bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study of the molecular structure of ethylene‐propylene copolymers obtained with catalysts of different composition
Authors: Yechevskaya Lyudmila G. , Bukatov Gennadii D. , Zakharov Vladimir A. , Nosov Andrey V. 
Published: April 2003

AbstractThe monomer composition and sequence distribution in ethylene‐propylene copolymers (EPCs) obtained with supported titanium/magnesium (TMC) and vanadium/magnesium (VMC) catalysts as well as with titanium trichloride was studied by means of 13C NMR spectroscopy. Based on these data ethylene‐propylene reactivity ratios were determined. The EPCs obtained on these catalysts are inhomogeneous in composition; the soluble fractions contain larger amounts of propylene. The microstructures of copolymers obtained on TMCs and TiCl3 are similar. For EPCs obtained on VMCs, propylene “head‐to‐head” or “tail‐to‐tail” inversions and a more homogeneous distribution of propylene are observed.
Functionalization of poly(methyl methacrylate) by free radical polymerization, 1. Transfer with functional thiols
Authors: Clouet Gilbert , Knipper Magali 
Published: April 2003

AbstractChain transfer constants (Ctr) for three phosphonated thiols in methyl methacrylate (MMA) polymerization at 60°C were determined from measurements of the degree of polymerization. These thiols were: diethyl 2‐mercaptoethyl phosphate (1), diethyl 2‐mercaptoethylamidophosphate (2), and tetraethyl mercaptomethylethylene bis(phosphate) (3). Transfer efficiencies of the thiols were found to be dependent upon their structures. The Ctr value of thiol 2 with MMA was the lowest in the present series, which can be attributed to a possible charged tautomeric form which eventually may reduce the electron density on the thiol, thus rendering the chain transfer reaction with the PMMA radical less feasible. Ctr values of thiol 1 were evaluated at 55, 60, 65, 70 and 75°C. This thiol behaves as an “azeotropic” transfer agent for MMA at 96°C.
Copolymerization at equilibrium. General treatment
Authors: Szymański Ryszard 
Published: April 2003

AbstractThe relationships for copolymerization of any number of comonomers at equilibrium are derived. The presented sets of equations allow to predict the comonomers equilibrium concentrations and the copolymer structure, as well as the equilibrium concentrations of polymers of any length and their composition, provided the initial state and equilibrium constants are known. If the ratio of concentrations of active centers and copolymer composition at equilibrium are known, the relationships allow to determine the equilibrium constants for homo‐ and cross‐propagations.
Photoprocesses in statistical, end‐labelled, and block copolymers containing naphthalene chromophores
Authors: Chen Liusheng , Winnik Mitchell A. , Al‐Takrity Emaad Taha Bakir , Jenkins Aubrey D. , Walton David R. M. 
Published: April 2003

AbstractFluorescence spectroscopy in highly dilute solutions has been used to study the emission from naphthyl groups attached to poly(methyl methacrylate) molecules prepared by (i) free‐radical polymerization, giving an essentially random distribution of naphthyl groups along the chain, and (ii) anionic polymerization, producing polymers with naphthyl groups in terminal units only. The influence of molecular architecture on the fluorescence is discussed. In particular it is shown that it is possible to incorporate one single naphthyl group at one end of a polymer chain but that attempts to introduce a controlled greater number lead to a product with a distribution of naphthyl‐group constents.
Fourier transform infrared spectroscopic study of polyacetylene, 1. Spectral assignment and characteristics of Z/E (“cis”/“trans”) geometric isomers
Authors: Chen Zhongxin , Liu Min , Shi Mingxiao , Shen Zhiquan , Hummel Dietrich O. 
Published: April 2003

