bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anionic polymerization of 1,2‐butylene oxide
Authors: Blanchard L. P. , Dinh K. T. , Moinard J. , Tahiani F. 
Published: April 2003

AbstractAnionic polymerizations of 1,2‐butylene oxide were carried out in vacuum‐sealed dilatometers in the range of 30–60°C. Potassium terbutoxide and dimsyl sodium were used as initiators; dimethyl sulfoxide (DMSO) and mixtures of DMSO with tetrahydrofuran were solvents. The polymer products were analyzed by gel permeation chromatography and infrared spectroscopy. The object of the investigation was to obtain information on the mechanism of the reaction and to elucidate some of its kinetic aspects. It has been shown that the polymerizations occur by two different processes, depending on the choice of experimental conditions. One of the processes involves free ions and ion‐pairs, the other, ion‐pairs alone. In the first case, where dimethyl sulfoxide is used as solvent, the order of the reaction with respect to the initiator concentration far exceeds unity (∼1.8), while in the second case, involving mixed solvents, the order of the reaction, for all practical purposes, is one.
Peculiarities of redox polymerization of methacrolein in aqueous media
Authors: Andreeva I. V. , Madorskaya L. Ya. , Sidorovich A. V. , Koton M. M. 
Published: April 2003

AbstractThe effect of the amount of metabisulfite and of the change (spontaneous or deliberate) in the pH of the medium on the viscosity and structure of the polymers is shown. These data as well as evidence on the structure of the polymers formed in the presence of “foreign” aldehydes suggest that in addition to the polymerization proceeding by the radical mechanism, heterolytic processes occur at the carbonyl group. As a result, structures of the semiacetal ester type are formed in the polymer chains of methacrolein.
Catalytic action of metallic salts in autoxidation and polymerization. VIII. Polymerization of methyl methacrylate by various metal acetylacetonate–cyclic ether hydroperoxides
Authors: Osawa Zenjiro , Kawamata Toshio , Naya Motoji , Ogiwara Yoshitaka 
Published: April 2003

AbstractPolymerization of methyl methacrylate by cyclic ether hydroperoxide–metal acetylacetonate systems for a number of different metals was carried out to compare with the tert‐butyl hydroperoxide–metal acetylacetonate initiating systems. The rate of polymerization of methyl methacrylate with cyclic ether hydroperoxides as initiating systems was much higher than that with tert‐butyl hydroperoxide. In cyclic ether hydroperoxide initiating systems, V(III), Co(II,III), Fe(III), Cu(II), and Mn(II) promoted the polymerization rate markedly, and Zn(II), Ni(II), Al(III), and Mg(II) had little or no effect; in the tert‐butyl hydroperoxide initiating system only V(III), Co(II), and Mn(II) enhanced polymerization rate, and most of other metals showed little or no effect. Furthermore, noticeable differences in color of solution and appearance during polymerization, and in relation between conversion and the degree of polymerization were observed. The effect of metal acetylacetonates on hydroperoxide initiators in polymerization of methyl methacrylate was also compared with that on the decomposition of hydroperoxides.
Sulfur compounds as synergistic antioxidants
Authors: Chien J. C. W. , Boss C. R. 
Published: April 2003

AbstractThe decomposition of tert‐butyl, cumyl, and polypropylene hydroperoxides catalyzed by SO2, H2SO4, dilauryl thiodipropionate, metal dithiolenes, and metal dithiocarbamates were studied. The principal reaction pathways leading to different products, which depend on the nature of the hydroperoxide and the sulfur compounds, were discussed. Even though metal dithiolenes are remarkable hydroperoxide decomposers, they are prooxidants for polymers under accelerated aging conditions. This is attributed to the instability of the peroxy radical‐metal dithiolene complex intermediates. Expressions for optimum composition for each component of a synergistic antioxidant system have been derived.
Generalized ring‐opening mechanism in cycloolefin polymerizations
Authors: Dall'Asta Gino , Motroni Giuseppe , Motta Luigi 
Published: April 2003

