bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cis‐trans double bond distribution in poly(1,3‐cyclopentylenevinylene); dependence on metathesis catalyst, cocatalyst, and additives
Authors: Ivin Kenneth J. , Laverty D. Theodore , O'Donnell James H. , Rooney John J. , Stewart Cecil D. 
Published: April 2003

AbstractAbout one hundred samples of poly(1,3‐cyclopentylenevinylene) (2) were prepared by ring‐opening polymerization of norbornene using a variety of metathesis catalysts based mainly on WCl6 or MoCl5, with EtAlCl2, BuLi, Ph4Sn, and (CH2CHCH2)4Sn as cocatalysts, and with methyl acrylate, diethyl maleate or diethyl fumarate as additives. Ir, Re, V, and Os compounds were also used as catalysts. The double bond pair sequences, trans‐trans (tt), trans‐cis (tc) etc. were determined from the 13C NMR spectra of these samples and the ratios rt(=tt/tc) and rc(=cc/ct) examined as a function of the fraction of double bonds σc having cis structure. For σc up to 0,35 all polymers showed random distribution of cis and trans structures (rtrc = 1), corresponding to a single type of propagating species. Polymers having σc = 0,35–0,85 invariably gave rtrc ≥ 1, with values greater than 5 in some cases. It is proposed that steric crowding of the active site leads both to high values of σc and to restriction of rotation about the metal‐carbene bond of the propagating metalcarbene species, such as to give rise to kinetically distinct conformations which tend to regenerate their own kind on addition of monomer.
Analysis of isotactic polystyrenes obtained with butyllithium and alfin catalysts by carbon‐13 nuclear magnetic resonance spectroscopy
Authors: Kawamura Tokiji , Uryu Toshiyuki , Matsuzaki Kei 
Published: April 2003

AbstractThe 13C NMR spectra of polystyrenes, prepared by butyllithium (BuLi) sec‐butyllithium (sec‐BuLi), propyllithium (PrLi), or Alfin catalyst, were measured at 25,03 MHz and the tacticity of the polymers was determined. The formation of mixtures of predominantly isotactic and syndiotactic polymers with BuLi as catalyst in styrene‐water system was ascertained. With sec‐BuLi and PrLi, only atactic polymers were obtained in the same system. The mechanism of the formation of isotactic polymers is discussed. The polymer obtained by Alfin catalyst had stereoblock structure containing rather long isotactic sequences alternating with atactic ones.
Asymmetric sorbents based on mono‐ and diamines and resolution of racemates by ligand‐exchange chromatography
Authors: Kurganov Alexander A. , Zhuchkova Ludmila Ya. , Davankov Vadim A. 
Published: April 2003

AbstractThe asymmetric sorbents A, B, C, and D were prepared by interaction of a chloromethylated styrene copolymer of the isoporous macronet type (5,5% of crosslinks) with the chiral amines (S)‐1‐phenylethylamine, (R)‐1,2‐propanediamine, and their derivatives. Resins A and B, based on 1‐phenylethylamine, do not sorb Cu(II) ions, whereas resins C and D, based on 1,2‐propanediamine saturated with Cu(II) ions, were successfully used for ligand‐exchange chromatography of amino acids, showing higher affinity to aminodicarboxylic acids than to diaminocarboxylic acids. Sorbent D displays an enantioselectivity of α ≥ 1,5 towards amino acids like Ala, Abu, Ser, or Lys and provides quantitative resolution of enantiomers of some other amino acids. L‐amino acids are retained longer by resins C and D than D‐isomers.
Diffusion of p‐nitroaniline in poly(tetramethylene oxide)‐poly(tetramethylene terephthalate) block copolymers
Authors: Masuko Toru 
Published: April 2003