AbstractAn FTIR spectroscopic study was carried out for rare‐earth polyacetylenesIUPAC name: poly(vinylene).
(PA) containing both Z (“cis”) and E (“trans”)We distinguish formally between configurations (Z, E = “cis”, “trans”) and conformations (cis, trans), though in the case of poly(vinylene) the physical quality is virtually the same.
geometric isomers. Spectral assignments were made by the study of PA samples with different Z/E ratios and by referring to the known assignment of the IR spectrum of PA obtained with Ti(OC4H9)4·Al(C2H5)3. The conjugation effect of Z or E CHCH sequences and their length distribution in PA are investigated by spectral subtraction and peak separation. It is shown that the frequency of v(CH) (out‐of‐plane deformation) is located in the regions 741 to 747 cm−1 and 940 to 1014 cm−1 for Z‐ and E‐PA, respectively, depending on the conjugation length. At the beginning of thermal isomerization of Z‐PA, long Z sequences are interrupted quite frequently; this causes a shift of v(CH) towards higher frequencies. In high E‐PA obtained by thermal isomerization of Z‐PA, uninterrupted long E sequences persist. This demonstrates that a crosslinking reaction between PA chains is not conspicuous during the thermal isomerization process.
Precipitation‐crystallization of poly(1,4‐phenyleneterephthalamide) from nematic solution
Authors: Chen Shouxi , Jin Yongze , Qian Renyuan , Cai Liying 
Published: April 2003

AbstractPrecipitation‐crystallization of poly(1,4‐phenyleneterephthalamide) (PPTA) from sheared nematic solutions was studied by polarized light microscopy. Three kinds of morphological structures, viz. spherulite, shish‐kebab, and band structures were observed in films prepared from sheared anisotropic solutions. An exhaustive study of the band structure by using various techniques to prepare the samples for electron microscopy was made. The results obtained indicated that the morphology of the band structure is composed of fibrils bent in a zigzag manner and highly oriented along the shearing direction of the molecular chains in the neighbouring bands with the angle ±14° as measured from selected‐area electron diffraction. A finer periodical structure of 300 Å arranged along the zigzag fibrils was observed.
Heats of dilution of poly[styrene‐ran‐(butyl methacrylate)] solutions measured with an automatic flow microcalorimeter
Authors: Kyohmen Masayuki , Inoue Keizo , Baba Yoshihiro , Kagemoto Akihiro , Beatty Charles L. 
Published: April 2003

AbstractIn order to obtain information about the thermodynamic behaviour of copolymers in solution, we built an automatic flow microcalorimeter equipped with a computer that satisfies the requirements of accuracy, reliability, and rapidity for the measurement of heats of dilution of copolymer solutions. By using this apparatus, the heats of dilution of the random copolymer, poly[styrene‐ran‐(butyl methacrylate)] in ethyl methyl ketone solutions were measured at 298 K. Furthermore, light scattering of the copolymer and its constituent homopolymer solutions was measured at 298 K. From the combination of the heat of dilution and the light scattering results, thermodynamic and intramolecular interaction parameters of the copolymer chain were determined.
Reactivity of vinyl monomers in the copolymerization and terpolymerization with sulfur dioxide
Authors: Florjańczyk Zbigniew , Floriańczyk Tadeusz , Kłopotek Beata B. 
Published: April 2003

AbstractThe relative reactivities of vinyl monomers in low‐temperature copolymerizations and terpolymerizations with SO2 in the presence of tert‐butyl hydroperoxide as initiator were compared. The highest copolymerization rates were found in systems containing an electron‐donor monomer of low resonance stabilization, and the resulting products have an alternating structure. In reactions with monomers of high resonance stabilization and electron‐acceptor properties, mainly homopropagation of the comonomer proceeds. In the terpolymerization of SO2 with two electron‐donor monomers, the relative reactivity of monomers depends mainly on their resonance stabilization. In the terpolymerization in systems SO2/electron‐donor monomer/electron‐acceptor monomer the relative reactivity of acceptor monomers decreases with increasing inductive effect in the molecule.
Precursors of hydrophilic polymers, 8. The structure of copolymers of 2‐dimethylaminoethyl methacrylate and 2‐methacryloyloxyethyltrimethylammonium iodide
Authors: Přádný Martin , Ševčík Stanislav 
Published: April 2003

