bluuebunny/crossref_metadata_2025 huggingface dataset:
Crosslinking reactions in pigmented olefinic polymers
Authors: Houde Carolyn , Schreiber H. P. , Rudin Alfred
Published: April 2003

Thermally initiated crosslinking reactions have been studied in a linear low‐density polyethylene, and an ethylene—propylene rubber. The polymers contained conventional thermal stabilizers or one of three surface‐coated rutile pigments. Enthalpies of crosslinking and reaction kinetics depended on the degree of terminal vinyl unsaturation in the polymers, that characteristic being greater in the rubber than in the polyethylene. The presence of thermal stabilizers did not exert any measurable influence on measured parameters of the crosslinking processes. The effects of rutile varied, depending on their surface acidity or basicity, as determined from chromatographic measurements. Basic rutile was found to reduce heats and to slow rates of reaction, while acidic rutiles did not affect the reactions. These observations may be attributed to interaction between the basic pigment surface and acidic moieties involved in the crosslinking reaction. © 1992 John Wiley & Sons, Inc.
Synthetic resins. XVIII. Chelation ion exchange properties of 2,4‐dinitrophenylhydrazone of 4‐hydroxy acetophenone–formaldehyde resins
Authors: Rath D. K. , Lenka S. , Nayak P. L.
Published: April 2003

A large number of copolymers were synthesized by condensing 2,4‐dinitrophenyl hydrazone of 4‐hydroxy acetophenone (4HA 2,4 DNPH) with substituted benzoic acids/phenols and formaldehyde in the presence of NaOH or HCl as catalyst. The resins were characterized by IR spectra. The decomposition temperature, solubility parameter, and viscositv of the polymers have been determined. The ion‐exchange properties have been studied using the batch equilibrium method. The measurement of the distribution of a given metal ion between an aqueous solution and the resins has been performed. The investigation was carried out over a wide range of pH and varying the ionic strength of the medium. © 1992 John Wiley & Sons, Inc.
Correlation of properties with structure in ziegler polypropylenes
Authors: Ibhadon A. O.
Published: April 2003

Isotactic polypropylenes, varying in molecular weight, crystallinity, and tacticity, were characterized by spectroscopic and chromatographic techniques in order to obtain suitable samples for investigating the effect of structure on properties. Mechanical and thermal properties were studied with respect to their structural dependence. Melting points and rates of crystallization were observed to be higher in the more stereoregular samples, while evidence of fractionation by molecular weight and tacticity was observed in less stereoregular samples. Tensile properties displayed marked dependence on polymer stereoregularity, while examination of fractured surfaces by microscopy showed that fracture occurred at regions of high impurity concentration. © 1992 John Wiley & Sons, Inc.
Kinetic study of the polycondensation of diisocyanates with polyols
Authors: Krol P. , Atamanczuk B. , Pielichowski Jan
Published: April 2003

On the basis of kinetic studies of noncatalyzed synthesis of carbamates in chlorobenzene solution, a kinetic model of polyurethane synthesis has been proposed. The model was built on a set of elementary, sequential—parallel reactions between functional groups of the main reagents involved in polyurethane synthesis. The assumption that reactivity of reagents did not depend of their mol wt allowed simulation of the kinetics of formation of allophanate branches for various process parameters. It has been found that the process temperature and initial ratio of reagents are of primary importance. A set of equations, describing the synthesis of linear polyurethanes, has been derived. The equations afford calculation of the degree of polymer chain branching and their application yields results similar to those obtained by the more general method based on numerical solution of the differential equations involved. Advantages resulting from the mathematical modeling of the process kinetics have been pointed out. © 1992 John Wiley & Sons, Inc.
Application of NMR spectroscopy to the characterization of elastomer/filler interactions
Authors: Legrand A. P. , Lecomte N. , Vidal A. , Haidar B. , Papirer E.
Published: April 2003

Proton spin–spin relaxation time measurements have been performed at 300 and 400 MHz on bound rubber‐filler mixes resulting from the solvent extraction of silica‐filled and silicafilled‐modified polybutadiene, on the one hand, and of carbon black‐filled and carbon blackfilled‐modified styrene butadiene rubber, on the other hand. Two relaxation times are observed for all samples. They are ascribed to the occurrence of tightly and loosely bound rubber components, respectively. The effect of the grafting modification of the fillers on the formation of bound rubber and its two components is discussed. © 1992 John Wiley & Sons, Inc.
Gas sorption in poly(butylene terephthalate). II. Influence of crystallinity and molecular orientation
Authors: Zhou Z. , Schultze J. D. , Springer J.
Published: April 2003

Sorption measurements of CO2, Ne, and Ar in poly(butylene terephthalate) (PBTP) films were studied by the gravimetric method with a recording microbalance at 298 K in the pressure range of 1–22 bar. The semicrystalline samples were annealed and oriented at 373 K. The sorption isotherms for CO2 in PBTP films in the glassy state can be well described by the dual‐sorption theory. The nonlinear sorption behavior of Ne and Ar can be satisfactorily analyzed using the sorption model developed for noble gases in PBTP. For the undrawn annealed films, it has been found that the increment of crystallinity leads to the reduction of the equilibrium gas concentration. For the oriented films, the gas concentration rises with increasing draw ratio. It appears that the sorption behavior for all tested gases in the oriented PBTP films does not depend on the changes of crystallinity and crystalline morphology under extension. The difference of the critical pressure p* indicates the change in the size of the frozen microvoids existing in the noncrystalline phase, which was altered by annealing and drawing. © 1993 John Wiley & Sons, Inc.
Studies of the preparation, structure, and properties of an acrylic chelating fiber containing amidoxime groups
Authors: Lin Weiping , Lu Yun , Zeng Hanmin
Published: April 2003

