bluuebunny/crossref_metadata_2025_split huggingface dataset:
High activity Ziegler–Natta catalysts for the preparation of ethylene copolymers
Authors: Nowlin T. E. , Kissin Y. V. , Wagner K. P. 
Published: April 2003

AbstractHigh activity ethylene polymerization catalysts have been prepared by the interaction of ethylmagnesium chloride in tetrahydrofuran with high surface area silica, followed by reaction with excess titanium tetrachloride in heptane. The catalysts were tested in ethylene—hexene copolymerization reactions in the presence of AlEt3 at 80°C. For comparison purposes, the copolymerization properties of a similar catalyst prepared without silica were also evaluated. Preparative conditions were identified which provide catalysts that possess high reactivity towards 1‐hexane. The silica and the amount of magnesium used in catalyst preparation strongly affect the copolymerization properties of the catalysts. Generally, catalysts prepared with silica showed much higher sensitivity to 1‐hexene (effective reactivity ratio r1 = 25–60) while a similar catalyst prepared without silica exhibited an r1 value of 125. Fractionation of the copolymer with a series of boiling solvents showed that all the catalysts exhibit a wide distribution of active centers with respect to reactivity ratios, with the r1 values varying from 5–7 to ca. 200. The width of a the center distribution depends on catalyst composition—it is the narrowest for the catalyst prepared without silica and is the widest for the catalysts with intermediate Ti : Mg ratios.
The kinetics of photoinitiated dead‐end polymerization
Authors: Joshi Makarand G. , Rodriguez Ferdinand 
Published: April 2003

AbstractThe kinetic expressions for a dead‐end polymerization initiated by the photolysis of a sensitizer are derived. The phenomenon of dead ending amplifies the inherent differences between the kinetics of photoinitiated and thermally initiated polymerizations. The analysis clearly shows that photoinitiation has distinct advantages over thermal initiation for improving yields in a polymerization which exhibits dead ending.
Flame retardation of polyurethanes by means of 1,4‐bis[(dialkoxyphosphinyl)hydroxymethyl]benzene
Authors: Mikroyannidis John A. 
Published: April 2003

AbstractNew phosphorus‐containing homopolyurethanes were synthesized by reacting various diisocyanates such as tolylene diisocyanate, methylenebis(4‐phenylisocyanate) and hexamethylene‐1,6‐diisocyanate with 1,4‐bis[(dialkoxyphosphinyl)hydroxymethyl]benzene (BDAB). In addition, copolyurethanes containing approximately 3% phosphorus were prepared by copolymerization of these diisocyanates with an equimolar amount of BDAB—hydroquinone mixture. BDAB was less reactive towards diisocyanates than hydroquinone due to the electron‐withdrawing inductive effect of the phosphinyl groups. The polymers synthesized were characterized by inherent viscosity measurements as well as by proton nuclear magnetic resonance (1H‐NMR) and infrared (IR) spectroscopy. The spectroscopic examination of polymers did not provide evidence for crosslinking by allophanate groups. Differential thermal analysis (DTA) studies of polymers revealed that the incorporation of BDAB in polyurethanes altered their thermal decomposition mode by increasing the exothermicity due to pyrolysis. Thermogravimetric analysis (TGA) of polymers showed that the phosphorus‐containing homopolyurethanes and copolyurethanes were thermally less stable than the corresponding common polyurethanes but afforded higher char yields. Determination of the limiting oxygen index (LOI) values showed that the phosphorus‐containing copolyurethanes exhibited a higher fire resistance than that of common polyurethanes.
Polymerization of methyl methacrylate with ferric laurate in combination with various substituted amines as initiators
Authors: Saha Sanjib Kumar , Chaudhuri Ajit Kumar 
Published: April 2003

AbstractThe effect of various substituted amines on the polymerization of methyl methacrylate initiated by ferric laurate—amine as the initiator system has been studied in carbon tetrachloride medium at 60°C. Amines used are n‐butyl amine, di‐n‐butyl amine. The rate of polymerization is found to follow the order: tertiary > secondary > primary amine. From the detailed kinetic studies it was found that the overall polymerization rate can be expressed by the equation:

The relative activity of the different amines has been found to be dependent on the relative electron‐donating tendency of the substituents present in the amine. The mechanism of the polymerization is discussed on the basis of these results, and various kinetic constants are evaluated.
Preparation of a polymeric membrane crosslinked by the viologen structure from a cyanopyridinium salt polymer
Authors: Kitamura Naoya , Nambu Yoko , Endo Takeshi 
Published: April 2003