AbstractQuaternization reactions of poly(2‐dimethylaminoethyl methacrylate) using methyl iodide were carried out up to 50% conversion in 18 chemically different solvents. Copolymers which contain moderate hydrophilic 2‐dimethylaminoethoxycarbonyl groups and strongly hydrophilic 2‐trimethylammoniumethoxycarbonyl iodide groups were obtained. Potentiometric titration showed that in some solvents the reaction proceeds by the zip mechanism, i.e. copolymers with a predominantly block structure are formed, while in other solvents the reaction proceeds along the macromolecular chain randomly, that is, giving rise to statistical copolymers.
Lichtstreubefunde zur Kettenspaltung von Polystyrol in sauerstoffreien CCl4‐ und CHCl3‐Lösungen bei Lichteinwirkung der Wellenlängen λ ≥ 270 nm
Authors: Woliński Leszek , Turzyński Zbigniew , Witkowski Konrad 
Published: April 2003

AbstractThe photodegradation of polystyrene (PS) in deoxygenated solutions of CCl4 and CHCl3 by irradiation with ultraviolet light of wavelengths λ ≥ 270 nm is investigated by quasielastic and integral light scattering techniques. Molar mass distributions w(M), number‐ and weight‐average molar masses M̄n and M̄w as well as the average number of chain scissions per macromolecule x(t) as a function of the time of irradiation t were determined. The results obtained prove that efficient photodegradation occurs in CCl4‐ and CHCl3‐solutions of PS, although measurable changes in molar mass of irradiated PS starts to occur only after several hours of irradiation.
ESR determination of rate constants for the radical polymerization of methyl phenethyl itaconate
Authors: Sato Tsuneyuki , Morino Kazutaka , Tanaka Hitoshi , Ota Tadatoshi 
Published: April 2003

AbstractPhenethyl 2‐(methoxycarbonylmethyl)acrylate (methyl penethyl itaconate) (1) was prepared and its polymerization with dimethyl 2,2′‐azoisobutyrate (2) was investigated kinetically in benzene. The polymerization rate (Rp) was found to be expressed by Rp = k·[2]0,5·[1]1,8 (at 50°C). Further, a higher dependence of Rp (2nd order) on the concentration of 1 was observed at 61°C. The overall activation energy of the polymerization was calculated to be a low value of 50,3 kJ/mol. The initiator efficiency (f) of 2 was determined to be 0,48 to 0,22 at 50°Cand 0,50 to 0,28 at 61°C. f decreases with increasing monomer concentration due to the high viscosity of 1. The poly(1) radical is stable enough to be observable by ESR at high temperatures (50–60°C). Rate constants of propagation (kp) and termination (kt) were estimated using the poly(1) radical concentration determined by ESR. kp [6,0 to 121/(mol·s) at 50°Cand 7,1 to 15 1/(mol·s) at 61°C] shows a trend to increase with the concentration of 1. On the other hand, kt [2,9·104 to 17·1041/(mol·s) at 50°Cand 6,9·104 to 45·1041/(mol. s) at 61°C] decreases with increasing MPI concentration. This behavior is responsible for the high order with respect to monomer concentration. Copolymerization of 1 (M1) with styrene (M2) at 50°Cgave the following results: r1 = 0,36, r2 = 0,40, Q1 = 0,82 and e1 = + 0,59. Using the above results, the rate constants of the cross‐propagations were estimated to be k12 = 22 1/(mol·s) and k21 = 308 1/(mol·s) at 50°C.
Photocrosslinking behavior of poly(vinyl alcohol)s with pendent styrylpyridinium or styrylquinolinium groups
Authors: Ichimura Kunihiro 
Published: April 2003