Polyacrylonitrile fiber was treated with hydroxylamine to form a chelating fiber containing the amidoxime group with high adsorption capacity to the Au3+ ion (up to 626 mg/g, when the nitrile group conversion reaches 53.7%), reasonable mechanical properties, and good thermal stability; the relationship among reaction conditions, fiber structures, and properties were investigated. The amidoxime group content rapidly increases to a steady value with increasing reaction time or HONH2 • HCl concentration, the fiber strength drops linearly with increasing reaction time, when the reaction takes place at the temperature where the morphology and order structure begins to be destroyed, and the amidoxime group content increases significantly, while fiber strength decreases remarkably. It is suggested that, to prepare a chelating fiber with high adsorption capacity and reasonable mechanical property, the reaction could be carried out at temperatures from 70 to 75°C, time of about 30 min, and concentration around 75 g/L. © 1993 John Wiley & Sons, Inc.
Estimation of free volume in poly(trimethylsilyl propyne) by positron annihilation and electrochromism methods
Authors: Yampol'skii Yu. P. , Shantorovich V. P. , Chernyakovskii F. P. , Kornilov A. I. , Plate N. A.
Published: April 2003

The free volume of poly(trimethylsilyl propyne) (PTMSP), a glassy polymer distinguished by extremely high gas permeability and diffusion coefficients, was determined by means of two probe techniques—the positron annihilation method and the electrochromism method. Lifetime analysis of positron annihilation spectra revealed an additional long‐lived component that is not typical for most of previously studied polymers. A model that has been developed earlier predicts that this lifetime corresponds to the larger size of free‐volume elements having an intrinsic radius of about 6 Å. Therefore, PTMSP should be similar to porous inorganic sorbents. A comparison with the literary data for zeolites and silica gel confirms this. According to the electrochromism method, the temperature dependence of the size of free‐volume elements for PTMSP is much weaker than that for regular glassy polymers like polystyrene. It was concluded that the great free volume in glassy PTMSP is associated with very loose packing of the chains. © 1993 John Wiley & Sons, Inc.
Reaction injection molding (RIM) system based on metathesis
Authors: Asrar Jawed
Published: April 2003

This paper describes the polymerization and the copolymerization of dicyclopentadiene and norbornene nitrile by metathesis polymerization. It is found that the metathesis polymerization of dicyclopentadiene, which is very fast and exothermic, can be controlled by the addition of norbornene nitrile. Though the norbornene nitrile delays the polymerization at room temperature, at high temperatures, because of the presence of nitrile group, polymerization is accomplished in reaction injection molding time. Physical and mechanical properties of the polymers and copolymers are described. © 1993 John Wiley & Sons, Inc.
A device for study of polymer crystallization kinetics via real‐time image analysis of small angle light scattering
Authors: Culberson Wayne T. , Tant Martin R.
Published: April 2003

A two‐dimensional position‐sensitive detector for real‐time small‐angle light scattering (RTSALS) of polymers is described. The device performs real‐time image analysis of the evolving light‐scattering pattern during crystallization. Such an approach provides a means of simultaneously measuring the rate of spherulite growth and the overall rate of crystallization, allowing calculation of nucleation density and/or rate. Although separation of nucleation effects from growth effects typically requires the application of two different experimental techniques, this device is unique in that it allows these two effects to be easily separated using only time‐dependent light‐scattering data. The device incorporates a CCD camera, a personal computer, and an imaging board as its major hardware components. Software designed specifically for this application performs real‐time analysis of the light‐scattering pattern at a rate of 1–3 images per second, thus allowing study of even moderately rapidly crystallizing polymers. (More recent software modifications have resulted in a speed enhancement to 5 images per s and further improvement is expected.) Intensities at various scattering and azimuthal angles are plotted at each time. In addition, the average spherulite radius is calculated and plotted. Application of the device is illustrated by measuring the spherulite growth rate of poly(ethylene terephthalate) as a function of temperature. © 1993 John Wiley & Sons, Inc.
Microcellular polymeric materials from microemulsions: Control of microstructure and morphology
Authors: Raj W. R. Palani , Sasthav Mohan , Cheung H. Michael
Published: April 2003

The effect of a crosslinking agent on the formation of porous solids by polymerizing microemulsions formulated with monomers was investigated. Phenomenological studies were carried out to evaluate the possibility of controlling the morphology of the porous polymeric materials by using precursor microemulsions having a distinct microstructure. A microemulsion system, containing methyl methacrylate (MMA), acrylic acid (AA), the crosslinking agent ethyleneglycol dimethacrylate (EGDMA), water, and sodium dodecylsulfate (SDS) as surfactant, was studied. An identical surfactant‐free system, formed using the same monomers, crosslinking agent, and water, but without surfactant, was also studied. Microemulsion samples from both these systems, having a water in oil droplet microstructure and also samples exhibiting bicontinuous microstructural characteristics, were used as precursor systems for polymerization. The morphology of the polymeric solids obtained was examined using scanning electron microscopy and thermogravimetric analysis. The results of this study indicate the possibility of forming porous polymeric solids having specifically tailored morphology and microstructure by the polymerization of monomer containing microemulsions. © 1993 John Wiley & Sons, Inc.
Kinetic analysis of bulk polymerization of diisocyanate and polyol
Authors: Gambiroz̆a–jukić M. , Gomzi Z. , Mencer H. J.
Published: April 2003

