bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regular odd‐number terpolyamides, 1. Synthesis
Authors: Coutin Bernard , Sekiguchi Hikaru , Prieto Arcadi , Muñoz‐Guerra Sebastián 
Published: April 2003

AbstractIn order to improve our comprehension of the crystalline structure of polyamides, two regular odd terpolyamides containing 3‐aminopropanoyl, 5‐aminopentanoyl and 7‐aminoheptanoyl units were prepared by the active ester polycondensation method. The choice of the sequencing order in the starting compounds (called here heterotrimers) and the various routes leading to them are discussed. It was found that both the reactions and the purification of intermediates were most conveniently performed by combining the heterodimer of the lower amino acids with the higher amino acid. The polycondensation was carried out through a multiple step process either in solution or in the solid‐state at a temperature below 200°C. 13C NMR spectra showed that no rearrangement during the polycondensation occurs under these conditions. The terpolyamides have sufficiently high molecular weights to provide good films for crystallographic studies. The two terpolyamides of inversed order do not cocrystallize even when coprecipitated from a solution, probably because of their different crystalline structures.
Propene polymerization in the presence of MgCl2‐supported Ziegler‐Natta catalysts, 4.. Effects of Lewis bases on polymer stereochemistry
Authors: Busico Vincenzo , Corradini Paolo , Martino Luigi De , Graziano Flavia , Iadicicco Annamaria 
Published: April 2003

AbstractThe stereochemistry of polypropenes obtained in the presence of several MgCl2‐supported Ziegler‐Natta catalyst systems comprising different Lewis bases has been investigated by 13C NMR spectroscopy, with special attention paid to the “less tactic” (heptane‐soluble) fractions. These have been found to consist of “tendentially isotactic” and “tendentially syndiotactic” stereosequences, in largely variable amounts (depending on the catalyst system). The microstructure of the former is in accordance with the enantiomorphic site model, whereas that of the latter suggests a stereocontrol arising from the asymmetry of the growing chain end. In both cases, propene insertion is primary (1–2). Polymerization conditions leading to the formation of “syndiotacticrich” polymers showing syndiotactic crystallinity have been identified.
Dilute solution properties of well‐defined multiblock copolymers: poly(4,4′‐isopropylidenediphenyl carbonate)‐block‐polystyrene
Authors: Dems Andrzej , Strobin Graz̊yna 
Published: April 2003

AbstractLight scattering, osmometric and viscometric studies were carried out with dilute solutions of well‐defined poly(4,4′‐isopropylidenediphenyl carbonate)‐block‐polystyrene multiblock copolymers, PC‐b‐PS, in non‐selective and selective solvent systems. The influence of copolymer composition, numbers and lengths of blocks in the copolymer chain and type of solvent used on the dilute solution properties, conformation of the investigated multiblock copolymers and on some thermodynamic parameters are discussed. The intrinsic viscosity [η], the unperturbed dimension 〈R02〉/Mand the second virial coefficientA2are larger in non‐selective solvents than expected from the averaged values of the parent homopolymers. In benzene, a selective solvent for polystyrene, formation of micelles is possible.
Pressure dependence of viscometric relaxation times measured with a new apparatus. Williams‐Landel‐Ferry behaviour of moderately concentrated solutions of poly(butyl methacrylate)s in 2‐propanol
Authors: Geerissen Heinz , Gernandt Friedhelm , Wolf B. A. , Lentz Harro 
Published: April 2003

AbstractA new rotational viscometer is presented which can be operated up to 2 000 bar and a maximum shear stress of 420 Pa. It allows, for the first time, to investigate the non‐Newtonian flow behaviour of moderately concentrated polymer solutions. Results of measurements with two representatives of the system 2‐propanol/poly(butyl methacrylate) with weight‐average molecular weights M̄w = 520 000 and M̄w = 2 050 000, and ratios of weight‐ to number‐average molecular weights M̄w/M̄n = 1,08 and M̄w/M̄w = 1,23, resp. in the region of moderate polymer concentrations are reported. For a ca. 7 wt.‐% solution of the higher‐molecular‐weight polymer one obtains viscometric relaxation times τ0 varying from 1 to 100 ms in the region from 1 to 2 000 bar and from 40 to 75°C; at the lower temperature the application of p can raise τ0 by one order of magnitude. The steady‐state shear compliance (proportional to τ0/η0, where η0 is the zero‐shear viscosity), is independent of pressure of varies only slightly. For the present system, which gels thermoreversibly upon cooling, η0 and τ0 as a function of temperature and pressure can be well represented by the Williams‐Landel‐Ferry equation.
Photoresponsive liquid crystals prepared from poly(biphenylyl vinyl ether‐alt‐maleic anhydride)s
Authors: Ikeda Tomiki , Hasegawa Shoichi , Sasaki Takeo , Miyamoto Takeshi , Lin Mao‐Peng , Tazuke Shigeo 
Published: April 2003

