bluuebunny/crossref_metadata_2025_split huggingface dataset:
A study of the mechanism of radiation‐induced polymerization of carbon suboxide
Authors: Barkalov I. M. , Kim I. P. , Mikhailov A. I. , Kiryukhin D. P. 
Published: April 2003

AbstractThe γ radiolysis of solid C3O2 at 77 K produces paramagnetic centers of several types. The ESR spectrum constitutes a number of narrow lines with an anisotropic g factor. Some of the centers are photounstable and are lost after optical bleaching. Heating the sample results initially in the loss of photounstable centers and then, in the temperature region in which solid C3O2 undergoes a phase transition (140 K), loss of the centers responsible for the center section of the ESR spectrum. In the temperature region 140–270 K concentration of the centers remained at the level of 1015−1016 g−1. At higher temperatures an intense polymerization of liquid C3O2 followed by a sharp increase in concentration of the paramagnetic centers was observed. It is assumed that in radiolysis at 77 K and on subsequent heating the formation of oligomeric centers in solid C3O2 results in a decreasing probability of their loss. Using a calorimetric technique, we studied the kinetics of the postradiation polymerization of C3O2. Small additions of acetone (cationic inhibitor) brought about the loss of the oligomeric centers and suppressed completely all postpolymerization. The polymerization rate increased with the concentration of the resulting polymer. An autocatalytic character of the process is supposed to be connected with the formation of polymer‐monomer complexes.
Application of high‐performance size‐exclusion chromatography to the determination of low‐molecular‐weight compounds in polyarylethers
Authors: Brydia L. E. , Garty O. M. 
Published: April 2003

AbstractThe production of high‐molecular‐weight polymers is often accompanied by the formation of oligomers and of side products. Since the presence of these and other low‐molecular‐weight compounds (e.g., monomers and additives) can have a significant effect on the ultimate performance properties of the basic polymer, their quantitative determination is of great importance. This article presents a facile method for separating and quantifying low‐molecular‐weight compounds in polymers. The advent of high‐performance size‐exclusion column‐packing materials extends the application of liquid chromatographic size separations to small molecules. By using two 500‐Å μ‐Styragel columns in series and a chloroform mobile phase, the polymers being studied elute near the solvent front with subsequent resolution of lower‐molecular‐weight components. The described method, which includes the use of an appropriate internal standard, results in determinations that are independent of mobile phase‐polymer interactions. The utility of this analytical technique is exemplified in the determination of cyclic dimers and other low‐molecular‐weight compounds in polysulfones and polyhydroxyethers.
ESCA applied to polymers. XXVI. Investigation of a series of aliphatic, aromatic, and fluorine‐containing polycarbonates
Authors: Clark D. T. , Feast W. J. , Tweedale P. J. , Thomas H. R. 
Published: April 2003

AbstractThe absolute and relative binding energies for the C1s, O1s, and F1score levels have been determined using x‐ray photoelectron spectroscopy (ESCA) for a series of aliphatic, aromatic, and fluorine‐containing polycarbonates. Comparisons of these experimentally determined, core‐level binding energies with theoretical calculations using the ground‐state potential model in the CNDO/2 SCF MO formalism as well as model compounds have been made on the C1sand O1score levels. The degree of polymerization for low‐molecular‐weight fluorine‐containing polycarbonates, as determined from ESCA measurements, is compared to measurements by vapor‐phase osmometry and19F‐NMR.
Polyesters containing ring units in main chains. I. Preparation and stereochemistry of monomers and polyesters
Authors: Matsumoto Naoji , Daimon Hiroshi , Kumanotani Ju 
Published: April 2003

AbstractCycloalkanone (C5–C8, C12, and C15) or cycloalkane (C5 and C6) ring‐containing monomeric diesters and the polyesters derived from them were prepared, and their configurations were studied by 13C‐NMR spectroscopy. Absolute configurations were determined for ring sizes 5, 6, and 7. Configurational change during reduction of a ketonic group of monomeric diesters with ring sizes 5 and 6 was discussed in terms of the steric effect of ring substituents on the ketonic group. In the polycondensation reaction epimerization of the ring units was observed in 5‐, 6‐, and 7‐membered cycloalkanones and not in others, which is explained by steric hindrance by the ring substituents against attack of tetrabutyl titanate catalyst on the ketonic group.
Grafting of polytetrahydrofuran from neoprene W in the presence of perchlorate salts
Authors: Eckstein Y. , Dreyfuss P. 
Published: April 2003