The step addition polymerization between toluene diisocyanate and poly(oxypropylene) diol and triol was carried out in bulk in a closed batch reactor under vacuum and at isothermal conditions. The reactions have been examined under the influence of the catalysts N‐phenyl‐β‐naphthylamine, triethylene‐tetraamine, and ferriacetylacetonate. The disappearance of the reactants and the appearance of one of the products were observed during the reaction. The kinetic analysis was brought about on the basis of the supposed reaction scheme and proposed kinetic model. The complex reaction was considered as serial–parallel. The experimental data fit well with the computed theoretical curves. The catalysts utilized were evaluated with respect to their selective catalysis of the primary diisocyanate–polyol reaction relative to the possible secondary reaction. The computed rate constants enabled the prediction of the composition of the reaction mixture. © 1993 John Wiley & Sons, Inc.
Kinetic parameters in non‐stoichiometric epoxy‐resin/m‐xylylenediamine reactions
Authors: Abuín Senén Paz , Pellín Mercedes Pazos , Núñez Lisardo , Gándara Jesús Simal , Losada Perfecto Paseiro
Published: April 2003

The curing reaction of bisphenol A epoxy resin has been widely studied. We have found that when initial reactants are highly pure the reaction epoxy resin/m‐xylylenediamine follows a predominantly autocatalytic path independent of the temperature. The purpose of this study was to discern if the kinetic model is appliable at high values of amine/epoxy equivalent ratio. Because of the nature and reactivity of m‐xylylenediamine (m‐XDA), the studies were carried out at low temperatures. Also, in order to obtain information about the formation mechanism of the system, different parameters such as reaction orders, activation energies, and reaction rate variation with concentration have been studied at different (1.5 : 1, 2 : 1, and 3 : 1) amine/epoxy equivalent ratios. © 1993 John Wiley & Sons, Inc.
Characterization of PAN‐based nonburning (nonflammable) fibers
Authors: Ko Tse‐Hao
Published: April 2003

In this article, a continuous stabilization process is used to make nonburning (nonflammable) fibers from polyacrylonitrile (PAN) fibers. The effect of the shrinkage behavior and the stretching process of PAN fibers during the stabilization process on the physical properties, morphology, and flammability of the resultant nonourning fibers is studied for the first time. The higher shrinkage of PAN fibers during the continuous stabilization process is found to increase the diameter, the core proportion, and flammability and decrease the Al value, density, mechanical properties, and formation of oriented molecular chains in the resultant nonburning fibers. The effect of the shrinkage behavior of PAN fibers on the fracture surface of the nonburning fibers is also discussed. The nonburning fibers show a fracture structure radiating from the fiber center to the boundary. The structures are composed of small and fine radial strip‐layer–like fibrils. Nonburning fibers developed using an optimum stretch process, not only had increased preferred orientation and density, but also had improved mechanical properties. Those fibers also have sufficient nonflammability. © 1993 John Wiley & Sons, Inc.
IR spectroscopic study on the thermal degradation of plastic security cover sheets of some documents
Authors: El‐Din Nabil Mohamed Safy
Published: April 2003

The change in IR spectra of plastic security cover sheets of ethylene vinylacetate copolymer during thermal treatment was investigated. The results obtained revealed that the temperature reduced the concentration of the ester group; moreover, the carbonyl band disappeared at high temperatures from 200 to 220°C, as well as broading of the absorption aliphatic–CH band. The change in the mechanical properties, degree of swelling in water, and refractive index of the samples during thermal treatment were also investigated. © 1993 John Wiley & Sons, Inc.
Thermal analysis of poly(acrylic acid)/poly(oxyethylene) blends
Authors: Chu Chia‐Hsi , Berner Bret
Published: April 2003

Blends between poly(acrylic acid) and two different poly(oxyethylenes), (1) polyethylene glycol (PEG‐1000) and (2) poly(oxyethylene) (20) sorbitan monooleate (Tween‐80), were studied by differential scanning calorimetry. The glass transition temperatures, Tg, of the various compositions of these blends were found to follow Fox's equation. At room temperature, blends containing no more than 60% PEG‐1000 were amorphous and exhibited only a single glass transition. For these blends with PEG‐1000, the glass transition temperatures for the annealed samples were higher than for the quenched samples due to the formation of a PEG crystalline phase. It was also found that addition of an amorphous polymer such as poly(acrylic acid) significantly reduced the degree of crystallinity of a semicrystalline polymer such as poly(oxyethylene). The Tween‐80 systems did not show phase separation at room temperature. The compatibility between this poly(acrylic acid) and this poly(oxyethylene) was attributed to hydrogen bonding and to the lower crystalline lattice energy of this poly(oxyethylene) through its effect on its ideal solution solubility. © 1993 John Wiley & Sons, Inc.
Effects of additions of high‐density polyethylene on the processability of linear low‐density polyethylene
Authors: Karbashewski E. , Kale L. , Rudin A. , Tchir W. J.
Published: April 2003

In considering the processing characteristics of typical linear low‐density polyethylenes, it is very likely that the nature and amount of the “high‐density” portion of the short chain branching distribution has a strong effect on rheological behavior. In this study, highdensity resins of varying molecular weight were blended into a linear low‐density polyethylene base resin to determine the effect on viscosity, elasticity, and onset of haze. It was determined that it is not only the high‐molecular‐weight characteristics of the high‐density portion but also the linear nature of the molecules that has a negative effect on processability. © 1993 John Wiley & Sons, Inc.
Representation of vapor–liquid and liquid–liquid equilibria for binary systems containing polymers: Applicability of an extended flory–huggins equation
Authors: Bae Y. C. , Shim J. J. , Soane D. S. , Prausnitz J. M.
Published: April 2003

