bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of chromium residues on the stability of gas‐phase high‐density polyethylene produced by supported catalysts
Authors: Scheirs J. , Bigger S. W. , Billingham N. C. 
Published: April 2003

AbstractThe thermo‐oxidative stability of high‐density polyethylene (HDPE) prepared by silica supported Ziegler‐Natta, bis(triphenylsilyl)chromate and bis(cyclopentadienyl)‐chromium(II) catalyst systems was examined by chemiluminescence (CL) techniques and thermogravimetric (TG) analysis. In particular, the technique of dynamic CL in nitrogen allows the concentration of polymer hydroperoxides and the relative stability of these to be simultaneously determined. Polymer hydroperoxides in Ziegler‐Natta catalyzed HDPE are relatively stable because titanium and aluminum residues are poor pro‐oxidants compared with chromium residues. HDPE produced by bis(cyclopentadienyl)chromium(II) has a low intrinsic thermo‐oxidative stability due to the chromium‐catalyzed conversion of polymer hydroperoxides into degradation products during thermal aging. Concentrations of residual chromium as low as 1 ppm can profoundly affect the oxidative stability of the polymer and exert a much greater influence than either the extent of branching or the degree of unsaturation. The appearance of the silica catalyst support before and after gas‐phase polymerization was studied by scanning electron microscopy. During polymerization the silica support shatters and the resulting submicron fragments are dispersed throughout the polymer particles. On exposure of the nascent polymer to the atmosphere, bis(cyclopentadienyl)chromium(II) is converted to a trivalent chromium species which remains associated with the silica substrate. The presence of trivalent chromium in the poisoned chromium catalyst was confirmed by UV/visible spectrophotometry and the nature of the Cr(III) species was investigated by diffuse reflectance Fourier transform infrared (FTIR) spectroscopy. The high surface area of the catalyst residue renders it a powerful pro‐oxidant despite its low concentration. © 1992 John Wiley & Sons, Inc.
Polymeric isocyanates by nontoxic routes. II. Nucleophilic displacement reaction on chloromethyl pendant groups by alkali cyanates
Authors: Gaonkar S. R. , Srinivasan K. , Kumar G. Sudesh 
Published: April 2003

AbstractThe environmental regulations regarding the solvent emissions have given impetus to the formulation of powder coatings and high solids coatings which require oligomeric or polymeric crosslinkers of desired functionality. We are exploring nontoxic routes for the preparation of polymeric isocyanates and isocyanate precursors. In this article, we report nucleophilic displacement of polymer‐bound alkyl halides by cyanate ion as a novel route to polymeric isocyanate crosslinkers with no intermediacy of either phosgene or low molecular weight isocyanates. The effects of solvent and phase‐transfer catalyst on the selectivity of the reaction are discussed. © 1992 John Wiley & Sons, Inc.
Synthesis of polystyrene‐block‐polyoxyethylene for use as a stabilizer in the emulsion polymerization of styrene
Authors: Jialanella Gary L. , Firer Edward M. , Piirma Irja 
Published: April 2003

AbstractFive well‐defined polystyrene‐block‐polyoxyethylene copolymers were synthesized by anionic polymerization for use as stabilizers in the emulsion polymerization of styrene. The size of the blocks and their relative weight ratios to each other were the main variables. The molecular weights of the blocks varied from M̄n = 1000–7000 for polystyrene, and M̄w = 3000–9000 for polyoxyethylene. The results of the styrene emulsion polymerization with these block copolymers as stabilizers indicate that for efficient anchoring the block length need not be more than 10 monomer units, possibly even less, and that the polyoxyethylene block M̄w = 3000 is just as capable of stabilizing the polystyrene particle as the higher molecular weight blocks. A very important factor was found to be the weight ratio of the two blocks: block copolymers with a polyoxyethylene content between 75 and 90 wt % were effective stabilizers for the emulsion polymerization of styrene © 1992 John Wiley & Sons, Inc.
Charge transfer complexes of polyimines containing trans‐1,2‐bis‐9‐carbazolylcyclobutane
Authors: Yang H. , Jin A. , Natansohn A. 
Published: April 2003