AbstractRing‐opening polymerizations of cycloolefins under low strain induced by tungsten based Ziegler‐Natta catalysts were previously shown to proceed via metathesis. Now, these investigations have been extended to highly strained four‐membered rings and to molybdenum‐, titanium‐, and ruthenium‐based ring‐opening catalysts. Ozonolysis of 1[14C] cyclobutene‐3‐methylcyclobutene copolymers confirmed the general validity of the metathesis mechanism.
Asymmetric interaction of optically active polymers with asymmetric small molecules. III. The effect of pH on asymmetric interaction of optically active acidic polymer with tryptophan
Authors: Ihara Y. , Koga J. , Kuroki N. 
Published: April 2003

AbstractThe interaction of optically active polymer prepared from L‐lysine and adipyl chloride by interfacial polycondensation with D‐ and L‐tryptophan was studied. It was found that selective interaction occurred, and the amount of L‐isomer bound to the polymer was greater than that of D‐isomer in the range from pH 3.0 to 7.5 at 25°C. At near pH 5.0, the maximum asymmetrical ratio was obtained. The optical rotatory dispersion and viscosity of the polymer were measured. The relationship between conformational differences of the polymer and asymmetric interaction is discussed.
Influence of γ‐irradiation on the transition temperatures of crystalline polytetrafluorethylene
Authors: Kusy R. P. , Turner D. T. 
Published: April 2003

AbstractThe influence of γ‐irradiation on the melting and two solid‐solid transitions, occurring near 19° and 30°C, of polytetrafluorethylene was studied by differential scanning calorimetry. A continuous depression of all three transition temperatures, with increasing dose was observed in a first scan of highly crystalline samples at a heating rate of 20°C/min. Additional information was obtained about the accompanying heats of transition. Values for the number of CF2 units excluded from the crystal lattice per 100 eV energy deposition were calculated by using an equation for the depression of the melting point by chemical impurities. The value obtained of G(–units) = 3.3 ± 0.3 is in agreement with a value of G(chemically damaged units) = 3.0 ± 0.1 previously reported on the basis of scavenging techniques. It is concluded that chemical radiation‐induced damage in this polymer may be estimated by reference to changes in the melting temperature. A value of G(–units) = 1.6 ± 0.2 was obtained by reference to the 19°C transition.
Cationic copolymerization of tetrahydrofuran with propylene oxide. IV. Use of antimony pentachloride as catalyst
Authors: Alvarez E. J. , Hornof V. , Blanchard L. P. 
Published: April 2003

AbstractPropylene oxide and tetrahydrofuran were polymerized cationically by an in situ catalytic system composed of antimony pentachloride and 1,2‐propanediol. The rates of polymerization were measured by vapor‐phase chromatography in the temperature range from −20°C to +20°C. The Arrhenius parameters pertaining to the reaction of each of the comonomers were evaluated and compared with data published earlier for other catalytic systems. The present catalyst system was incapable of initiating a homo‐polymerization of tetrahydrofuran in the absence of propylene oxide, while the latter was readily homopolymerized. In a copolymerization system, the rates of consumption of both monomers were first‐order in respect to the catalyst, but the reaction ceased when all of the propylene oxide had been consumed. The relative reactivity of the two monomers as characterized by the copolymerization parameters r1 (PO) = 1.15 and r2 (THF) = 0.70 suggests that in the copolymerization system, tetrahydrofuran is capable of a reaction with its own active center. This is discussed in terms of a possible mechanism involving the effects of penultimate units and extensive chain transfer. The latter is well evident from the molecular weights of resulting copolyethers, which do not exceed one thousand.
Synthesis and properties of stereoregular 2,3,4‐tri‐o‐acetyl‐[1 → 6]‐α‐D‐gluco‐, ‐manno‐, and ‐galactopyranans
Authors: Lin John Wei‐Ping , Schuerch Conrad 
Published: April 2003

