bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of propene pressure on the isotacticity of polypropene produced with typical C1‐symmetric metallocene and Ziegler‐Natta catalysts
Authors: Schneider Martin Julius , Kaji Eiichi , Uozumi Toshiya , Soga Kazuo 
Published: April 2003

AbstractPolymerization of propene was conducted at 40°C under reduced pressure (0.35 – 1.0 atm) using the C1‐Symmetric threo‐iPr(3‐tBuCp)(3‐tBuInd)ZrCl2/MAO and TiCl4/MgCl2/Al(iBu)3 catalyst systems and the effect of propene pressure on the microstructure of the resulting isotactic polypropene was investigated. In the case of C1‐symmetric metallocene, the [mmmm]‐pentad fraction decreased moderately with decreasing propene pressure, but the magnitude of decrease was much smaller than those reported by Busico et al. using typical C2‐symmetric metallocenes. Whereas, the [mmmm]‐pentad fraction of isotactic polypropene obtained with the conventional Ziegler‐Natta catalyst did not change so much in the pressure range. Thus, epimerization of the growing polymer chain was found to be drastically dependent upon the catalyst system.
Coordination polymers from 1,3,4‐thiadiazole‐2,5‐dithiol and metal ions
Authors: Ortega Pedro , Vera Leonel R. , Guzmán Miguel E. 
Published: April 2003

AbstractThe copolymerization of 1,3,4‐thiadiazole‐2,5‐dithiol (bismuthiol) with 1+, 2+, and 3+ valent metals is reported. Polymerization conditions were mimicked by means of Job's technique of solutions mixing. The polymers in aqueous solutions do not conduct electricity, but electrolytes are formed in proportion to polymer formation and the pH changes. The metal concentration in solutions confirms the metal‐ligand stoichiometry. The UV absorption of the ligand (at 320 nm) decreases and light scattering by polymer (at 380 nm) increases with polymer formation. The stoichiometry of polymers (obtained from the conductivity inflection point and metal analysis) is as follows. Mt2+: bismuthiolate = 1 : 1; Al3+ : bismuthiolate = 2 : 3 and Ag+ : bismuthiolate = 2 : 1. Equations describing polymer formation on the basis of the solution conductivities are presented, and a model of polymer formation is proposed. It is concluded that 2+ valent metals from linear polymers but Al3+ forms branched polymers.
Studies on the pH‐dependent swelling properties and morphologies of chitosan/calcium‐alginate complexed beads
Authors: Lee Ok‐Sub , Ha Byung‐Jo , Park Soo‐Nam , Lee Yoon‐Sik 
Published: April 2003

AbstractChitosan/calcium‐alginate beads were prepared by a coacervation method in aqueous medium. Their swelling properties and morphologies were studied. Complexed beads with a mean diameter of 500 μm were obtained by dropwise addition of a sodium alginate solution into a chitosan‐calcium chloride solution. From scanning electron microscopic studies, we observed that chitosan modifies the morphology of calcium‐alginate beads. The swelling properties of chitosan/calcium‐alginate beads are different from those of calcium‐alginate beads. In the case of the calcium‐alginate beads, the swelling volume increases as the pH of the medium increases. However, chitosan/calcium‐alginate beads show a maximum swelling volume at pH 9.0.
Thermally stimulated current and DSC studies of the dual glass transitions in side‐chain liquid crystalline copolysiloxanes containing 4‐[(S)‐2‐methylbutoxy]phenyl 3‐chloro‐4‐alkenyloxybenzoate side groups
Authors: Chang Huey‐Ling , Hsu Chain‐Shu 
Published: April 2003

