bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanism of inhibitory action of metal bis(dialkylethylene)dithiolates. II. Interaction of Ni‐bis(diphenylethylene)dithiolate with hydroperoxides
Authors: Ivanov S. K. , Kateva J. 
Published: April 2003

AbstractDuring the oxidation of tetraline or cumene, initiated with α,α′‐azobisisobutyronitrile (AIBN) in the presence of Ni‐bis(diphenylethylene)dithiolate (NiDT), induction periods can be observed, proving the interaction between tetralylperoxy and cumylperoxy radicals on the one hand and the metal helate on the other. During the initiation of the oxidation process of tetraline by tetralylhy‐droperoxide and of cumene by cumylhydroperoxide in the presence of NiDT, prooxidation effects in the beginning of the oxidation are observed. The measured stoichiometric coefficients of inhibition (ƒ) depend on the concentration of NiDT. During the absorption of oxygen, an effect of oscillation is observed. The decomposition of tetralylhydroperoxide under the influence of NiDT runs with consumption of the scavenger of free radicals, N‐phenyl‐β‐naphtylamine (PNA), moving the homolytical character of the reaction. A mechanism of the decomposition of hydroperoxides in the initial stage in the presence of NiDT is proposed.
γ‐radiation‐induced crosslinking of polystyrene
Authors: Shimizu Yuichi , Mitsui Hiroshi 
Published: April 2003

AbstractThe γ‐radiation‐induced crosslinking of polystyrene was studied at 30–100°C in vacuo with a dose rate of 6.35 × 105 rad/hr. The amount of hydrogen formation increased with increasing irradiation time, and the rate of the formation decreased with the time. The results were well described by the zero‐order formation kinetics with respect to the hydrogen concentration combined with the first‐order disappearance. The apparent rate constant for the formation of hydrogen increased somewhat with rising irradiation temperature, and the one for the disappearance was little affected by the temperature. The gel fraction increased with the time by the irradiation beyond the critical time for incipient gel formation, and the rate of gel formation decreased with the time. The gel formation was retarded by rising irradiation temperature, and only a little gel fraction was observed at 100°C. The G values for the crosslinking and main‐chain scission were obtained from the gel data by using the Charlesby–Pinner equation. On the basis of these results, the mechanism of the γ‐radiation‐induced crosslinking of polystyrene was discussed.
Heat‐resistant polymers containing thianthrene analogs units. I. Polyimides
Authors: Niume K. , Nakamichi K. , Takatuka R. , Toda F. , Uno K. , Iwakura Y. 
Published: April 2003

AbstractPolyimides that contained thianthrene and dibenzo‐p‐dioxins units were synthesized. The tricyclic fused rings were successfully incorporated by polymerizing the diamines of the units with aromatic tetracarboxylic dianhydrides. The resulting polyamic acids were converted to polyimides by thermal cyclodehydration. The influence of the tricyclic units on the properties of the polyimides has been investigated. Polyimides that contained dibenzo‐p‐dioxins (ODP) exhibited sufficient thermal stability but were insoluble even in concentrated sulfuric acid. The introduction of a methyl group did not produce an appreciable increase in solubility. Thianthrene polyimides were considerably less stable than the equivalent polymers derived from open‐chain diamine, 4,4′‐diaminodiphenyl sulfide but were partly soluble in acid solvents. The results are discussed in terms of packing the polymer molecules.
Kinetics and mechanism of the cationic polymerization of tetrahydrofuran in solution. THF–CH2Cl2 and THF–CH2Cl2/CH3NO2 systems
Authors: Matyjaszewski Krzysztof , Słomkowski Stanisław , Penczek Stanisław 
Published: April 2003