AbstractPolymerization 1,6‐anhydro‐2,3,4‐tri‐O‐benzyl‐β‐D‐mannopyranose at −60°C with phosphorus pentafluoride (0.9 mole‐%) gives stereoregular 2,3,4‐tri‐O‐benzyl‐[1 → 6]‐α‐D‐mannopyranan with substantially higher viscosity ([η] = 2.8 dl/g) than the corresponding gluco‐ and glactopyranan derivatives prepared similarly. Debenzylation with sodium in liquid ammonia produces stereoregular [1 → 6]‐α‐D‐mannopyranan of viscosity up to [η] = 0.54 dl/g. Stereoregular 2,3,4‐tri‐O‐acetyl‐[1 → 6]‐α‐D‐glycopyranans are most simply prepared by acetylation of the corresponding crude [1 → 6]‐α‐D‐glycopyranans obtained directly from the debenzylation reaction. The galactan is extremely difficult to acetylate by conventional methods if isolated in a pure form. Physical and spectral properties of these highly stereoregular synthetic 2,3,4‐tri‐O‐acetyl‐[1 → 6]‐α‐D‐glycopyranans are presented. Optical rotary dispersion curves of 2,3,4, tri‐O‐acetyl‐[1 → 6]‐α‐D‐glycopyranans show small Cotton effects in the 200–230 nm region, superimposed on strong background rotation. Circular dichroism spectra show a single n →* acetate absorption band for each polymer. The sign of the band appears to be determined largely by the C‐2 configuration. Stereoregular 2,3,4‐tri‐O‐acetyl‐[1 → 6]‐α‐D‐glycopyranans in 2,2,2‐trifluoroethanol solution are likely to possess a random rather than helical conformation.
Polymerization of 4‐vinylpyridine with acylating agents
Authors: Moore J. A. , Goldstein J. A. 
Published: April 2003

AbstractThe reaction of 4‐vinylpyridine (4‐VP) with acylating agents in diethyl ether was investigated. Acetyl chloride (AcCl) and trifluoroacetic anhydride [(TFAc)2O] yield colored oligomers with 4‐VP, denoted P‐4VP—AcCl (III) and P‐4VP—(TFAc)2O (IV). Nuclear magnetic resonance spectrometry was used to analyze these products. A structure (XII), representing a random copolymer resulting from 1,2‐polyaddition and 1,6‐polyaddition to 4‐VP, is proposed for III and IV. Alternative mechanisms which explain these observations are discussed. Acetic anhydride (Ac2O) does not acylate 4‐VP. It is proposed that this result is caused by the inability of Ac2O to quaternize 4‐VP as an initial step leading to polymerization.
Cationic copolymerization of tetrahydrofuran with propylene oxide. V. Effect of diol cocatalyst structure and concentration with antimony pentachloride as catalyst
Authors: Alvarez E. J. , Hornof V. , Blanchard L. P. 
Published: April 2003

AbstractThe effects of the chemical nature and the concentration of diol cocatalysts in the copolymerization of propylene oxide (PO) and tetrahydrofuran (THF) catalyzed by antimony pentachloride were studied. The least bulky diol, 1,2‐ethanediol, was found to be the most active species, judging from the highest rate of copolymerization. The variation of rate was much smaller with the other diols used. Furthermore, the position of the hydroxyl groups did not have much effect on the rate. The concentration of cocatalyst strongly influenced the rate of consumption of both monomers. This is explained by the effect of diol concentration on the equilibrium that exists between the catalyst and the cocatalyst on one side, and the active oxonium complex on the other. The mechanism of cocatalytic effects is discussed in terms of newer concepts of ionic polymerization. Specific solvation of ion‐pairs is visualized as partly responsible for the overall effect of the cocatalysts. Water in quantities commeasurable with those of the cocatalyst was found to retard the reaction. It also gave rise to oligomeric products, as evidenced by gel‐permeation chromatography.
Asymmetric polymers. XXVI. Optically active polyamides: (–)poly‐(S)‐4‐tert‐butoxymethyl‐ and 4‐hydroxymethyl‐6‐hexanamide
Authors: Overberger C. G. , Kozlowski John H. 
Published: April 2003