AbstractPolyimines containing trans‐1,2‐bis‐9‐carbazolylcyclobutane (CzD) and a spacer of a variable number of methylene groups (3–10 and 12) were synthesized from the diformylated CzD and the corresponding aliphatic diamine. The charge transfer complexes (CTCs) of these polyimines with electron‐acceptors such as tetracyanoethylene (TCNE) and 2,4,7‐trinitro‐9‐fluorenone (TNF) were analyzed in solution and in the solid state using electronic and CP‐MAS 13C‐NMR spectra. Model studies indicate that TCNE does not form a stable complex in the solid state with CzD, while TNF forms a complex in the molar ratio of 1 : 1. Solid‐state CTCs of the polyimines with either acceptor retain some solvent which helps in formation of some supramolecular organization. After the solvent is eliminated the CTCs are amorphous and do not show decomplexation. Cross‐polarization experiments and T1ρH measurements in the solid‐state NMR spectra demonstrate that the polymer CTCs are very mobile, with a solution‐like behavior. © 1992 John Wiley & Sons, Inc.
Homogeneous catalytic hydrogenation of liquid carboxylated nitrile rubber
Authors: Bhattacharjee Susmita , Bhowmick Anil K. , Avasthi B. N. 
Published: April 2003

AbstractHomogeneous catalytic hydrogenation of olefinic bonds in liquid carboxylated nitrile rubber (L‐XNBR) has been carried out selectively in the presence of nitrile and carboxyl functionality using a six‐membered cyclopalladate complex of 2‐benzoyl pyridine as catalyst. The degree of hydrogenation has been calculated from IR and NMR spectroscopic studies. For example, 68% hydrogenation has been obtained for a sample (containing 0.057 carboxyl equivalent/100 g and 26.1% acrylonitrile) under 2.7 MPa hydrogenation pressure, 0.18 mmol/L catalyst, at 333 K for 1 h in acetone solution. The overall extent of hydrogenation depends on the catalyst‐to‐double‐bond ratio. The kinetics of hydrogenation of L‐XNBR has been investigated. The reaction exhibits a pseudo‐first order dependence on the concentration of the substrate. The rate constant of the reaction is reduced by the increase in carboxyl and nitrile content of the polymer. The effect of temperature on reaction kinetics has also been studied and the activation energy of hydrogenation of L‐XNBR is 20.2 kJ/mol. Intrinsic viscosity of the polymer remains unchanged during the reaction. A significant lowering of the glass transition temperature and improvement of thermal stability have been observed on hydrogenation. © 1992 John Wiley & Sons, Inc.
Radiation‐induced graft polymerization of acrylic acid onto fluorinated polymers. I. Kinetic study on the grafting onto poly(tetrafluoroethylene‐ethylene) copolymer
Authors: Hegazy El‐Sayed A. , Dessouki Ahmed M. , El‐Assy N. B. , El‐Sawy Naeem M. , El‐Ghaffar M. A. Abd 
Published: April 2003

AbstractDirect radiation‐induced grafting of aqueous acrylic acid (AAc) onto poly(tetrafluoroethylene‐ethylene) (ET) film has been studied. The effect of grafting conditions such as monomer concentration, exposure dose, dose rate, and film thickness on the grafting yield was investigated. The dependence of the grafting rate on monomer concentration was found to be 1.2 order. The dependence of the grafting rate on dose rate was found to be 0.6 order regardless of the film thickness. The relationship between the grafting rate and film thickness gave a negative first‐order dependence. The results suggest that the grafting process is mainly controlled by monomer diffusion, and it was concluded that this grafting system proceeded by the front mechanism. The swelling behavior increases linearly with degree of grafting. The electrical conductivity and mechanical properties for the trunk and grafted polymer were investigated at different irradiation doses in air and under vacuum irradiations. © 1992 John Wiley & Sons, Inc.
Preparation of dibenzofuran‐type amorphous polyetherketone by novel etherification reaction
Authors: Fukawa Isaburo , Tanabe Tsuneaki 
Published: April 2003

