bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies on diphenylguanidine–accelerated sulfur vulcanization of styrene butadiene rubber in the presence and absence of dicumylperoxide
Authors: Das C. K. , Banerjee S. 
Published: April 2003

AbstractDiphenylguanidine (DPG) raises the rate of decomposition of dicumylperoxide (DCP) and the crosslinking maxima due to DCP is lowered to some extent by DPG. When the molar proportion of DPG–S is approximately 1:1, no additive results of crosslink formation (as reported for NR) are observed. Zinc oxide and stearic acid increase the rate of crosslinking as well as the crosslinking maxima. In the present study it appears most probable that DPG‐accelerated sulfuration of SBR is an ionic process. At a constant level of DCP and sulfur crosslink density increases when the amount of DPG is increased; a constant level of DCP and DPG crosslinking increases with rising sulfur concentration.An increase in the concentration of DPG or sulfur leads to greater formation of the complex as well as a change in its composition. The effect of DPG is more pronounced, for by reducing the number of sulfur atoms more sulfur is available for crosslinking. Sulfur absorbs little SO2 or H2S; if it is already saturated, there is no perceptible effect. DPG does absorb H2S or SO2 and the rate and maxima of crosslinks is increased. The effect of SO2 is higher because of the higher Ka values of H2SO3 and consequently higher concentration of HSO3−. Reversion is a free‐radical process inhibited by free DPG present in the system. In the presence of zinc oxide and stearic acid the reaction follows a polar mechanism as well as a radical mechanism.
The cationic dimerization of 1,1‐diphenylethylene. II. Cation formation with titanium tetrachloride in dichloromethane solution
Authors: Sauvet G. , Vairon J. P. , Sigwalt P. 
Published: April 2003

AbstractThe initiation reaction of 1,1‐diphenylethylene (DPE) dimerization by TiCl4 in dichloromethane has been studied at −30 and −70°C in the presence and absence of added cocatalyst. When water was added to the medium, the concentration of active centers was proportional to cocatalyst concentration. When carbocations R+ are formed without a cocatalyst, their usually low concentration depends on initial concentrations of reagents; thus |R+| ∝ |C|0/|M|0, which indicates that the olefin has an inhibiting effect. The simplest hypothesis applicable to these two observations is the existence of a secondary reaction parallel to initiation which traps the initiator in an inactive form; for example, as a complex with the monomer. The two kinetic schemes, which are proposed according to the stoichiometry of the inactive complex (bimolecular C,M or trimolecular C,M2), support mechanisms that would involve solvent cocatalysis, electronic transfer, or direct addition of TiCl4 on the monomer double bond. Consideration of these rival theories reveals that the most likely is the direct addition of TiCl4 on monomer, but unfortunately the known instability of the corresponding organotitanium intermediates does not allow their characterization.
Radical block polymerization of vinyl chloride. I. Ozonized polypropylene oligomers as heterofunctional initiator
Authors: Smets G. , Weinand G. , Deguchi S. 
Published: April 2003

AbstractIsotactic polyproplyene has been peroxidized in the solid state by treatment with ozone at room temperature, eventually followed by treatment with oxygen at 100°C. The total active oxygen content—peroxides and hydroperoxides—was determined iodometrically, and the hydroperoxide content with triethyl arsine, following the method of Horner and Jürgens. Post‐treatment with oxygen causes a very strong increase in total active oxygen content; the relative amount of hydroperoxides compared with that without oxygen treatment is, however, markedly decreased. The stability and rate of decomposition of PPO2 have been considered in relation to the solubility parameter of the different monomers and solvents. It was used at 30–40°C for initiating the emulsion polymerization of styrene, methyl‐, and butyl methacrylate and methyl, ethyl, n‐butyl, and 2‐ethyl‐hexyl acrylate. These polymers contain an average number of peroxide links per macromolecule, ranging between 7 and 23; they can be used for the block polymerization of a second vinyl monomer, e.g., vinyl chloride.
Direct pyrolysis in the mass spectrometer of aromatic polysulfonates and polythiosulfonates
Authors: Bottino F. , Foti S. , Montaudo G. , Pappalardo S. , Lüderwald I. , Przybylski M. 
Published: April 2003

AbstractThe thermal degradation mechanism of three aromatic polysulfonates and polythiosulfonates was investigated by direct pyrolysis in the ion source of a mass spectrometer. Thermal degradation reactions were followed directly by this method by detecting the thermal and electron impact induced fragments. The results obtained have provided evidence that sulfur dioxide extrusion from the polymer backbone takes place in these polymers above 300°C. The synthesis and molecular characterization of the polymers studied are reported in the text.
Synthesis and study of block copolycondensates containing polysiloxane and unsaturated polyester blocks in the chain. I. Poly(unsaturated esters‐b‐siloxanes) with blocks linked by SiOC bonds
Authors: Madec Pierre‐Jean , Marechal Ernest 
Published: April 2003