AbstractRacemic and optically active hexahydro‐5‐tert‐butoxymethyl‐2H‐azepin‐2‐one were polymerized, and the resulting poly‐4‐tert‐butoxymethyl‐6‐hexanamides were treated to remove the tert‐butyl protective group. ORD and CD spectra of (–)‐poly‐(S)‐4‐tert‐butoxymethyl‐6‐hexanamide and (–)poly‐(S)‐4‐hydroxymethyl‐6‐hexanamide were compared with spectra of their low molecular weight models, (S)(–)‐6‐acetamido‐4‐tert‐butoxymethyl‐N‐methylhexanamide and (S)( – )‐6‐acetamido‐4‐hydroxymethyl‐N‐methylhexanamide, in 2,2,2‐trifluoroethanol, p‐dioxane–water mixtures, and methanol–water mixtures.
Icosahedral carboranes. XIX. Preparation of linear trifluoropropyl‐substituted polycarboranylenesiloxanes
Authors: Scott Robert N. , Knollmueller Karl O. , Hooks Haywood , Sieckhaus John F. 
Published: April 2003

AbstractA series of linear trifluoropropyl‐substituted polycarboranylenesiloxanes with molecular weights between 3,500 and 13,000 has been prepared by the tetramethylguanidine–sulfuric acid‐catalyzed condensation of various silanol‐terminated monomers as well as by simple hydrolytic condensation of m‐B10H10C2(SiMePfOSiMePfCl)2 and B5H5C2‐(SiMePfCl)2 (where Pf = CH2CH2CF3). The polymers containing the C2B5H7 and C2B10H12 carboranes range from hard glasses to viscous gums and rubbers, are more thermally stable than fluorinated silicones with comparable resistance to solvents, and are potentially useful as high‐temperature fuel tank sealants.
Organoaluminum catalyst for polymerization reaction. Synthesis of isotactic polyacetaldehyde by AIR3–alkali metal hydroxide catalysts in situ
Authors: Aoyagi Takanobu , Araki Takeo , Tani Hisaya 
Published: April 2003

AbstractThe catalytic behavior of binary systems derived from AIR3 and alkali metal hydroxide in a molar ratio of 1 to 0.5 in situ for stereospecific polymerization of acetaldehyde was studied for the purpose of preparation of isotactic polyacetal. The polymer obtained can be readily stretched to a film. The polymerization proceeds slowly (in ∼20 hr). The polymer yield and stereospecificity of the polymerization by AlEt3–LiOH (1:0.5) catalyst were not significantly changed by the nature of solvent or dilution as far as studied. AlEt3–NaOH, AlEt3–KOH, AlEt3–CsOH, AliBu3–LiOH and AlMe3–LiOH in molar ratios of 1 to 0.5 behaved similarly. AlMe3–NaOH, AlMe3–KOH and AliBu3–NaOH also gave isotactic polymer of high stereoregularity but in lower yields.
Copolymerization with depropagation. VIII. A general solution for reversible multicomponent polymerization
Authors: Kang B. K. , O'Driscoll K. F. , Howell J. A. 
Published: April 2003

AbstractA method is described for calculating instantaneous polymer composition for an n‐component system polymerizing under conditions where reversibility of the propagation reaction must be considered. The resulting equations are compared with Monte‐Carlo simulations and were also tested experimentally by using the terpolymerizing system acrylonitrile–methyl methacrylate–α‐methylstyrene over both a wide temperature and concentration range.
Interaction of urea with poly(2‐hydroxyethyl methacrylate) hydrogels
Authors: Ratner Buddy D. , Miller Irving F. 
Published: April 2003