Abstract4‐Fluorobenzophenone reacted with potassium carbonate in the presence of silica catalyst in diphenyl sulfone solvent to yield 4,4′‐dibenzoyldiphenyl ether. This new etherification reaction was extended to three difluoro aromatic ketones. 4,4′‐Bis(4‐fluorobenzoyl)diphenyl ether (I) reacted with potassium carbonate to yield a crystalline poly(oxy‐1,4‐phenylene‐carbonyl‐1,4‐phenylene) (PEK) and 4,4′‐bis{4‐[4‐(4‐fluorobenzoyl)phenoxy]benzoyl}benzene (II) gave a crystalline poly(oxy‐1,4‐phenylene‐carbonyl‐1,4‐phenylene‐oxy‐1,4‐phenylene‐carbonyl‐1,4‐phenylene‐oxy‐1,4‐phenylene‐carbonyl‐1,4‐phenylene‐carbonyl‐1,4‐phenylene)(PEKEKEKK). 2,8‐Bis(4‐fluorobenzoyl)dibenzofuran (III) or 2,8‐bis(4‐chlorobenzoyl)dibenzofuran (IV) reacted with potassium carbonate to yield a poly(oxy‐1,4‐phenylene‐carbonyl‐2,8‐dibenzofuran‐carbonyl‐1,4‐phenylene) (PEKBK). The PEKBK was a noval amorphous polymer with the glass transition temperature of 222°C and it showed excellent thermal stability [T. Tanabe and I. Fukawa, Jpn. Pat., Kokai 64–74223 (1989)]. Several amorphous dibenzofuran type polyetherketone copolymers were prepared by coplycondensation of III with 4,4′‐difluorobenzophenone (V) or 1,4‐bis(4‐fluorobenzoyl)benzene (VI) [T. Tanabe and I. Fukawa, Jpn. Pat., Kokai 1153722 (1989)]. © 1992 John Wiley & Sons, Inc.
Polymerization of coordinated monomers. XXI. Ab initio molecular orbital study on the binary molecular complex composed of methyl methacrylate and boron trifluoride
Authors: Sato Kota , Sakuma Yoshiro , Iwabuchi Susumu , Hirai Hidefumi 
Published: April 2003

AbstractThe stereo‐ and electronic structures of the binary molecular complex composed of methyl methacrylate and boron trifluoride are obtained by using an ab initio molecular orbital method with an STO‐3G basis set. The total energy change on the binary molecular complex formation is −1.3 X 10−2 Hartree (−8.2 kcal/mol). The electron transfer from methyl methacrylate to boron trifluoride and the change in the energy level of the lowest unoccupied molecular orbital of methyl methacrylate on the complex formation with boron trifluoride are much smaller than those on the complex formation with boron trichloride. A twisted form in which the dihedral angle between the vinyl plane and the ester plane is 16.9° is the most stable structure of the binary molecular complex composed of methyl methacrylate and boron trifluoride. A strong bonding overlap population between a β‐hydrogen of methyl methacrylate and a fluorine of boron trifluoride is found in this conformation. © 1992 John Wiley & Sons, Inc.
Furyl‐maleimidein situ generated ab‐monomers: Synthesis, characterization, and Diels‐Alder polymerization
Authors: Mikroyannidis John A. 
Published: April 2003

