bluuebunny/crossref_metadata_2025_split huggingface dataset:
13C nuclear magnetic resonance studies on the stereochemical configurations of 2,4‐dimethoxypentane and poly(alkyl vinyl ethers)
Authors: Matsuzaki Kei , Ito Hiroshi , Kawamura Tokiji , Uryu Toshiyuki 
Published: April 2003

Abstract13C nuclear magnetic resonance (CMR) spectra were obtained for 2,4‐dimethoxypentane, which is a model compound of poly(methyl vinyl ether), and the effects of the solvent and temperature on the chemical shifts were investigated. CMR spectra of poly‐(alkyl vinyl ethers) were also determined and analyzed. The diad tacticities were obtained from β‐methylene carbon resonances of poly(methyl vinyl ether), poly(ethyl vinyl ether), and poly(isobutyl vinyl ether), but not from those of poly(isopropyl vinyl ether) and poly(tert‐butyl vinyl ether). The methoxyl carbon resonance of poly(methyl vinyl ether) and the ethoxyl methylene carbon resonance of poly(ethyl vinyl ether) showed splittings corresponding to pentad and triad sequences, respectively. The α‐methine and quaternary carbon resonances of poly(tert‐butyl vinyl ether) showed splittings corresponding to pentad and triad sequences, respectively.
Stereospecific bulk polymerization of methyl methacrylate initiated by its tactic polymers
Authors: Buter R. , Tan Y. Y. , Challa G. 
Published: April 2003

AbstractMethyl methacrylate (MMA) was polymerized by radical initiation at 90°C by its own preformed tactic polymers, i.e., conventional (c‐PMMA), isotactic (i‐PMMA), and syndiotactic (s‐PMMA) PMMA, and also by a preformed 1:1 stereocomplex of i‐PMMA and s‐PMMA. The collected polymers were separated into two fractions by extraction with boiling acetone and characterized by 60 MHz NMR spectra and viscometry. Higher polymerization rates were obtained in the presence of stereo‐regular PMMA than in the presence of c‐PMMA. Moreover, it appeared that i‐PMMA promoted the formation of s‐PMMA, and conversely s‐PMMA the formation of i‐PMMA, especially in the initial stages of the reaction. A higher M̄v of the preformed polymer yielded a higher rate and a higher stereospecificity of the polymerization. No polymerization took place in the absence of performed PMMA. The results support a replica mechanism proposed by Szwarc, in which polymerization is preceded by a specific arrangement of monomeric units along the polymeric chain into a distinctive pattern. Such arrangement coupled with a strong tendency of the isotactic and syndiotactic species to associate may lead to the present stereospecific replica polymerization. This association is demonstrated by rapid gelation during polymerization and by lowering of reduced viscosity in very dilute mixtures of i‐PMMA and s‐PMMA in MMA.
Radical polymerization of methyl methacrylate in the presence of stereoregular poly(methyl methacrylate). II. Syndiotactic PMMA as matrix
Authors: Buter R. , Tan Y. Y. , Challa G. 
Published: April 2003

AbstractMethyl methacrylate (MMA) was polymerized by radical initiation at 25°C in DMF in the presence of preformed syndiotactic PMMA (sMA) with about 90% syndiotactic triads and of different M̄v, viz., sMA‐1, 1.6 × 105; sMA‐2, 3.0 × 105; and sMA‐3, 8.7 × 105. The MMA:sMA ratio was 6:1. The collected polymers were separated into two fractions by extraction with boiling acetone and characterized by 60 MHz NMR. In all cases isotactic PMMA (i‐PMMA) was produced, especially in the initial reaction stages, which associated with the syndiotactic substrate to form acetone‐insoluble 1:2 i/s‐stereocomplexes. The isotacticity decreased with conversion and was highest in the presence of sMA‐3. Characterization of the acetone‐soluble fractions indicated that i,s‐stereoblock polymers were also produced. From these results it is concluded that this reaction can be considered a stereospecific replica polymerization, the driving force being the strong tendency of i‐PMMA and s‐PMMA to associate. With sMA of M̄v below about 1.2 × 105, no i‐PMMA is formed; in other words, no replica polymerization occurs. For polymerizations in the presence of sMA‐2, the critical M̄v of propagating chains, with has to be exceeded before stereoassociation is strong enough to effectuate replica polymerization, has been estimated to be 0.6 × 105.
Radical polymerization of methyl methacrylate in the presence of stereoregular poly(methyl methacrylate). III. Influence of temperature
Authors: Buter R. , Tan Y. Y. , Challa G. 
Published: April 2003