AbstractThe polymeric membrane crosslinked by a viologen structure was prepared by the reduction of the homopolymer with a pendant cyanopyridinium structure, poly(1‐vinylbenzyl‐4‐cyanopyridinium perchlorate), chemically or electrochemically. The homopolymer in the state of membrane was reduced chemically by aqueous sodium dithionite (Na2S2O4) to obtain the polymer containing viologen group (64 mol%) despite a heteogeneous reaction. When the membrane was reduced electrochemically, the resulting viologen moiety in the membrane showed reversible one‐ and two‐electron redox behavior.
Die swell–molecular structure model for linear polyethylene
Authors: Koopmans R. J. 
Published: April 2003

AbstractAn empirical relation between capillary die swell and molecular structure, defined by total weight average molecular weight (MwT), molecular weight distribution (MWD), and fraction high molecular weight content (FRB with MwB ≥ 164.000) is established. Via a Box–Behnken experimental design setup blends of Ziegler–Natta catalyzed linear polyethylenes are prepared to allow a statistical analysis of the die swell–molecular structure relation. The contradicting results of Rogers and Mendelson et al. for the die swell–molecular structure relation are shown to be compatible and are to be considered as special cases of the general model presented here. The existence of a die swell maximum is shown. The relative amount (FRB) and size (MwB) of the high molecular weight molecules define this elastic property of linear polyethylene melts.
Photoinduced polymerization and oligomerization of 4‐vinylbenzophenone
Authors: Tsubakiyama Kyoji , Yamamoto Masahide , Nishijima Yasunori 
Published: April 2003

AbstractThe photopolymerizations of 4‐vinylbenzophenone (VBP) in various solvents were investigated to make clear the photoininiation characteristics. It was found that direct photoirradiation produces polymers, oligomers (trimers), and dimers. The dimers were identified as trans‐ and cis‐1,2‐bis(4‐benzoylphenyl)cyclobutanes. The fraction of trans‐form in the cyclobutane dimers produced was about 80%, and was little affected by the reaction conditions. The quantum yields ([VBP] = 0.1M in benzene) was estimated to be 3 × 10−2 for the dimerization and 2 × 10−4 for the initiation of polymerization. The photoreactions via π,π* triplet state of the monomer was suggested from the results.
Direct polyesterification with thionyl chloride in pyridine improved by a modification of monomer sequences in copolymers
Authors: Higashi Fukuji , Sugimori Shigeru , Mashimo Toshio 
Published: April 2003

AbstractThe direct polyesterification with thionyl chloride (SOCl2) in pyridine was further investigated. Copolycondensations of dicarboxylic acids, bisphenols, and hydroxybenzoic acids were significantly affected by the reaction temperatures and combinations of monomers which could change relative rates of alcoholyses of the activated dicarboxylic acids and the hydroxyacids consequently to vary monomer sequences in the copolymers resulted. The sequences were tried to be varied more directly by stepwise reactions of monomers in copolycondensations of dicarboxylic acids, bisphenols, and p‐hydroxybenzoic acid (PHB), as well as PHB and m‐hydroxybenzoic acid (MHB). The reactions proceeded smoothly and satisfactorily when carried out by initial reaction of dicarboxylic acids and PHB followed by bisphenols likely to favor sequential to random distributions of monomers. Reverse addition of PHB and bisphenols, and then dicarboxylic acids resulted in rapid precipitation due to some oligomerization of PHB at an earlier stage of reaction, and largely retarded the reaction. This was also the case for the copolycondensation of PHB and MHB. Copolymers of high inherent viscosities with up to 65 mol % PHB could be obtained by initial reaction of MHB followed by PHB.
Flexible polyaniline
Authors: Kitani Akira , Kaya Masanori , Tsujioka Syo‐Ichi , Sasaki Kazuo 
Published: April 2003

AbstractFlexible polyaniline having excellent mechanical properties (e.g., elongation at break = 41% and tensile strength = 1.8 kg cm−2) was prepared by electrochemical reduction of ordinary polyaniline in organic solvents. The flexibility is directly related with the polymer morphology which was definitely affected by the nature of electrolyte anion. Perchlorate or tetrafluoroborate anion were found suitable to obtain flexible polyaniline. At the same time, it is essential that the polymer so prepared should be reduced (undoped) in some suitable organic solvents before making a flexible free standing film.
A positron annihilation lifetime study of isothermal structural relaxation in bisphenol‐A polycarbonate
Authors: Hill A. J. , Jones P. L. , Lind J. H. , Pearsall G. W. 
Published: April 2003