AbstractThe synthesis of side‐chain liquid crystalline copolysiloxanes containing ω‐[4‐[4‐[(S)‐2‐methylbutoxy]phenoxycarbonyl]‐2‐chlorophenoxy]alkyl side groups is presented. Differential scanning calorimetry, optical polarizing microscopy and X‐ray diffractometry reveal smectic mesomorphism for most of the obtained polymers. The copolysiloxane with three methylene units in the spacer is the only one showing no mesomorphic property. The other four copolysiloxanes, containing four, five, six or eleven methylene units in the spacer, display a smectic A phase. All of the obtained polymers present dual glass transition behavior by both DSC and thermally stimulated current (TSC) techniques. The first glass transition (Tg1) at lower temperature is due to the segmental motions of the polysiloxane backbone, while the second glass transition (Tg2) is due to the cooperative relaxation motions of spacers and mesogenic units.
Endgroup‐functionalized polytetrahydrofurans by polymerization with functional triflate esters, 1. PolyTHF‐macromonomers
Authors: Dubreuil Marjorie F. , Goethals Eric J. 
Published: April 2003

AbstractFunctional esters of trifluoromethanesulfonic acid (triflate esters) have been synthesized by reaction of functional alcohols (allyl alcohol, 2‐hydroxyethyl acrylate (HEA) and methacrylate (HEMA), 4‐hydroxybutyl acrylate (HBA)) with triflic anhydride in the presence of 2,6‐di‐tert‐butylpyridine. These esters were used in situ as initiators for the polymerization of tetrahydrofuran (THF), with the purpose to synthesize endgroup‐functionalized polyTHF's. The method was first tested with the system butanol/triflic anhydride. With this combination, quantitative formation of the ester and, subsequently, controlled polymerization of THF was realized. Similar results were obtained with the system allyl alcohol/triflic anhydride. With 2‐hydroxyethyl acrylate (HEA) and 2‐hydroxyethyl methacrylate (HEMA), the synthesis of the triflate ester was accompanied by the formation of substantial amounts of ether formed by reaction of the triflate ester with a second molecule of alcohol. This was attributed to an enhanced reactivity of the triflate ester due to nucleophilic assistance by the carbonyl group in γ‐position. This assistance is not possible with 4‐hydroxybutyl acrylate (HBA) and with this alcohol, the formation of the ester was almost quantitative. The synthesis of polyTHF acrylate macromonomer was successful with the latter system.
Thermal and thermo‐oxidative degradation of polystyrene in the presence of ammonium sulfate
Authors: Zhu Xinsheng , Elomaa Matti , Sundholm Franciska , Lochmüller Charles H. 
Published: April 2003

AbstractAmmonium sulfate was compounded into polystyrene (PS) to modify thermal degradation of PS. At elevated temperatures, ammonium sulfate decomposes into ammonia, sulfuric acid and further into sulfur trioxide and water. The aim of the study was to investigate how these acidic and oxidizing compounds affect the thermal and thermo‐oxidative degradation behaviour of polystyrene. Thermal degradation was studied by thermochromatography (ThGC). In addition, isothermal pyrolysis at 340°C was carried out and the dissolved parts of the residues were analyzed by size exclusion chromatography (SEC). The random chain scission index Sr (based on the components of evolving gases), the chain scission number Sx (based on the number‐average molar mass), the oxygen effect K, and the synergistic effect Z were used to describe thermal and thermo‐oxidative degradation processes. The increases of Sr and Sx with the increase of ammonium sulfate imply that thermal degradation of PS is modified. The synergistic effect Z indicated that, at low addition levels, ammonium sulfate synergistically promotes thermo‐oxidative degradation with oxygen. At high addition levels, it promotes thermo‐oxidative degradation with oxygen.
Investigation of a fine‐grain MgCl2‐supported Ziegler catalyst by stopped‐flow propene polymerization: Model for the formation of active sites induced by catalyst fragmentation during polymerization
Authors: Mori Hideharu , Yoshitome Masaki , Terano Minoru 
Published: April 2003