For some binary systems, an extended Flory–Huggins equation is applicable to both vaporliquid equilibria (VLE) and liquid–liquid equilibria (LLE) using the same adjustable parameters. New LLE and VLE data are reported for polystyrene (PS) (MW = 100,000)/cyclohexane and for poly(ethylene glycol) (PEG) (MW = 8,000)/water. Experimental results for the PS/cyclohexane system agree well with the semiempirical model, whereas those for PEG/water do not, probably because, for PEG/water, the temperature range of the VLE data is about 55°C lower than that of the LLE data. Excellent fits were obtained for our previously published experimental results for PS/cyclohexane (upper critical solution temperature, UCST), PS/ethyl acetate (lower critical solution temperature, LCST), PS/tert‐butyl acetate and PS/methyl acetate (both UCST and LCST), and PEG/water (closed‐loop). The semiempirical model also fits well with new data obtained for the polymer blend PS/poly(vinyl methyl ether). © 1993 John Wiley & Sons, Inc.
Studies on co[poly(ethylene terephthalate‐p‐oxybenzoate)] thermotropic copolyester (I): Synthesis and thermogravimetric behavior
Authors: Shinn Ted‐Hong , Chen Jang‐Young , Lin Chen‐Chong
Published: April 2003

A series of co[poly(ethylene terephthalate‐p‐oxybenzoate)] thermotropic copolyester was synthesized from various ratios of two different moieties of either poly(ethylene terephthalate) (PET) or its oligomer as moiety (II) with p‐acetoxybenzoic acid as moiety (I) through the polycondensation process. The polymeric products obtained were then ground and subjected to solid‐state polymerization under vacuum for various polymerization times. Thermogravimetric analysis (TGA) and the derivative thermogravimetric analysis (DTG) were performed with these samples obtained. Also, a commercial product, Eastman 10109, was analyzed in comparison with these samples. It was found that the copolyesters made of PET and of its oligomer in a p‐oxybenzoate (POB):PET = 80 : 20 composition ratio and subjected to 8 and 4 h solid‐state polymerization times, respectively, showed the most similar thermogravimetric behavior with Eastman 10109. © 1993 John Wiley & Sons, Inc.
Morphology development for three‐component emulsion polymers: Theory and experiments
Authors: Sundberg Eric J. , Sundberg Donald C.
Published: April 2003

Three‐component emulsion polymer systems constitute an overall four‐component system from a morphological viewpoint. The aqueous phase is always the continuous phase within which 22 distinct and thermodynamically stable particle morphologies may exist. Six uniquely different categories of particles compose this morphological menu and may be identified as core–shell–shell, hemicore, hemishell, trisectional, “snowman,” and cored hemisphere. Extension of previously published free‐energy thermodynamic analyses of two component emulsion polymers has resulted in the ability to predict the most likely equilibrium morphology to be found for three‐component particles. Predictions have been carried out for each possible three‐component combination of poly(methyl methacrylate), polystyrene, poly(dimethyl siloxane), and polycarbonate. The results show that in nearly every instance two or three different morphologies are computed to possess nearly equivalent free energies, whereas all other possibilities would result in much higher free energies. This indicates that more precise knowledge of all interfacial tensions is required when considering three‐component systems than was found to be generally needed for two‐component systems. Experiments were carried out for each polymer combination using a very surface‐active emulsifier (sodium lauryl sulfate) and, separately, a weakly surface‐active emulsifier (natural pectin). For this choice of polymers and emulsifiers, only three of the six unique morphological categories were found experimentally. In all cases, the thermodynamic analysis predicted the experimentally determined morphology to possess the lowest or next to lowest free energy. © 1993 John Wiley & Sons, Inc.
Water transport in graphite/epoxy composites
Authors: Lee Myung Cheon , Peppas Nikolaos A.
Published: April 2003

The diffusive and mechanical behavior of tetraglycidyl diaminodiphenyl methane (TGDDM) resin‐based composites and diglycidyl ether of bisphenol‐A (DGEBA) resin‐based graphite/epoxy composites were investigated during water sorption at different temperatures. The water‐absorption kinetics in both systems at 50, 70, 90, and 100°C were fitted by a Fickian diffusion model. However, a Langmuir‐type, two‐step sorption behavior was observed for water transport in DGEBA‐based systems at 50 and 70°C. Using scanning electron microscopy, internal cracks due to water absorption were found in the DGEBA‐based samples after conditioning at 90 and 100°C in water, whereas no cracks were detected in TGDDM‐based samples conditioned in water at 100°C. Ultrasonic testing did not show significant modulus or density change of the TGDDM‐based samples conditioned in water at 100°C. No significant changes of dynamic modulus or damping factor were observed for the TGDDM‐based samples redried after immersion in 100°C water, whereas slight changes were observed above 120°C for the samples containing absorbed water. However, both water‐containing and redried DGEBA‐based samples showed a decrease of dynamic modulus and an ω‐transition around 120°C. A single‐fiber fragment test revealed that the absorbed water at 80°C reduced significantly the interfacial shear strength of DGEBA/DDA resin‐AS4 fiber samples and DGEBA/DDA resin‐AU4 fiber samples. © 1993 John Wiley & Sons, Inc.
Compatibility behavior in thermoplastic polymer blends containing poly(t‐butylstyrene‐co‐acrylonitrile)
Authors: Hseih D. T. , Peiffer D. G.
Published: April 2003