Abstract2‐Furoyl chloride reacted with the monomaleamic acids 1a‐1d derived from a aromatic diamine to yield a new series of maleamic acids 2a–2d. The latter were cyclodehydrated to afford maleimides 3a‐3d which behaved as AB‐monomers for a Diels‐Alder polymerization. In addition, the monomaleamic acid 4 derived from 4‐aminophenol reacted with 2‐furoyl chloride to yield maleamic acid 5. It was cyclodehydrated to maleimide 6 which is a novel polymer precursor. The monomers were characterized by IR and 1H‐NMR spectroscopy. Their thermal polymerization was investigated by DTA. Maleamic acids 2a–2d and 5 were cured at 280°C for 22 h to yield polymers which were characterized by TGA and isothermal gravimetric analysis (IGA). They were stable up to 340–376°C and afforded anaerobic char yield of 55–64% at 800°C. © 1992 John Wiley & Sons, Inc.
Ionic conductivity and compatibility studies of blends of poly(methyl methacrylate) and poly(propylene glycol) complexed with LICF3SO3
Authors: Mani R. , Mani T. , Stevens J. R. 
Published: April 2003

AbstractStable to atmospheric moisture, adhesive and transparent polymer electrolytes have been prepared by blending poly(methyl methacrylate) (PMMA) with poly(propylene glycol)‐425/LiCF3SO3 complexes. The blending of the polymers has been achieved by a method developed in our laboratory: free radical polymerization of methylmethacrylate in the polyether/salt matrix. A series of polymer blend complexes varying in PMMA content (up to 20% by weight) and oxygen/metal ratios (25, 16, and 8) have been synthesized and their properties studied. All the samples prepared in this study were found to be optically clear unlike the higher molecular weight poly(propylene glycol)‐2000 (PPG‐2000) system which required a minimum salt concentration to compatibilize a specific amount of PMMA with PPG. The mechanisms by which the salt holds the otherwise incompatible polymers together in a single phase have been investigated by FT‐IR. Our studies show a weak coupling of the ether oxygens in the PPG with the ester groups of the PMMA through the lithium cations. Discrete changes has been observed in the FT‐IR spectrum of PMMA when doped with the lithium salt hitherto unnoticed with other dopants. Gel permeation chromatography results of the PMMA samples isolated from the solid electrolytes indicate the molecular weight to vary between 43000 and 121000 with relatively narrow distributions, 1.6−2.0. The ionic conductivities of the polymer blend electrolytes were fairly high (10−5 S/cm) at room temperature. The PMMA neither significantly influenced the Tg of the blend complexes nor effected the ionic conductivities drastically. The ionic conductivity as a function of temperature followed the empirical Vogel‐Tammann‐Fulcher equation. The blending of PMMA with PPG/LiCF3SO3 complexes was found to impart good adhesiveness to the solid electrolytes while making them stable to atmospheric moisture. © 1992 John Wiley & Sons, Inc.
Characterization of propylene‐ethylene block copolymers using solid state 13C‐NMR spectroscopy
Authors: Prasad J. V. 
Published: April 2003

AbstractCommercial block copolymers of propylene with ethylene (PEBC) are multiphase systems comprising block and random copolymers as well as small amounts of homopolymers. At present, no satisfactory method exists for characterizing the “blocky” structure of these copolymers. This article aims to fulfill this need. Accordingly, the block and random copolymers of propylene with ethylene have been investigated using 13C CP/MAS NMR with high‐power dipolar decoupling. Comparisons have been made between the spectra of block and random copolymers and it is shown possible to distinguish between them by means of an additional signal, appearing at 32.5δ, in block copolymers (attributable to block junctions). © 1992 John Wiley & Sons, Inc.
Polymers containing polynuclear aromatics linked by one‐carbon bridges
Authors: Jones Martin B. , Larson Julie E. 
Published: April 2003

AbstractThe conversion of naphthalene, anthracene, and phenanthrene to polymeric material via Friedel‐Crafts chemistry was investigated. Synthesis of the polymers was accomplished by: (1) self‐condensation of the chloromethylated aromatic substrate in the presence of AlCl3 or SnCl4 or (2) treatment with chloromethyl ethyl ether (CMEE) and SnCl4, producing the chloromethylated substrate in situ, followed by self‐condensation polymerization. Soluble or insoluble polymers were preferentially produced by varying the stoichiometry, time, or temperature of the reaction. The resulting polymers consisted of the polycyclic aromatic nuclei bridged by methylene groups. The regiochemistry of the polymer linkages was determined through the use of IR, 1H‐ and 13C‐NMR. The polymers showed relatively high thermal and thermo‐oxidative stabilities (380–495°C). © 1992 John Wiley & Sons, Inc.
Imide‐aryl ether ketone block copolymers
Authors: Hedrick James L. , Volksen W. , Mohanty Dillip K. 
Published: April 2003