AbstractPhotoresponsive groups (azobenzene and cinnamic acid derivatives) were incorporated into alternating copolymers of maleic anhydride and vinyl ethers with pendant 4′‐methoxy‐4‐biphenylyl moieties bound via ethylene glycol spacers. The resulting polymers were examined with respect to their liquid crystalline behavior and photochemical reactivity in relation to the isothermal phase transition behavior.
Catalysts for syndiotactic‐specific polymerization of styrene: A tentative interpretation of some experimental data
Authors: Zambelli Adolfo , Pellecchia Claudio , Oliva Leone , Longo Pasquale , Grassi Alfonso 
Published: April 2003

AbstractThe experimental data available in the literature concerning syndiotactic‐specific polymerization of styrene and the data reported in this paper, mainly concerning the comparison of the behaviour of different catalytic systems, lead to the tentative suggestion that the true catalytic species might be complex cations similar to those involved in α‐olefin polymerization.
Monomer‐isomerization polymerization, 27. Monomer‐isomerization in competition with polymerization of α‐olefins with Ziegler‐Natta catalysts
Authors: Endo Kiyoshi , Otsu Takayuki 
Published: April 2003

AbstractThe monomer‐isomerization was studied in the polymerization of α‐olefins with the catalytic systems TiCl3/(C2H5)3Al and Ti(OC4H9)4/(C2H5)3Al. The isomerization to the corresponding olefins with internal double bond was found to occur during the polymerization. With the system TiCl3/(C2H5)3Al only a small amount of isomerized olefin was produced as result of the rapid polymerization of the α‐olefins. Significant isomerization was observed to take place with a poor polymerization catalyst such as Ti(OC4H9)4/(C2H5)3Al. Isomerization and polymerization of α‐olefins with Ziegler‐Natta catalysts were found to depend on the oxidation state of titanium.
On the reactivity of styryl‐terminated polystyrene macromonomers in anionic copolymerization with butadiene
Authors: Arnold Manfred , Frank Willy , Reinhold Günther 
Published: April 2003

AbstractStyryl‐terminated polystyrene macromonomers (MA) with molar masses ranging from M̄n = 1 600 to 38 000 g/mol were copolymerized with butadiene (B) by application of the initiator system butyllithium/sodium tert‐butoxide in cyclohexane. The temporal insertion of both monomers into the growing graft polymer chain was observed by means of size‐exclusion chromatography and gravimetrical analysis. The values of 1/rB = kBMA/kBB (kBMA, kBB: rate constants of MA and B insertion, respectively) show that the reactivity of the macromonomers is clearly influenced by their molar mass, the conversion of butadiene, and thus by the obtained molar mass of the growing graft polymer as well as by the mole ratio of the macromonomer and comonomer in the reaction mixture. An almost “ideal” insertion was observed for macromonomers with molar masses of up to about M̄n = 5000 g/mol and a conversion of about 50%. An increase in the values of molar mass, conversion and concentration of the macromonomers has the effect of lowering 1/rB.
Polymer‐supported rare‐earth catalysts for polymerization of styrene
Authors: Zhao Jian , Yang Mujie , Zheng Yi , Shen Zhiquan 
Published: April 2003

AbstractA neodymium complex supported on an ethylene‐vinyl alcohol copolymer (EVA · Nd) was prepared for the first time and the polymerization of styrene in the presence of a new type of catalyst system composed of this complex was studied. The new catalytic system [EVA · NdAl(i‐Bu)3CCl4] (i‐Bu = isobutyl) is characterized by its catalytic activity in comparison with that of conventional rare‐earth catalysts. When [Nd] = 10−3 mol/L, [Styrene] = 5 mol/L, [Al]/[Nd] = 120 and [CCl4]/[Nd] = 35, then the conversion to polystyrene (PS) was 55% in 6 h, and the catalytic activity reached 1972 g PS/g Nd which is higher by a factor of 45 than that of conventional rare‐earth catalysts. The polymerization reaction shows a short induction period where the rate is first order with respect to the monomer concentration. The activation energy is 27,6 kJ/mol. This polymerization may proceed according to a free‐radical or a Ziegler‐type coordination mechanism.
Synthesis and ring‐opening polymerization of 1,4:2,5:3,6‐trianhydro‐D‐mannitol and structure studies by MNDO calculations
Authors: Strietholt Wilhelm A. , Thiem Joachim , Höweler Udo F. B. 
Published: April 2003

