bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sulfur vulcanization of natural rubber accelerated with 2‐mercaptobenzothiazole plus tetramethylthiuram disulfide
Authors: Bandyopadhyay P. K. , Banerjee S. 
Published: April 2003

AbstractThe sulfur vulcanization of NR by a MBT‐TMTD mixed accelerator system both in the presence and absence of ZnO and stearic acid with or without DCP has been studied. The rate of decomposition of DCP in the presence of both MBT and TMTD is quite similar to that in the MBT system alone. The reduction in crosslinking due to DCP is dependent mainly on MBT. The decomposition product of TMTD may contribute to it only at the later stage of vulcanization. Though TMTD has no influence on the decomposition rate, it reacts with MBT at least in the initial stage of vulcanization and suppresses the retardation caused by MBT on DCP vulcanization in accordance with the free sulfur decrease, the nature of crosslinking formation both in the presence and absence of DCP, and the methyl iodide treatment of the vulcanizates. The vulcanization process of the MBT‐TMTD‐S‐NR system has been interpreted in terms of both free radical and polar mechanisms. The domination of either of these depends on the dominant amount of either MBT or TMTD in the acclerator ratio. According to the initial high rate of crosslink formation, free sulfur decrease and also the initial additiveness of crosslinking in stocks containing DCP, the vulcanization process of MBT‐TMTD‐ZnO‐St. acid‐S‐NR system has been explained in terms of an ionic mechanism. The pronounced synergistic nature of such systems has been interpreted by the enhanced activation of MBT‐S‐ZnO‐St. acid complex due to the dithiodicarbamate ion formed in the initial stages of vulcanization, and also by the activation of TMTD accelerated vulcanization due to the mercaptobenzothiazylion.
A method for determining the permeability and solubility of sulfur in poly(dimethylsiloxane) (RTV)
Authors: DiGiacomo G. , Spaulding E. 
Published: April 2003

AbstractA method has been devised whereby the S8 permeability and solubility in silicon resin are determined by observing the reaction between sulfur vapors and silver particles within the polymer. The particles (∼10 μm diameter), which may vary between 0.1 and 100 μm in diameter, are dispersed in the polymer at a concentration up to 20% within a glass cylinder (also an aluminum container). The polymer is cured according to procedure and exposed to S8 saturated vapors at various temperatures (55°–125°C), leaving one end of the cylinder open. The Ag particles are a perfect sink for sulfur, which is consumed as soon as it reaches the reaction boundary that separates the reacted and unreacted Ag particles. Consequently, a distinct black region containing Ag2S product is left behind as the boundary advances. The line displacement, measured at time intervals for the several temperatures, is used to calculate the gas permeability in the polymer as a function of temperature on the basis of a mass transport model developed from diffusion theory. The S8 solubility in the polymer is calculated from the permeability and diffusivity. The latter is determined independently by measuring the time that the Ag2S reaction is delayed when a layer of plain polymer separates a silver surface and the sulfur environment.
Kinetics of hydrolysis, acetylation, and deamination reactions on polyamide fibers in homogeneous medium
Authors: Lokhande H. T. , Bhattacharyya Niyati 
Published: April 2003

AbstractChemical reactions on polymers in homogeneous medium were used to characterize the structure of the macromolecules. The polymer was in the form of polyamide fibers dissolved in m‐cresol to give a fairly highly concentrated solution (approximately 6%). Kinetic studies of hydrolysis, acetylation, and deamination reactions on the polyamide fibers were carried out in homogeneous medium at different temperatures. All the three reactions studied followed first‐order kinetics. Rate constants and apparent activation energies were determined for these reactions, which show two rates—an initial fast rate followed by a slow one. A new microfibrillar model of the polymer dissolved in m‐cresol is proposed, and the existence of two rates is explained on the basis of the two‐phase structure of the proposed microfibril. The fast rate is attributed to the free chain segments, and the slow rate is shown to correspond to the regions which are strongly hydrogen bonded and which hold the various chains together to give the microfibrillar structure of the polymer in the homogeneous phase. The apparent activation energy for hydrolysis was 3.20 and 0.18 kcal/mole for the fast and slow rates, respectively. The apparent activation energy values for acetylation were 1.50 and 0.80 kcal/mole, while those for the apparent deamination reaction were 6.90 and 4.60 kcal/mole, respectively. Lower values of apparent activation energies are attributed to the ease of reaction in the difficult‐to‐penetrate regions of the microfibril due to the role played by the solvent of the homogeneous phase in carrying the reacting species inside these regions while simultaneously breaking the hydrogen bonds between the polypeptide chains. The apparent deamination reaction is shown to be a resultant reaction of simultaneous deamination and “amination” through hydrolytic breakdown of the polypeptide chain.
Polymer miscibility in mixed organic liquids having acid‐base interaction—a modified two‐dimensional approach
Authors: Chen Show‐An , Lai Wen‐Jen 
Published: April 2003