AbstractA fine‐grain catalyst, as a model of catalyst fragmentation in the course of polymerization, was prepared by grinding an original MgCl2‐supported Ziegler catalyst. In order to clarify the nature of the active sites generated after catalyst fragmentation, the kinetic parameters for propene polymerization with both catalysts were estimated using the stopped‐flow method. The active sites concentration of the fine‐grain catalyst was higher than that of the original MgCl2‐supported catalyst, indicating that the grinding treatment induced the formation of new active sites. However, the propagation rate constant and stereoregularity of polypropene remained unaffected. This is an indication that the nature of the active sites formed after the grinding treatment was the same as that of active sites on the original MgCl2‐supported catalyst.
Studies on the phase separation of polyetherimide‐modified epoxy resin, 2. Effect of molecular weight of PEI on the structure formation
Authors: Cui Jun , Yu Yinfeng , Chen Wenjie , Li Shanjun 
Published: April 2003

AbstractThe effect of molecular weight on the structure formation of polyetherimide modified epoxy system was studied. Using time‐resolved light scattering (TRLS) and scanning electron microscopy (SEM), the process of phase separation and the morphology of the blends were investigated. As the curing reaction proceeds, the phase separation occurs first in the large molecular weight polyetherimide (PEI) modified epoxy resin and the time of occurrence of phase separation is increased with the decrease of the inherent viscosity of PEI. Because of the different viscosity of the blends, the blends display varied morphologies from a PEI particle dispersion to co‐continuous phases. Changing of the PEI molecular weight may be another possible route to control the morphology of the PEI modified epoxy resins.
Synthesis and characterization of halogen‐containing polyisophthalamides
Authors: Álvarez Julio C. , García José M. , De la Campa José G. , de Abajo Javier 
Published: April 2003

AbstractTwo series of aromatic polyamides were prepared from m‐phenylenediamine (MPD) and 4,4′‐diaminodiphenyl sulfone (DDS) in combination with a set of new halogenated diacyl chlorides, namely, 5‐fluoroisophthaloyl chloride, 5‐chloroisophthaloyl chloride, 5‐bromoisophthaloyl chloride and 5‐iodoisophthaloyl chloride. The polymers were synthesized in high yields and in high molecular weight (as determined by gel permeation chromatography) by means of the low temperature condensation method. Noticeable changes in the spectral characteristics of the halogen‐modified polyisophthalamides were observed compared to those of the corresponding unmodified polyisophthalamides. Slight improvements were observed for the glass transition temperatures, which increased 5–30°C relative to those of the conventional polyisophthalamides. Moreover, a correlation was found between the size of the halogen substituents and the increase in Tg values. Thermogravimetric analysis showed that the new polymers are almost as thermally resistant as the unmodified ones, while solubility in organic solvents was some‐what poorer.
Radical products of poly(triphenylcarbinol) thermolysis
Authors: Shishlov Nikolay M. , Akhmetzyanov Shamil S. , Novoselov Igor V. , Nikiforova Galina I. 
Published: April 2003

AbstractAt least three kinds of stable paramagnetic species are formed in films of poly(triphenylcarbinol) 1 upon thermolysis in vacuo up to 500°C. “Low temperature” radicals of triarylmethyl type (RTAMT1) are created in the 120 ÷ 220°C temperature region. These radicals give rise to a symmetric ESR signal (g = 2.0026 ± 0.0003; ΔH ≈ 1.0 mT) with poorly resolved hyperfine structure and to an absorption band (AB) of allowed transition with λmax = 407 nm in UV spectra. The spectral region of forbidden transitions, assumed for the RTAMT1, is masked by a nonradical AB, in particular by that of quinoid structure of Chichibabin hydrocarbon type with λmax = 595 nm. From 220°C to 280°C the “high temperature” radicals RTAMT2 appear, with a strong bathochromic shifted AB of forbidden transition (λmax = 710 nm). Maximum concentration of RTAMT2 (≈︁1020 spin/g) is achieved at ≈︁280°C. Possible structures of both kinds of RTAMT are discussed. At T ≥ 300°C paramagnetic species that differ from RTAMT are formed in 1.
Stereoselectivity in cyclic and acyclic metathesis reactions
Authors: Basset Jean‐Marie , Leconte Michel , Lefebvre Fredéric , Hamilton James G. , Rooney John J. 
Published: April 2003