AbstractPositron annihilation lifetime spectroscopy has been used to study the isothermal relaxation response of compression molded bisphenol‐A polycarbonate at temperatures of 263, 273, and 303 K. The temperature dependence of both the lifetime and intensity of the ortho‐Positronium (o‐Ps) pickoff component is discussed in terms of ductile‐to‐brittle transition behavior and free volume theory. An additive exponential model and the Williams–Watt model were used to analyze the relaxation as a function of temperature and provided results consistent with the anticipated molecular mobility of polycarbonate at sub‐Tg temperatures.
Synthesis and characterization of polyimides containing heterocyclic units
Authors: Subramaniam Prema , Srinivasan Mahalingam 
Published: April 2003

AbstractFive new polyimides containing phenoxaphosphine as well as dibenzothiophene, phenoxathiin, and thianthrene units have been synthesized from 10‐phenylphenoxaphosphine‐2,3,7,8‐tetracarboxylic dianhydride‐10‐oxide and heterocyclic diamines by the cyclopolycondensation method. These polyimides had inherent viscosities in the 0.75–1.10 dL/g range in conc. H2SO4 at 30°C. All the polymers were characterized by elemental analysis, density, solubility, crystallinity, IR spectra, and thermal methods.
High performance size exclusion chromatography of polyamic acid
Authors: Walker C. C. 
Published: April 2003

AbstractMolecular weight studies of polyamic acids are complicated by polyelectrolyte effects. Although early work on the molecular weight determination of polyamic acids employed salts to suppress this polyelectrolyte effect, recent publications reveal that such salts can cause precipitation of polyamic acids from solution, however, a mobile phase consisting of 0.03M LiBr/0.03M H3PO4/1% vol THF in dimethyl formamide was reported to successfully suppress the noted polyelectrolyte effect without causing the precipitation of polyamic acid and give satisfactory size exclusion chromatograms using columns packed with “macro‐porous” glasses. However, the development time was long (ca. 4 h) and considering the lability of the polyamic acids, the results must be viewed with skepticism. We find that use of a similar “mixed” mobile phase with Zorbax® PSM‐Bimodal columns using size exclusion chromatography in the high performance mode (HPSEC) provides well resolved and reproducible chromatograms and molecular weight data with development times of < 15 min. Aside from the avoidance of long development times, which can lead to questionable results, this procedure permits the facile routine analysis of polyamic acid on a daily basis. The procedure has great utility as an analytical tool to support fundamental studies of polyamic acid chemistry and two examples of this application are given.
Plasma polymerization of mixed monomer gases
Authors: Sakata Jiro , Yamamoto Minoru , Tajima Ichiro 
Published: April 2003

AbstractIn this paper, plasma polymerization of mixed monomer gases was studied. In the films, the elements derived from each monomer are contained, and they are distributed homogeneously at a certain depth. The films are made up by the copolymers in which both monomers are combined. The chemical compositions of the copolymers can be controlled by changing the proportions of the two monomer gases. The films having gradual compositional change toward depth can be prepared by using a mixture of two monomer gases and changing their proportions during the plasma polymerization. These copolymeric and gradient copolymeric films were formed on porous glass hollow fibers, and gas permeability of these composite membranes was measured. The gradient copolymerization methods are available for the preparation of the membranes for gas separation.
Application of NIRA techniques for the determination of polymer end and functional groups
Authors: Roy R. B. , Kradjel C. 
Published: April 2003

AbstractNear infrared reflectance analysis (NIRA) provides a quick and reliable method for the measurement of end and functional groups in polymers and polymeric products. Feasible applications of Technicon InfraAlyzer for the simultaneous determination of OH and COOH numbers from polyester resins, and percent nitrogen estimation in crosslinkable acrylamido derivatives of partially esterified cellulosic materials were studied. The analytical results obtained show that NIRA techniques provide accurate and precise measurement of functional and end groups from the polymer samples used for this study. In addition, the statistical data showed that the number of samples used in learning sets were adequate for the generation of reliable calibration equations.
Superactive and stereospecific catalysts. I. Structures and productivity
Authors: Hu Youliang , Chien James C. W. 
Published: April 2003