AbstractA mixture of two organic liquids, each of which is a solvent for a given polymer, may become a nonsolvent mixture, if there is strong acid‐base interaction between the two solvents. Experimental results of such cases are presented for five polymers. These results are then correlated with the proposed modified form of the two‐dimensional approach. In the modification, an additional term for taking into account the acid‐base interaction is added to the expression for the hydrogen‐bonding solubility parameter of the liquid mixture; the dispersion forces and polar interactions are assumed to be undisturbed by the occurrence of the acid‐base interaction.
Mechanical and processing requirements for a shock mitigating phenolic foam
Authors: Mendelsohn M. A. , Meier J. F. , Rudd G. E. , Rosenblatt G. B. 
Published: April 2003

AbstractA high load‐bearing shock‐mitigating phenolic foam was developed to meet specific compression‐deflection and gas permeability requirements. It was required that the foam display an almost constant compressive stress within the limits of 50–68 psi at strains ranging from 10% to 60%. Furthermore, the foam had to possess a highly open‐celled structure so that its resistance to gas flow would be minimal. These properties were obtained from a chemical formulation utilizing a combination of two phenolic resins, a phosphoric‐sulfuric acid catalyst system, a surfactant combination that included both a hydrophilic and a lipophilic surfactant, and a fluorocarbon blowing agent.
Blocked isocyanate‐terminated prepolymers in a delayed‐cure durable‐press finish for wool. Influence of isocyanate and blocking group structure on reactivity
Authors: Guise G. B. , Freeland G. N. , Smith G. C. 
Published: April 2003

AbstractA series of prepolymers containing terminal blocked isocyanate groups was prepared by reaction of isocyanate‐terminated prepolymers [derived from a poly(propylene oxide) diol (MW = 2000) or a triol (MW = 3000) and different diisocyanates] with various blocking agents. Their curing rates with a polyepoxide crosslinking agent were measured to assess their suitability for a delayed‐cure durable‐press treatment for wool. The curing rates varied over a wide range, but commonly used blocking groups such as phenols, caprolactam, β‐diketones, and alcohols were not sufficiently reactive for the intended application, although others, e.g., oximes and certain blocking agents containing a basic center such as N,N‐diethylhydroxylamine, hydroxypyridines, and hydroxyquinolines, had the required reactivity. Blocking by 1,3‐dipolar cycloaddition of nitrones was examined, but the reactivities were too low. Prepolymers containing blocked aromatic isocyanates were more reactive than those containing blocked aliphatic isocyanates. Difunctional butanone oxime‐blocked pre‐polymers cured slightly more slowly than analogous trifunctional prepolymers.
Copolyamides derived from brassylic acid
Authors: Kim Ki‐Soo , Yu Arthur J. 
Published: April 2003

AbstractPolyamides were prepared from C6 to C12 diamines with brassylic acid, a linear C13 dicarboxylic acid, derived from Crambe seed oil. One distinct characteristic of these polymers is their low moisture adsorption as compared to nylon 66 and nylon 6. To modify the properties of these nylons, multi‐component copolyamides were prepared from hexamethylene diamine and mixtures of brassylic acid with adipic, terephthalic, or isophthalic acids. It was found that the melting points of the co‐polyamides were changed by the choice and the levels of the diacids used. The melting point‐composition curves all show a eutectic minimum. The glass transition temperature of nylon 6,13 is also changed by the incorporation of other diacids. Water adsorption of nylon 6,13 increases with increased substitution of brassylic acid by other diacids in the order of adipic > isophthalic ≥ terephthalic. Mechanical properties of some copolyamides are in the same range as the commercial nylon 11 and nylon 12. The low moisture absorption, reduced fabrication temperature, and the wide range of properties obtainable through copolymerization make copolyamides derived from brassylic acid potentially suitable as specialty tubing, powder coatings, and molded machine parts. They will be commercially viable when brassylic acid becomes available on a large scale and is competitively priced.
The retention and removal behavior of perchloroethylene and dichloromethane in polyester fabric
Authors: Slaten B. Lewis 
Published: April 2003