AbstractBase‐catalyzed intramolecular nucleophilic substitution of various dianhydrosorbitol derivatives (2, 4, or 6) led to formation of trianhydromannitol (7), a tricyclic system of three interlinked oxolane rings. By treatment with trifluoromethanesulfonic acid, ring‐opening reactions were achieved to give oligomeric soluble material with a number‐average degree of polymerization \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {DP} _n \approx 5 - 10 $\end{document} Molecular weights were determined by GPC, and by desorptive chemical ionization (DCI) with ammonia a molecular weight assignment gave information on the degree of crosslinking. A complex but consistent picture allows to explain the propagation reactions of protonated trianhydromannitols 8 and 9, and further reactions of the protonated intermediates 13–15 to result in crosslinked products 16 and 17. By semiempirical quantum chemical calculations, geometries, energies and charge distributions of 7 as well as its protonated species were obtained. This allowed comparisons with their chemical reactivity and ring‐opening specificity.
Nouveaux copolymères alternés préparés à partir du dicyanure de propène‐1 ylidène‐1 avec le styrène et la vinyl‐1 pyrrolidone‐2
Authors: Monthéard Jean‐Pierre , Boinon Bernard , Rodriguez Firmin , Pham Quang‐Tho , Waton Hugues 
Published: April 2003

AbstractA trisubstituted ethylene, 1‐propene‐1‐ylidene dicyanate has been prepared via Knoevenagel reaction of acetaldehyde and malonitrile with β‐alanine as a catalyst. This product has been copolymerized in bulk — with 2,2′‐azoisobutyronitrile as an initiator — with styrene and 1‐vinyl‐2‐pyrrolidone. Preliminary 1H and 13C NMR studies of the copolymers are in good agreement with an alternating structure besides minor proportions of homopolymers of styrene or 1‐vinyl‐2‐pyrrolidone. The propagation mechanism has also been studied with 1H‐1H correlation spectroscopy.
Molecular‐weight distributions in the thermally initiated emulsion polymerization of styrene
Authors: Said Ziad F. M. 
Published: April 2003

AbstractIn both thermal emulsion polymerization of styrene in the temperature range 60–80 °C, and peroxodisulfate‐initiated polymerization at 60 °C, weight‐average to number‐average molecular‐weight ratios (M̄w/M̄n) approach 1,5 when potassium octadecanoate is used as emulsifier. A low activation energy for thermal initiation (≈66,0 kJ/mol) was deduced which may indicate a catalytic effect of the emulsifier during the thermal initiation process. Participation of the emulsifier is probably attributed to a transfer of one of two monomer radicals, produced thermally, to the emulsifier, with subsequent desorption to the aqueous phase, leaving one radical in the polymerization locus.
Hypochromy in polystyrene systems
Authors: Kowal Joanna , Jamróz Dorota 
Published: April 2003

AbstractThe hypochromy of polystyrenes of different degrees of isotacticity in relation to ethylbenzene, and of isotactic polystyrene in relation to atactic polystyrene, was estimated. All polymers showed hypochromy, ca. 2% in case of atactic polystyrene and 5–9% in case of isotactic polystyrene. One may conclude that the helical regions of the solid polymers are partly retained in solution.
Binding of dyes by teichoic acid in competition with other polyanions
Authors: Pal Medini Kanta , Ghosh Tapash Chandra 
Published: April 2003

AbstractWhen a cationic dye is added to a mixture of different anionic polymers, the dye will be distributed amongst them according to the binding strengths of the polymers. In such a competitive binding, DNA uses its intercalation ability to win the competition, provided the ligand can be intercalated within the DNA base pairs. For poorly or non‐intercalating ligands like 1,9‐dimethyl‐methylene blue or pinacyanol, the effective mode of binding is only electrostatic. For such ligands the strong polyelectrolyte poly(styrene sulfonate) wins the competition for cationic dyes, as shown by spectroscopic and dichroic probes. The results of the competitive binding of pinacyanol between the two weak chromotropes teichoic acid and DNA are not distinctly indicative, but the dichroic probe hints at a relatively stronger chromotropic ability of DNA.
Sulfonation of low‐density polyethylene films. Infrared absorption coefficients for the sulfonic group
Authors: Arribas Carmen , Rueda Daniel R. 
Published: April 2003