AbstractTwo series of catalysts were made, one from MgCl2–A solution containing MgCl2, EH (2‐ethylhexanol), and EB (ethyl benzoate) dissolved in decane and another from MgCl2–B solution containing MgCl2, EH, and phthalic anhydride which reacted to form the corresponding phthalic ester. Reactions of these solutions with TiCl4 with or without another ester produced a family of eight catalysts. They form two groups, one having monoesters as modifiers, and the other containing diesters as modifiers. The surface area, pore volume, x‐diffractions, polymerization activity, and catalytic stereospecificity of these catalysts have been compared. The diester catalysts differ from the monoester catalysts in every respect. By comparison the corresponding member of the diester catalysts have half as much Ti per Mg, more than 10 times the pore volume, more than a 100‐fold the surface area, about 50% more productivity, and greatly increased steroespecificity.
Synthesis and characterization of liquid crystalline copolymethacrylates, copolyacrylates, and copolysiloxanes containing 4‐methoxy‐4′‐hydroxy‐α‐methylstilbene and 4‐hydroxy‐4′‐methoxy‐α‐methylstilbene constitutional isomers as side‐groups
Authors: Percec Virgil , Hsu Chain Shu , Tomazos Dimitris 
Published: April 2003

AbstractThe synthesis of methacrylates and acrylates containing 4‐methoxy‐4′‐hydroxy‐α‐methylstilbene and 4‐hydroxy‐4′‐methoxy‐α‐methylstilbene constitutional isomers attached to the polymerizable group through flexible spacers containing 11, 8, 6, 3, and respectively 2 methylenic units is described. The radical copolymerization of a 1/2 or 2/1 mole ratio of the two constitutional isomeric monomers led to thermotropic side‐chain liquid crystalline polymers in all cases. The synthesis of copolysiloxanes based on the same constitutional isomeric mesogens as side groups, and flexible spacers containing 11, 8, 6, 5, and respectively 3 methylenic units is also described. All polymers were characterized by differential scanning calorimetry and optical polarization microscopy. The polymers containing 11 methylenic units in the spacer exhibit Sc mesomorphism, while the other polymers are nematic. Copolymethacrylates do not undergo side‐chain crystallization. Only the copolyacrylate containing 11 methylenic units in the spacer exhibits side‐chain crystallization. All the copolysiloxanes display side‐chain crystallization. The number of melting transitions seen for these polymers decreases with increasing spacer length. Copolysiloxanes containing dissimilar spacer length were also prepared. Only the copolymer synthesized with highly dissimilar spacer lengths, i.e., containing 3 and 11 methylenic units, does not undergo side‐chain crystallization. These results have demonstrated that while the type of mesophase is dictated only by the spacer length, the degree of decoupling of the motion of the side‐groups from the motion of the main chain is strongly dependent on the nature of the polymer backbone. For the same mesogenic unit and spacer length, the thermal stability of the mesophase is also dictated by the nature of the polymer backbone. The use of constitutional isomers of mesogenic units as side groups in liquid crystalline polymers provides at least qualitative information on the degree of decoupling of the side groups from the polymer main chain.
Investigation of the formation of poly(ethylene terephthalate) with model molecules: Kinetics and mechanism of the catalytic esterification and alcoholysis reactions. I. Carboxylic acid catalysis (monofunctional reactants)
Authors: Otton Jean , Ratton Serge 
Published: April 2003

AbstractMonofunctional compounds (benzoic acid, heptyl alcohol, and 2‐butoxy‐ethanol) were used to investigate the kinetics of the esterification and the alcoholysis reactions. Carboxylic acids (benzoic acid) are the only catalysts present in the reaction medium. The factors which influence the kinetics of the esterification reaction were studied: the nature of the carboxylic acid (substituents on the benzene ring), the nature of the alcohol, the composition of the reaction medium (alcohol alone or with another solvent, ester, or water). The results point out for an acyl type (AAC2) mechanism. The alcoholysis reaction needs the presence of carboxylic acid as a catalyst to occur significantly. A similar mechanism is proposed for both reactions: nucleophilic attack by the oxygen atom of the alcohol at the ion pair formed by protonation of the acid (esterification reaction) or by protonation of the ester (alcoholysis).
New telechelic polymers and sequential copolymers by polyfunctional initiator‐transfer agents (inifers). LIII. Lithiation of 2,4,4‐trimethyl‐1‐pentene and isopropylidene‐capped polyisobutylenes by butyllithiums in the presence of complexing agents
Authors: Peng K. L. , Kennedy J. P. , Wilczek L. 
Published: April 2003