AbstractPolyester fabric was exposed to solvent at different bath temperatures. The retention of solvent by the fabric was determined. The removal of the retained solvent from the fabric was determined as a function of time and also as a function of temperature. The retention of perchloroethylene varied from >9% at 121°C to <0.01% at room temperature. The removal of perchloroethylene from the fabric was also a function of temperature, but even at 120°C significant quantities of perchloroethylene remained after 5 min of heating with nitrogen flow across the fabric. Dichloromethane was retained (>5%) at its boiling point and had similar slow removal rates as were found for perchloroethylene. Retention and removal rate data for both solvents as a function of time and temperature are presented.
Miscible blends of poly(butylene terephthalate) and the polyhydroxyether of bisphenol A
Authors: Robeson L. M. , Furtek A. B. 
Published: April 2003

AbstractMelt blends of poly(butylene terephthalate) (PBT) and the polyhydroxyether of bisphenol A (phenoxy) exhibit excellent transparency above the melting point of PBT as well as for the quenched molded specimens. Dynamic mechanical and calorimetric characterization revealed single and sharp glass transitions intermediate between those for the individual constituents. Increasing phenoxy content in the blends depressed the crystallization rate of PBT due to dilution and viscosity (Tg increase) effects. The apparent miscibility is believed due to the potential specific interactions between phenoxy pendant hydroxyl (proton donor) and the ester carbonyl of PBT (proton acceptor). Heat of fusion results surprisingly show an increase in the degree of PBT crystallinity as the phenoxy content of the blend is increased. No explanation is offered at this point for this unexpected behavior.
A kinetic investigation of thermal degradation of poly(vinyl formals)
Authors: Chanda Manas , Kumar W. S. Jaywanth , Raghavendrachar P. 
Published: April 2003

AbstractSeveral samples of poly(vinyl formal) having the same vinyl alcohol content (8–9%) but varying contents of vinyl acetate (6–22%) and vinyl formol (70–85%) were prepared and subjected to thermogravimetric analysis, in air and nitrogen atmospheres, employing both isothermal and dynamic methods. Kinetic parameters determined from both the isothermal and dynamic TGA data are compared. The activation energy is seen to be largely dependent on the degree of conversion, implying a complex degradation reaction. The activation energy is also much less for degradation in air than in nitrogen, which can be explained by a reaction with oxygen‐producing structures favoring degradation. The activation energy is less sensitive to variation in polymer composition for degradation in air than in nitrogen. Thus, in the dynamic process, the activation energy value decreases (from 36 to 23 kcal/mole) with increasing acetate content (from 6 to 22%) in nitrogen atmosphere, while in air the activation energy value increases only moderately (from 21 to 27 kcal/mole) with increasing acetate content (from 6 to 22%). The order of reaction is nearly unity, irrespective of the composition of the polymer, both in air and nitrogen.
Permeability of polyglutamic acid ester membranes to benzene vapor
Authors: Minoura Norihiko , Nakagawa Tsutomu 
Published: April 2003

AbstractPermeability of poly(γ‐methyl L‐glutamate) (PMLG), poly(γ‐hexahydrobenzyl L‐glutamate)‐(PHBLG), and poly(γ‐n‐amyl L‐glutamate) (PALG) membrane to benzene vapor was studied. Permeability coefficients of all the membranes were large, of the order of 10−9–10−6 cm3(STP) cm/cm2 sec cm Hg, and increased markedly with increasing relative vapor pressure and temperature. The large permeability was due to the large diffusion coefficient. The sorption behavior of the PALG–benzene system was interpreted in terms of the theory of the mixing of solvent with side chains. The Arrhenius plots of diffusion coefficients for PMLG and PHBLG showed a break at about 29 and 40°C, respectively, where the volume‐expansion curves of each polymer also showed a break, which is thought to be related to the side‐chain motion. The diffusivity data for PALG were examined in terms of Fujita's free‐volume theory, and it was found that the value of the average free‐volume fraction in the pure polymer for PALG was much larger than that for vinyl polymers. This means that the side‐chain motion of PALG is easy and is the reason that the diffusion coefficients for PALG are large. These results indicate that the diffusion of benzene in these polypeptides takes place in the side‐chain regions between helices.
The origin of residual internal stress in solvent‐cast thermoplastic coatings
Authors: Croll S. G. 
Published: April 2003