AbstractPoly(vinyl alcohols) (PVA's) with pendent styrylpyridinium (SbQ), styrylquinolinium (QQ), or oxystyrylquinolinium (OQQ) exhibit anomalously high photosensitivity, even if the content of photosensitive groups is very low. This phenomenon was studied by measuring the sensitivity to crosslinking quantitatively using monochromatic light. When the content of SbQ or OQQ exceeds ca. 1 mol‐%, the photoinduced gelation behaviour was found to be in the line with Charlesby's equation, suggesting that the absorbed light energy leads specifically to interamacromolecular photodimerization of SbQ or OQQ. Under these circumstances, the quantum efficiency for the photodimerization of SbQ and OQQ was estimated to be in the ranges of 0,31–0,37 and 0,10–0,17, respectively. The applicability of PVA‐SbQ to water‐developable photoresists for microfabrications is discussed. The sensitivity characteristics of PVA having OQQ and analogous groups is also mentioned in view of the application to Ar laser resists.
Calculation of domain sizes in block copolymers with broad interphase
Authors: Bühler Fritz , Gronski Wolfram 
Published: April 2003

AbstractThe domain dimensions of poly(styrene‐b‐isoprene) diblock copolymers with polyisoprene spheres in a continuous polystyrene matrix, in which the interphase is broadened by a random poly(isoprene‐co‐styrene) copolymer block, are significantly smaller than in unmodified block copolymers. The depression of domain sizes and the reduced exponent of the molecular weight dependence in these systems are calculated on the basis of Helfand's theory in which the surface and the conformational entropy were appropriately modified. The domain dimensions of unmodified block copolymers, for which hitherto larger than experimental radii were predicted by the original theory, are also in good agreement if calculated by the proposed phenomenological approach.
Spezifische Adsorbentien für das Peptidantibiotika synthetisierende Enzymsystem Gramicidin S Synthetase, 2. Kupplung niedermolekularer Spacer/Ligand‐Verbindungen mit reaktiven polymeren Trägern und Untersuchung der Adsorptionswechselwirkung dieser polymeren Produkte mit Gramcidin S Synthetase
Authors: Schlünsen Jürgen , Manecke George , Schröter‐Kermani Christa , Kleinkauf Horst 
Published: April 2003

AbstractThe inhibition constants (KI) of aliphatic and aromatic amide derivatives of phenylalanine and proline for GS1 and GS2 of the enzyme system gramicidin S synthetase were determined. These compounds act as competitive inhibitors. Some of these compounds (spacer/ligand compounds) were reacted with epoxy‐activated Sekpharose 6B or with crosslinked poly(vinyl alcohol). The resulting—for GS1 or GS2 more or less specific—adsorption materials, were used for the purification of these multi‐enzyme systems.
The dynamic mechanical properties of poly(alkyl 2‐cyanoacrylates)
Authors: Cheung King H. , Guthrie John , Otterburn Michael S. , Rooney John M. 
Published: April 2003

AbstractVarious poly(alkyl 2‐cyanoacrylates) and poly(allyl 2‐cyanoacrylates) having different molecular weights have been prepared. Dynamic mechanical analysis was carried out over the temperature range 23°Cto 230°Cat a fixed frequency of 110 Hz, in order to study the effect of temperature on the storage modules, loss modulus and loss tangent of the films. From these data, the glass transition temperature of the polymers could be determined and the effect of the alkyl group on the stiffness of the polymers could be evaluated. It is shown that crosslinking occurs in the case of poly(allyl 2‐cyanoacrylates) when it is subjected to temperatures above its glass transition temperature. This crosslinking is seen as a rapid increase in the storage modulus. This increase is eliminated if the polymer samples are thermally aged prior to dynamic mechanical analysis.
X‐ray studies on diethynylbenzene derivatives in view of the solid‐state polymerization
Authors: Kai Yasushi , Yamamoto Akira , Xu Duanjun , Kasai Nobutami , Hagihara Masahiko , Yamamoto Yukio , Takahashi Shigetoshi , Hayashi Koichiro 
Published: April 2003