AbstractMethyl methacrylate (MMA) was polymerized by radical initiation at 0, 25, 50, 75 and 100°C in DMF in the presence of preformed isotactic PMMA (iMA) or preformed syndiotactic PMMA (sMA) with different M̄v and also without preformed PMMA (“blank” polymerizations). From the tacticities of the formed polymers it is concluded that blank polymerization does not conform to simple Bernoulli statistics, but follows at least first‐order Markov statistics. The formation of long syndiotactic sequences in the presence of iMA and long isotactic sequences in the presence of sMA denotes still higher‐order Markov statistics. The stereoregulating action is improved by higher M̄v of the preformed polymer (matrix) and lower reaction temperature. These influences can be explained by assuming an equilibrium between polymer growth on the matrix and in the “free” solution. For polymerizations in the presence of iMA or sMA below 300°K, the differences in activation enthalpies (ΔHs/i‡ – ΔHi/s‡) are practically equal to that for the blank polymerization, ca. 900 cal/mole, whereas the differences in activation entropies (ΔSs/i‡ – ΔSi/s‡) differ considerably. (ΔSs/i‡ – ΔSi/s‡) values are highly negative in the presence of iMA and highly positive in the presence of sMA. From these results it is concluded that the isotactic and syndiotactic polymer matrices exert a steric influence on the monomer addition process, thus promoting so‐called stereospecific replica polymerization.
Oxidative coupling as a potential route to polymers of group IV acetylenes
Authors: Parnell D. Ray , Macaione Domenic P. 
Published: April 2003

AbstractBis tert‐butyl‐, trimethylsilyl‐ and trimethylgermyl‐diacetylenes were prepared from the corresponding ethynyl Group IV compounds via oxidative coupling. Bis(trimethylstannyl)diacetylene could not be prepared by oxidative coupling, but was prepared via another technique. Coupling of diethynyldimethylsilane did not lead to the expected polymer, as cleavage of the silicon–ethynyl bond occurred. However, coupling of 1,3‐bis(dimethylethynyl)disiloxane did lead to polymer containing alternating diacetylene and disiloxane units.
Effect of ultrasound on free‐radical polymerization in a continuous stirred tank reactor
Authors: O'Driscoll K. F. , Sridharan A. U. 
Published: April 2003

AbstractMethyl methacrylate has been continuously polymerized in toluene solution with AIBN as an initiator at 60°C in a jacketed steel vessel of 890 ml volume with holding times of several hours. Provision was made for good mixing and introduction of a steady stream of monomer, solvent, and initiator. The effluent stream was analyzed for polymer content and molecular weight distribution by gel‐permeation chromatography. After the reactor had been operating for three holding times, an ultrasonic probe in the reactor was turned on, and the effect of the ultrasound on the steady‐state operation of the reactor was observed. The ultrasound caused a rapid increase in the conversion level. A small, concomitant increase in the degree of polymerization was also noted. It is proposed that the ultrasound breaks polymer chains, giving polymeric free radicals which increase in size while increasing the rate of polymerization. Simulation of the polymerization in the stirred tank reactor has been achieved by using a digital computer, and a quantitative treatment of the effect of ultrasound has been developed.
Free‐radical polymerization of methyl methacrylate in presence of the Cr(C5H7O2)3–Al(i‐C4H9)3 catalyst system
Authors: Deshpande A. B. , Kale S. M. , Kapur S. L. 
Published: April 2003