AbstractExperiments on polystyrene and poly(isobutyl methacrylate) coatings cast from toluene have shown that residual internal stress is independent of dried coating thickness and initial solution concentration. A theory is presented that predicts the magnitude of the stress and shows that it has no dependence on thickness or initial solution concentration. Internal strain is calculated from the volume of solvent lost after the coating has solidified. This solidification point is identified with the solvent concentration that is sufficient to depress the glass transition of the polymer to the prevailing experimental temperature. A one‐to‐one correlation is confirmed between the volume of solvent lost from solution during drying and the volume change of the polymer film.
Polymerization of vinyl chloride in presence of substituted olefins: Effects on molecular weight and melt rheology
Authors: Langsam Michael 
Published: April 2003

AbstractVinyl chloride (VCM) was polymerized by free‐radical suspension procedures in presence of methyl‐substituted olefins such as propylene, isobutylene, cis‐2‐butene, trimethylethylene, and tetramethylethylene. Dilute solution viscosities of polymer formed in the presence of these olefins were measured and compared to that of trichloroethylene, a chlorinated chain‐transfer agent. A pseudo‐chain‐transfer coefficient for these olefins was calculated based on solution viscosity determinations and found to be exponentially proportional to the number of allylic hydrogens. The effects on melt flow of the olefin distribution in the polymer chain were examined. Olefins at the ends of polymer chains were found to have no effect on melt rheology, whereas those in internal portions of chains were found to significantly increase melt flow.
Styrene divinyl benzene copolymers. I. Texture of macroporous copolymers with ethyl‐2‐hexanoic acid in diluent
Authors: Jacobelli H. , Bartholin M. , Guyot A. 
Published: April 2003

AbstractThe texture and the pore size distribution of a set of styrene divinylbenzene copolymers, prepared by suspension polymerization with various compositions and various amounts of ethyl‐2‐hexanoic acid as diluent, have been studied using nitrogen adsorption‐desorption isotherms, mercury porosimetry, and scanning‐electron microscopy. It appears that pore volume and surface area may be well predicted in a large range of conditions (divinylbenzene contents between 20 and 60%, ethyl‐2‐hexanoic acid contents between 35% and 60%). In this range of conditions there are three structures: the elementary nuclei are spherical particles of about 100–200 Å in diameter. They are organized in microspheres of about 500–1000 Å, and the microspheres form aggregates (2500–5000 Å) more or less separated by large holes. The smaller pores (<40 Å) are in the microspheres, between the nuclei; they are present only if the amount of divinylbenzene is high enough. Intermediate pores (40–500 Å) are, in the aggregates, between the microspheres, although the larger pores between the aggregates range from about 500 Å to more than 10,000 Å, depending on the amount of diluent.
Mechanical properties of polycarbonate antiplasticized with a charge‐transfer complex
Authors: Kryszewski M. , Ulanski J. , Gale¸ski A. 
Published: April 2003

AbstractPolymers doped with low‐molecular‐weight charge‐transfer (CT) complexes exhibit interesting electrical and photoelectrical properties. On the basis of the results of thermally stimulated depolarization (TSD) for polycarbonate (PC) doped with tetracyanoethylene‐t‐stilbene complex and its components, some information about the mechanism of mutual interaction was obtained. The measurements of stress relaxation, mechanical moduli, and ultimate strength in a wide temperature range fully confirmed the predicted behavior of PCs doped with CT complex and its components. Doping the PC with CT complex and its components lowers the glass‐transition temperature and increases the modulus in the range −60 to +60°C. The effects of doping on the mechanical properties of PC are explained in terms of α‐ and β‐relaxations.
Novel binary chlorides containing TiCl3 as components of coordination catalysts for ethylene polymerization. II. Behavior of the resulting catalyst systems
Authors: Greco A. , Bertolini G. , Bruzzone M. , Cesca S. 
Published: April 2003

