bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nuclear magnetic resonance in a swollen polycarbonate. Fine structure of 1H NMR line
Authors: Tekely Piotr , Turska Eligia 
Published: April 2003

AbstractSeveral components have been found to be present in the 1H NMR absorption line in polycarbonate (poly(oxy‐1,4‐phenyleneisopropylidene‐1,4‐phenyleneoxycarbonyl)), swollen in carbon tetrachloride. The α‐component, in the form of a Gaussian function is due to polymer chains present in areas with considerable degree of order. The intermediate β‐component can be fitted with good accuracy by the calculated spectrum, by treating the magnetic dipole‐dipole interaction as a perturbation of the proton two‐spin system. The effect of second neighbours gives a finite width to components of that line. Such a type of fine structure determines with good accuracy the distance between two protons in the ortho‐position in the phenyl ring executing some specific motions. Such phenyl rings can be present in tie‐molecules of limited mobility performing a conformational reorientation motion. The γ‐component is due to the micro‐Brownian motion of polymer chains present in the system and also to lower molecular weight fractions of the polymer. This component can be generally described by an appropriate Lorentz function.
Molecular motion in solid polyethylene as studied by 2D wide line NMR spectroscopy
Authors: Hentschel Dietmar , Sillescu Hans , Spiess Hans Wolfgang 
Published: April 2003

Abstract2D NMR spectra have been measured at variable temperatures between −100°C and +110°C in a sample of melt crystallized deuterated polyethylene (PE). The line shape could be decomposed into a central part originating from deuterons in the amorphous regions and outer parts from crystalline regions of PE. The “NMR crystallinity” determined from this separation was 72% in agreement with the X‐ray crystallinity of 74%. Changes of the crystalline NMR line shape were interperted in terms of oscillations around the chain axis, the r.m.s. oscillation amplitude varying from 5° at 40°C to 12° at 110°C. The central part of the NMR line shape indicates the existence of a “narrow” and a “medium” component due to different motional processes in the amorphous regions.
Composés modèles pour étudier la synthèse de polyesters insaturés
Authors: Fradet Alain , Brigodiot Maryvonne , Maréchal Ernest 
Published: April 2003

AbstractIn order to study the side reactions occuring during the synthesis of unsaturated polyesters, several 2‐hydroxypropyl esters were synthesized by reduction of the corresponding acetylmethyl esters 1a–i. It was found that on heating they are partly isomerized to the 1‐methyl‐2‐hydroxyethyl esters. The extent of isomerization was determined at various temperatures by NMR spectroscopy, both in solution and in bulk. An analysis of the NMR spectra is given and a mechanism of the isomerization is suggested.
15N NMR spectroscopy, 17. Stereospecificity of the polymerization of D,L‐alanine‐NCA and D,L‐valine‐NCA
Authors: Kricheldorf Hans R. , Hull William E. 
Published: April 2003

AbstractD,L‐Alanine‐NCA containing 1,5% 15N and D,L‐Valine‐NCA containing 2,4% 15N, were synthesized and polymerized under various conditions. 36,48 MHz 15N NMR spectra of the resulting poly(D,L‐amino acid)s were measured in trifluoroacetic acid, and the peak for the isotactic triad in each polymer was assigned by comparison with other alanine‐ and valine containing polypeptides. In the case of D,L‐alanine‐NCA the formation of isotactic blocks was favored, when the “activated monomer mechanism” was operating. In the case of D,L‐valine‐NCA, however, syndiotactic blocks were predominantly formed under the same reaction conditions. The initiation with primary amines results in almost atactic sequences. A helical secondary structure of the growing peptide chain is found to be an unnecessary condition for the stereospecificity of a NCA polymerization. The synthesis of Boc‐D,L‐Ala‐D,L‐Ala‐OMe from tert‐butoxycarbonyl‐D,L‐alanine and D,L‐alanine methyl ester was carried out under various conditions, and the stereospecifity was investigated by means of natural abundance 15N NMR spectra. The results are discussed with respect to the polymerization of D,L‐alanine‐NCA and D,L‐valine‐NCA.
Radical polymerization of methacrylic acid in the presence of poly(4‐vinylpyridine) in methanol
Authors: Fujimori Kiyohisa 
Published: April 2003