AbstractBlock copolycondensates containing both unsaturated polyester and polysiloxane blocks have been prepared by copolycondensation of reactive oligomers; the bonds between the blocks are either SiOC or SiC. This article is devoted to poly(ethylene adipate‐co‐maleate‐b‐siloxane) with SiOC bonds. The reactive oligomers are studied, before or after modification, by tonometry, end‐group titration, GPC, and NMR. Contrary to the block copolycondensates of the same kind described in the literature, those reported in this work have high molecular weights (five block of each kind). These high‐molecular‐weight block polycondensates have been obtained by a careful study of the parameters of the polycondensation.
Synthesis and study of block copolycondensates containing polysiloxane and unsaturated polyester blocks in the chain. II. Poly(unsaturated esters‐b‐siloxanes) with blocks linked by SiC bonds and poly(butadienes‐b‐siloxanes)
Authors: Madec Pierre‐Jean , Marechal Ernest 
Published: April 2003

AbstractPoly(unsaturated esters‐b‐siloxanes) whose blocks are linked by SiC bonds and poly(butadienes‐b‐siloxanes) have been obtained by polycondensation of ω,ω′‐diepoxy polydimethylsiloxanes and ω,ω′‐dicarboxylic poly(unsaturated esters). The reaction between polysiloxanes with SiH end groups and allylepoxy has been studied; the resulting ω,ω‐diepoxy polysiloxanes have the expected structure. The polycondensation of oligomers with, respectively, epoxy and carboxylic end groups has been studied and the optimal conditions established. The samples with SiC bonds are not affected by hydrolysis in pure water. The poly(siloxanes‐b‐unsaturated esters) can be cured by UV light.
A theoretical investigation of molecular core binding and relaxation energies in a series of oxygen‐containing organic molecules of interest in the study of surface oxidation of polymers
Authors: Clark D. T. , Cromarty B. J. , Dilks A. 
Published: April 2003

AbstractNonempirical LCAO MO SCF computations (in the ΔSCF formalism) have been carried out of binding energies and relaxation energies for an extensive series of oxygen‐containing organic systems encompassing most of the common functionalities. The molecules for which experimental data are available for comparison demonstrate the adequacy of the treatment for describing the relative binding energies for both the Cls and Ols core levels. A sound basis is therefore provided for the discussion of relative core binding energies (Cls and Ols) for functionalities for which experimental data are not available, that is, hydroperoxides, peroxides, peroxyacids, and peroxyesters, a knowledge of which is essential for investigations of the surface oxidation of polymers by means of ESCA. Cls shifts are discussed in terms of primary and secondary substituent effects of oxygen, which greatly simplify the analysis of complex unresolved spectra, whereas for the Ols levels a similar but less straightforward situation exists. The relaxation energies associated with both Cls and Ols core ionization follow a dependence on the binding energy for a given structural type.
Preparation and degradation of salts of poly(methacrylic acid). I. Lithium, sodium, potassium, and caesium salts
Authors: McNeill I. C. , Zulfiqar M. 
Published: April 2003

AbstractThe polymers of lithium, sodium, potassium, and caesium salts of methacrylic acid have been prepared by free radical polymerization of the respective monomers in methanol solution. The degradation behavior of the polymers has been investigated by thermal volatilization analysis, thermogravimetry, and product analysis. These materials are stable to about 350°C under programmed heating at 10°C/min in vacuo. The principal degradation products are monomer, the corresponding isobutyrate, carbonate, oxide, carbon dioxide, and a fraction of liquid volatiles that is complex and contains a variety of aldehydes and ketones. The mechanism of degradation is discussed in detail.
Gas permeation in freeze‐dried cellulose acetate membrane
Authors: Kakuta A. , Ozaki O. , Ohno M. 
Published: April 2003

AbstractGas permeation rates for helium, nitrogen, argon, and oxygen have been studied by using freezedried cellulose acetate membrane. When the gas permeation rate in freeze‐dried cellulose acetate membrane is high, the gas permeation rate through the pores is predominant. On the other hand, when this rate is small, it is predominant at the dense part, except for the pores. Therefore the gas permeation rate in freeze‐dried cellulose acetate membrane can be explained by the sum of two gas permeation rates.
Radiation degradation susceptibility of vinyl polymers: Nitriles and anhydrides
Authors: Helbert John N. , Poindexter Edward H. , Stahl Glenn A. , Chen Chi‐Yu , Pittman Charles U. 
Published: April 2003