AbstractPolymerization of methyl methacrylate has been studied with the chromium acetylacetonate–triisobutyl aluminum catalyst system in benzene medium at 40°C. These studies have been carried out at an Al/Cr ratio of 12 to compare the behavior with the previously studied chromium acetyl acetonate–triethyl aluminum catalyst system. The enhanced yield and gelling of polymer suggests a free‐radical mechanism of polymerization. Further, the kinetics of polymerization and the heterotactic structure of polymer as determined by NMR examination have led to confirmation of the freeradical mechanism of polymerization of methyl methacrylate by an excess of triisobutylaluminum in the presence of catalyst complex.
Thermally stable sulfone‐containing poly(amide‐imides)
Authors: Adduci J. M. , Sikka S. K. , Miqueles L. E. , Ramirez R. S. 
Published: April 2003

AbstractNovel sulfone containing poly(amide‐imides) have been prepared by reacting 3,4‐dicarboxy‐4′‐(chloroformyl)‐diphenylsulfone dianhydride with various aromatic diamines. Relatively high molecular weight polymers were obtained by using a two‐step procedure. Transparent poly(amide‐imide) films, varying in color from dark yellow to colorless, were formed by thermally treating polyamic acid solutions. All films showed good thermal stability.
High‐resolution small‐angle x‐ray investigations on poly‐o‐bromostyrene in benzene solutions
Authors: Durchschlag H. , Kratky O. , Olaj O. F. , Breitenbach J. W. 
Published: April 2003

AbstractSmall‐angle x‐ray investigations on poly‐o‐bromostyrene in benzene solution at extremely high resolution (corresponding to a Bragg's value of 3200 Å) proved to be able to link together the ranges covered by small‐angle x‐ray scattering and light scattering. On the other hand, there are problems encountered in molecular weight determination of chain molecules, since both methods at extremely small angles and at finite concentrations reach the limits of particle scattering. The differing results obtained by means of the two methods for the molecular weight of a rather high molecular weight sample of poly‐o‐bromostyrene are ascribed to entangelements stabilized by dipole–dipole interactions. These, due to the differing Bragg's angles and concentration ranges in the two methods, affect the experimental results to a different degree.
Semiconducting polymers based on charge‐transfer complexes. I. Synthesis of electron‐donor‐containing poly‐N‐acylethylnimines
Authors: Litt Morton H. , Summers James W. 
Published: April 2003

AbstractPolymers were made which contained 10‐methyl, 3‐phenothiazinyl, and 4‐(methylthio)phenoxy electron‐donating groups on side chains. N‐Acyl‐substituted poly‐ethylenimines were chosen because the repeat distance along the polymer chain is the same as the repeat distance in most aromatic charge‐transfer complexes (about 6.4 Å) and the side chains do not interfere with each other. This paper describes synthetic routes for preparation of these electron‐donor‐containing polymers. Synthesis of a polyacrylate donor is also described.
Comparison of photo‐ and radiation‐induced radical formation in polyethylene by ESR spectroscopy
Authors: Tsuji Kozo 
Published: April 2003

AbstractThe behaviors of free radicals produced in polyethylene irradiated with ultraviolet light and electron beams were compared in connection with primary processes of radical formation and trapping regions of free radicals. In the case of irradiation with ultraviolet light, an ESR spectrum observed at −196°C immediately after irradiation is an eight‐line spectrum due to alkyl radicals of the type CH2ĊHCH3, while in the case of ionizing radiation, a six‐line spectrum due to CH2ĊHCH2 was observed. The former radicals are produced by the Norrish type I reaction of the carbonyl groups contained in the polymer, followed by radical rearrangement; and the latter are formed by dissociation of hydrogen atom from the excited state of the polymer or ion‐molecular reactions. From the sensitivity to oxygen molecules, it was deduced that free radicals are trapped in amorphous regions after ultraviolet irradiation, but mainly in crystalline regions after irradiation with electron beams. Saturation studies of ESR spectra seem to support this conclusion.
Benzobistriazolophenanthroline polymers
Authors: Evers Robert C. 
Published: April 2003