The phase behavior of a series of binary component polymer blends of poly(ε‐caprolactone) (PCL) and poly(t‐butylstyrene‐co‐acrylonitrile) (TBSAN) containing varying contents of acrylonitrile (AN) was examined to determine the influence of copolymer composition and PCL content on blend miscibility or immiscibility. Thermal measurements were extensively used to determine phase behavior, i.e., a single compositionally dependent glass transition temperature implies blend miscibility. Otherwise, immiscibility is assumed to dominant blend behavior. It was determined that TBSAN and PCL form miscible blends over a broad range of AN content, i.e., spanning from below 43.2 mol % (19.8 wt %) to about 66.4 mol % (39.6 wt %), a range considerably different from that found in poly(styrene‐co‐acrylonitrile) copolymers. TBSAN‐containing blends were found to be immiscible when the AN content is less than about 43 mol % or greater than about 67 mol %. Small‐angle light‐scattering and polarized light microscopy was used to probe the substantial morphological changes in the miscible blends. Little change was observed in the immiscible blends. These results clarify the phase separation observed in these blend systems. © 1993 John Wiley & Sons, Inc.
Transport of sodium chloride, urea, and creatinine through membranes derived from methylmethacrylate‐co‐methacrylic acid and its ionomers
Authors: Bdair Ameen , Aras Leyla , Sanli Oya
Published: April 2003

Permeabilities of cast films of methylmethacrylate‐co‐methacrylic acid (MMA—MAA) and its 5% neutralized Na1+, CS1+, Zn2+, Ba2+, and Al3+ ionomers for urea, sodium chloride, and creatinine were determined using a double (donor and acceptor) compartment cell. Film permeability was increased as the ionic potential decreased and it was more marked with urea as compared with sodium chloride and creatinine. Tensile properties of the above samples were also tested and variations in Young's Moduli were based on the effect of type of aggregates produced by the cations in the matrix of the copolymer. © 1993 John Wiley & Sons, Inc.
On the neck‐like deformation in high‐speed spun polyamides
Authors: Haberkorn H. , Hahn K. , Breuer H. , Dorrer H.‐D. , Matthies P.
Published: April 2003

The neck‐like deformation process occurring in high‐speed melt spinning of polyamide 66 and polyamide 6 filaments was investigated at take‐up speeds of 4200 to 5500 m/min by on‐line laser light scattering, thermographic contrast compensation, and wide‐angle X‐ray scattering (WAXS) measurements. New information about the onset of crystallization along the spinline was obtained by measuring simultaneously diameter and temperature profiles in the neighborhood of the neck. Crystallization rates, as a function of take‐up speed, are estimated for both polyamides. Based on the present experimental results of diameter profiles, temperature profiles, and WAXS patterns, a picture of the physical mechanism responsible for the neck‐like deformation of high‐speed melt spun polyamides is proposed. © 1993 John Wiley & Sons, Inc.
Bulk anionic copolymerization of ε‐caprolactam in the presence of macroactivators derived from polypropylene glycol
Authors: Chen Yun , Chen Show‐An
Published: April 2003

Bulk anionic copolymerization of ε‐caprolactam (CPL) was conducted, under four different conditions by changing temperature (110 or 125°C) and [NCO]/[NaH] ratio (1, 2, or 3), in the presence of NCO‐terminated polypropylene glycol (P1) and its CPL‐blocked prepolymer (P2). Under the same conditions and reaction time, the conversion of CPL and reduced viscosity of the P2 system were higher than those of the P1 system. However, at the same conversion the P1 system showed higher viscosity for reactions at 125°C with [NCO]/[NaH] = 3 and at 110°C with [NCO]/[NaH] = 2. These results were attributed to cyclotrimerization of NCO groups of P1 (formation of isocyanurate) at the initial stage, which not only consumed the effective concentration of NCO but also increased the viscosity of the P1 system. Comparing IR spectra of the reaction products of model compounds, phenyl isocyanate and CPL‐blocked phenyl isocyanate, with NaH/CPL also supported this conclusion. The crystalline melting temperature (Tm = 198–208°C) and melting enthalpy of the final products depended on the conversion of CPL and the types of macroactivators. © 1993 John Wiley & Sons, Inc.
Modification of nylon‐6 with semirigid poly(p‐diphenylmethyl terephthalamide)
Authors: Shu Yao‐Chi , Lin Ming‐Fung
Published: April 2003

In this research, flexible nylon‐6 was reinforced by semirigid aromatic polyamide poly(p‐diphenylmethyl terephthalamide) (PMA) through physical polyblending and chemical copolymerization using p‐aminophenylacetic acid (P‐APA) as a coupling agent. From the DSC measurement, it was shown that the Tg of the polyblends was increased with the increase of PMA content. It was discovered that the Tg and Tm of multiblock copolyamides would be higher than those of polyblends and triblock copolyamides. The multiblock copolyamides exhibited a homogeneous texture rather than an aggregated one. Scanning electron microscopy revealed that the polyblends were a dispersed‐phase structure. We found that from the wide‐angle X‐ray diffraction pattern the triblock copolyamides and polyblends had two diffraction peaks, i.e., 2θ = 20° and 24°. However, the multiblock had only one at 2θ = 20°, which evidently indicates that a new crystal structure of multiblock copolyamides was formed. As for the mechanical properties, the multiblock copolyamides were found to have more significant reinforcing effects than those of polyblends and triblock copolyamides. © 1993 John Wiley & Sons, Inc.
Poly(vinyl chloride) composition. I. Mechanical properties and structure of poly(vinyl chloride) and fire‐retardant additives
Authors: Stoeva S. , Benev D. , Karaivanova M.
Published: April 2003