AbstractThe interaction of poly(2‐hydroxyethyl methacrylate) [poly(HEMA)] and other similar hydrogels with dilute urea solution has been studied by a variety of techniques, including swelling experiments, fluorescence quenching, near infrared spectroscopy and fundamental band infrared spectroscopy. The results obtained indicate that the anomalous swelling behavior of poly(HEMA) gels in the presence of such dilute urea solutions is probably not due to the disruption of a secondary hydrophobic bond structure as has been generally believed. Although poly(HEMA) gels do contain sites that can participate in hydrophobic bonding, the evidence gathered indicates that dilute urea solutions have no effect on such bonds. A plausible model that does fit all the data involves the interaction of urea with a secondary structure composed of hydrogen‐bonded hydroxyl groups, stabilized by the exclusion of water molecules from the regions containing the bonds.
Investigation of the mechanism of polymerization of butadiene by π‐allylic nickel complexes
Authors: Bourdauducq P. , Dawans F. 
Published: April 2003

AbstractVarious π‐allylic nickel complexes were synthesized by reacting bis(1,5‐cyclooctadiene)‐nickel with an allylic ester of trifluoroacetic acid. A study of the stereospecific polymerization of 1,3‐butadiene initiated by these catalysts showed the strong influence of the initial substitution in the π‐allylic ligand as well as of the solvent used for synthesis of the catalysts on the course of the reaction, i.e., on both the polymerization rate and the stereospecificity. Moreover, new catalytic species were isolated by adding electron‐accepting or electron‐donating ligands to some of the π‐allylic complexes. In that way, we were able to modify the behavior of the catalysts and, in some cases, to enhance catalytic activity considerably.
Influence of the average content of sulfur in polysulfide polymers on the depolymerization of polysulfide polymers by dithionite ions
Authors: Radosavljević Slobodan D. , Tenc‐Popović Mirjana E. , Rekalić Vladimir J. 
Published: April 2003

AbstractThe results of our studies show that it is possible to depolymerize polysulfide polymers with a nominal sulfur content in excess of 2 per segment of polymer, without previous desulfurization, in order to obtain disulfide polymers. For this purpose it is necessary to take larger amounts of sodium dithionite per segment of polymer, than with a disulfide polymer, to obtain approximately the same of the average molecular weight of the depolymerized product. It is also possible to complete depolymerization with an amount below 2 moles of sodium hydroxide per mole of sodium dithionite, though the upper limit of the ratio of Na2S2O4 to NaOH, at which depolymerization occurs, remains unchanged, i.e., 1:4. During the depolymerization reaction the occurrence of larger or smaller amounts of hydrosulfide, depending on the labile sulfur content, as well as the change of the color of the reaction dispersion, first white, then bright yellow or gray, thereafter white again and, finally, dingy pink, was observed. The reaction, representing in the best way the optimum conditions of depolymerization and the actual relations in the reaction system, is proposed.
Sulfur‐containing polymers. IV. Preparation and properties of poly(sulfenyl thiocarbonates)
Authors: Kobayashi Norio , Fujisawa Tamotsu 
Published: April 2003

AbstractPoly(sulfenyl thiocarbonates) have been prepared for the first time by the stepwise condensation of chlorocarbonylsulfenyl chloride with diols and dithiols. The polymers were obtained in high yield. Generally they were crystalline solids and were soluble in chlorinated hydrocarbons. On treatment with benzyl mercaptan in the presence of triethylamine, the polymers afforded a diol, carbonyl sulfide, and a disulfide compound. This reaction was extended to the preparation of alternating copolydisulfides.
Polymerization of methyl methacrylate by the binary system of the copper–amine complex type resin and carbon tetrachloride
Authors: Koyama Kiyoshi , Nishimura Masato 
Published: April 2003