AbstractDiffusion coefficients of p‐nitroaniline in poly(tetramethylene ether)glycol terephthalate‐poly(tetramethylene terephthalate) (4GT) block copolymers, containing 4GT wt fraction of 0,345, 0,514, and 0,712, have been determined from sublimative desorption kinetics in the range from 60 to 120°C. The temperature dependence of diffusion coefficients in each diffusion system has been found to be a Williams‐Landel‐Ferry (WLF) type. When the glass transition temperatures (Tg) of the soft segments are selected as reference temperatures, the WLF parameters of C and C in the case of diffusion at temperatures above Tg+100 K can be obtained from a new method, proposed in the present paper, on the basis of Fujita's expression of diffusion coefficient in terms of free volume. Parallel studies of dynamic mechanical properties of these copolymers and the assumption of iso‐free volume state at Tg provide the values of free volume parameters of Bd and expansion coefficients of free volume. Both the quantities so obtained decrease to a small extent with increasing 4GT wt fraction. Alternatively, the temperature dependence of diffusion coefficients in the present study can be expressed exactly by Arrhenius plots. The activation energies of diffusion based on Eyring's rate processes are almost independent of, but the activation entropies decrease significantly with, increasing 4GT wt fraction. An expression of the latter in terms of the free volume parameters is presented.
Crosslinking statistics, 2. Relative reactivities of amylose hydroxyl groups
Authors: Luby P. , Kuniak Ľ. 
Published: April 2003

AbstractReproducibility of crosslink distribution in polysaccharides crosslinking depends on the homogeneity of the reaction mixture. If the condition of reaction homogeneity is met, the distribution of substituents (or crosslinks) should directly determine the relative reactivities of the functional groups. The resulting molecular size distribution of fragments of monosaccharide units connected by crosslinks in such a case should be given by the statistical laws of network formation. This principle is exemplified on amylose crosslinked by epichlorohydrin in a homogeneous water‐alkali medium. The relative reactivities of functional groups are investigated in two ways: (1) by specific reactions; (2) calculated theoretically from the molecular size distribution of fragments of crosslinked glucose units. Good agreement of both results supported the above mentioned assumptions. The reactivity of amylose hydroxyls increases strongly in the order OH‐3<OH‐6<OH‐2.
Synthesis and polymerization of methacryl esters having two kinds of nucleic acid bases
Authors: Hattori Masahira , Shimoda Mitsuo , Kinoshita Masayoshi 
Published: April 2003

AbstractMethacrylic acid esters having two different and same kinds of nucleic acid bases such as theophylline‐theophylline, theophylline‐thymine, theophylline‐uracil, and uracil‐uracil, were synthesized, and polymerized in DMF or DMSO at 70°C using 2,2′‐azoisobutyronitrile as an initiator. The polymers obtained were found to have molecular weights in the range of about 1800‐4000, according to vapor pressure osmometr y and gel filtration measurement. The white powdery polymers were soluble in DMSO, DMF, and trifluoroacetic acid, but insoluble in water, alcohols, and common organic solvents.
Polybutadiènes hydroxytéléchéliques, 3. Silylation des fonctions alcool des polybutadiènes hydroxytéléchéliques radicalaires et détermination de la fonctionnalité moyenne en nombre par 1H NMR
Authors: Fages Geneviève , Pham Quang‐Tho 
Published: April 2003

AbstractA number of hydroxytelechelic polybutadiene samples were silylated. The completeness of the silylation reaction allows the determination of the number average functionality by continuous wave 1H NMR. The protonated groups of the silylated alcohol functions were identified at 100 and 250 MHz. It is observed that these three primary alcohol functions do not have the same reactivity towards hexamethyldisilazane as silylating agent.
Synthesis and studies of some organic poly(ammonium phosphate)s, 1
Authors: Vyas Prakash C. , Oza Chandra K. , Sharma Ravi S. , Jain Kailash C. 
Published: April 2003