AbstractThe crystal structures of three diethynylbenzene derivatives, 3‐[2‐(3‐acetoxy‐1‐propynyl)‐4,5‐dimethylphenyl]‐2‐propynyl acetate (1a), 3‐[4‐(3‐acetoxy‐1‐propynyl)‐2,5‐dimethylphenyl]‐2‐propynyl acetate (1b), and 3‐[2‐(3‐acetoxy‐1‐propynyl)‐4,5‐dimethoxyphenyl]‐2‐propynyl acetate (2), were determined by means of X‐ray diffraction. The unique monomer packings interpret the characteristic freatures of these compounds in the solid‐state polymerization upon irradiation with γ rays.
Polymerization of lactams, 81. Anionic polymerization of lactams accelerated with N‐iminolactams, 2 ϵ‐caprolactam (6‐hexanelactam)
Authors: Brožek Jiří , Marek Miroslav , Roda Jan , Králíček Jaroslav 
Published: April 2003

AbstractThe anionic polymerization of ϵ‐caprolactam (CL), initiated with the sodium or potassium salt of CL, was shown to be accelerated with 1‐(1‐pyrrolin‐2‐yl)‐2‐pyrrolidone (1), 1‐(1‐azacyclohept‐1‐en‐2‐yl)‐2‐pyrrolidone (2), 1‐(1‐azacyclonon‐1‐en‐2‐yl)‐2‐pyrrolidone (3), 1‐(1‐azacyclohept‐1‐en‐2‐yl)‐1‐azacycloheptan‐2‐one (4) and 1‐(phenyliminomethyl)‐2‐pyrrolidone (5), both above the below the melting temperature of the polymer (150‐230°C). The postpolymerization of the product was followed at 180°C for certain cases.
Polymerization of lactams, 84. Anionic polymerization of lactams accelerated with N‐iminolactams, 3. The role of 1‐(1‐pyrrolin‐2‐yl)‐2‐pyrrolidone in the anionic polymerization of 2‐pyrrolidone
Authors: Brožek Jiří , Roda Jan , Králíček Jaroslav 
Published: April 2003

AbstractThe anionic polymerization of 2‐pyrrolidone was accelerated with 1‐(1‐pyrrolin‐2‐yl)‐2‐pyrrolidone (1), labelled with nuclide 15N. The incorporation of 1 into the polymer was followed by the change of isotope concentration, and the apparent rate constants were derived for some elementary reactions in the investigated polyreaction. The interchange reaction between 1 and monomer was also measured. 1 can be considered a slow activator, each molecule incorporating into the polymer being the precursor of a growth centre.
Zwitterionic polymerization of butyl cyanoacrylate by triphenylphosphine and pyridine
Authors: Cronin John Paul , Pepper David Charles 
Published: April 2003

AbstractThis paper describes a re‐examination of the kinetics and molecular weights formed in the zwitterionic polymerization of butyl cyanoacrylate by triphenylphosphine (Ph3P) and pyridine (Py) in THF, and an extension to include the solvents, diethyl ether (Et2O), dimethoxyethane (DME) and hexane. In THF, the previously observed kinetics were confirmed, yielding evidence for absence of termination, and values for rate constants for initiation (ki) and propagation (kp) with substantial agreement between the values for Kp obtained from both systems. At 20°C, the mean value found for kp in THF was 3 · 105 l · mol−1 · s−1; in Et2O, some 10 times lower, and in hexane, 10 times lower again. The temperature dependence of kp in THF was confirmed to be extremely low and anomalous; in Et2O rather greater and near‐normal, corresponding to an energy of activation of ca. 5 kcal · mol−1. A correction procedure enabled the large experimental scatter in the kp values to be reduced sufficiently to reveal trends downwards at higher concentrations of propagating species, i.e. evidence for their dissociation on dilution. In Py‐initiated polymerizations, excess of pyridinium salts did not depress kp; evidence that the propagating species are preponderately paired ions, not free. It is concluded that at 20°C these species are mainly ‘tight’ ion‐pairs in all solvents, and remain so in Et2O at all temperatures down to −80°C. In THF, over this temperature range, there is increasing solvation producing an increasing proportion of more reactive ‘solvent‐separated’ ion‐pairs. The molecular weights produced under all conditions were high (Mn usually 1 to 3 · 106). Those produced by high concentration of Ph3P did not conform to theory; others followed the ‘no‐termination’ theory as modified to allow for a small effect of transfer.
Bioactive polymers, 51. Synthesis and characterization of a macromolecular prodrug of ampicillin
Authors: Dumitriu Severian , Popa Marcel 
Published: April 2003

