bluuebunny/crossref_metadata_2025 huggingface dataset:
Radiation pyrometry on semitransparent sheets. I: Gray media
Authors: Hajji N. , Spruiell J. E.
Published: May 2005

Radiation pyrometry is often used in the measurement of temperature during polymer processing operations such as film blowing. Since polymers are semitransparent in the infrared, the temperature measured by the pyrometer will correspond to some average of the internal temperature distribution. In the present study, an expression is derived for this average when a sheet with a thermal gradient across its thickness is considered. This expression is used to study the effect of the absorption characteristics of the sheet on this average when the material is a gray medium.
Thermoplastic polyheterocycles. I: Polyalkylene‐benzoxazoles
Authors: Preston J. , Tropsha Y. , Trexler J. W.
Published: May 2005

Polyalkylenebenzoxazoles of high molecular weight (inherent viscosity values from 0.76 to 2.95) were prepared from 4,6‐diaminoresorcinol dihydrochloride and aliphatic diacids in polyphosphoric acid by heating at 180 to 200°C for 3–5 h. Melting points of the polymers ranged from 148 to 423°C, depending on the length of the alkylene chain. Glass transition temperatures were relatively low, ranging from 50 to 100°C and did not show the pronounced odd/even effect noted for melting points. In all cases, rapid weight loss occurred above 400°C. No evidence for the formation of a molecular composite was observed in an attempt to prepare in situ a rod‐like polybenzoxazole in a polyalkylenebenzoxazole.
Thermodynamics of processing synthetic fibers
Authors: Mukhopadhyay S. K.
Published: May 2005

This paper deals with a new approach to nonlinear and nonequilibrium thermodynamics. The new concept, developed by P. H. Lindenmeyer, states that in a heat‐setting process, with the same average processing temperature, the addition of a sinusoidal fluctuation (approximately) can produce two opposite changes depending upon the frequency and amplitude of the temperature fluctuation. Preliminary experimental results obtained on nylon 6 monofilaments using a flexible thermomechanical analyzer have clearly shown that the physical properties (in this case torque‐twist modulus) depend not only upon the average temperature but also upon its time rate of change.
Spin coating of very thin polymer films
Authors: Extrand Charles W.
Published: May 2005

Very thin films of natural rubber, polystyrene, and poly(methylmethacrylate) have been spun‐cast on silicon wafers from dilute solutions of toluene and cyclohexane. Layers were uniform across the wafers, ranging from 0.5 to 170 nm, as measured by ellipsometry. Their average thickness e increased with solution concentration and decreased with rotational rate w. Changing the volume of the solution pipetted onto the wafers did not affect the final thickness, whereas changing the solvent did. The previously reported empirical relation for much thicker films, e α ω−1/2, held over the range investigated here.
The effect of lithium chloride on polybenzimidazole and polysulfone blend fibers
Authors: Chung Tai‐Shung
Published: May 2005

Polybenzimidazole (PBI) and polysulfone (PS) do not form miscible blends; however, the tensile properties of the polymer blend in fibers, and the fiber process window, are strongly dependent on the presence of LiCl. The addition of LiCl opens the molecular chains and reduces dope viscosity. As a result, LiCl increases the stiffness of PBI/PS fibers while making them brittle. The process window for fabricating useful fibers seems to be narrowed by the presence of LiCl. PBI/PS fibers spun from a dope that does not contain LiCl have a broad process window and their overall fiber performance is superior. LiCl also reduced the degree of sulfonation during the stabilization process.
Photoinitiated crosslinking of low density polyethylene. III: Degradation and stabilization of photocrosslinked polyethylene
Authors: Qing Yan , Wenying Xu , Rånby Bengt
Published: May 2005

Electron spectroscopy (ESCA) and reflectance infrared spectroscopy (ATR) were used to measure surface oxidation of photocrosslinked polyethylene. The deterioration of bulk properties during an artificial weathering test was also measured. It was found that the UV‐irradiation during crosslinking process decreases the stability of the material considerably. Three kinds of antioxidants and photostabilizers (hindered phenols, hindered amines, and organic sulfides) which have no absorption in the UV region of 300 to 400 nm were added before crosslinking to improve the stability of the crosslinked material. Neither the rate nor the degree of photocrosslinking at different depths of the sample were affected significantly by these additives. It was found possible to prevent the decrease in stability due to the photocrosslinking by using small amounts of a stabilizer, e.g. 0.05% Tinuvin 770 (hindered amine).
Spherulitic crystallization: An analysis of inverse stefan problems in cartesian, cylindrical, and spherical coordinate systems
Authors: Wang Yu F. , Lloyd Douglas R.
Published: May 2005

Spherulitic crystallization presents an inverse Stefan problem, which is solved by numerical methods using the DuFort‐Frankel scheme and Lagrangian coordinate systems. The numerical solution shows excellent agreement with the analytical solution in the Cartesian coordinate system. A systematic error in the numerical solution for the spherical and cylindrical coordinate systems is examined by a material balance for the system. The systematic error was found to decrease rapidly as the dimensionless time increased and the grid spacing decreased.
Viscoelastic properties of a 60 mol% para‐hydroxybenzoic acid/40 mol% poly(ethylene terephthalate) liquid crystalline copolyester. II: Effect of shear history
Authors: Driscoll P. , Hayase S. , Masuda T.
Published: May 2005