AbstractThe polycondensation of aromatic dihydrazidines (bisamidrazones) with 1,4,5,8‐naphthalenetetracarboxylic acid or 1,4,5,8‐naphthalenetetracarboxylic dianhydride in polyphosphoric acid led to high yields of soluble benzobistriazolophenanthroline polymers. Inherent viscosities in methanesulfonic acid of 0.25–2.51 dl g were recorded. Prior to polymer synthesis, a series of model compounds were prepared by reactions analogous to the polycondensation reaction. The polymer structure was established by elemental analysis and spectral comparisons of the polymers with model compounds. The thermal properties of the polymers were studied by thermal gravimetric analysis, differential thermal analysis, differential scanning calorimetry, and softening under load. Onset of breakdown in an air atmosphere occurs in the 440–450°C range. No softening under load was observed up to 450°C.
Les anions‐radicaux de l'isoprène et du butadiène intermédiaires de synthèse en chimie organique
Authors: Brossas J. , Pinazzi C. P. , Clouet F. 
Published: April 2003

AbstractWe have synthesized a series of alkadiene and dialcohol homologs of terpenoid natural products by using anion‐radicals of isoprene and butadiene. The reactions of the two monomers were initiated anionically by use of alkali metal–aromatic hydrocarbon complexes. The polymerization was stopped at the dimer stage. This method constitutes a route of synthesis for numerous organic compounds, such as alcohols and hydrocarbons.
Competition between thermal decomposition and hydrolysis of 2,2'‐azobis(2‐amidinopropane) in aqueous solution
Authors: Ito Katsukiyo 
Published: April 2003

AbstractThe thermal decomposition and hydrolysis of 2,2′‐azobis(2‐amidinopropane) were examined as functions of pH. The rate of decomposition decreased with increasing pH. The specific rates at 60°C were 3.85 × 10−5 1/sec at pH 0.90 and 2.5 × 10−5 1 see at pH ≥ 8.5. The hydrolysis in alkaline solution yielded 2,2′‐azobis(2‐carbamylpropane) which was stable to thermal decomposition. The relation between the specific rate of hydrolysis kh′ and the concentration of hydroxyl ion was obtained as kh′ = 4.0 × 10−2 [OH]0.50 1/sec at 60°C. In alkaline solution, the rate of hydrolysis was considerably larger than that of thermal decomposition. A mechanism for this hydrolysis is propesed.
Synthesis of photocrosslinkable polyesters by the Knoevenagel reaction
Authors: Ravve A. , Pasternack G. , Brown K. H. , Radlove S. B. 
Published: April 2003

AbstractA new group of photocrosslinkable polyesters formed by the Knoevenagel reaction is described. The approach permits preparation of photoesensitive polymers, where physical properties can be potentially varied through choice of the polyol and the dicarboxylic acid. The following compounds were prepared and studied: (1) products from a Knoevenagel reaction of poly(trimethylopropane azelate cyanoacetate) with benzaldehyde, furaldehyde, and 2‐ethylbutyraldehyde and (2) products from a Knoevenagel reaction of poly(1,3‐propyl malonate) with benzaldehyde, p‐methoxybenzaldehyde, and 2‐ethylbutyraldehyde. Conventional unsaturated polyesters such as poly(1,3‐propyl fumarate) and poly(1,3‐propyl maleate) were prepared and used for comparison.
Polymerization of 1,2‐butylene oxide initiated by triphenylmethyl salts. I. Kinetics with 1,2‐dichloroethane as solvent
Authors: Hornof V. , Gabra G. , Blanchard L. P. 
Published: April 2003