AbstractSilver, mercury, and lead perchlorates can be used to prepare graft copolymers of polytetrahydrofuran from neoprene. Iron and aluminum perchlorates lead to graft copolymers but the conversion is low. The most efficient graft copolymerizations are obtained at high salt‐to‐neoprene ratios, long reaction times, and low monomer‐to‐neoprene concentration ratios. Very surprisingly, high initial monomer‐to‐neoprene concentration ratios lead to low graft copolymerization efficiencies.
Polyelectrolyte effects on the charge transfer complex formation between FMN and indole derivatives
Authors: Ishiwatari Tsutomu , Okubo Tsuneo , Ise Norio 
Published: April 2003

AbstractThe complex formation of flavin mononucleotide (FMN) with tryptamine, indoleacetate, and trytophan was investigated in the presence of polyelectrolytes; that is, sodium polyethylene sulfonate (NaPES), sodium polystyrene sulfonate (NaPSS), and a copolymer of diethyldiallylammonium chloride and sulfur dioxide (DECS). The complexation of FMN and tryptamine was strongly retarded by the macrocations and macroanions, whereas that of FMN and indoleacetate was enhanced by the macrocations. Furthermore, the equilibrium constants of FMN‐tryptophan complex were insensitive to the addition of polyelectrolytes. These results suggest that the complexation of FMN was strongly influenced by the electrostatic interactions between the reactant ions and macroions, in addition to those between the reactant ions, in conformity with the secondary salt effect.
High‐molecular‐weight poly(amino acid)s by the direct polycondensation reaction promoted by triphenyl phosphite and LiCl in the presence of polyvinylpyrrolidone
Authors: Higashi Fukuji , Sano Kenji , Kakinoki Hideo 
Published: April 2003

AbstractPoly(α‐amino acid)s of high molecular weight were obtained by the direct polycondensation reaction of α‐amino acids in the presence of polyvinylpyrrolidone (PVP) as a matrix of triphenyl phosphite and LiCl in N‐methylpyrrolidone (NMP). Molecular weights of the polymer produced were improved by use of an increasing amount of matrix of higher molecular weight. Most favorable results were obtained by the reaction at 80°C for 16 hr at a monomer concentration of 0.33 mole/liter in a NMP solution that contained about 3 wt % LiCl in the presence of an equivalent unit mole of PVP with the molecular weight of 3.6 x 105. The polymer from β‐alanine with high molecular weight, which is difficult to obtain by the NCA method, was easily prepared by this process.
Functional monomers and polymers. LXXI. Conformation and interaction studies of poly‐L‐lysine derivatives with pendant nucleic acid bases
Authors: Ishikawa Tomohiro , Inaki Yoshiaki , Takemoto Kiichi 
Published: April 2003

AbstractCopolymers of L‐lysine and L‐lysine derivatives which contained nucleic acid bases substituted on the Nε position were synthesized by grafting nucleic acid derivatives onto poly‐L‐lysine. The conformation and interaction of these copolymers in solution were studied by using spectroscopic measurements. They existed in helical conformation at neutral pH values, and the polymer complex formation among them was examined by ultraviolet (UV) measurements in organic solvents. A decrease in the nucleic acid base content of the copolymers resulted in a decrease in helical structures and also in interactions with the polymer‐containing complementary bases.
Polymer containing fluorinated ketone groups. I. DSC and NMR studies of poly(p‐vinyltrifluoroacetophenone) and polymers of similar structure
Authors: Cheng C. H. , Pearce E. M. 
Published: April 2003

AbstractThe unexpected crystallinity of free radically polymerized poly(p‐vinyltrifluoroacetophenone) (PVTFA) due to lateral order was previously found in this laboratory. To further the understanding of the relationship between chemical structure and crystalline order in polymers of the PVTFA type, polymers of similar structure were synthesized and characterized by differential scanning calorimetry (DSC). These polymers were poly(p‐vinyldifluoroacetophenone) (PVDFA), poly(p‐vinylphenylheptafluoropropyl ketone) (PVHFK), poly(p‐vinylacetophenone) (PVA), and poly(p‐vinylphenyltrifluoromethyl carbinol) (PVPTC). Only PVTFA had a crystalline melting temperature (188°C); 220‐MHz nuclear magnetic resonance (NMR) measurements on the microstructure of PVTFA and PVDFA revealed broad peaks for the chain protons. The PVTFA was therefore assumed to be predominantly atactic. The results suggested that the unusual crystallinity of PVTFA was related to the unique size and interaction of the trifluoroacetyl moiety on the polymeric side chain.
Polymers containing fluorinated ketone groups. II. NMR studies of the reaction of methylbenzyl trifluoromethyl ketones with alcohols in carbon tetrachloride
Authors: Cheng C. H. , Pearce E. M. 
Published: April 2003