AbstractThe rate of radical polymerization of methacrylic acid (MA) was found enhanced in the presence of poly(4‐vinylpyridine) (P4VP) of various molecular weights (M̄η) in methanol. The rate maximum shifted from 1 : 1 mole ratio of [P4VP]/[MA], based on the repeating units, to a larger polymer‐monomer ratio and also the rate enhancement was smaller, when P4VP of smaller M̄η was used. The overall energy of activation was 36,1 and 60,7 kJ/mol in the presence and absence of P4VP, respectively. The M̄η of poly(methacrylic acid) (PMA) prepared with P4VP was about 10 times larger than the M̄η of PMA prepared without P4VP.
Synthesis of oligopeptides by copolymerization of aminoacetonitrile and various aminonitriles with basic catalysts
Authors: Ree Keiu , Minoura Yuji 
Published: April 2003

AbstractThe copolymerizations of aminoacetonitrile (AAN) with α‐aminopropionitrile (α‐APN), α‐aminoisovaleronitrile (α‐AVN), α‐aminoisocapronitrile (α‐ACN), and N‐methylaminoacetonitrile (MAAN) were carried out to obtain co‐oligoamidines by using basic catalysts such as barium sec‐butoxide ((s‐BuO)2Ba) at 100°C in dioxane. The resulting co‐oligoamidines were converted into co‐oligopeptides by hydrolysis. The rate of the homopolymerization of aminonitriles decreased in the following order: AAN>α‐APN>MAAN>α‐AVN>α‐ACN. From the composition curves in the copolymerizations, the reactivity of AAN with respect to other aminonitriles was the following: AAN‐AAN>AAN‐α‐APN>AAN‐MAAN>AAN‐α‐AVN>AAN‐α‐ACN.
Copolymerization of carbon dioxide with propylene oxide in the presence of catalysts based on alkylmetal compounds and pyrogallol
Authors: Rokicki Andrzej , Kuran Witold 
Published: April 2003

AbstractCarbon dioxide was copolymerized with propylene oxide (PO, 2‐methyloxirane) in the presence of a catalyst system based on alkylmetal compounds (MtRn, Mt = Zn, Cd, Al) and pyrogallol (PG) at mole ratios 1:1, 2:1, and 3:1, respectively. The reaction was found to produce an alternating copolymer poly(propylene carbonate), [poly(oxycarbonyloxypropylene)], using Zn and Cd containing catalysts and non‐alternating copolymers with Al containing catalysts. For the system ZnR2/PG (mole ratio 2 : 1), the most active system, the influence of substituents R at the zinc atom, as well as effects of solvents and complexing agents on the copolymer yield and intrinsic viscosity were investigated. The results are discussed in terms of an anionic coordinative copolymerization mechanism.
Kinetic evidence for the mechanistic difference in the aqueous polymerization of acrylonitrile
Authors: Hariharan S. S. , Maruthamuthu Meenakshi 
Published: April 2003

AbstractKinetic evidence indicated two different mechanistic pathways in the polymerization of acrylonitrile initiated by peroxodiphosphate‐vanadyl ion redox system in aqueous solution depending upon the concentration of the reducing metal ion employed. The mechanistic difference lies in the termination reaction, exclusively mutual termination occurring in the concentration range [VO2+]=2,5·10−3 to 5·10−3 mol·dm−3 and exclusively linear termination taking place in the concentration range [VO2+] =10−2 to 25·10−3 mol·dm−3.
Über die lichtstreuergebnisse in polystyrol‐lösungen, 1. Gegenüberstellung von theorie und experiment
Authors: Woliński Leszek , Witkowski Konrad , Turzyński Zbigniew 
Published: April 2003

AbstractFrom theoretically and experimentally obtained light scattering cross sections of some polystyrene solutions and the discrepancy between theory and experiment the question of correlated fluctuations of the components of the scattering tensor δεik is discussed. It is found that this discrepancy can be explained only in part by the consideration of the intermolecular interference effects and the supposed change of the scattering cross section of the solvent in the solution.
Die beschreibung von radikalischen polymerisationen durch integrale beziehungen
Authors: Stickler Manfred 
Published: April 2003

AbstractIntegral equations are given for the kinetic analysis of several free‐radical polymerization schemes. These relationships combine conversion and reaction time as variables directly accessible by experiment. In this way is obtained a higher accuracy than with the usual differential treatment and a deeper quantitative insight into individual reaction steps is possible. A modified Mayo equation is derived which takes into account monomer consumption and initiator decomposition and which, in the case of a polymerization with primary radical termination, also enables the estimation of the ratio disproportionation/combination solely by time‐conversion and molecular weight data.
Mechanismus der photopolymerisation des styrols, 2. Zur photochemie und photokinetik der intermediären photo‐(4π + 2π)‐addukte des styrols
Authors: Kauffmann Harald Friedrich 
Published: April 2003