AbstractLong chain organic poly(ammonium phosphate)s (1a–g and 2) were prepared by a precipitation technique by reaction of poly(lithium phosphate) with organic ammonium salts. Their compositions were established by nitrogen and phosphorus analyses and their polymeric nature was confirmed by molecular weight determinations via end group titrations and by the viscosity method. Studies of conductance at different concentrations indicated their polyelectrolytic behaviour. Paper chromatographic studies supplied additional evidence of a long chain polymeric structure, like Graham's salt and poly(lithium phosphate).
Synthesis and conformational study of poly(L‐lysyl‐L‐valyl‐L‐lysine) in the solid state and in aqueous solution
Authors: Ciaschi Roberto , D'Alagni Maria , Mignucci Gianfranco 
Published: April 2003

AbstractThe synthesis and some conformational properties of aqueous solutions of poly(L‐lysyl‐L‐valyl‐L‐lysine) at different ionization degrees, are reported. IR, UV, CD, and X‐ray measurements were performed on the sequential polypeptide in solution and in the solid state within the pH ranges of 6,4 to 7,2 (charged state) and of 10,4 to 11,0 (uncharged state). The presence of β‐ and probably α‐helical and random coil conformations is detected by IR spectroscopy in the solid state. X‐ray data show that the polymer in the charged form is likely packed as antiparallel β‐pleated sheets, whereas in the uncharged state there are some evidences for an α‐helical packing. The study of aqueous solutions of the polymer by UV spectroscopy seems to indicate that β‐ and a mixture of α‐ and β‐helices exist in the charged and uncharged state, respectively. However, the coexistence of random coil or other conformations cannot be excluded. The corresponding CD spectra support the interpretation supplied in the solid state. The results of this investigation further suggest that the introduction of valyl residues in a copolymer chain, containing residues which are α‐helix formers, favours the β‐conformation.
Synthesis and conformational study of poly(L‐valyl‐L‐valyl‐L‐lysine) in solution and in solid state
Authors: D'Alagni Maria 
Published: April 2003

AbstractThe synthesis and the conformational study of poly(L‐valyl‐L‐valyl‐L‐lysine) were carried out in aqueous and in organic solvents as well as in the solid state. X‐ray measurements indicate the presence of β‐helices. IR, UV, and CD spectra suggest the occurrence of β‐, unordered, and α‐conformations both in solution and in the solid state. The gradual transition from the charged to the uncharged state seems to increase the β‐helical structure at the expense of the random coil content. The same trend is observed passing from water solution to methanol/water, acetonitrile/water and trimethyl phosphate/water mixtures. Again, as for other sequential copolypeptides containing the valyl residue, more than one conformation is detected and the β‐structure results the most ordered in the solid state.
Polymerisation von fulvenen, 2. Spektroskopischer strukturbeweis für kationische polyfulvene
Authors: Slongo Mario , Schönholzer Stefan , Rentsch Christoph , Neuenschwander Markus 
Published: April 2003

AbstractThe cationic polymerisation of pentafulvenes 1a–g yields highly unsaturated macromolecules. The structure of the resulting polymers 2a–g has been proved by combination of spectroscopic methods, especially by analysis of the 13C NMR‐spectra.
Polymerisation von fulvenen, 3. Strukturbeweis für kationische polyfulvene durch vergleich mit modellverbindungen
Authors: Schönholzer Stefan , Slongo Mario , Rentsch Christoph , Neuenschwander Markus 
Published: April 2003

AbstractThe structure of cationic poly(6,6‐dimethylfulvene) (2a) has been confirmed by synthesis of 4 model compounds 6, 7, 8, 9 and comparison of the spectral data with those of the polyfulvene. 5‐Isoproylidenetricyclo[5.2.1.02.6]dec‐3‐ene (6) shows the same sensitivity towards oxygen as 2a. The reaction of 6 with oxygen yields a 1:1‐copolymer, for which structure 10 has been proved by means of spectroscopic methods.
ZnCl2 complexes of para‐substituted phenyl methacrylates in radical copolymerization with styrene
Authors: Szumilewicz Joanna , Połowiński Stefan 
Published: April 2003