AbstractCationic polymerization of tetrahydrofuran (THF) in CH2Cl2 solvent and in mixed CH2Cl2/CH3NO2 solvent was initiated with 1,3‐dioxolan‐2‐ylium cations with AsF and SbF anions. Dissociation constants of the polytetrahydrofuranium ion pairs into ions were measured (e.g., KD = 1.5 × 10−5M at 25°C and [THF]0 = 7.0M; CH2Cl2 solvent) and were found to be more than 100 times lower than in CH3NO2 solvent at the same [THF]0 and temperature. The rate constants k and k, measured for degrees of dissociation ranging from 0.03 to 0.35 in CH2Cl2, were the same within an experimental error of measurements (±15% of the value of kp). Dependence of k( = k = k) on the dielectric constant was a monotonous function in three different solvents, namely, CCl4, CH2Cl2, and CH3NO2, which covered a large range of dielectric constants of the medium (from D = 5 to D = 22) and degrees of dissociation of the macroion pairs, α (from 0.03 to more than 0.70). Thus a decrease in the dielectric constant increases the rate constant k in the whole range of studied polarities of the medium. This result confirms an earlier conclusion that the rate constant of propagation does not depend on the state of aggregation of ions and k = k.
Linear polythioesters. II. Products of interfacial polycondensation of 1,4‐di(mercaptomethyl)‐naphthalene, 1,5‐di(mercaptomethyl)naphthalene, and a mixture of 1,4‐ and 1,5‐di(mercaptomethyl)‐naphthalene with terephthaloyl and isophthaloyl chlorides
Authors: Podkoscielny Wawrzyniec , Charmas Władysław 
Published: April 2003

AbstractNew polythioesters of naphthalene derivatives produced by interfacial polycondensation of 1,4‐di(mercaptomethyl)naphthalene and 1,5‐di(mercaptomethyl)naphthalene and their mixture with isophthaloyl and terephthaloyl chlorides were obtained. To define the optimal conditions of interfacial polycondensation the following factors that influence the process were studied: the ratio of the aqueous phase to the organic (water–benzene), the concentration of the hydrochloride acceptor, the contribution of emulsifier and catalyst, and the temperature of the reaction. Yield for all reaction products and the reduced viscosity of phenol–tetrachloroethane soluble in the mixture were found. The structure of polythioesters with high‐value reduced viscosity and good yield was determined by elementary analysis, infrared (IR) spectra, and x‐ray analysis; the glassy temperature, initial decomposition, and maximum velocity of decomposition were obtained by thermogravimetric analysis (TGA); and the thermal, mechanical, and electrical properties of the polythioesters were determined. Their molecular weight was not measured because of their low solubility. The good yields, short process time, and good chemical and thermal properties of the polymers showed that the interfacial polycondensation method could be effective in obtaining polythioesters by using aliphatic–aromatic dimercaptans of naphthalene with terephthaloyl and isophthaloyl chlorides.
Synthesis of polyimides from 2,5‐di(carboxymethyl)terephthalic dianhydride and diamines
Authors: Ueda Mitsuru , Takahashi Masayoshi , Hishiki Shohei , Imai Yoshio 
Published: April 2003

AbstractA new six‐membered tetracarboxylic dianhydride, 2,5‐di(carboxymethyl)terephthalic dianhydride, was synthesized in six steps, starting with pyromellitic dianhydride. The polyimides were prepared from dianhydride and diamines in a two‐step procedure. The polyamic acids, which were formed in the first step by the ring‐opening polyaddition in DMAc, had inherent viscosities of 0.1–0.7 and were converted to the polyimides by thermal cyclodehydration. These polyimides were insoluble in organic solvents. Thermogravimetric analysis (TGA) in air and nitrogen atmospheres revealed that rapid decomposition began above 400°C for aromatic polyimides.
Rate of spontaneous deactivation of styryl and α‐methylstyryl carbanions
Authors: Okamoto Akio , Watanabe Eiichi , Mita Itaru 
Published: April 2003

AbstractThe deactivation of α‐methylstyryl and styryl carbanions followed by spectral change and titration was studied kinetically. First‐order rate constants were obtained for the deactivation of oligo‐α‐methylstyryl lithium, disodium, and dipotassium in tetrahydrofuran and of polystyryl potassium in varying degrees of polymerization in benzene that contained a small amount of tetrahydrofuran and n‐hexane. It was observed that the addition of cryptate [222] exerts a significant effect on the system of oligo‐α‐methylstyryl disodium in tetrahydrofuran. The effect of dilution, degree of polymerization of the polymer, and counterions on the rate of deactivation of carbanions was discussed.
Monolayer properties of mixtures of poly(n‐stearyl methacrylate), poly(n‐lauryl methacrylate), and their corresponding copolymers
Authors: Yoshikawa Satoshi , Ueno Minoru , Meguro Kenjiro 
Published: April 2003