Natural, activated, and modified microzeolites were studied individually and in combination with ammonium sulfamate as high‐melting dispersed additives. The strength—deformation properties of poly(vinyl chloride) were improved within the interval of 3–8 wt % additive. The strengthening effect due to the considered dispersed additives can be ascribed to the optimal adhesive interaction of the phase‐boundary surface and to the formation of a partially ordered dispersed phase. The tetrahedral configuration of the modified microzeolite that contains 3.5–4% zinc in its crystal lattice remains unchanged, but exhibits a reduced birefringence. These relationships are of exceptional importance for the use of poly(vinyl chloride). The introduction of certain amounts of the additives improves the melt flow of the polymer and facilitates the processibility of the compositions. © 1993 John Wiley & Sons, Inc.
Synergic action of aging and moisture on native and different grades of commercial gutta‐percha (trans‐polyisoprene)
Authors: Arvanitoyannis Ioannis , Kolokuris Ioannis , Robinson Colin , Blanshard John M. V.
Published: April 2003

The aim of this paper was to study the plasticizing effect of subjecting native/commercial gutta‐percha samples to controlled levels of different humidities. It was expected that this study would provide the practicing endodontist with invaluable insight into the mechanical properties of commercial gutta‐percha cones (i.e., retrievability, malleability, flexibility, and torsional and bending ability). The “conditioning” of the gutta‐percha samples depended greatly on the percentage of compatible/incompatible substances. The mixtures of native gutta‐percha with compatible (i.e., wax) showed greater elongation, tensile strength, and number of rotations, but lower deformation angle than the mixtures of native gutta‐percha with incompatible substances (i.e., salts, metal oxides). The observed lower values for tensile strength and torsional strain, relative energy to break, and the Young's modulus and the higher values for elongation and number of rotations for wet samples compared to the dry ones were attributed to the plasticizing effect of gutta‐percha due to the insertion of water molecules in the polymer chains. © 1993 John Wiley & Sons, Inc.
Gas permeation properties of hexafluoro aromatic polyimides
Authors: Matsumoto Kenji , Xu Ping
Published: April 2003

Two hexafluoro‐substituted aromatic polyimides, 6FDA‐p‐PDA and 6FDA‐4,4′‐ODA, were synthesized. The influence of some synthetic conditions on physical properties and gas permeabilities of the 6FDA polyimide membranes were studied. Gas permeabilities and permselectivities of six different gases for the homogeneous films have been determined at 15–35°C and at pressures up to 10 atm. 6FDA polyimide composite membranes with asymmetric structure were prepared by the solution‐casting method. The membranes showed exceptionally high permeation fluxes and permselectivities. No capability deterioration of asymmetric membrane was observed during 19 days operation with pure gases. © 1993 John Wiley & Sons, Inc.
Cross‐linking structure of keratin. IV. The number of cross‐linkages in low‐sulfur components and the volume fraction of high‐sulfur domains in various α‐keratin fibers
Authors: Arai Kozo , Hirata Taishi , Nishimura Shushi , Hirano Mitsushige , Naito Sachio
Published: April 2003

Various α‐keratin fibers that had been treated with an 11M LiBr solution containing N‐ethylmaleimide showed typical rubberlike elasticity in a solution composed of equal volumes of 8M LiBr and diethylene glycol mono‐n‐butyl ether. Stress—strain relations of the swollen fibers were treated with a two‐phase model: a mechanically stable phase of higher cross‐linked domains and a rubber phase with lower cross‐link density. Stress—strain curves for a variety of keratins (three different human hairs, six different wools, mohair, cashmere, llama, alpaca, angora, and opossum) were analyzed by applying non‐Gaussian chain statistics to the swollen keratin network, including microdomains, which act as reinforcing filler particles in rubber. The phase structures of unswollen domains and swollen rubber were considered to originate from different structural components characteristic of α‐keratin, namely, the high‐sulfur matrix and the low‐sulfur microfibrils being randomized by swelling. It has been suggested that (1) the modulus of swollen fibers increases with increase of the content of disulfide (SS) in keratins, (2) the volume fraction of high‐sulfur domains increases with increase of SS content, and (3) the number of intermolecular cross‐links in the rubber region of low‐sulfur proteins is virtually the same among keratins and reaches about 65–75% of the SS linkages in the corresponding proteins. Some discussion has been made on the SS bonding in situ, namely, SS linkages between the low‐sulfur proteins, between the low‐sulfur and the high‐sulfur proteins, and between the high‐sulfur proteins in keratins. © 1993 John Wiley & Sons, Inc.
Orientation distribution in the noncrystalline regions of biaxially drawn poly(ethylene terephthalate) film: A chain‐intrinsic fluorescence study
Authors: Gohil R. M. , Salem D. R.
Published: April 2003