AbstractCopolymerization of phenyl methacrylate, p‐tolyl methacrylate, and p‐chlorophenyl methacrylate with styrene was carried out in the absence and in the presence of ZnCl2. It was found by 13C NMR, 1H NMR, and IR spectroscopy that complexes of zinc chloride with the corresponding methacrylates are formed. Reactivity ratios as well as Q and e values for the monomers and complexes were calculated. A correlation between e values and 13C chemical shift of the vinyl group of monomers and complexes with ZnCl2 was found.
The high pressure polymerization of pure ethylene
Authors: Buback Michael 
Published: April 2003

AbstractA series of pure ethylene polymerizations performed to maximum pressures of 2,5 kbar and temperatures up to 250°C is discussed. The rate data which are obtained via quantitative infrared and near infrared spectroscopy closely fit to an overall polymerization rate law of the order 2,5 ± 0,2 in the ethylene concentration. The overall activation energy is determined to be 136,3 ± 6 kJ/mol. For the initiation reaction an activation energy of 209,8 ± 12 kJ/mol is derived. This fairly large value establishes that in dense high purity ethylene a thermally initiated (spontaneous) reaction to high molecular weight material occurs.
Théorie des chaînes de Markov et distribution moléculaire dans les copolycondensats linéaires, 2. Systèmes d'ordre II
Authors: Durand Dominique , Bruneau Claude‐Marcel 
Published: April 2003

AbstractApplication of a mathematical model — based jointly on Graph Theory and Markov chains theory — to the molecular distribution in monodimensional systems of order II (i.e. systems with functional groups belonging to two distinct co‐reactive species A and B) allows one to obtain very general matrix expressions for the molecular distribution functions of many linear copolycondensates.
Polymer‐solvent interactions in mixed solvents, 1. Isotactic, syndiotactic and atactic poly(methacrylic acid) in water/2‐chloroethanol mixtures
Authors: Bottiglione Vincent , Morcellet Michel , Loucheux Claude 
Published: April 2003

AbstractThe viscosimetric behaviour and the preferential solvation of syndiotactic, isotactic, and atactic poly(methacrylic acid), [poly(1‐carboxy‐1‐methylethylene)] are studied in water/2‐chloroethanol mixtures. The experimental results show that the preferential solvation of the polymer is strongly dependent on its local conformation. In the case of the syndiotactic sample, a close correlation has been established between the compact structure ↔ coil conformational transition and the variation of the preferential and absolute solvation of the polymer by 2‐chloroethanol, asserting the importance of hydrophobic interactions in the stabilization of the compact structure. Experimental data concerning the isotactic sample suggest the existence of an “inverse compact structure” in 2‐chloroethanol‐rich mixtures.
Polymer‐solvent interactions in mixed solvents, 2. Isotactic, syndiotactic and atactic poly(methacrylic acid‐co‐benzyl methacrylate) in water/2‐chloroethanol mixtures
Authors: Bottiglione Vincent , Morcellet Michel , Loucheux Claude 
Published: April 2003

AbstractThe viscosimetric behaviour and the preferential solvation of syndiotactic, isotactic and atactic copolymers of methacrylic acid and benzyl methacrylate are studied in water/2‐chloroethanol mixtures. The experimental results show that the presence of benzyl groups stabilizes the compact structure. In the case of the syndiotactic samples, the extent of the preferential hydration domain, which is related to the existence of the compact structure, is dependent on the composition of the copolymer. Experimental results also suggest that the presence of the benzyl groups destabilizes the inverse compact structure existing in 2‐chloroethanol‐rich mixtures.
Conformational change of poly(L‐lysine) by formation of complexes with poly(styrene sulfonate)
Authors: Kōmoto Tadashi , Cho Chong Su , Kawai Tohru 
Published: April 2003