AbstractThe monolayer properties of poly(n‐stearyl methacrylate), poly(n‐lauryl methacrylate), and their mixtures at various ratios of the two polymers have been studied from the measurements of their surface pressure–area isotherms at air–water interface. The monolayer properties of their mixtures have been compared with those of their corresponding copolymers. The results show that the isotherms of the mixed monolayers have two break points at higher pressures than that of poly(n‐lauryl methacrylate). This suggests that the mixtures may form more stable films that consist of separate phases of the two homopolymers, although each phase may contain a small amount of the other. The isotherms of the copolymer monolayers indicate a phase transition from liquid condensed to solid film between 50 segment mole % and 70% poly(n‐stearyl methacrylate). The monclayer of these copolymers has properties that differ from those of the corresponding mixtures of two pure homopolymers and is more compatible than the mixtures of pure homopolymers.
Coenzyme models. 15. A polymeric model system for the NADH‐dependent dehydrogenase enzymes
Authors: Shinkai Seiji , Tanake Kenji , Ide Toyoko , Manabe Osamu 
Published: April 2003

AbstractCopolymers of 4‐vinylpyridine (4‐VP) and N‐(p‐vinylbenzyl)‐1,4‐dihydronicotinamide (VNicH) were synthesized, and a carbonyl substrate (benzil) was reduced to alcohol in an aqueous ethanol solution in the absence and presence of metal ions (Zn2+ and Ni2+) as part of a model study of NADH‐dependent enzymes. The reduction rates by VNicH in polymers were four to seven times greater than that of the corresponding monomeric analog (N‐benzyl‐1,4‐dihydronicotinamide). Added metal ions catalyzed the reduction by VNicH‐29 (VNicH content, 29 mole%) but inhibited the reduction by VNicH‐9 (VNicH content, 9 mole%). It was suggested that metal catalysis occurs only when metal ions are bound closely near the dihydronicotinamide moiety.
Diffusion‐controlled reaction. V. Effect of concentration‐dependent diffusion coefficient on reaction rate in graft polymerization
Authors: Imre Kaya , Odian George 
Published: April 2003

AbstractThe effect of diffusion on radiation‐initiated graft polymerization has been studied with emphasis on the single‐ and two‐penetrant cases. When the physical properties of the penetrants are similar, the two‐penetrant problem can be reduced to the single‐penetrant problem by redefining the characteristic parameters of the system. The diffusion‐free graft polymerization rate is assumed to be proportional to the v power of the monomer concentration C, in which the proportionality constant a = kpR/k, where kp and kt are the propagation and termination rate constants, respectively, and Ri is the initiation rate. The values of v, w, and z depend on the particular reaction system. The results of our earlier work were generalized by allowing a non‐Fickian diffusion rate, obtained from an extension of the Fujita free‐volume theory, which predicts an essentially exponential dependence on the monomer concentration of the diffusion coefficient, D = D0 [exp(δC/M)], where M is the saturation concentration. It was shown that a reaction system is characterized by the three dimensionless parameters v, δ, and A = (L/2)[aM(v−1)/D0]1/2, where L is the polymer film thickness. Graft polymerization tends to become diffusion controlled as A increases. Larger values of δ and v cause a reaction system to behave closer to the diffusion‐free regime. The transition from diffusion‐free to diffusion‐controlled reaction involves changes in the dependence of the reaction rate on film thickness, initiation rate, and monomer concentration. Although the diffusion‐free rate is w order in initiation rate, v order in monomer, and independent of film thickness, the diffusion‐controlled rate is w/2 order in initiator rate and inverse first‐order in film thickness. The dependence of the diffusion‐controlled rate on monomer is dependent in a complex manner on the diffusional characteristics of the reaction system.
Kinetics of vinyl fluoride polymerization
Authors: Raucher Daniel , Levy Moshe 
Published: April 2003

AbstractVinyl fluoride was polymerized, at low temperatures and pressures, by photo‐ and γ‐ray initiation. The kinetics of this heterogeneous polymerization reaction was studied and a general scheme was proposed to explain the experimental results. The scheme is based on the assumption that the main site of the polymerization is in the “polymer phase.” The solvent used determines the rate of the reaction by its effect on the swelling of the polymer. The degree of polymerization is determined mainly by transfer reactions.
Thermal stability of homo‐ and copolymers of vinyl fluoride
Authors: Raucher Daniel , Levy Moshe 
Published: April 2003