AbstractThe chemical modification of the surface of low‐density polyethylene films exposed to an atmosphere of fuming sulfuric acid for different periods of time has been investigated. The degree of surface sulfonation for each treated film was calculated as the weight‐increase per unit area. The correlation of the absorbance of infrared bands associated to the sulfonic group with the degree of sulfonation of the films allowed to determine the IR absorption coefficients, especially for the band at 1 040 cm−1.
Some spectroscopic evidence on deformation mechanisms in elastomeric networks at very high elongations
Authors: Silva L. K. , Mark J. E. , Boerio F. J. 
Published: April 2003

AbstractBimodal elastomeric networks are unusually tough materials in that they generally show large increases in modulus at high elongations. In the present study such networks were prepared by end‐linking mixtures of very short and relatively long chains of poly(dimethylsiloxane) (PDMS) [Si(CH3)2O]n, which is known to have easily deformable SiOSi bonds. Their stress‐strain isotherms were then determined in order to locate the range of elongations over which the upturns were most pronounced. Raman and infrared spectra were then obtained in this range using both a double monochromator Raman spectrophotometer and a Fourier transform infrared spectrophotometer with attenuated total reflection. The elongations imposed were found to cause small but not negligible frequency shifts for the stretching and bending modes of the SiOSi backbone. These shifts are probably due to rotational isomerization of the PDMS skeletal bonds, but there could also be a small contribution from bond‐angle deformations. The results thus support the usual assumption that the increases in modulus observed for bimodal networks are primarily due to the very limited number of spatial configurations available to the short network chains, particularly in the case of chains having skeletal bonds that are less easily deformed than those in PDMS.
A new class of highly reactive acrylic monomers, 2. Light‐induced copolymerization with difunctional oligomers
Authors: Decker Christian , Moussa Khalil 
Published: April 2003

AbstractAcrylic monomers containing a cyclic carbonate group in their structural unit have been shown to copolymerize very rapidly and extensively with urethane and phenoxy oligomers having two acrylic functional end groups. With the most reactive resin, 90% conversion was reached within 20 ms of UV exposure in the presence of air. The kinetics of these ultrafast polymerizations was studied by infrared spectroscopy and their actual profiles were recorded in real time by RTIR spectroscopy. The rate of polymerization and the amount of residual unsaturation were determined for the three monomers studied, and compared to the performance of the mono‐, diand triacrylates commonly used as reactive diluents in UV‐curable systems. Quantum yield measurements indicate a very efficient propagation reaction, with kinetic chain lengths in the order of 104 mol per initiating radical, even in the presence of air. The crosslinked polymers obtained with these new monomers exhibit both a great hardness and a high flexibility, together with a good resistance to organic solvents, chemicals and UV radiation, which makes them well suited for applications as protective coatings.
X‐ray diffraction characterization of amorphous poly(propylene)
Authors: Marigo Antonio , Marega Carla , Zanetti Enrico , Zannetti Roberto , Paganetto Guglielmo 
Published: April 2003

AbstractThe differential radial distribution functions of a sample of amorphous (atactic) poly(propylene) and of an isotactic one were compared, showing the absence, in the former sample, of interatomic correlations beyond 8 Å (1 Å = 0,1 nm). The influence of the length of atactic and isotactic chain segments on the calculated X‐ray interference functions was investigated. A model based on the arrangement of atactic chains in close‐packed spheres fits well the experimental X‐ray diffraction pattern of the amorphous sample.
Study on dipole moments of macromolecules, 3. Dipole moments of poly(4‐methoxystyrene) and poly(4‐bromostyrene) and their dependences on solvent and temperature
Authors: Shima Mikiko , Yamaguchi Noriko , Sato Mari 
Published: April 2003