AbstractCircular dichroic studies were made on the conformational change of poly(L‐lysine) (PLL) by complex formation with sulfonated polystyrenes (PSS) as functions of pH, temperature and polymer compositions in comparison with the complexes of PLL with sulfated poly(vinyl alcohol) (PVS). The coil‐to‐helix transition of PLL by complex formation at neutral and acidic pHs, which took place in the PLL/PVS (with high degrees of sulfation) complexes, was prevented in the PLL/PSS complexes due to the less chain flexibility of PSS than PVS. Above pH 11, the α‐helix of PLL was partially broken into random coil by complex formation with PSS. The drastic decrease in the solution viscosity by the complex formation revealed a large contraction of PSS chain and subsequently a large strain of the α‐helical PLL chain so as to give the breakdown of the α‐helix. This is denoted a strain‐induced conformational change of PLL. It was found that the α‐helix of PLL was thermally stabilized by the complex formation with PSS as in the case of PLL/PVS complexes. A β‐to‐α transition of PLL by the complex formation with PSS was also found, while the β‐form was maintained in the PLL/PVS (with high degrees of sulfation) complexes.
Photostability of some carbenium salts
Authors: Velichkova Rumyana S. , Toncheva Veska D. , Panayotov Ivan M. 
Published: April 2003

AbstractThe photolysis of triphenylmethyl salts with anions such as SbCl, FeCl and AsF was investigated in inert and oxygen atmosphere. On irradiation by visible light the characteristic bands of the cation disappeared in 20 min and in 15 h at concentrations of 10−4 M and 10−3 M, respectively. The main photolytes identified were triphenylmethane, triphenylchloromethane, triphenylcarbinol, benzophenone, fluorenone, fluorene, 9‐hydroxy‐9‐phenylfluorene, 9‐phenylfluorene besides 2–3% nonidentified products. The results showed that the product composition of the photolyzed mixture depended only slightly on the atmosphere used, the differences in the amounts of the products being more significant.
Terpolymérisation acrylonitrile — styrène — acrylate de méthyle, 1. Etude cinétique de la terpolymérisation en émulsion, en réacteur fermé
Authors: Rios Leonardo , Pichot Christian , Guillot Jean 
Published: April 2003

AbstractBinary and ternary copolymerizations of the acrylonitrile (A) / styrene (S) / methyl acrylate (M) system were carried out by emulsion polymerization, using sodium lauryl sulfate as emulsifier and potassium persulfate as initiator. Kinetic studies of the reaction mixture by gas chromatography and simulation calculation of the copolymer composition versus conversion show that the classical theory of copolymerization (propagation rate by Markov chain 1st order) can be applied to the emulsion polymerization of this system, even at high conversion level. It was found that, when a conversion limit is obtained, the polymerization can be started again owing to a new addition of the more rapidly consumed monomer (styrene, in this case); it appears that both polymerization process and conversion effect do not involve appreciable variations of the polymer radical reactivity.
Study on polymer solutions in solvent mixtures in the vicinity of the critical point of the solvents, 2. Systems methanol/cyclohexane/poly(tetrahydrofuran) and water/butyl cellosolve/poly(ethylene glycol)
Authors: Dondos Anastasios , Izumi Yoshinobu 
Published: April 2003

AbstractTurbidimetric and viscometric results obtained with the ternary systems methanol/cyclohexane/poly(tetrahydrofuran) and water/butyl cellosolve/poly(ethylene glycol) are reported. The turbidimetric results show that a small quantity of polymer changes extensively the coexistence curve of the solvent mixture, especially near the critical point of the two solvents. The viscometric results show that both polymers, poly(tetrahydrofuran) and poly(ethylene glycol) present abnormally high dimensions near the critical point of the two liquids.
Langfristige konformationsänderung von makromolekülen in lösung, 1. Polyacrylamide
Authors: Kulicke W.‐M. , Kniewske R. 
Published: April 2003