AbstractThe coupling reaction of ampicillin with the polysaccharide xanthane in DMSO, using dicyclohexylcarbodiimide as activator, was studied. To find the conditions for maximum yield a regression equation was established, describing the dependence of the yield of coupling product on the reaction parameters (drug/support mole ratio, activator/support mole ratio and duration), starting from an experimental, centrated rotable complex, second order program. The coupling product was spectroscopically characterized and the in vitro release rate of ampicillin in a weakly basic medium was established along with the determination of its antimicrobiological activity.
Structure of dimers and trimers obtained in the cationic oligomerization of propylene
Authors: Audisio Guido , Priola Aldo , Rossini Alessio 
Published: April 2003

AbstractA structural investigation was carried out on the product of the cationic oligomerization of propylene with the aim of identifying the main isomers present in the dimer and trimer fractions. BF3‐proton donor complexes were used as cationic catalysts. The different isomers, after hydrogenation, were separated by GLC analysis and identified by GC‐MS analysis after comparison with reference products. The structures of the obtained isomers give clear evidence that hydride and methanide shifts may be operative. The influence of the experimental conditions (temperature, type of catalyst) in obtaining the various isomers was evaluated. The number of isomers, mainly those due to methanide shift, increases with increasing reaction temperature. The identified oligomer structures give indications about the chemistry of the first steps of the cationic oligomerization of propylene.
Polyadditions of diisocyanatodiketenes, 3‐(ω‐isocyanatoalkyl)‐4‐(ω‐isocyanatoalkyliden)‐2‐oxetanones, and polymeranalogous reactions with the resulting polymers
Authors: Mormann Werner , Hoffmann Silke 
Published: April 2003

AbstractReactions of diisocyanatodiketenes, 3‐(ω‐isocyanatoalkyl)‐4‐(ω‐isocyanatoalkylidene)‐2‐oxetanones (3a–c), with oligomeric diols (4 or 5) as well as 1,4‐butanediol afforded linear polyurethanes containing reactive diketene moieties. From these poly(diketene‐urethane)s polymeranalogues products were prepared by reaction with ethanol, ammonia, water or acetic acid. The resulting polyurethanes containing ß‐ketoester, ß‐ketoamide or keton moieties were characterized by IR spectroscopy, viscosimetry, differential scanning calorimetry and size exclusion chromatography. The properties of the products based on diols 4 or 5 are mainly determined by the oligomeric diols, whereas the (modified) diisocyanate part has a great influence e.g. on the thermal behaviour of the polyurethanes.
ß‐helices of D,L‐alternating valine peptides
Authors: Lorenzi Gian Paolo , Tomasic Lera 
Published: April 2003

AbstractNew conformational data for members of the series Boc‐(D‐Val)m‐(L‐Val‐D‐Val)(n‐m)/2‐OMe (m = 0 or 1; n = total number of residues) are presented and used together with earlier results to formulate general conclusions regarding types and relative stabilities of ß‐helices formed by D,L‐alternating valine peptides. The helices, single‐ or double‐stranded, are of the tightest geometry, the single‐stranded helices having only 4,4 residues per turn(ß4,4 ‐helices) and the double‐stranded ones only about 5,6 residues per turn (↑↓ß5,6‐and ↑↑ß5,6‐helices). The double‐stranded helices are of the type with the highest possible number of interstrand H‐bonds [2(n‐1)] and the antiparallel ones are always strongly preferred. In chloroform solution right‐and left‐handed ß4,4‐helices and left‐handed ↑↓ß5,6 and ↑↑szlig;5,6‐helices are formed by the oligovalines studied with different preferences depending on the peptide chain length and on the parity of the number (odd or even) of residues. The reasons for these preferences are discussed.