AbstractBinary chlorides described in part I yielded very active catalyst systems for HDPE synthesis when they were associated with (i‐C4H9)3Al. Very high initial polymerization rates were observed for systems bases on MnCl2·TiCl3, MnCl2·2TiCl3, or FeCl2·2TiCl3 (III), but high yields, i.e., above 30 kg polymer/g Ti, could be reached only using moderate pressure of ethylene. Hydrogen consumption during ethylene polymerization was observed in the case of catalysts based on AlCl3·3TiCl3, CrCl3·3TiCl3, and other binary chlorides containing elements of the VIII group. Relevant amounts of ethane were found in the case of systems III, V, and VIII. All the mixed chlorides studied were able to reduce cyclohexene in the presence of H2 and (i‐C4H9)3Al, even though with different kinetic courses. Compounds II, III, V, and VIII and (MgCl2)1.5·TiCl3 and AlCl3·3TiCl3 were very active. The results have been explained on the basis of solubilization processes involving the heterogeneous catalysts which actually were experimentally verified during cyclohexene reduction. Analogous processes may occur also during HDPE synthesis.
Studies in the photodimerization of the diglycidyl ether of 4,4′‐dihydroxychalcone
Authors: Zahir Sheik A. 
Published: April 2003

AbstractIn order to elucidate the reaction mechanism involved in the photocrosslinking of epoxide resins containing the 4,4′‐dioxychalcone functional group as part of the polymer backbone, the behavior of the monomeric model compound, namely, the digylcidyl ether of 4,4′‐dihydroxychalcone, when subjected to UV irradiation has been studied in some detail. The initial photochemical reaction is trans‐cis isomerization to a photostationary state, the trans/cis ratios in this state being wavelength dependent. This is followed by a slow dimerization to dimers of the truxillic and truxinic type, the products being mainly formed from the trans isomer under our conditions of irradiation (λ = 350 nm). GPC studies on the irradiated products also reveal the formation of low molecular weight oligomers. Irradiation in the solid phase resulted in the conversion of 37% of the reacted monomer into polymer, whereas irradiation in the solution phase led to 23% of the reacted monomer being converted into low molecular weight polymer. A slow depolymerization of the dimer into the monomeric chalcone is also believed to occur on irradiation at 350 nm.
Quaternary phosphonium compounds as latent accelerators for anhydride‐cured epoxy resins. I. Latency and cure characteristics
Authors: Smith J. D. B. 
Published: April 2003

AbstractQuaternary phosphonium compounds have been found to be extremely effective latent accelerators for anhydride‐cured bisphenol A epoxy resins; at concentrations from 0.01% to 0.25%, fast gel times are found in the temperature range of 135°–200°C combined with very good storage properties at ambient temperatures. Using these materials as accelerators, it is possible to formulate long‐life, one‐component epoxy resins. From gel time data, Arrhenius plots were made for some of these phosphonium compounds, and results indicate low activation energy values of the order of 16.1 kcal/mole. Reaction mechanisms are proposed to explain the effectiveness of these phosphonium compounds as latent accelerators. The initiation mechanism probably involves the formation of hydrogen‐bonded phosphonium–epoxy or phosphonium–anhydride complexes which rearrange on the application of heat to form activated species resulting in polymerization of the epoxy–anhydride components. The transfer of a proton from the phosphonium complex(es) to other epoxy or anhydride molecules would appear to be the rate‐determining step in this initiation mechanism. Comparison of other well‐known accelerators used for the anhydride cure of bisphenol A epoxy resins shows quaternary phosphonium compounds to be among the most effective accelerators disclosed to date.
Suspension bromination of high‐density polyethylene
Authors: Arroyo Nestor A. , Hiltner Anne 
Published: April 2003

AbstractHigh‐density polyethylene powder has been brominated in suspension. The product was characterized by various physicochemical methods to determine the nature and effect of the substitution. Analysis of the infrared spectra indicates an initial addition reaction to terminal vinyl double bonds, followed by a substitution reaction on the polymer chain. The kinetic and thermal data show that the pseudo‐first‐order reaction occurs in the amorphous regions only. The brominated sites function as chain defects to decrease the crystallinity of the melt‐recrystallized polymer, prevent annealing, and cause intensity changes in the mechanical α relaxation. Limits are observed in these effects, however, which confirms the expected “blocky” rather than random nature of the substitution.