AbstractThe viscosity of aqueous polyacrylamide solutions does not remain constant. During a period of many weeks it decreases by as much as 30%. Simultaneously a loss of flocculation activity occurs. This unusual behaviour — also called ageing or solution instability — is examined. Viscosity and light scattering investigations were made. The viscosity was also determined by addition of substances which influence hydrogen bonds. It could be demonstrated, that in high molecular weight polyacrylamide hydrogen bonds are effective. Light scattering measurements result in curved angular dependence of scattered light, which must be regarded as real and specific for the high molecular weight polyacrylamides in water. The Zimm plot for polyacrylamide in ethylene glycol was undistorted. The refractive index increment decreases with time during the investigations. From the Zimm plots it follows, that the radius of gyration decreases with time. The molecular weight however remains constant. Based on the experimental results a mechanism is assumed with a long‐term conformational change of the macromolecules. The orientated segments — stabilized by hydrogen bonds — are slowly destroyed by occupation of “active sites” by water molecules. Chain degradation as well as disentanglement could be excluded. A molecular interpretation is given.
Study of surface potential characteristics of corona charged ethyl cellulose layers for its relevance in electrothermography
Authors: Pillai P. K. C. , Gupta A. K. , Goel Malti 
Published: April 2003

AbstractA solution cast layer of ethyl cellulose on aluminium substrate shows high charge acceptance on corona charging. Its surface potential decay characteristics are studied at room temperature and at higher temperatures. Addition of a thermosensitive dye in the polymer matrix shows enhanced contrast potential at constant IR exposure. Optimum conditions for suitability of the polymer in electrothermography is determined by studies on different weight proportions of dye. The effect of layer thickness on surface potential characteristics is also investigated.
Anionic copolymerisation of elemental sulfur with 2,2‐dimethylthiirane
Authors: Duda Andrzej , Penczek Stanislaw 
Published: April 2003

AbstractThe copolymerization of elemental sulfur (2) with 2,2‐dimethylthiirane (1), initiated with sodium thiophenolate in benzene solution was studied. By 1H NMR and laser Raman spectroscopy of the resulting copolymers 3 it could be shown that true copolymers with short polysulfide chains are formed and that starting with a sufficiently large ratio of 2/1 diads of 1 are absent.
Polymer modification and synthesis using sulfenyl derivatives, 11. New polymers from oxidation of adducts of benzene‐ and toluenesulfenyl chlorides with cis‐1,4‐polybutadiene
Authors: Gordon Cameron G. , Asif S. , Chishti A. 
Published: April 2003

AbstractAdducts of cis‐1,4‐polybutadiene with both benzene‐ and toluenesulfenyl chlorides were conveniently oxidised in a second stage modification with m‐chloroperbenzoic acid to yield novel sulfone thermoplastic polymers. These have higher glass transition temperatures and are more thermostable than the parent adducts.
Chlorination of polyethylene single crystals
Authors: Guzmán Julio , Fatou José Gomez , Pereña José Manuel 
Published: April 2003

AbstractChlorination under mild conditions of suspensions of polyethylene single crystals demonstrated that a selective attack on the fold surface takes place. Two polyethylene molecular weight fractions (Mn = 47000 and Mn = 150 000) were used and single crystals were grown isothermally from p‐xylene at 88°C. The chlorine content was changed from 4 wt.‐% to 30 wt.‐% and to this level no evidence for crystal attack and loss of crystallinity was found. The melting temperatures of chlorinated single crystals decrease with increasing chlorination up to about 15 wt.‐% chlorine content and then stay constant for higher chlorine contents. Moreover, the heat of melting of the chlorinated single crystals is constant and is independent of the chlorine content up to 25 wt.‐%. These results are compared with those of samples of chlorinated polyethylene recrystallized from solution and from the melt.