AbstractPrior to the study of poly(o‐ and p‐vinylbenzyl trifluoromethyl ketone) (PVTFK) polymers and their reaction with alcohols, the reactions of some simple model compounds with alcohols were investigated. The reaction of fluorinated ketones toward alcohols was determined by proton nuclear magnetic resonance (NMR) spectroscopy. Two fluorinated ketones–p‐methylbenzyl trifluoromethyl ketone (p‐MTFK) and o‐methylbenzyl trifluoromethyl ketone (o‐MTFK)–were prepared. Studies of the reaction of p‐MTFK and o‐MTFK to various alcohols based on NMR produced equilibrium constants (1M in CCl4) at 31°C that ranged from 0.1 to 6.0. The equilibrium constants for p‐MTFK with alcohols were larger than those for o‐MTFK. In addition, the equilibrium constants for primary alcohols were larger than those for secondary and tertiary alcohols. Steric effects in this reaction could explain the lowered equilibrium constants for o‐MTFK and the secondary and tertiary alcohols.
Radical polymerization of N‐vinylpyrrolidone in the presence of syndiotactic poly(methacrylic acid) templates
Authors: Koetsier D. W. , Tan Y. Y. , Challa G. 
Published: April 2003

AbstractRadical polymerization of N‐vinylpyrrolidone along poly(methacrylic acid) templates of high syndiotatic content was followed dilatometrically in dimethylformamide, which was used as solvent. The effects of template concentration, template molar mass, and temperature on polymerization rate and average molar mass of the formed polyvinylpyrrolidone (PVP) were examined. Template concentrations were varied around the critical concentration for homogeneous segmental distribution, C*. Below this concentration, template coils can act as separate microreactors wherein growing PVP radicals exhibit maximum rate enhancement, i. e., relative rate νR = νR,max. In the free solution, blank polymerization occurs, i. e., νR = 1. Consequently, νR can be approximated by the equation νR = ϕνR,max + (1 − ϕ), where ϕ represents the volume fraction occupied by template coils. The slight increase in UR and PVP molar mass with the template chain length is supposed to be caused by the influence of translational diffusion on the termination step. Over the investigated temperature range of 50–70°C, the activation energy and entropy were almost identical for blank and template polymerization. An expected decrease of ΔE≠ and ΔS≠ in template systems is supposed to be compensated by the effects of desolvation of the template macromolecules during the propagation step.
Electroinitiated graft copolymerization
Authors: Funt B. Lionel , Hsu Li‐Chien 
Published: April 2003

AbstractA technique has been developed for initiating a graft copolymerization electrochemically. A copoly(styrene/vinylbenzophenone) linear copolymer was prepared to serve as the electroactive starting material. The benzophenone sites on this molecule are readily activated at the cathode. Macroradical ions result from the direct transfer of electrons to benzophenone groups of the electroactive backbone polymer. In solution in N,N‐dimethylformamide with tetraethylammonium perchlorate (TEAP) as supporting electrolyte the passage of current produced a dark blue solution similar to that observed with radical anions obtained with benzophenone directly. When monomer such as acrylonitrile or methyl methacrylate was added, a graft copolymer was formed. Electrolysis of solutions of the backbone polymer in tetrahydrofurn (THF), with sodium tetraphenylboride as supporting electrolyte, produced relatively stable, persistent macroradical anions and, under appropriate conditions, the reddish‐violet macrodianions. Both types initiated graft copolymerization of acrylonitrile and methyl methacrylate. Graft copolymers were characterized by gel permeation chromatography (GPC), infrared (IR), and solvent extraction. High grafting efficiency (i. e., free from homopolymer) can be obtained under appropriate conditions. Suitable mechanisms are proposed, compared, and discussed.
Emulsion polymerization of acenaphthylene. I. A study of particle nucleation in water phase and in aqueous emulsions
Authors: Chen Chi‐Yu , Piirma Irja 
Published: April 2003