We have studied development of the in‐plane distribution of “amorphous orientation” during sequential and simultaneous biaxial drawing of poly(ethylene terephthalate) film, using polarized intrinsic fluorescence. The machine direction (MD) draw ratio was always fixed at 3.5, and the transverse direction (TD) draw ratio was varied. The rate of increase in the proportion of TD‐oriented chains with increasing TD draw ratio is almost identical in the sequential and simultaneous processes up to a draw ratio of 2.7. At this point, sequential drawing starts to involve transverse realignment of MD‐oriented chains, which accelerates redistribution of orientation from the MD to the TD. Consequently, in sequential drawing, a “balanced” biaxial orientation distribution is achieved at a TD draw ratio significantly below the MD draw ratio, whereas at the same TD draw ratio in the simultaneous process, MD orientation remains dominant. At equal MD and TD draw ratios, the non‐crystalline chains in sequentially drawn film are predominantly oriented along the TD, but their orientation distribution is isotropic in simultaneously drawn film. High‐temperature annealing at fixed dimensions diminishes the proportion of TD‐oriented chains in films with transverse draw ratios < 2.5. We attribute this to a more highly developed crystallite network in the MD, which constrains orientational relaxation along the MD. A balanced distribution of amorphous orientation is directly responsible for achieving balanced tensile strength and balanced extensibility. © 1993 John Wiley & Sons, Inc.
The effects of γ irradiation on toughening mechanisms in rubber‐modified polymers
Authors: Birkinshaw C. , Buggy M. , Quigley F.
Published: April 2003

High‐impact polystyrene (HIPS) and acrylonitrile butadiene styrene (ABS) have been subject to γ irradiation in doses up to 20 and 12.5 Mrad, respectively. During tensile testing, both longitudinal extension and lateral contraction were simultaneously measured, allowing determination of volume strain, and from this to identify the relative contributions of crazing and shear yielding to the tensile deformation process. Both materials show a dose‐related increase in the strain at which crazing commences, though the relative change with dose in HIPS is much greater than in ABS. However, the contribution of crazing to total deformation remains high in HIPS when compared with ABS. Shear yielding is an important deformation process in ABS and the results indicate that this is relatively unaffected by irradiation, whereas the ability to craze is severely limited. The reduced ability to craze observed in both materials is considered to be the result of crosslinking in the rubbery phase. The notched impact strength of ABS is particularly sensitive to irradiation and again reflects the reduced ability to craze observed in the tensile testing. ABS fracture surfaces examined by scanning electron microscopy display reduced ductility in the irradiated material. © 1993 John Wiley & Sons, Inc.
Volatility of additives from polymers. Concentration dependence and crystallinity effects
Authors: Luston̆ J. , Pastus̆áková V. , Vas̆s̆ F.
Published: April 2003

The evaporation of 2‐hydroxy‐4‐methoxybenzophenone (HMB) from polypropylene was studied by an isothermal method at different concentrations of HMB ranging from 0.3 to 1.2 wt %. The evaporation of the additive was correlated according to first‐order kinetics. and rate constants of evaporation were calculated. A linear dependence of the rate constants of volatility on the initial concentration of the additive in the polymer was observed. This result suggests that in the given system, volatility is governed by evaporation from the polymer surface. Volatility of HMB from polypropylene depends on the degree of crystallinity of polypropylene. Samples with different degrees of crystallinity were prepared by quenching of the polymer blends and subsequent annealing at 423K. Isothermal measurements at 383 and 423K yielded higher rate constants for annealed samples than for quenched samples. The rate constant of evaporation at 383K was 20% higher for the annealed sample, whereas at 423K it was 27.5% higher. These results are interpreted on the basis of the concentration changes occurring during annealing. © 1993 John Wiley & Sons, Inc.
Effect of Fe(III) on the polymerization of butyl methacrylate initiated by a charge‐transfer mechanism
Authors: Baruah Shashi D.
Published: April 2003

The effect of the Lewis acid, iron(III) tris(oxalato)ferrate(III) tetrahydrate (Fe‐[Fe(C2O4)3].4H2O) (A) on the polymerization of butyl methacrylate (BuMA) initiated by a charge‐transfer mechanism has been studied in dimethyl sulfoxide (DMSO) at 60°C. 2,4‐dinitrophenylhydrazine (DNPH) was used as a nitrogen donor compound to initiate the polymerization in the presence of carbon tetrabromide (CBr4). Induction periods are observed for the polymerization initiated by DNPH and CBr4. The rate constant at 60°C for the polymerization of BuMA in the presence of A is 1.70×105L/mols−1. The molecular weight of polymers decreases with the increase of [ A ]. A probable reaction mechanism is proposed to explain the observed results. © 1993 John Wiley & Sons, Inc.
Structure‐property relationship of HTPB‐based propellants. I. Effect of hydroxyl value of HTPB resin
Authors: Manjari R. , Joseph V. C. , Pandureng L. P. , Sriram T.
Published: April 2003

Composite propellants based on hydroxyl‐terminated polybutadience (HTPB) resin are the most common contemporary solid propellants for launch vehicle and missile applications. A series of HTPB resins, manufactured by free‐radical polymerisation using a peroxide initiator, with varying molecular weights and hydroxyl values, was used in propellant formulation experiments with a view to studying the resin production variables and their influence on the resultant propellant properties. It is seen that HTPB resins with a wide range of hydroxyl values could be effectively utilized in propellant formulations. Also, propellants with higher strain capability and chain flexibility could be produced from lower hydroxyl value resins. © 1993 John Wiley & Sons, Inc.
Effect of imidization temperature on properties of polymide films
Authors: Chen Ker‐Ming , Wang Tsung‐Hsiung , King Jinn‐Shing , Hung Aina
Published: April 2003