Abstract1,2‐Butylene oxide was polymerized in 1,2‐dichloroethane in the temperature range −20 to + 10°C. Triphenylmethyl salts of hexafluoroantimonate (Ph3CSbF6), hexafluoroarsenate (Ph3CAsF6), and hexafluorophosphate (Ph3CPF6) were employed as initiators. The reactions are characterized by a fast initiation process accompanied by rapid consumption of monomer. This initial stage is followed by a relatively slower polymerization during which the rate of monomer consumption is first‐order in respect to monomer. Variation of the counteranion produces very little influence on the rate. The difference between the thermodynamic parameters found for the first and second stages of the reaction are explained on the basis of two different polymerization mechanisms. The linear dependence of rate on initiator concentration indicates that propagation takes place by ion‐pairs only within the range investigated here.
Polymérization anionique de l'isoprène par les insertions ternaires graphite–métal alcalin–solvant
Authors: Essel Alain , Pham Quang Tho , Golé Jean 
Published: April 2003

AbstractThe examination by HR–NMR of the microstructure of polyisoprenes synthesized in the presence of alkali metal–graphite compounds reveals that the polymerization has an anionic character. The microstructure of the polymers depends on the nature of the active centers, which depends on the solvent used in the preparation of the graphite compounds or as polymerization medium. With powdered alkali metal–graphite compounds, the propagation does not differ from the anionic one occurring in a homogeneous medium. Except for K–graphite, an enhancement of the 1–4 addition mode is observed if grains of Li or Na–graphite are used in mass polymerization. This change in the microstructure could be explained by the competition between the rate of propagation and the rate of diffusion of the growing chains from the grains to the homogeneous phase of the polymerization medium.
Energy transfer processes involving ultraviolet stabilizers. Quenching of singlet oxygen
Authors: Guillory J. P. , Cook C. F. 
Published: April 2003

AbstractThe role of electronically excited singlet (1Δg) oxygen molecules in the photooxidation of polymers has received increased attention in recent years. Little information regarding the interaction of ultraviolet stabilizers with singlet oxygen is known, however. In this study, singlet oxygen was produced by a microwave discharge in a flow system and rate constants were obtained for quenching by ultraviolet stabilizers. It was found that some nickel chelate stabilizers are effective quenchers of singlet oxygen and their quenching behaviors can be correlated with ultraviolet stabilization effectiveness in thin polypropylene and polyethylene films. The best oxygen quenchers of those examined are nickel chelates with sulfur donor ligands.
Reversible crosslinking in cellulose. VII. Memory effect of the crosslinking medium in the dyeing of crosslinked cotton
Authors: Sakamoto Munenori , Yamada Yoshio , Tonami Hiroaki 
Published: April 2003

AbstractCellulose β‐mercaptoethylaminocarboxylate made from unmercerized cotton was partially oxidized in various solvents of different swelling power followed by treatment with excess methyl iodide to yield partially disulfide‐crosslinked cotton samples of about the same degrees of crosslinking containing sulfonium groups of about the same contents. The effect of the solvent in crosslinking on the equilibrium and kinetics of dyeing with three dyes (Orange II, Direct Scarlet B, and Direct Sky Blue A) of different molecular size was investigated. The 1:1 ionic bonding was observed at equilibrium between sulfonic acid groups in dye molecules and sulfonium groups in modified cottons in cases of Orange II and Direct Scarlet B. The equilibrium uptake of the largest dye, Direct Sky Blue A, was much influenced by the solvent used in crosslinking; the higher the degree of swelling in crosslinking, the larger the equilibrium uptake. The diffusion rate of Direct Scarlet B was much affected by the solvent used; the higher the degree of swelling, the higher the diffusion rate. The pore structure of the crosslinked cotton was discussed. The crosslinked cotton seemed to have a “memory” of the state at the time of crosslinking and to have a tendency to come back close to that state when placed in a dye bath.
Photopolymerization of methyl methacrylate with the use of bromine as photoinitiator
Authors: Ghosh Premamoy , Mitra Partha Sarathi , Banerjee Amar Nath 
Published: April 2003