AbstractAs the first phase in the study of the emulsion polymerization of acenaphthylene (AcN), the oligomerization kinetics of the in‐aqueous‐phase soluble portion of the AcN monomer was investigated. The reactions were carried out in the absence and presence of anionic emulsifiers. The monomer disappearance rate was followed by ultraviolet (UV) spectroscopy and spectra were established for these species. It was found that aqueous phase AcN oligomerized with K2S2O8 initiator at 50°C to yield SOK+ ‐ended oligo ‐AcN species which showed a UV hypsochromic shift in polar solvents. The oligomerization had a second‐order dependence on monomer concentration. The presence of sodium oleate (SO) and sodium dodecyl sulfate (SDS) emulsifiers at below and above their critical micelle concentrations decreased the rate constant of the aqueous phase oligomerization. These observations led to the suggestion of a mixed micellization concept in the particle nucleation mechanism.
Methods for the determination of the number of polytetrahydrofuran branches in neoprene‐g‐polytetrahydrofuran
Authors: Eckstein Y. , Lee D. P. , Quirk R. P. , Dreyfuss P. 
Published: April 2003

AbstractMethods for the determination of the number of the number of polytetrahydrofuran branches in neoprene‐g‐polytetrahydrofuran were examined. Only two suitable methods were found; namely, termination of oxonium ions by triphenylphosphine followed by 31P‐NMR and termination with NH4OHNH4Cl buffer and reaction with fluorescamine followed by fluorescence spectroscopy. Both methods led to the conclusion that Neoprene W has 9 ± 1 active halogens per mole that can be used to initiate tetrahydrofuran polymerization when silver salts are added. Among the methods examined in this study the fluorescence method was the most reliable, most reproducible, fastest, and simplest.
Splitting of the disulfide bonds in polysulfide polymers by hydrazine
Authors: Rekalić Vladimir J. , Tenc‐Popović Mirjana E. , Radosavljević Slobodan D. 
Published: April 2003

AbstractThe action of hydrazine on desulfurized tetrasulfide polymer obtained from bis‐2‐chloroethyl formal leads to SS bond splitting and depolymerization. Our studies show that successful depolymerization can be initiated only in a strong alkali medium at 95–98°C. During this process cleavage of the disulfide bonds and the formation of polymers of lower molecular weight with SH end groups takes place. From the results of the experiments performed it can be seen that the degree of depolymerization increases with an increase in the amount of hydrazine, in the mole ratio of sodium hydroxide, and in the time of reaction. When 0.7–1.0 mole of hydrazine per segment of polymer and 4 mole of sodium hydroxide per mole of hydrazine are used, a polymer of low average molecular weight in the form of water‐soluble sodium salt (fraction I) and a polymer in dispersion form (fraction II) are obtained. Similar results could be attained if the amount ot hydrazine were decreased and the mole ratio of sodium hydroxide were simultaneously increased to more than 4 mole per segment of hydrazine used. In a constant amount of sodium hydroxide with a smaller quantity of hydrazine or a shorter reaction time the amount of water‐soluble polymer (as a sodium salt) decreases and the amount of polymer in dispersion form increases. If a portion of the polymer in dispersion is coagulated with a portion of the polymer in the mother liquid, the yield of the depolymerized product is higher, but the average molecular weight is also higher than those of fraction I. The influence of the average contents of sulfur on the efficiency of the depolymerization is tested in polymers that contain 2.5 (i.e., 3) atoms of sulfur per segment of polymer. The result is that the depolymerization of the polysulfide polymer could be carried out without previous desulfurization, but the molecular weights of the products obtained with an equivalent quantity of hydrazine are much higher than those obtained by depolymerization of the disulfide polymer.
Thermal oxidative stability of poly‐p‐xylylenes
Authors: Nowlin T. E. , Smith Jr. D. Foss , Cieloszyk G. S. 
Published: April 2003

AbstractThe air oxidation of poly‐p‐xylylene films was studied at temperatures between 125 and 200°C. The oxidation kinetics were obtained from neutron activation (NA) oxygen analyses and infrared (IR) Spectroscopy. A correlation between the NA oxygen analyses and mechanical properties indicated that the amount of oxygen incorporated into these polymers before a significant degradation mechanical properties is about 1000 ppm for poly(dichloro‐p‐xylylene) and 5000 ppm for poly(monochloro‐p‐xylylene) or poly‐p‐xylylene. The activation energy for the oxidation of these polymers was about 30 kcal/mole. Long‐term‐use (100,000 hr) temperatures were also estimated for each of the poly‐p‐xylylenes studied. The 100,000‐hr maximum continuous‐use temperature is 112°C for poly(dichloro‐p‐xylylene), 72°C for poly(monochloro‐p‐xylylene), and 57°C for poly‐p‐xylylene.
Model reactions for stereochemistry of Ziegler‐Natta polymerization: Asymmetric hydroisomerization of α‐olefins by chiral titanium tetra‐alkoxides/tri‐isobutyl aluminum catalytic systems
Authors: Carlini Carlo , Chiellini Emo , Solaro Roberto 
Published: April 2003