AbstractThe effect of γ irradiation on a series of vinyl polymers, which included polymethacrylonitrile, poly(α‐chloroacrylonitrile), poly(dimethyl itaconate), poly(acrylic anhydride), and poly(methacrylic anhydride), was studied as part of a program to develop improved positive lithographic resists. Radiation‐induced degradation was observed for polymethacrylonitrile, poly(α‐chloroacrylonitrile), and poly(methacrylic anhydride). Molecular weight degradation as a function of dose was monitored by membrane osmometry or GPC techniques. For γ‐irradiated poly(dimethyl itaconate) and poly(acrylic anhydride) crosslinking was found to predominate over chain scission. [G(s)–G(x)] values, calculated from molecular weight inverse versus dose curves, indicate that both nitrile polymers degraded more efficiently than a poly(methyl methacrylate) reference standard on the basis of Mn changes. The radiation behavior of the first three polymers confirms earlier findings than vinyl polymers with quaternary carbons predominantly degrade when subjected to ionizing radiation.
Kinetics and mechanism of the cationic polymerization of tetrahydrofuran in solution: THF‐CH3NO2 system
Authors: Matyjaszewski Krzysztof , Słomkowski Stanisław , Penczek Stanisław 
Published: April 2003

AbstractPolymerization of tetrahydrofuran (THF) in CH3NO2 solvent was initiated with 1,3‐dioxolan‐2‐ylium cations with AsF and SbF anions, as well as with esters of FSO3H and CF3SO3H acids. Polymerization shows in this solvent a living feature: values of kp (determined directly from the semilogarithmic kinetic plots) were the same for all of the listed above initiators; thus kp is the same for AsF, CF3SO, FSO, and SbF anions. The identity of the kp values for complex and noncomplex (ester‐forming) anions comes from the fact that in CH3NO2 solvent equilibrium between macroesters and macroion pairs is shifted almost completely (Ke = 33.0 at 25°C and |THF|0 = 7.0M) to the macroions side. Dissociation constants of the polytetrahydrofuranium ion pairs (CF3SO and SbF anions) were measured (e.g., KD = 2 × 10−3 M at 25°C and |THF|0 = 7.0M; i.e., at D = 22.8, ΔHD = −3.8 ± 6 kcal mole; ΔSD = −25 ± 2 eu). On the basis of the known values of KD, and therefore dissociation degrees α, rate constants of propagation on the free and paired THF cations (k and k) were determined for a large range of degrees of dissociation (α from 0.15 to 0.52). The rate constants k and k were found to be the same within an experimental error of measurements (± 15% of the value of kp). Apparently, the polytetrahydrofuranium cations are highly solvated or even separated from their anions by molecules of THF itself. At these conditions the reactivities of the solvated “free” and solvated (or separated) paired cations became undistinguishable.
Polymerization of N‐(fluoro phenyl) maleimides
Authors: Barrales‐Rienda J. M. , Ramos J. González , Chaves M. Sánchez 
Published: April 2003

AbstractPoly(N‐aryl maleimide)s of characteristic structures have been synthesized and some of their physical properties studied. These include N‐(2‐fluoro phenyl), N‐(3‐fluoro phenyl), N‐(4‐fluoro phenyl), N‐(2,4‐difluoro phenyl), N‐(2,5‐difluoro phenyl), N‐(2,3,5,6‐tetrafluoro phenyl), and N‐(pentafluoro phenyl). The polymerization of N‐(fluoro phenyl) maleimides by free‐radical initiation in bulk or in solution and by anionic catalyst have been studied to compare the characteristics of polymerization by γ‐ray irradiation with that by free‐radical initiation. The polymers were characterized by elemental analysis, intrinsic viscosity, spectroscopy (IR and NMR), programmed thermogravimetric analysis, and x‐ray diffraction. Spectra of polymers prepared by radiation and anionic polymerization were nearly identical with those of polymers prepared by free‐radical polymerization initiated by AIBN in bulk or in solution and by the self‐initiated thermal polymerization. A variety of reaction conditions were tried, but all attempts to change the molecular structure of the polymers were unsuccessful. Rates of thermal degradation for poly[N‐(fluoro phenyl) maleimide]s have been analyzed by using a multiple‐heating‐rate procedure. Overall activation energy, order of reaction, and frequency factor have been evaluated. On the basis of the comparison between the overall activation energy of the thermal degradation of poly[N‐(fluoro phenyl) maleimide]s and NMR spectra of their corresponding monomers, it can be concluded that the 1H shifts due to ethylenic protons are so characteristic in sign and magnitude as to be useful in thermal stability elucidation. Some qualitative explanations were given on the stability of these polymers as affected by the type and size of the substituent. The x‐ray diffractograms of all samples show two rather broad peaks indicative of noncrystalline structures. The location of the peaks does not depend upon preparation conditions and temperature. Poly(N‐maleimide)s of fluoroanilines have not been hitherto described.
Emulsifier‐free emulsion polymerization of tetrafluoroethylene by radiation. III. Simultaneous formation of hydrofluoric acid
Authors: Suwa Takeshi , Watanabe Terutaka , Okamoto Jiro , Machi Sueo 
Published: April 2003