AbstractThe polymerization of vinyl monomers initiated by binary initiator systems composed of a copper–amine complex type resin and organic halides has been studied. These binary systems initiated the polymerization of various vinyl monomers. A kinetic study of the polymerization of methyl methacrylate initiated by the copper–amine complex resin–CCl4 system was carried out, and it was found that the polymerization proceeds by way of a radical mechanism. This fact was also supported by the copolymerization of methyl methacrylate with styrene. The overall activation energy of the polymerization of methyl methacrylate was estimated as 8.4 kcal/mole. The activity of the initiator systems was greatly dependent upon the dissociation energy of carbon–halogen bonds in the organic halides. A possible initiation mechanism with the binary systems is proposed and discussed.
γ‐radiolysis of acetylated cotton cellulose: An ESR study
Authors: Chidambareswaran P. K. , Sundaram V. , Singh B. B. 
Published: April 2003

AbstractThe nature and behavior of free radicals induced in acetylated cotton celluloses irradiated with γ‐rays have been studied by electron spin resonance (ESR) spectroscopy. Dehydrogenation and deacetylation appear to be responsible for the free radicals observed from samples irradiated at 77°K. The degree of substitution enhanced the yield of acetyl radicals when the samples were irradiated at 77°K and adversely affected the overall radical concentration when irradiation was done at 300°K. In addition, the ESR spectra of samples irradiated under vacuum at 300°K were more intense than those obtained from samples irradiated in air. The nature, yield, and post‐irradiation behavior of the primary radicals are discussed in the light of the ultimate chemical effects observed.
Radiation‐induced polymerization of glass‐forming systems. III. Effect of melting point and glass transition temperature on the formation of the glassy phase
Authors: Kaetsu Isao , Okubo Hiroshi , Ito Akihiko , Hayashi Koichiro 
Published: April 2003

AbstractThe general empirical rules about glass formation of organic compounds including monomers were studied. It was found that the difference of Tm (melting point) and Tg (glass transition temperature) was the most important factor in glass formation, that is, the glass‐forming property of organic systems, mono‐ or multicomponent, could be expressed as a function of Tm and Tm – Tg at the cooling temperature −196°C. The glassforming property was further divided into four classes according to the relation between Tm and Tm – Tg, and each class was related to several patterns in DTA curves. From these results it was clarified that the phases are completely or partially glassified depending on the different values of Tm – Tg in eutectic and noneutectic compositions. The overall phase diagrams covering the whole composition with the variation of Tm and Tg were determined, and they also supported the relationship between Tm – Tg and the glass‐forming property. The distinct glass‐forming property of binary systems with large molecular interaction was attributed to the great lowering of Tm and elevation of Tg in those systems. The effect of the number of components on glass formation was also studied; it was shown that if Tm, Tg, and ΔH (sum of heat of melting and of mixing) are given, the number of components necessary to glassification can be estimated.
Radical reactions initiated by chelate complexes of transition metals. X. Catalytic decomposition of α,α′‐azobisisobutyronitrile
Authors: Horanská V. , Bartoň J. , Maňásek Z. 
Published: April 2003

AbstractThe decomposition of αα′‐azobisisobutyronitrile (AIBN) in the presence of bis(‐)‐ephedrine copper (II) chelate was studied in 1,3,5‐trimethylbenzene. It was found that the chelate accelerated the decomposition of AIBN and at the same time interacted with the free radicals arising in the course of this process. The decomposition of AIBN as well as the decay of paramagnetic Cu+2 particles is a reaction of order 0.3 with respect to the chelate and of order 1.3 and 1.1 with respect to AIBN, respectively. The activation energy of the AIBN decomposition in the presence of chelate is 13–22 kcal/mole for the molar ratio [AIBN]0/[Chelate]0 ranging from 1 to 100. On the basis of the kinetic results and analysis of reaction products the mechanism of the interaction of chelate with AIBN is discussed.