AbstractMetathesis polymers of norbornene and 1‐methylnorbornene were prepared using a well‐defined aryloxy(chloro)neopentylidene tungsten initiator which behaves in a stereo and regioselective manner giving predominantly cis polymers and a strong head‐to‐tail bias in the case of 1‐methylnorbornene. This is in accord with the observation that this initiator is also very stereoselective in acyclic metathesis.
Relation between the alternating monomer unit sequence and the cis and trans linkage configurations at the cyclic maleic anhydride units in the copolymers of styrene and maleic anhydride prepared in carbon tetrachloride
Authors: Ha Nguyen T. H. , Fujimori Kiyohisa , Craven Ian E. 
Published: April 2003

AbstractThe monomer unit triad sequence distribution and the cis/trans linkage configurations at the cyclic maleic anhydride (MA) units in the copolymers of styrene (ST) and MA prepared in CCl4 with AIBN at 50°C were quantitatively determined by 13C DEPT NMR spectroscopy. So much as 61 % of the linkages at the MA units were found to be in cis configuration, which was considered to be formed by a participation of the 1:1 electron donor‐acceptor complex formed between ST and MA in the propagation step. The mole fraction of the cis configuration was found to be proportional to the mole fraction of alternating triad sequences when the monomer unit sequences approach to be completely alternating. This supported the proposal that, in alternating and semi‐alternating copolymerizations, the alternating sequences were formed mainly by the addition of the complex. The equilibrium constant of the complexation in CCl4 at 23°C was determined to be 0,21 L/mol.
Thermal and morphological study of fractionated poly(3‐hydroxybutyric acid‐co‐3‐hydroxypropionic acid)
Authors: Cao Amin , Ichikawa Masafumi , Ikejima Tetsuya , Yoshie Naoko , Inoue Yoshio 
Published: April 2003

AbstractThe thermal and morphological characteristics of fractionated poly(3‐hydroxybutyric acid‐co3‐hydroxypropionic acid)s (P(3HB‐CO‐3HP)) with narrow comonomer compositional distribution, as well as the natural poly(3‐hydroxybutyric acid) (P(3HB)) and chemosynthetic poly(β‐propiolactone) (PPL) were studied by means of differential scanning calorimeter (DSC) and infrared spectroscopy (IR). It is seen that melting point (Tm), heat of fusion (ΔH) and glass transition temperature (Tg) decrease with the increase of the content of 3HP units up to 60.5 mol‐%. Employing 13C NMR in the solution, the sequence distributions of the fractionated copolyesters were revealed not to be in accordance with the results of the random statistical model. The carbonyl IR absorption bands were further resolved by curve fitting into several components stemming from the bond stretchings in the different molecular environments known as the amorphous, crystalline and intermediate regions. It is demonstrated that the contributions which belong to the crystalline regions show intrinsic absorption peaks at 1724.0, 1723.8 and 1729.1 cm−1 for P(3HB), P(3HB‐CO‐3HP)s and PPL, respectively. In the case of P(3HB‐CO‐3HP)s, the relative intensities of contributions originating from the crystalline regions decrease with the increase of 3HP units up to 60.5 mol‐%. However, only the P(3HB) type of lattice structure is formed despite the variation of the 3HP unit content. Moreover, the effect of the substrates (silicon wafer and KBr) used for preparation of the IR samples on the crystallization behavior was also investigated.
Polymers of carbonic acid, 21. Ring‐opening polymerization of cyclobis(diethylene glycol carbonate) by means of BuSnCl3, SnOct2 or Bu2SnO as catalysts
Authors: Kricheldorf Hans R. , Lossin Martina , Mahler Andreas 
Published: April 2003