AbstractSimultaneous formation of hydrofluoric acid (HF) in the radiation‐induced polymerization of tetrafluoroethylene (TFE) was investigated. HF concentration in PTFE latex was determined mainly by conductometric titration with 0.01 and 0.001N NaOH. The amount of HF formed is almost independent of agitation speed and the amount of n‐hexadecane added and is maximal at ca. 70°C corresponding to the rate of polymerization.The rate of HF formation increases with the initial pressure of TFE monomer and dose rate and decreases with polymerization or TFE consumption. This fact suggests that HF is formed mainly by TFE reactions and not by the degradation of PTFE.The mechanism of HF formation in this reaction system in the absence of oxygen is shown in the following two schemes: scheme I is the reaction of TFE with primary radicals (OH·, H·, e) from the radiolysis of water; scheme II is the reaction of water with the species from the radiolysis of TFE. On the assumption that HF is formed only according to scheme I, the G value of HF formation G(HF)calc can be calculated as 11.25. All observed G values G(HF)obs are larger than G(HF)calc. When the polymerization is carried out at 20 kg/cm2 under various dose rates, G(HF)obs increases with the dose rate. When the polymerization is carried out at 3.0 × 104 rad/hr under various pressures, G(HF)obs decreases with the decrease in pressure from 20 to 2 kg/cm2 and is fairly close to G(HG)calc at 2 kg/cm2. This indicates that HF formation is due mainly to scheme II at high pressure (in the presence of enough TFE) and to scheme I as the pressure is lowered.
High‐molecular‐weight hydrolyzed polyacrylamides. II. Potentiometric titrations
Authors: Fenyo J. C. , Laine J. P. , Muller G. 
Published: April 2003

AbstractPotentiometric titrations in water of high‐molecular‐weight partly hydrolyzed polyacrylamides were analyzed by the Lifson—Katchalsky rodlike model. A fair concordance was found between theory and experimental curves with pK0 of acid functions of about 4.75 when 0 < τ < 0.49. Two methods were derived to calculate the parameter n of the extended Henderson‐Hasselbach equation by using a series expansion of pKa vs. α, not yet reported in the literature. A new equation for n was established and comparison between two sets of values of n, obtained by using the theoretical ΔpK curves and series expansion is discussed.
Prediction of the directional effect of pressure on the reactivity ratios in free‐radical copolymerizations
Authors: Jenner Gérard 
Published: April 2003

AbstractThe Q–e concept of the Alfrey and Price1 has been applied successfully to the prediction of the pressure effect on the individual reactivity ratios in free‐radical copolymerizations. Although the Q value of a given monomer is generally little affected by an increase in pressure, the e value is pressure dependent. The knowledge of the Q and e values at high pressures permits the prediction of variations in reactivity ratios with pressure. Some important consequences have been drawn from this concept.
Cationic copolymerization of isobutene and conjugated small‐ring dienes
Authors: Tsao Jung‐Hsien , Lenz Robert W. 
Published: April 2003

Abstract1‐Methyl‐3‐methylenecyclobutene (MMCB) and 1,2‐dimethylenecyclobutane (DMCB) copolymerized readily with isobutene with aluminum chloride as initiator in methyl chloride solution at temperatures from −95 to −78°C. No polymers were obtained with methylenecyclobutene (MCB) under similar conditions. The copolymerization of MMCB with isobutene took place through a 1,5‐addition reaction while that of DMCB through both 1,2‐ and 1,4‐addition reactions. Large amounts of gel were present in the copolymers obtained from DMCB if the reaction was carried to high conversion. The commonly observed effects of dienes (i.e., rate retardation and molecular weight depression) on cationic copolymerization reactions were observed but to a much higher degree with these small ring dienes. The thermal crosslinking behavior of the resulting copolymers was investigated. In conjunction with the copolymerization studies, homopolymers of MMCB, DMCB, and 3,3‐dimethyl‐1‐isopropylidene‐2‐methylenecyclobutane (IMCB) were prepared and their chemical structures examined.
Effect of dose rate on radiation‐induced polymerization of styrene adsorbed on silica gel
Authors: Kusama Yasuo , Udagawa Akira , Takehisa Masaaki 
Published: April 2003

