ortho coupling product leads to the formation of a small amount of a thermally stable unsymmetrical dimer.
Zur definition eines nichtganzzahligen Kopplungsgrades für Gemische ein‐ und zweikettiger Polymermoleküle
Authors: Olaj Oskar Friedrich , Gleixner Günther 
Published: April 2003

AbstractIn free radical polymerization the polymers usually represent a mixture consisting of molecules from one (degree of coupling k = 1) and two (k = 2) independently grown chains. In case the chain lengths at the moment of stabilization obey the same most probable Schulz‐Flory distribution over the total conversion interval (as e.g. at low conversions) the molecular weight distribution (m. w. d.) is a superposition of two Schulz distributions with degrees of coupling k = 1, and k = 2, respectively. Frequently, however, this m. w. d. has been described by a Schulz distribution with a non‐integer k. It is pointed out that the deviations of such a representation of the m. w. d. from the correct one may not always be negligible. Furthermore, there is no unique way to ascribe a degree of coupling k to such an m. w. d. Thus, the use of a non‐integer k should be avoided for the characterization of these polymers, especially when the interrelations between the m. w. d. and the kinetic parameters are to be discussed.
Condensation polymerization of diphenyl 2,2′‐diiodobiphenyl‐4,4′‐dicarboxylate with some di‐ and tetraamino compounds
Authors: Banihashemi Ahmad , Kiaizadeh F. 
Published: April 2003

AbstractIn connection with the research for new thermostable high molecular weight materials several polybenzimidazoles were prepared by condensing diphenyl 2,2′‐diiodobiphenyl‐4,4′‐dicarboxylate (1) with 3,3′‐diaminobenzidine (2), bis(3,4‐diaminophenyl) ether, 3,3′,4,4′‐tetraaminobenzophenone, 1,2,5,6‐tetraaminoanthraquinone, and 1,2,4,5‐tetraaminobenzene. Depending on the reaction time and temperature, partial replacement of iodine atoms by phenoxy groups occurred in the polymers. Model compounds were prepared by condensation of ester 1 with o‐phenylenediamine, 2,3‐diaminopyridine, and 3,4‐diaminopyridine. IR, UV, and 1H NMR spectra of the model compounds were taken. The high thermostability of the polymers could be shown by thermogravimetry.
Darstellung und Derivatisierung von linearem Polyvinylamin zur selektiven Komplexbildung in homogener Phase
Authors: Bayer Ernst , Geckeler Kurt , Weingärtner Karl 
Published: April 2003

AbstractPoly(1‐aminoethylene) (polyvinylamine) (4) was prepared by hydrazinolysis of poly(1‐succinimidoethylene) (2) [poly(N‐vinylsuccinimide)]. The water‐soluble polymer 4, with more than 95% of primary amino groups, was used as basic material for the synthesis of macromolecular complex forming reagents. By the reaction of poly(1‐ammonioethylene chloride) (3) [poly(vinylamine hydrochloride)] with 2‐pyridinecarbaldehyde a complex forming polymer 5 was obtained, which is highly selective for iron. Poly{1‐[bis(carboxymethyl)amino]ethylene} (6) from 4 and chloroacetic acid is a reagent for copper, whereas poly[1‐(3‐methylthioureido)‐ethylene] (7) from 4 and N‐methylisothiocyanate shows a good selectivity for mercury. The ultrafiltration technique allows a continuous procedure for the separation of the polymer complexes. The formation and stability of the prepared complexes of 4and its derivatives 5, 6, and 7 in homogeneous phase are investigated and discussed.
Enantioselektive Trifluoracetylierung mit Hilfe chiraler Polyamide
Authors: Günster Engelbert J. , Schulz Rolf C. 
Published: April 2003

Abstract(S)‐Poly(2‐aminobutyric acid) (1) [(S)‐poly(imino‐1‐methyl‐3‐oxotrimethylene)] was transformed into its N‐trifluoroacetyl derivative 4. The IR spectra and the circular dichroism of both substances were compared. In addition, (S)‐poly[N‐(1‐phenylethyl)acrylamide] (2) ((S)‐poly‐[1‐(1‐phenylethylaminocarbonyl)ethylene]) was trifluoroacetylated leading to polymer 5. 4 was found to react as trifluoroacetylating agent with L‐1‐phenylethylamine (L‐3) twice as fast as it reacts with D‐3. Accordingly, the reaction of 4 with D,L‐3 leads preferentially to the L‐form of N‐(1‐phenylethyl)trifluoroacetamide with optical yields up to 6%. The reaction of 5 with D,L‐3 affords the D‐form of N‐(1‐phenylethyl)trifluorcacetamide with optical yields up to 13%.
Anionic polymerization of 2,2,4,4‐tetramethyl‐6,6‐diphenylcyclotrisiloxane a model siloxane monomer of heterogeneous composition of a reactive grouping
Authors: Mazurek M. , Ziȩtera J. , Sadowska W. , Chojnowski J. 
Published: April 2003

AbstractThe anionic polymerization of 2,2,4,4‐tetramethyl‐6,6‐diphenylcyclotrisiloxane (1), its copolymerization with hexamethylcyclotrisiloxane (2), and the homopolymerization of 2 were studied. It was found that the polymerization of 1 initiated with potassium trimethylsilanolate proceeds with the formation of 2,2,4,4,6,6‐hexamethyl‐8,8‐diphenylcyclotetrasiloxane (3). When using lithium butyldimethylsilanolate/HMPT as initiator an inversion of the reactivity order in the homopolymerization of 2 and 1 was observed. The results indicate that both propagation and depropagation occur with a high degree of regioselectivity, which is dependent on the applied catalyst.