AbstractImide‐aryl ether ketone block copolymers were prepared and their morphology and thermal and mechanical properties investigated. Two aryl ether ketone blocks were incorporated; the first was an amorphous block derived from bisphenol–A and the second block was a semi‐crystalline poly(aryl ether ether ketone) prepared from a soluble and amorphous ketimine precursor. Bis(amino) aryl ether ketone and aryl ether ketimine oligomers were prepared via a nucleophilic aromaic substitution reaction with molecular weights ranging from 6,000 to 12,000 g/mol. The oligomers were co‐reacted with 4,4′‐oxydianiline (ODA) and pyromellitic dianhydride (PMDA) diethyl ester diacyl chloride in N‐methyl–2‐pyrrolidone (NMP) in the presence of N‐methylmorpholine. The copolymer compositions, determined by H‐NMR, of the resulting amic ester based copolymers ranged from 8 to 50 wt % aryl ether ketone or ketimine content. Prior to imide formation, the ketimine moiety of the aryl ether ketimine block was hydrolyzed (p‐toluene sulfonic acid) to the ketone form producing the aryl ether ether ketone block. Compositions of this block were maintained low to retain solubility. Solutions of the copolymers were cast and cured to effect imidization, producing clear films with high moduli (ca. 2200 MPa) and elongations (33–100%). The copolymers displayed good thermal stability with decomposition temperatures in excess of 450°C. Multiphase morphologies were observed irrespective of the co‐block type, block length or composition. © 1992 John Wiley & Sons, Inc.
Synthesis, characterization, and modification of poly(tert‐butyl methacrylate‐b‐alkyl methacrylate‐b‐tert‐butyl methacrylate) by group transfer polymerization
Authors: Choi Weon‐Jung , Kim Yang‐Bae , Kwon Soon‐Ki , Lim Kwon‐Taek , Choi Sam‐Kwon 
Published: April 2003

AbstractDifferent poly(tert‐butyl methacrylate) (PTBMA)‐poly(alkyl methacrylate) (PAMA, alkyl=CH3, n‐C4H9) triblock copolymers were synthesized by group transfer polymerization. They were obtained by first preparing “living” PAMA using a difunctional initiator, followed by polymerization of TBMA in THF at room temperature, in the presence of a nucleophilic catalyst. The segment molecular weights and compositions of TBMA segment could be controlled by regulating the feed ratio of two monomers and the ratio of monomer to initiator. As supported by 1H‐NMR, IR analysis, and titration, the PTBMA blocks could be quantitatively hydrolyzed into poly(methacrylic acid) (PMAA) blocks whereas the PAMA blocks were not hydrolyzed. The water‐soluble amphiphiles prepared by neutralization of the PMAA block displayed surface‐active behavior in water, which was characterized by a critical micelle concentration. The thermogravimetric analysis demonstrated the loss of tert‐butyl groups. © 1992 John Wiley & Sons, Inc.
Studies on diacetylenic vinyl compounds. VI. ESR studies on the polymerization of diacetylene containing acrylate and methacrylates
Authors: Burillo Guillermina , Ogawa Takeshi , Hwang Jimmy S. 
Published: April 2003