Some mechanical and electrical properties of the BPDA/ODA/PDA polyimide film prepared on mylar followed by various cure schedules have been studied. It has been found by FTIR that the imidization reaches its maximum after a 200°C cure schedule for this polyimide. However, the optimum condition of curing is a 350°C cure schedule. Following this cure schedule, one can obtained a polymide film with good mechanical and electrical properties. © 1993 John Wiley & Sons, Inc.
Structure of poly(vinyl alcohol)‐iodine complex formed in the amorphous phase of poly(vinyl alcohol) films
Authors: Choi Yoon‐So , Miyasaka Keizo
Published: April 2003

The effect of syndiotactivity of poly(vinyl alcohol) (PVA) both on the formation and thermal stability of the complex formed in the amorphous phase of PVA films is investigated, and then a model of the complex is presented. The amount of the complex formed in syndiotacticity‐rich PVA is much larger than that formed in atactic PVA under a given iodine‐soaking condition, and the former complex has a higher thermal stability in the soaking solution than the latter. The complex formed in the amorphous phase is proposed to have such a structure as that in which a linear polyiodine I5− or I5− with a 3.1 A˚ periodicity is enveloped by four PVA segments of syndiotactic configuration with extended conformation. In this model, these four PVA chains participating in a complex are supposed to be fixed by interchain hydrogen bonds. The observed X‐ray meridional intensity curve of iodinated PVA film can be explained by a series of two I5−. © 1993 John Wiley & Sons, Inc.
Gelled membrane composed of dioctyldithiocarbamate substituted on poly(vinylchloride) and di (2‐ethylhexyl) dithiophosphoric acid
Authors: Levin Gideon , Bromberg Lev
Published: April 2003

Substitution of chlorine of poly(vinylchloride) (PVC) by dioctyldithiocarbamate (DODTC) groups results in a modified polymer (MP) with a glass transition temperature of between −43 and 84°C, depending on the degree of substitution. Formation of a gelled membrane composed of MP and di (2‐ethylhexyl) dithiophosphoric acid (DTPA), as both an ion carrier and a solvent, was demonstrated. The gelled membrane can be formed with the weight ratio between (MP) : (DTPA) as low as 1 : 99 or higher. The membrane is capable of selective separation of metal ions. © 1993 John Wiley & Sons, Inc.
The use of ultrasound to initiate ring‐opening polymerization
Authors: Stoessel S. J.
Published: April 2003

It has been discovered that a combination of heat and high‐power ultrasound can be used to initiate ring‐opening polymerization in cyclic bisphenol A polycarbonate oligomers. The polymerization can be conducted with or without the use of added chemical initiators. The use of ultrasound was extended to prepare glass‐filled composites. © 1993 John Wiley & Sons, Inc.
Microphase separation and crystallization of crystalline‐amorphous type block copolymer. I. Effect of solvent
Authors: Ishikawa Satoshi , Sasaki Sintaro , Fukutomi Takashi
Published: April 2003

The formation process of the microphase separation and crystallization of a crystallineamorphous type diblock copolymer [poly(tetrahydrofuran‐b‐isoprene)] in solution were studied by transmission electron microscope and wide‐angle X‐ray diffraction measurements. The morphologies formed from three kinds of solvent systems are discussed in relation to the crystallization of poly(tetrahydrofuran) sequence. © 1993 John Wiley & Sons, Inc.
Photocross‐linking of low‐density polyethylene. II. Structure and morphology
Authors: Qu Bao Jun , Rånby Bengt
Published: April 2003

Morphological structure and other properties of polyethylene photocross‐linked in the melt (XLPE) have been studied by wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), density, and swelling measurements. The WAXD measurements show that the crystallinity of polyethylene decreases with increasing gel content in the XLPE samples and that the regularity and the size of crystals are affected by photocross‐linking. DSC data confirm that photocross‐linking occurs preferentially in the amorphous and interfacial regions and causes depression of the melting point and decreases the heat of fusion. The density of XLPE apparently decreases with increasing gel content, which is due to decreased crystallinity and lattice expansion. The cross‐link density determined by the swelling measurements and evaluated using the Flory–Rehner equation correlates well with the changes in crystallinity and melting point. © 1993 John Wiley & Sons, Inc.
Radiation stability of PTFE with different crystallinity
Authors: Zhong Xiaoguang , Yu Li , Zhao Wenwei , Zhang Yuefang , Sun Jiazhen
Published: April 2003

In this work, the effects of radiation on polytetrafluoroethylene (PTFE) samples with different crystallinity were studied. Using Suwa's equation for calculating the number‐average molecular weight of PTFE, the radiation‐induced reduction in molecular weight was followed and the G values of scission of PTFE were also obtained on the basis of the changes in molecular weight. The G (scission) for as‐polymerized PTFE was 2.15 ± 0.01, whereas for sintered sample, which has a relative low crystallinity, G (scission) = 6.0 ± 0.14. © 1993 John Wiley & Sons, Inc.
The effect of plasma‐deposited siloxane coatings on the barrier properties of HDPE
Authors: Morra M. , Occhiello E. , Garbassi F.
Published: April 2003

Thin polymeric films were deposited from siloxane plasma on the surface of polyethylene. The surface composition of the films was measured by X‐ray photoelectron spectroscopy (XPS) and the permeability to O2 by an analytic gas permeability fractometer. No significant improvement of barrier to O2 was observed with 200 nm‐thick coatings. When the siloxane layer was subjected to a further O2 plasma treatment, a threefold decrease of permeability to oxygen was recorded. Results are discussed on the light of the effect of the O2 plasma on the siloxane backbone. © 1993 John Wiley & Sons, Inc.