AbstractCyclobis(diethylene glycol carbonate), (DEGC)2, was synthesized by polycondensation of diethylene glycol with diethyl carbonate followed by thermal depolymerization of the crude polycarbonate in vacuo. BuSnCl3‐initiated polymerizations of (DEGC)2 in chlorobenzene at 100°C gave poor results. Therefore, all further polymerizations were conducted at 145°C in bulk. Two series of polymerizations were performed with BuSnCl3 as catalyst, so that either the time was varied at constant monomer/initiator (M/I) ratio, or the M/I ratio at constant time. Two analogous series were conducted with SnOct2 With both catalysts high yields but only moderate molecular weights were obtained. SnOct2 yielded polycarbonates having octoate end‐groups, which were detected by 1H NMR spectroscopy. (DEGC)2 was also polymerized with Bu2SnO at M/I = 200 or 500 with variation of time. The highest yields and molecular weights were obtained at the shortest time, whereas longer times caused rapid depolymerization. Therefore, Bu2SnO appeared to be the most reactive catalyst. Both 1H and 13C NMR spectra proved that all poly(diethylene glycol carbonates) prepared in this work possess an alternating sequence of ether and carbonate groups.
An “in situ” reaction of propagating chain‐end as iodoacetal in the polymerization of butyl vinyl ether initiated by I2 and HI/I2 systems
Authors: Deák György , Kéki Sándor , Gnandt Csaba , Zsuga Miklós 
Published: April 2003

AbstractThe polymerization reaction of butyl vinyl ether with initiating systems I2 and HI/I2 was investigated with glass fiber photometry and conductometry by monitoring the characteristic changes in the absorbance versus time curve and in the conductivity versus time curve. Aldehyde end‐groups were observed and a mechanism of their formation is proposed.
Copolymerization of 1,3‐dienes with CpTiCl3‐MAO. Some cases in which the mode of monomer coordination affects the copolymer structure
Authors: Ricci Giovanni , Porri Lido 
Published: April 2003

AbstractThe following pairs of monomers were copolymerized using the catalyst system CpTiCl3/methylaluminoxane (MAO): 1,3‐butadiene/(E)‐1,3‐pentadiene, 1,3‐butadiene/4‐methyl‐1,3‐pentadiene and 4‐methyl‐1,3‐pentadiene/(Z)‐1,3‐pentadiene. The copolymers were characterized by NMR and infrared examination. 4‐Methyl‐1,3‐pentadiene/(Z)‐1,3‐pentadiene and 1,3‐butadiene/(E)‐1,3‐pentadiene gave copolymers having a composition intermediate between that of an ideal and that of an alternating copolymer. 1,3‐Butadiene/4‐methyl‐1,3‐pentadiene gave block copolymers only. These results have been interpreted on the basis of a different mode of coordination of the monomers. The cis‐η4 coordination is by far the most stable for 1,3‐butadiene and (E)‐1,3‐pentadiene, while for (Z)‐1,3‐pentadiene and 4‐methyl‐1,3‐pentadiene there is probably an equilibrium between the cis‐η4 and trans‐η2 form. Both these forms are reactive in the case of (Z)‐1,3‐pentadiene, while only the trans‐η2 form is so in the case of 4‐methyl‐1,3‐pentadiene.
XPS analysis of poly[(3‐hydroxybutyric acid)‐co‐(3‐hydroxyvaleric acid)] film surfaces exposed to an allylamine low‐pressure plasma
Authors: Mas André , Jaaba Hassan , Schué François , Belu Anna M. , Kassis Camille M. , Linton Richard W. , Desimone Joseph M. 
Published: April 2003