AbstractLow concentrations of bromine (0.008–0.06M) were used to initiate photopolymerization of MMA in bulk and in diluted (near bulk) systems, the diluents or solvents used being benzene, toluene, dioxane, tetrahydrofuran, carbon tetrachloride, chloroform, methylene chloride, and methanol. Polymerization in bulk follows usual free‐radical kinetics. Inert solvents (benzene, toluene) as well as the other solvents used enhance the rate of polymerization MMA even when used in the range of catalytic concentrations (0.04–0.4M). An initiation mechanism involving solvent molecules appears to be predominant in diluted systems.
Poly α‐ester degradation studies. V. Thermal degradation of polyglycollide
Authors: Cooper D. R. , Sutton G. J. , Tighe B. J. 
Published: April 2003

AbstractThe thermal degradation of polyglycollide [poly(methylene carboxylate)] has been studied over the temperature range 250–400°C by using the combined kinetic and analytical technique previously described. The results obtained from thermogravimetry and product analysis were in many ways similar to those from previous work involving higher poly‐α‐esters. Thus the reaction was predominantly first‐order and the major degradation product was glycollide monomer. This confirms the observations of Carothers and is best interpreted in terms of an intramolecular ester interchange process. Kinetic studies have shown that the first‐order rate constant k is related to temperature T by the expression:

The results from gas evolution analysis showed consistent and marked deviation from first‐order behavior. This is interpreted in terms of the greater sensitivity of this technique to traces of acidic degradation products. Solution viscometry was used to demonstrate the effect of degradation conditions on molecular weight change in both thermogravimetric and gas evolution techniques.
Sulfur‐containing polymers. X. Aromatic poly(sulfenyl thiocarbonates)
Authors: Kobayashi Norio , Osawa Akiko , Fujisawa Tamotsu 
Published: April 2003

AbstractAromatic poly(sulfenyl thiocarbonates) have been synthesized by the interfacial polycondensation of bis(dithiocarbonyl chlorides) with bisphenols. Bisphenols having the hydroxyl groups on separate rings gave polymers in high yields. The inherent viscosities of the polymers ranged from 0.22 to 0.51. In general, they were soluble in chloroform, sym‐tetrachloroethane, hexamethylphosphoramide, m‐cresol, and dimethylformamide and formed transparent tough films on evaporation of chloroform solutions. Almost all of the polymers were amorphous and gave melt‐spun fibers. The polymer films decomposed upon ultraviolet irradiation with liberation of carbonyl sulfide.
Thermomechanical behavior of a polyphenylquinoxaline
Authors: Augl Joseph M. , Booth Hubert J. 
Published: April 2003

AbstractCrosslinking of linear poly[2,2′‐(1,4‐phenylene)‐6,6′‐bis(3‐phenylquinoxaline)] (PPQ) by isothermal heat exposure in the temperature range between 425 and 490°C was investigated by means of torsional braid analysis. The change in glass transition temperature due to isothermal exposure was used as a kinetic parameter. In order to determine the effect of molecular weight and type of polymer chain ends, three PPQ samples were prepared that differed only in molecular weight and polymer chain endgroups. The apparent activation energy of isothermal crosslinking was independent of molecular weight and chain endings. Its value of 60 kcal/mole is the same as that for the thermal degradation of PPQ (determined by isothermal weight loss measurements). The rates of change of Tg at a particular temperature, however, are a function of both molecular weight (at least for these polymers that do not have a sufficiently high molecular weight) and the type of polymer chain ends. It was observed that isothermally crosslinked PPQ gave a higher break point in the TGA curve and also an increased char yield at 800°C than the linear precursor.