AbstractThe thermal stability of poly(vinyl fluoride) (PVF) was studied by thermal gravimetry and mass spectrometry (TGA and TGA–MS). In low‐molecular‐weight polymers a two‐step decomposition pattern was observed. It consisted of the dehydrofluorination to a polyene chain followed by decomposition of the resulting polyene at higher temperatures. Copolymers of vinyl fluoride–vinyl acetate (VF–VAc) and vinyl fluoride‐vinyl chloride (VF–VCl) showed a simultaneous evolution of hydrofluoric acid and acetic acid and hydrofluoric acid and hydrochloric acid, respectively. This suggests that after the elimination of the weakest link a spontaneous elimination of neighboring HF molecules takes place.
The effect of frequency on the plasma polymerization of ethane
Authors: Morita S. , Bell A. T. , Shen M. 
Published: April 2003

AbstractThe plasma polymerization of ethane has been studied in the frequency range of from 50 Hz to 13.56 MHz. The rate of polymer deposition is strongly dependent on frequency, with significantly higher rates being observed at frequencies below 6 MHz. The effects of frequency can be interpreted in terms of a mechanism that assumes that polymer is formed by the reaction of surface free radicals, created by the bombardment of the growing polymer by charged species, with gas phase free radicals, formed by collisions of energetic electrons with monomer molecules.
Kinetic study of the γ radiolysis of polyethylene
Authors: Mitsui Hiroshi , Shimizu Yuichi 
Published: April 2003

AbstractA kinetic study was made of the formation of hydrogen and trans‐vinylene unsaturation in the radiolysis of polyethylene induced by γ rays with a dose rate of 6.35 × 105 rad/hr at 30–100°C in vacuo. The rates of the formation of hydrogen and trans‐vinylene unsaturation were described by the zero‐order formation kinetics with respect to each concentration combined with the first‐order disappearance. The apparent rate constant for the formation of hydrogen increased gradually with rising irradiation temperature to give the activation energy of 0.6 kcal/mole. On the other hand, those for the disappearance of hydrogen and the formation and disappearance of trans‐vinylene unsaturation were almost independent of temperature. The G values for crosslinking and main‐chain scission were obtained from the gel data by using the Charlesby‐Pinner equation, and the activation energy of 1.5 kcal/mole was given for both of them. On the basis of these results the reactions induced by γ rays in solid polyethylene were discussed.
Photoinitiated cationic polymerization by dialkylphenacylsulfonium salts
Authors: Crivello J. V. , Lam J. H. W. 
Published: April 2003

AbstractDialkylphenacylsulfonium salts in which the anions are of the general type BF, AsF, PF, and SbFare a new class of useful photoinitiators for cationic polymerization. On irradiation these salts underwent reversible ylid formation with the simultaneous generation of strong Brϕnsted acids. The photoinitiated cationic polymerization of a number of monomers with dialkylphenacylsulfonium salts demonstrated the utility of these new photoinitiators.
Anionic copolymerization of optically active α‐methylbenzyl methacrylate and trityl methacrylate. I. Reactivity of monomers
Authors: Ohta Koji , Okamoto Yoshio , Hatada Koichi , Yuki Heimei 
Published: April 2003

AbstractThe monomer reactivity ratios were determined in the anionic copolymerization of (S)‐ or (RS)‐α‐methylbenzyl methacrylate (MBMA) and trityl methacrylate (TrMA) with butyllithium at −78°C, and the stereoregularity of the yielded copolymer was investigated. In the copolymerization of (S)‐MBMA (M1) and TrMA (M2) in toluene the monomer reactivity ratios were r1 = 8.55 and r2 = 0.005. On the other hand, those in the copolymerization of (RS)‐MBMA with TrMA were r1 = 4.30 and r2 = 0.03. The copolymer of (S)‐MBMA and TrMA prepared in toluene was a mixture of two types of copolymer: one consisted mainly of the (S)‐MBMA unit and was highly isotactic and the other contained both monomers copiously. The same monomer reactivity ratios, r1 = 0.39 and r2 = 0.33, were obtained in the copolymerizations of the (S)‐MBMA–TrMA and (RS)‐MBMA–TrMA systems in tetrahydrofuran (THF). The microstructures of poly[(S)‐MBMA‐co‐TrMA] and poly‐[(RS)‐MBMA‐co‐TrMA] produced in THF were similar where the isotacticity increased with an increase in the content of the TrMA unit.
Solid‐state polymerization of long‐chain vinyl compounds. II. Effect of molecular arrangement on polymerizability of octadecyl acrylate
Authors: Shibasaki Yoshio , Fukuda Kiyoshige 
Published: April 2003