AbstractDipole moments of poly(4‐methoxystyrene) (PMeOSt) and poly(4‐bromostyrene) (PBrSt) were determined from dielectric constant and density measurements on dilute solutions of the polymers in benzene, 1,4‐dioxane and toluene, over the range of temperatures from 25 to 55°C. The average dipole moments per constitutional repeating unit (μ) obtained in benzene (Bz), 1,4‐dioxane (Dox), and toluene (Tol) at 25°C are as follows: 1,219 D (Bz), 1,253 D (Dox) and 1,175 D (Tol) for PMeOSt, and 1,371 D (Bz) and 1,413 D (Dox) for PBrStIn SI units: 1 D ≈ 3,33564 · 10−30 C · m.
. The dipole moment ratio, Dr = 〈μ2〉2/μ20, was found to be 0,942 for PMeOSt and 0,467 for PBrSt in Bz at 25°C, for which the observed values of the dipole moments of 4‐methoxytoluene and 4‐bromoethylbenzene were used as μ0 for the respective polymer. The variation of the dipole moment ratio with temperature was linear but very small, dDr/dT giving a negative value for PMeOSt but a positive value for PBrSt.
Biaxial and uniaxial extension studies of polydimethylsiloxane networks prepared by end‐linking in solution
Authors: Xu Ping , Mark James E. 
Published: April 2003

AbstractPolydimethylsiloxane chains were tetrafunctionally end‐linked with tetraethoxysilane in solution, with either a linear dimethylsiloxane oligomer or hexadecane as solvent. Stress‐strain isotherms for the networks thus prepared were obtained in the extracted but unswollen state, both in elongation and in compression (biaxial extension, which was achieved by inflation of sheets of the materials). Measurements were carried out to the rupture points in order to provide as large a range of deformation as possible. Comparison of the experimental and theoretical stress‐strain isotherms indicated that the experimental results were in good agreement with the constrained junction theory of rubberlike elasticity. The results showed that the constraint parameter k decreases with decrease in the volume fraction v2c of polymer present during cross‐linking and incorporated into the network structure, which means that networks prepared at high dilutions have fewer chain‐junction entanglements, as expected. However, the experimental values of the phantom modulus [f] are also a function of the weight fraction of soluble (uncross‐linked) polymer which had been present. This confirms the expectation that networks prepared at high dilutions have imperfections such as loops and dangling ends. There is an excellent agreement, however, between experiment and theory with respect to the relationships among k, the Mooney‐Rivlin 2C1 estimate of the phantom modulus, and v2c.
Cationic polymerization of vinyl monomers with latent initiators, 3. 1‐(p‐methoxybenzyl)tetrahydrothiophenium hexafluoroantimonate as a new potent cationic initiator
Authors: Kikkawa Atsushi , Takata Toshikazu , Endo Takeshi 
Published: April 2003

AbstractCationic polymerization of styrene in the presence of 1‐(p‐methoxybenzyl)tetrahydrothiophenium hexafluoroantimonate (3) as an efficient cationic initiator was investigated. 3 was synthesized in an excellent yield by the reaction of p‐methoxybenzyl bromide with tetrahydrothiophene and the subsequent exchange of bromide ions for hexafluoroantimonate ions. In the polymerization of styrene, 3 acted as a potent thermally latent initiator which initiates the polymerization at a slightly higher temperature than room temperature, although no polymerization occurs at room temperature for 30 min. 3 is a much more active initiator than the previously reported benzylsulfonium salt 1. The enhanced activity of 3 was also confirmed in the polymerization of glycidylb phenyl ether.
Constitutional isomerism in step‐growth polymers: Theoretical aspects of systems with two nonsymmetric monomers
Authors: Gentile Frank T. , Suter Ulrich W. 
Published: April 2003

AbstractA model was developed to determine the constitution of step‐growth polymers synthesized from the nonsymmetric monomers XabX and YcdY under various modes of mixing. Depending upon the inherent kinetics of the system and the modes of addition of monomers, polymer constitution can be varied over wide ranges. Results are shown for single‐stage polymerizations with all variations of kinetic parameters and mixing modes. The results show that the synthesis of truly “random” polymers is very difficult with this monomer system.
New approach to dextran derivatives containing primary amino functions
Authors: Vandoorne Filip , Bruneel Dorine , Vercauteren Ronny , Schacht Etienne 
Published: April 2003

AbstractDextran derivatives containing primary amino functions were prepared by reacting 4‐nitrophenyl carbonate‐substituted dextran with the mono‐protected diamine N‐tritylenediamine (7). Acidic treatment of the resulting dextran N‐[2‐(N‐trityl)aminoethyl]carbamate (8) yields dextran N‐(2‐aminoethyl)carbamate (5a). Alternatively, aminodextran derivatives were prepared by adding 4‐nitrophenyl carbonate‐substituted dextran to a large excess of a diamine or a triamine.