AbstractHomogeneous and stable layers were deposited through allylamine plasma polymerization (75 W, 100 Pa, 15 min) onto poly[(3‐hydroxybutyric acid)‐co‐(3‐hydroxyvaleric acid)] (91 : 9 wt.‐%) (P(HB‐co‐9%HV)) film surfaces, XPS analysis using take‐off angles of 20° and 70° and performed 10 days and 20 days after plasma treatment gives information on the composition (in atom%) of the modified surface: C, 62.74; N, 19.60; O, 17.65. The unexpected oxygen percentage is weaker if argon plasma pretreatment (25 W, 40 Pa, 5 min) is applied. Then, a succinct mechanism is proposed. The study of changes in element ratios and binding energy values shows that the majority of incorporated functional groups seem to be amide and imine groups.
New polymer syntheses, 92. Biodegradable, thermotropic copolyesters derived from β‐(4‐hydroxyphenyl)propionic acid
Authors: Kricheldorf Hans R. , Stukenbrock Thomas 
Published: April 2003

AbstractBinary copolyesters were prepared by polycondensation of the trimethylsilylester of acetylated β‐(4‐hydroxyphenyl)propionic acid (HPPA) with acetylated 4‐hydroxybenzoic acid (HBA), vanillic acid (VA), 6‐hydroxy‐2‐naphthoic acid (HNA), 4‐hydroxycinnamic acid (HCA) or 4′‐hydroxybiphenyl‐4‐carboxylic acid (HBCA). Only the binary copolyester derived from 4‐hydroxybenzoic acid proved to be enantiotropic nematic, whereas all other binary copolyesters were more or less crystalline and infusible. Furthermore eight ternary copolyesters were prepared, which all proved to be soluble and thermotropic. 13C NMR spectroscopy proved a random nature of the sequences of the copolyesters, which were only obtained when transesterification catalysts such as Ti(OiPr)4 or MgO were used for the polycondensations. Optical microscopy revealed that five of the eight copolyesters form a homogeneous nematic phase above 220 or 250°C. However, in three cases the nematic melt contained crystalline particles which did not melt below 400°C. According to the WAXS powder patterns and DSC measurements most binary and ternary copolyesters are semicrystalline and form an imperfect orthorhombic crystal lattice. In three cases, the solid phase is best described as a hexagonal columnar mesophase.
A new photoinitiator system based on p‐nitroaniline in the presence of aliphatic tertiary amines
Authors: Costela Angel , García‐Moreno Inmaculada , Dabrio Javier , Sastre Roberto 
Published: April 2003

AbstractSeveral kinetic aspects of the polymerization of dodecyl acrylate photoinitiated with p‐nitroaniline in the presence of an aliphatic tertiary amine, either 2‐(N,N‐diethylamino)ethanol or 2‐(N,N‐dimethylamino)ethyl methacrylate, acting as coinitiator, were studied. Under low absorption conditions, the rate of polymerization was found to be proportional to the square‐root of the incident light intensity, the initiator and the coinitiator concentrations. The polymerization behaviour was analyzed also under aerobic conditions. Under identical irradiation conditions, both initiation and polymerization processes present higher rates and quantum yields than those obtained with conventional aromatic ketone photoinitiators.
ABC triblock polyampholytes containing a neutral hydrophobic block, a polyacid and a polybase
Authors: Giebeler Ellen , Stadler Reimund 
Published: April 2003

AbstractWell defined ABC triblock copolymers of polystyrene‐block‐poly(2‐vinylpyridine)‐block‐poly(tert‐butyl methacrylate) and polystyrene‐block‐poly(4‐vinylpyridine)‐block‐poly(tert‐butyl methacrylate) were synthesized by sequential living anionic polymerization in tetrahydrofuran. Triblock copolymers with narrow molecular weight distribution were obtained. Hydrolysis of the poly(tert‐butyl methacrylate) block yields polystyrene‐block‐polyvinylpyridine‐block‐poly(methacrylic acid) which demonstrates pH‐dependent solution properties. Interpolymer complexation of the polyvinylpyridine and poly(methacrylic acid) blocks in the micellar solution is studied in dependence of the pH in solution by potentiometric, conductometric and turbidimetric titration, and in bulk by FTIR spectroscopy.