AbstractTo clarify the effect of a molecular arrangement of long‐chain monomers on polymerizability, γ‐ray‐initiated postpolymerization of polymorphic crystals of octadecyl acrylate and the melt has been investigated. According to thermal, x‐ray, and infrared (IR) analyses octadecyl acrylate exhibit three crystalline modifications similar to, but different in transition behavior from, those of octadecyl methacrylate. The α‐form is stable in the range of 19–32°C (mp) and at lower temperatures the β‐form is stable, whereas the sub‐α‐form appears transiently in α → β transition. The monomer molecules in triclinic packing (α‐form) show little tendency to polymerize, whereas those in hexagonal packing (β‐form) have high polymerizability that increases with temperature. The polymerizability in the molten state at fairly high temperatures is rather low, however. Thus the polymerization rate, saturated conversion, and polymer molecular weight exhibit maxima just above the melting point of α‐form. It is concluded that the hexagonal packing of monomer molecules with particular orientation in the layered structure and rotational freedom around the molecular axis, together with some conformational freedom of functional group, is favorable to the polymerization reaction. In addition, the mechanism of polymerization in the layered structure is discussed, assuming a cone‐type distribution for the polymerization probability.
Chemical modification of polymers. XII. Control of triboelectric charging properties of polymers by chemical modification
Authors: Gibson Harry W. , Bailey F. C. , Mincer Joseph L. , Gunther Wolfgang H. H. 
Published: April 2003

AbstractChemical modification of polymers leads to changes in triboelectric charging properties which are proportional to the degree of conversion. This contrasts to physical mixtures in which the surface energy causes one component to dominate the surface, hence the charging properties. Relationships between molecular structure and triboelectric charging have been deduced from the results. Thus the direction of change of triboelectric charging on chemical modification is governed by the nature of the reaction and the magnitude of the change is governed by the extent of reaction.
Equilibrium anionic polymerization of β‐methoxycarbonylpropionaldehyde
Authors: Hashimoto Kazuhiko , Sumitomo Hiroshi 
Published: April 2003

Abstractβ‐Methoxycarbonylpropionaldehyde (MCPA) was polymerized in tetrahydrofuran (THF) with benzophenone–monolithium complex as the initiator. An equilibrium between the monomer and its polymer was observed in the temperature range of −96 to −78°C. MCPA had lower polymerizability than ether‐substituted aldehydes and their corresponding unsubstituted aliphatic aldehydes in the temperature range. The thermodynamic parameters were evaluated from the temperature dependence of the equilibrium monomer concentration: ΔHss = −4.3 ± 0.2 kcal/mole, ΔSss = −21.9 ± 1.0 cal/mole deg, Tcss = −76°C. Not only an ether substitution but also an ester substitution in propionaldehyde caused the decrease in the absolute values of the thermodynamic parameters for the aldehyde polymerization. These substituent effects may have been the result mainly of the strong intermolecular dipole–dipole interactions of polar groups in monomer states.
Investigation of polycarbodiimide additive effects on the acid‐catalyzed hydrolysis of PBT
Authors: Lum Richard M. 
Published: April 2003

AbstractThe effects of a polycarbodiimide additive on the thermal stability of PBT are investigated using evolved gas analysis techniques. Measurements of the dynamic variations in sample‐cell pressure during PBT pyrolysis indicate that the maximum decomposition rate for the sample containing the additive is shifted to higher temperatures. The low‐temperature evolution of tetrahydrofuran (THF) and CO2 is significantly reduced, suggesting that stabilization is achieved by increasing polymer resistance to acid‐catalyzed hydrolysis. A condensed‐phase mechanism is indicated, since volatile species characteristic of the additive compound are not observed.
Particle nucleation in emulsion polymerization. IV. Nucleation in monomer droplets
Authors: Hansen F. K. , Ugelstad J. 
Published: April 2003

AbstractNucleation in finely dispersed monomer emulsions in competition with homogeneous and micellar mechanism was studied. The emulsions were prepared with a high‐pressure homogenizer under varying homogenizing conditions and made stable by the addition of hexadecane to the monomer. Sodium dodecyl sulfate was used as emulsifer. The number of particles in latexes polymerized with potassium persulfate and benzoyl peroxide initiators was measured and plotted as a function of the free emulsifier concentrations. With persulfate initiator the particle number achieved a minimum in the transition region between droplet and water phase–micellar nucleation mechanisms. With very fine emulsions Smith–Ewart case II kinetics with n = 0.5 applied. The reaction rate, which differed from conventional emulsion polymerizations, decreased with time up to the point at which n began to increase. In these runs the particle size distribution became nearly monodisperse.