AbstractA number of diacetylene containing acrylate and methacrylates have been synthesized and the interaction between their propagating radicals and the diacetylene groups was studied by ESR spectroscopy. In the case of polymerization at 70°C using AIBN as an initiator, the propagating radicals of methacrylates are temporarily trapped with the diacetylenes with rapid exchange of the electron, thus showing strong signals of the propagating radicals. Gamma irradiation of the frozen state produces a blue color in samples, and the ESR signals were found to be those of uninteracted acrylate and methacrylates. From a comparison of spectral widths, there seems to exist an intramolecular interaction between the radicals and the diacetylene group at the frozen state. © 1992 John Wiley & Sons, Inc.
2,4,6‐Tribromophenyl acrylate‐co‐glycidyl methacrylate polymers: Synthesis, characterization, and reactivity ratios
Authors: Narasimhaswamy T. , Sumathi S. C. , Reddy B. S. R. 
Published: April 2003

AbstractCopolymers of 2,4,6‐tribromophenyl acrylate (TBPA) (1) and glycidyl methacrylate (GMA) (2) with different feed ratios are synthesized in toluene using benzoyl peroxide as a freeradical initiator at 70 ± 1°C. The copolymer composition is calculated using 1H‐NMR spectroscopy by comparing the intensity of aromatic and aliphatic protons. The copolymers are characterized with FT‐IR and proton decoupled 13C‐NMR spectroscopic techniques. The reactivity ratios are calculated by Kelen‐Tüdos method and are r1 = 1.08 ± 0.53, r2 = 0.52 ± 0.26. Gel permeation chromatography is used for determining the M̄n, M̄w molecular weights and dispersity index. Thermogravimetric analysis is employed for the determination of thermal stability of homo‐ and copolymers. The glass transition temperatures of the poly(TBPA), poly(GMA), and copoly(TBPA‐GMA) are determined by differential scanning calorimetry. © 1992 John Wiley & Sons, Inc.
The crosslinking of chitosan fibers
Authors: Wei Y. C. , Hudson S. M. , Mayer J. M. , Kaplan D. L. 
Published: April 2003

AbstractA need exists for the development of totally biodegradable packaging materials. Chitosan is an under‐utilized polymer which possesses many of the desired characteristics for this application. This article describes the crosslinking of chitosan fibers. Epichlorohydrin (ECH) was selected as a convenient base catalyzed crosslinking agent. The strength of chitosan fibers, especially wet tenacity, is improved by crosslinking. © 1992 John Wiley & Sons, Inc.
Preparation and properties of polyarylates both from 2,2′‐bibenzoyl chloride and bisphenols and from biphenyl‐2,2′‐diol and aromatic dicarboxylic acid chlorides
Authors: Liou Guey‐Sheng , Kakimoto Masa‐Aki , Imai Yoshio 
Published: April 2003

AbstractPolyarylates having inherent viscosities up to 1.02 dL/g were synthesized both by the phase‐transfer catalyzed two‐phase polycondensation of 2,2′‐bibenzoyl chloride with various bisphenols and by the high‐temperature solution polycondensation of biphenyl‐2,2′‐diol with aromatic dicarboxylic acid chlorides. All the polyarylates were amorphous and soluble in a variety of organic solvents including N,N‐dimethylformamide, N‐methyl–2‐pyrrolidone, chloroform, m‐cresol, and pyridine. Transparent and flexible films of these polymers could be cast from the chloroform solutions. These polyarylates had glass transition temperatures in the range of 120–250°C and began to lose weight at around 380°C in air. © 1992 John Wiley & Sons, Inc.
Synthesis, characterization, and curing of well‐defined allyl ether‐maleate functional ester oligomers: Linear versus nonlinear structures
Authors: Johansson Mats , Trollsås Mikael , Hult Anders 
Published: April 2003

AbstractA series of allyl ether‐maleate functional star‐shaped esters with from one to four arms has been synthesized. The structures that have been made are an analogous series with increasing molecular weight and functionality where the increase in molecular weight has been made nonlinear, i.e., star‐shaped. The resins are monodisperse in the sense that each arm has a well‐defined structure and that, within a certain sample, only one type of molecule exists. The viscosity and rheological behavior of the resins have been studied. The curing kinetics of the star‐shaped (branched) resins and the properties of the films formed have also been studied. These properties have been related to differences in functionality and to differences in the molecular architecture of the resins. © 1992 John Wiley & Sons, Inc.