AbstractThe unsensitized photoinitiation of styrene polymerization is accompanied by the formation of some typical oligomeric key substances, which are indicative of two 4π + 2π‐photo‐intermediates (I), viz. 1‐phenyl‐1,2,3,8a‐tetrahydronaphthalene (1) and 2‐phenyl‐1,2,3,8a‐tetrahydronaphthalene (1′). Owing to the very different absorption coefficients of monomer and I, formation and consumption and, therefore, the photo stationary concentration of I exhibits a pronounced dependence on the wavelength λe of the light used for irradiation. Under conditions, where the exciting light is not homogeneously but totally absorbed in the system (λe = 291 nm, corresponding to the 0–0 band of the lowest 1Lb←1A transition in styrene), the intermediates I can be enriched to such an extent, that they are detectable not only by UV‐absorption (310⩽/nmλ/nm ⩽ 360) but also—with the aid of a special high vacuum technique—by 1H NMR spectroscopy, which gives unambiguous proof for the molecular structure suggested for I. Moreover, the photochemistry, the photokinetics and the photophysical behaviour of I were investigated in detail. In the absence of any fluorescence (φ < 10−4) of the intermediate the overall quantum yield for consumption was found to be φ–1 = 1. It is shown, that the photo‐retro‐Diels‐Alder process is the dominating reaction (φ2M = 0,94) and the 1,3‐H‐sigmatropic rearrangement does not contribute more than φPhT⩽0,06. Together with the mean natural molar absorption coefficients φI = 18400 dm3·mol−1·cm−1 for λ = 313 nm and φI = 7300 dm3·mol−1·cm−1 for λ = 335 nm the photostationary concentration [I]∞ is calculated to range from [I]∞ = 8,7.10−6 mol. dm−3 at λe = 313 nm to [I]∞ = 1,2.10−6 mol.dm−3 at λe = 335 nm, which proved to be independent of the intensity of the incident light J0.
Novel butadiene‐isobutene copolymers obtained by means of coordination catalysts: Synthesis and physico‐chemical characterization
Authors: Priola A. , Corno C. , Ferraris G. , Cesca S. 
Published: April 2003

AbstractThe synthesis of novel butadiene (B)‐isobutene (I) copolymers, prepared with coordination catalysts, is reported and discussed. The best results were obtained by using at −40°C ternary systems, based on TiCl4, (i‐C4H9)3Al or (i‐C4H9)2AlH, and benzophenone or acetophenone, previously aged at −78 °C. The formation of the novel B–I copolymers was accompanied by polybutadiene (cis‐ and trans‐1,4‐units were prevalent) and, sometimes by cationic I–B copolymer. The new copolymers, after isolation, underwent thorough spectroscopic investigations. IR analysis yielded the microstructure of B units: trans‐1,4=55%, cis‐1,4=31%, and 1,2=14%. 1H NMR spectroscopy showed that I unit is present only in alternating triad BIB and ruled out the presence of any I homosequence. The study, by 13C NMR, of both the original and hydrogenated copolymer evidenced that only trans‐1,4‐B is linked to I units and hence the copolymer structure is described by IBI and IBnI (where n≥2) sequences. A copolymer containing 30% of I showed the following mole fractions of triads centered on B: FIBI=0,158; FBBI+IBB=0,382; and FBBB=0,462. The mechanistic implications of the copolymer structure are discussed.
Thermal analysis of oxidized poly(acrylonitrile‐co‐methyl methacrylate)
Authors: Radhakrishnan Ganga , Nagabhushanam T. , Joseph K. T. , Santappa M. 
Published: April 2003

AbstractPoly(acrylonitrile‐co‐methyl methacrylate) films were oxidized in an air oven and in an oxidation chamber at temperatures of 80 to 200°C. Differential thermal analysis of these oxidized films showed that the exothermic peaks increased with increasing oxidation temperature. The change of viscosity, the insolubility in dimethylformamide and IR analyses indicate both intramolecular and intermolecular reactions.
Die thermische polymerisation von methylmethacrylat, 2. Bildung des ungesättigten dimeren
Authors: Stickler Manfred , Meyerhoff Günther 
Published: April 2003

AbstractThe spontaneous thermal polymerization of methyl methacrylate (MMA) is accompanied by the production of serveral oligomers among which a linear unsaturated dimerH‐1(dimethyl 1‐hexene‐2,5‐dicarboxylate) is predominant. The reaction kinetics of this dimer formation was investigated in bulk and in solution. The temperature dependence of the second order dimerization constant was determined asReaction mechanisms for the thermal dimer formation of MMA are discussed.
Characterisation of poly(acrylamide) in solution
Authors: Klein Joachim , Conrad Klaus‐Dieter 
Published: April 2003