AbstractThe effect of dose rate on the rate of polymerization and molecular weight distribution of radiation‐induced polymerization of styrene adsorbed on silica gel was studied in a wide dose rate range of 4.4 × 104 to 3 × 108 rad/hr by γ rays of 60Co and electron beams with a Cockcroft‐Walton‐type accelerator. Dose rate dependence on the initial rate of polymerization was about 1 below 3 × 107 rad/hr, and it decreased gradually at high dose rates. Throughout the dose rate range, graft polymerizations and homopolymerizations by cationic and radical mechanisms proceeded simultaneously. Dose rate dependence of the cationic polymerization was 1 below 3 × 107 rad/hr, while dose rate dependence of the radical polymerization was 0.65 below 3 × 107 rad/hr. At high dose rates, molecular weight and fraction of graft polymer decreased, and fraction of cationic polymerization increased. A very high‐molecular‐weight graft polymer was formed above 4.4 × 105 rad/hr at the initial stage of the polymerization. The dose rate dependence of this polymerization was larger than 1 and decreased with increase in dose rate. The polymerization seems to be related to an excitation of monomer or growing chain.
Stabilization of high nitrile polymers. I. Effect of dienophilic compounds
Authors: Marien Bruce A. 
Published: April 2003

AbstractThe effect of certain stabilizers on the discoloration of high nitrile polymers is discussed in terms of an in situ Diels‐Alder reaction. Dienophiles react with cis azadienes formed during thermal degradation of the nitrile polymer to interrupt conjugated sequences prior to oxidative chromophore formation. Several nondienophilic additives decompose upon heating to release a strong dienophile that stabilizes the polymer.
The kinetics of unterminated polymerization reactions
Authors: Baer S. , Kremer M. L. 
Published: April 2003

AbstractThe kinetics of the intermediates in unterminated polymerization reactions were studied. It was found that in a first‐order initiation (A) all intermediates accumulate monotonically. In a second‐order initiation (B) the first intermediates pass through a maximum, whereas the later ones strictly accumulate. An initiator‐started polymerization can follow course A or course B, depending on the initial ratio of the concentrations of the initiator and monomer.
Radical copolymerization of optically active l‐menthyl vinyl ether with maleic anhydride, dimethyl maleate, and dimethyl fumarate
Authors: Kurokawa Masahiro , Minoura Yuji 
Published: April 2003

AbstractThe copolymerizations of l‐menthyl vinyl ether (l‐MVE) with the monomers, that is, maleic anhydride (MAn), dimethyl maleate (DMM), and dimethyl fumarate (DMFu), were undertaken to obtain optically active copolymers. The optically active l‐menthyl group in the side chain of copolymers was removed by the ether cleavage reaction with dry‐hydrogen bromide gas. The ethercloven copolymers were still optically active. Hence it was concluded that asymmetric carbon atoms were introduced into the copolymer main chain, the reason given being that l‐MVE and comonomers (MAn, DMM, and DMFu) made the stereoselective charge‐transfer complex one another and copolymerized stereospecifically. From the results of the measurements of optical rotatory dispersion (ORD) and circular dichroism (CD) for copolymers before and after the ether cleavage reaction, the mode of bond opening for α,β‐substituted monomers (MAn, DMM, and DMFu) was discussed and the microstructures of copolymers were prepared.
Monomer chain‐transfer constants from emulsion copolymerization data: Styrene and α‐methylstyrene
Authors: Rudin Alfred , Samanta M. C. , Van Der Hoff B. M. E. 
Published: April 2003

AbstractRadical chain‐transfer constants can be deduced from corresponding measurements of rates and degrees of polymerization in copolymerization experiments. It is particularly useful to carry out such copolymerization in emulsion systems where the normal termination reactions are relatively less important and chain‐transfer processes are significant in determining the number‐average degree of polymerization. The method is illustrated for copolymerization of styrene and α‐methylstyrene at three temperatures. Rate constants for transfer of styryl and α‐methylstyryl radicals to either monomer were measured. All the rate constants are consistent with the relative stabilities of the product radicals which could be formed by the various transfer reactions. The procedure described here can be extended for measurements of rate constants for reactions of other potential transfer agents.