AbstractHomogeneous catalytic systems based on optically active low‐molecular‐weight and macromolecular titanium alcoholates and tri‐isobutyl aluminum were used in the isomerization and hydrogenation of chiral and prochiral olefins. The reactions performed in a nitrogen and hydrogen atmosphere show a different behavior in regard to reaction rate, composition of reaction mixture, and stereochemical control. The catalyst based on macromolecular titanium alcoholate displays lower activity and a varying influence on the stereochemical pathway with respect to the catalysts based on low‐ molecular‐weight alcoholates. The data obtained in both cases strongly support the absence of a stereocontrol by the growing chain in the stereoelective polymerization of racemic α‐olefins by Ziegler‐Natta catalysts based on optically active precursors. Finally evidence is provided in favor of the intermediate step responsible for asymmetric isomerization which does not occur via η‐allyl complex.
Free radical grafting of monomers to polydienes. III. Kinetics and mechanism of styrene grafting to polyisoprene
Authors: Cameron G. Gordon , Qureshi M. Younus 
Published: April 2003

AbstractThe radical‐induced grafting of styrene onto polyisoprene (PIP) in benzene solution at, 60°C was studied in rubber concentration (up to 0.5 monomer mole liter‐1) in which the polymerization of styrene shows ideal kinetics with no retardation by PIP. The proportion of polystyrene incorporated as graft is independent of the initiator (benzoyl peroxide) concentration and was found to be consistent with the kinetic expression derived by Cameron et al. The graft fraction of polystyrene which is higher than in the corresponding styrene‐polybutadiene system reflects the higher reactivity of PIP toward radicals. Azobisisobutyronitrile produces no graft copolymer in this system.
Interfacial sythesis of polyphosphonate and polyphosphate ester. VII. Temperature effects and reaction loci in polycondensations of hydroquinone with phenylphosphonic dichloride and 4‐methythiophenyl phosphorodichloridate
Authors: Millich F. , Lambing L. L. 
Published: April 2003

AbstractPolyphosphate and polyphosphonate esters of molecular weights > 10,000 were synthesized by base‐promoted, liquid‐vapor and liquid‐liquid interfacial polycondensations of hydroquinone (HQ) with 4‐methylthiophenyl phosphorodichloridate (MTPP) and phenylphosphonic dichloride (PPD). The barium hydroxide‐initiated liquid‐vapor polycondensation of PPD and HQ in the temperature range of 15–95°C shows that [η] increases with reaction temperature and unfractionated yields exhibit a maximum at about 45°C. The analogous liquid‐vapor polycondensation of MTPP and HQ between 25 and 854C also shows a maximum yield at 45°C, whereas [η] decreases with increase in reaction temperature. The results are contrasted with temperature dependencies of base‐catalyzed, liquid‐liquid polycondensation of HQ with MTPP and PPD. A different insight is obtained by analyzing the temperature effects on fractionated products. The relative importance of degradative saponification reactions are ranked as attack on chain ester linkages > phosphorus chloride reactant > end groups of growing chains.
Polyimides derived from bis‐N‐hydroxyimides. II. Synthesis and properties of polyimide‐esters
Authors: Imajo Hidetomo , Kurita Keisuke , Iwakura Yoshio 
Published: April 2003

AbstractPolycondensation of bis‐N‐hydroxyimides, N,N′ dihydroxypyromellitic diimide, and N,N′ ‐dihydroxybenzophenonetetracarboxylic diimide with dicarboxylic acid chlorides was carried out in dimethylacetamide in the presence of triethylamine to produce novel polyimide‐esters. The resulting polymers had inherent viscosities up to 0.27 dl/g. These polyimide‐esters and model compounds exhibited high reactivity toward nucleophiles such as aniline and n‐butylamine, which brought about rapid reductions in the viscosity of the polymers. These polymers were fairly resistant to organic solvents but soluble in m‐cresol. Thermal stability oft he polyimide‐esters was evaluated by thermogravimetry and their good heat‐resistant properties were confirmed.