AbstractUsing a set of laboratory poly(acrylamide) samples in the molecular weight region M̄w = 5.105 to M̄w = 6.106 the following relations have been established, the polymer concentration c given in g/cm3:

([η], intrinsic viscosity; s0, sedimentation constant)
Mainly based on light scattering experiments a more detailed description on molecular dimensions and solution structure of PAAm/H2O and PAAm/ethylene glycol systems is given. In both systems the relation a = 3v − 1 (a and v being the exponents of the intrinsic viscosity — and root‐means‐square end‐to‐end distance — molecular weight functions) holds.
Polymer conformation and NMR chemical shifts, 1. 1H NMR spectrum of alternating methyl methacrylate‐styrene copolymer
Authors: Koinuma Hideomi , Tanabe Tsuneaki , Hirai Hidefumi 
Published: April 2003

AbstractNMR chemical shifts of the methoxyl and α‐methyl protons in the alternating methyl methacrylate‐styrene copolymer are calculated by taking into account the contributions of the diamagnetic shielding and the magnetic anisotropy effect of the benzene rings in styrene units. The conformational probabilities of the copolymer chain are calculated according to Flory's matrix method. It is deduced from the calculation that NMR should occur at higher field for the methoxyl and at lower field for the α‐methyl protons of the methyl methacrylate unit in meso configuration with an adjacent styrene unit (regarding the methoxycarbonyl and phenyl groups) than for the corresponding protons in the unit of racemic configuration. Further, the differences between the chemical shifts for these protons in meso and racemic dyads are nearly equivalent to the differences in chemical shifts between two adjacent peaks of the observed triplet spectra. This result indicates that the spectral assignment based on a theoretical calculation is quite consistent with the one made by a conventional simulation method: from the lower magnetic field, peaks of cosyndiotactic, coheterotactic, and coisotactic triads appear in this order for the methoxyl protons and in the opposite order for the α‐methyl protons. Magnetic anisotropy effect contributes to these tacticity‐dependent chemical shifts to a far greater extent than diamagnetic shielding. The variation of the chemical shifts due to measuring temperature, probability of isotactic addition, and interactions between groups more than five bonds apart is also discussed.
The solid‐state polymerization of some bis(arylsulfonate) esters of 2,4‐hexadiyne‐1,6‐diol
Authors: Ando David J. , Bloor David , Hubble Christopher L. , Williams Richard L. 
Published: April 2003

AbstractExisting evidence suggests that the solid‐state polymerization of disubstituted diacetylenes is controlled by (a) the packing of the monomeric units in the crystal lattice, and (b) the elastic strain which is present in partially polymerized crystals. To investigate these ideas further, a number of closely related bis(arylsulfonate) derivatives of 2,4‐hexadiyne‐1,6‐diol, analogous materials to the extensively investigated bis(p‐toluenesulfonate) ester of this diol, have been synthesized, and their solid‐state reactivity studied. Topochemical polymerization was observed only for those compounds with benzenesulfonate and p‐methoxybenzenesulfonate substituents. In the case of the latter, structurally different reactive and unreactive crystalline modifications were obtained. Polymerization kinetics for the reactive modification differ strikingly from those of the p‐toluenesulfonate compound, despite the fact that the initial elastic strains in the two materials appear comparable.
Polymerization of propylene with γ‐Al2O3‐ or SiO2‐supported titanium tetrachloride catalyst
Authors: Soga Kazuo , Izumi Katsuyuki , Terano Minoru , Ikeda Sakuji 
Published: April 2003

AbstractThe preparation of γ‐Al2O3‐ and SiO2‐supported titanium tetrachloride catalysts for the polymerization of propylene is described. The ESR spectra of these products, measured at −196°C, display broad signals with g‐values of 1,942 and 1,952 in the cases of γ‐Al2O3 and SiO2, respectively, which are assignable to Ti(III) species. The concentration of the Ti(III) species depends strongly upon the conditions of treatment. With these products as catalysts the polymerization of propylene takes place at 40 −75°C in the absence of any activator. The polymerization activity significantly depends upon the conditions of catalyst treatment, but it is approximately proportional to the concentration of the Ti(III) species. The molecular weight and the isotacticity of the resulting polymer remain almost unchanged. These results lead to the conclusion that Ti(III) is the active species in these catalysts.
The initiation of polymerisations by aluminium halides
Authors: Grattan David W. , Plesch Peter H. 
Published: April 2003