AbstractLithiated isopropylidene‐telechelic polyisobutylenes (i.e., PIBs capped with

end groups) are most interesting novel intermediates for further transformations, e.g., functionalization, polymerization. This report concerns model lithiation experiments of 2,4,4‐trimethyl‐1‐pentene (TM1P) that guided us toward the subsequent quantitative lithiation of isopropylidene‐telechelic PIBs. Thus, lithiation of TM1P with, n‐, s‐, and t‐butyllithium, in the presence of various complexing agents (i.e., TMEDA, t‐BuOK, 1,2‐DPE, CH3OCH2CH2OCH3, THF, and 12‐crown‐4) followed by silylation with Me3SiCl (for the purpose of quantitation) gave three products: 2(trimethylsilylmethyl)‐4,4‐dimethyl‐1‐pentene (TM1P‐Si), 2(trimethylsilylmethyl)‐4,4‐dimethyl‐2‐pentene (TM2P‐Si2). The relative product composition strongly depends on the BuLi/complexing agent ratio and temperature. Among the different butyllithiums and complexing agents the best overall results were obtained with the s‐BuLi/TMEDA combination. Complete lithiation of TM1P with minimum dilithiation was obtained using the molar ratio [s‐BuLi]: [TMEDA]: [TM1P] = 2 : 2 : 1. The apparent activation energy of lithiation by s‐BuLi/TMEDA was found to be 6.7 ± 0.8 kcal/mol. Guided by TM1P model experiments, quantitative monolithiation of isopropylidene‐capped polyisobutylene (including ca. 4% chain and isomerization) was achieved using the molar ratio [s‐BuLi] : [TMEDA] : [CC] = 5 : 4 : 1.
Grafting of maleic anhydride to n‐eicosane
Authors: Russell K. E. , Kelusky E. C. 
Published: April 2003

AbstractMaleic anhydride was grafted to the linear hydrocarbon, n‐eicosane, at 165°C in the presence of the free radical initiator, 2,5‐dimethyl‐2,5‐di(t‐butylperoxy)‐3‐hexyne. The anhydride has a low solubility in eicosane and a multiple addition procedure was adopted. Grafted product which separated from the reaction mixture was fractionated and analyzed. The fractions contained on average 2–5.5 anhydride units/eicosane residue. 1H‐ and 13C‐NMR studies show that the grafts consist of single succinic anhydride rings. At the concentrations of maleic anhydride chosen for homogeneous reaction ( < 0.02 M) and at 165°C, poly(maleic anhydride) is above its ceiling temperature, so that succinic anhydride radicals cannot add maleic anhydride to form polymer side chains. Instead, these radicals abstract hydrogen atoms to yield grafts consisting of single anhydride units.
Linear A–B and AA–BB polyamides with backbone aryl, alkyl, and alkenyl units
Authors: Ahmed Sharf U. , Livant Peter D. , Sikes Allison M. , Mathias Lon J. 
Published: April 2003

AbstractHigh performance linear AA–BB and A–B polyamides were generated using polymerization schemes that gave polymers in higher yields and having better performance than previous methods. Polymers were characterized with FTIR, solution and solid‐state 13C‐NMR and showed the incorporation of aryl, alkyl, and alkenyl linkages in the polymer backbone. Thermal analysis showed that a significant weight percent of the polymers remained at 1000°C.
Thermal degradation of aliphatic polyamides studied by field ionization and field desorption mass spectrometry
Authors: Schulten Hans‐Rolf , Plage Bernd 
Published: April 2003

AbstractThe aliphatic polyamides nylon 6.6, 6.9, 6.10, 6.12, 12.6, 12.10, and 12.12 of the diamine dicarboxylic acid‐type were pyrolyzed in the ion source of a double‐focusing mass spectrometer and the thermal degradation products were recorded by field ionization (FI) and field desorption (FD) mass spectrometry (MS). In the FI mode, several series of thermal degradation products differing in the number of polymer repeating units were detected up to 1000 Daltons. The main products were oligomers and, in addition, protonated dinitriles and various protonated nitriles are formed in large amounts except for nylon 6.6 and nylon 12.6. These two polymers form, in contrast to all other samples, large amounts of protonated amides and diamines. The technique employed allows distinction between oligomers already present in the original polymer and oligomers formed by thermal fission of bonds in the polymer chain. Reaction mechanisms are given that explain the products observed. High resolution experiments and accurate mass measurements were performed to confirm the proposed structures. In the FD mode, cationized oligomers (attached mostly to a sodium cation) were observed below 200°C with the dimers being the base peak for most samples. In contrast to the FI results, the monomers were only detected at very low intensities. Similarly, only weak signals for additional thermal degradation products were registered except for nylon 12.6. At higher temperatures the FD mass spectra gave protonated and doubly protonated oligomers in the high mass range up to 2000 Daltons, which resulted in complementary structural information about the polymers.