AbstractThe polymerisation of isobutylene by aluminium chloride and bromide in corresponding alkyl halide solution was studied by conductivity measurements and radio‐tracer techniques in high‐vacuum apparatus. Some of the reaction mixtures were killed with tritiated water. The conductivity changes during and after polymerisation and the unexchangeable tritium in the polymers support the theory that initiation is by addition of AlX to the double bond of the monomer with consequent formation of a carbenium ion which then propagates. Subsidiary experiments with styrene and 2,5‐norbornadiene and with a saturated hydrocarbon confirmed our conclusions. Contrary to accepted views, we found tertiary carbenium tetrahaloaluminates to be stable electrolytes in our very pure alkyl halide solvents. The very slow addition of isobutylene to solutions of aluminium halide in alkyl halide reduced their conductivity markedly and produced non‐reacting mixtures from which the monomer but no polymer could be recovered. This is shown to prove the long suspected complexing of isobutylene with aluminium halide and rules out all theories of initiation based on interaction of initiator molecules with monomer. It is shown that our theories can explain most features of the polymerisations; our results are compared with those of others.
Amorceurs radicalaires fonctionnels, 1. Acides tert‐butyldioxycarbonylbenzoïques
Authors: Ladousse Alain , Blavin Florence , Ducasse Yves , Filliatre Claude , Maillard Bernard , Villenave Jean‐Jacques 
Published: April 2003

AbstractAmong the methods to introduce functional groups in macromolecular compounds, the initiation of free radical polymerization by functional peroxyesters was investigated. m‐ and p‐tert‐butyldioxycarbonylbenzoic acids (3 and 8) were synthetized and their properties were studied. Differential scanning enthalpimetric study of the thermolysis kinetics of 3 and 8 led to the conclusion that these compounds are a little more stable than O,O‐tert‐butyl hydrogen monoperoxyphthalate (1). Thus, they could be applied under similar conditions. Solution and bulk polymerizations of styrene initiated by 3 or 8 were found to be efficient methods to obtain polystyrene substituted by carboxylic functions.
Synthesis and mesomorphic structures of new amphipathic liposaccharides
Authors: Douy André , Gervais Monique , Gallot Bernard 
Published: April 2003

AbstractAmphipathic liposaccharides were synthesized by condensation of glyco‐amino acid Oβ of Ovomucoid with fatty acids containing 8 to 24 carbon atoms. Condensation was achieved by reaction of the carboxyl group of the acid (via acid chloride or O‐acylisourea as active ester) with the amino group of the asparagine residue in the glyco‐amino acid. X‐ray diffraction showed that liposaccharides exhibit in the dry state and in concentrated water solution a hexagonal structure. In this structure, long and parallel cylinders formed by the hydrophobic paraffinic chains of liposaccharides are arranged in a two dimensional hexagonal array while hydrophilic carbohydrate chains and water fill the space between the cylinders. Freeze fracture electron microscopy allowed the visualization of the hexagonal structure. The influence of the water content and of the length of the paraffinic chains on the periodic structure of the amphipathic liposaccharides was analyzed.
Kinetically controlled formation of macrocyclic oligomers in the ring‐opening polymerization
Authors: Matyjaszewski Krzysztof , Zieliński Marek , Kubisa Przemysław , Słomkowski Stanisław , Chojnowski Julian , Penczek Stanisław 
Published: April 2003

AbstractKinetic schemes are solved for polymerization systems involving competition between linear growth and cyclisation by back‐biting to an optional chain unit and/or to the last unit (end‐to‐end ring closure). A fast reaction of a growing centre with an end group may lead to a situation, called here “kinetic enhancement in macrorings”, in which the transient concentration of cyclics formed in polymerization system exceeds their equilibrium concentration. Sometimes, a peculiar kinetics may be observed in which propagation proceeds on linear active macromolecules, but the polymerization leads almost exclusively to the cyclic products. On the other hand, fast propagation due to a high reactivity of monomer may lead to kinetic reduction of macrorings. Several situations are considered with examples taken from cationic polymerization of cyclic acetals and siloxanes (kinetic enhancement) or anionic polymerization of ϵ‐caprolactone (kinetic reduction). Kinetic schemes are numerically solved by computer for some arbitrarily assumed rate constants. This is the first paper of a series aiming to relate the kinetically controlled concentration of macrorings to the polymerization mechanism and the numerical values of the rate constants.