Temperature sweeps of dynamic viscoelastic properties have shown that phydroxybenzoic acid (PHB)‐based liquid crystalline polyesters, specifically in this case those copolymerized with poly(ethylene terephthalate) (PET), can be subjected to considerable supercooling if initial heating curves are compared to subsequent cooling curves, indicating that this type of material can be in quite different states even at the same temperature, depending on thermal history. Utilizing this supercooling behavior, viscoelastic properties of a 60 mol% PHB/40 mol% PET material produced by Unitika were monitored before and, particularly, after large‐scale shear deformation to determine how potential structure changes induced by the shear are reflected in viscoelastic properties immediately, and with time. According to dynamic viscoelastic temperature sweep data four quite different initial states were employed including conditions with, as well as largely free of, crystallites. However, in all cases, post‐shear monitoring showed decreased G′ and G″ values with almost no evidence of return towards initial values within approximately 25 min. These results, in addition to furthering somewhat the fundamental understanding of the flow and relaxation properties of liquid crystalline polymers, may be useful in polymer processing, where large‐scale shear deformations employed in forming processes appear to be capable of changing considerably the subsequent behavior of such materials.
Kinetic model and thermal properties of a thermally cured thermosetting polycarbonate
Authors: Delgado R. , McNeill D. M. , Hawley M. C. , Demeuse Mark
Published: May 2005

Diethylene gycol bis(allyl carbonate) is widely used for the production of optical plastic for lenses, safety glasses and guards, watch crystal, and instrument windows. The monomer polymerizes via a free radical mechanism using benzoyl peroxide as an initiator to form a thermosetting polycarbonate. This polymerization process involves a long cure cycle at temperature below 100°C. Differential scanning calorimetry (DSC) and rheometric dynamic testing are used to characterize the thermal and kinetic properties. These properties include the heat of reaction, activation energy, rate constants of polymerization, and time and extent of cure at gelation.
Developing critical extrusion parameters for nylon 6, nylon 66, and nylon 46 polyamide from the rheology data
Authors: Shah Pravin L.
Published: May 2005

This paper describes a new approach to the rheological characterization of engineering plastics such as nylon 6, 66, and 46 polyamides using a capillary rheometer. The melt viscosity data as a function of temperature, shear rate, and residence time were measured and evaluated to demonstrate how to accurately predict critical extrusion parameters, such as barrel temperature profile, stock temperature window, and the screw design requirements, for extruding strip, tubing, and profiles. The results of this work provide a practical and simple quality control tool to select a polyamide resin for optimum processing, and to develop critical processing parameters for extrusion.
Toward a high‐impact isotactic polystyrene
Authors: Cazzaniga Luigi A. , Cohen Robert E.
Published: May 2005

Brittle isotactic polystyrene has been toughened by the presence of emulsified rubber particles. Semicrystalline diblock copolymers of isotactic polystyrene and polybutadiene functioned successfully as emulsifying agents, as revealed by the results of scanning and transmission electron microscopy. Semiquantitative measures of the toughness of the various materials were obtained via a home‐built micromechanical testing device. The minimum amount of copolymer required to achieve emulsified morphologies and significant toughness depended on the thermal history of the material being tested.
Strength development in powder processing of poly(tetrafluoroethylene)
Authors: Hambir S. S. , Jog J. P. , Nadkarni V. M.
Published: May 2005

Poly(tetrafluoroethylene) (PTFE) is a versatile engineering plastic with excellent chemical and electrical resistance, a wide working temperature range, and a low coefficient of friction. PTFE is processed by the powder processing technique because of its high melt viscosity. The powder processing of polymers involves cold compaction of the polymeric powders, followed by sintering of the preforms at elevated temperatures. Sintering is a critical operation since the mechanical properties of the products are determined by the interparticle coalescence and diffusion of polymer chains across the interface. The results of the studies of the strength development during sintering of PTFE are reported here. The strength was measured in terms of the tensile strength at break, and the dependence of the tensile strength on compaction pressure, particle size, and processing time is discussed. The time dependence of strength development could be described by a diffusion controlled process in which the strength is proportional to the 1/4th power of the processing time.
Molecular dynamics of polybenzimidazole and contributions from chaos
Authors: Iwamoto N.
Published: May 2005

Molecular dynamics has been used to study possible dynamic mechanisms that may contribute to the property degradation known to exist for polybenzimidazole (PBI) upon hydration. During this study, chaotic movements of a chain pair were observed. Changes in onset and duration of this movement were also observed, which depended upon both hydration state and stress direction involved. Such trends suggested that specific mechanistic pathways may exist that could directly lead to property (such as modulus) loss.
Multiobjective dynamic optimization of a nonvaporizing nylon 6 batch reactor
Authors: Wajge Rajesh M. , Gupta Santosh K.
Published: May 2005

Multiobjective dynamic optimization has been carried out on a nonvaporizing nylon 6 batch reactor. Three objective functions have been identified, viz., minimization of the concentration of unreacted monomer in the product, minimization of the dimer concentration, and minimization of the reaction time, for producing polymer having a specified value, μn, d, of the number average chain length. Two problems have been studied in this paper, each consisting of two objective functions taken from the above set. Pareto solutions have been generated using an algorithm based on Pontryagin's minimum principle and the method of Lagrangian multipliers. The effects of various physical and computational parameters have been studied, and methods have been developed to overcome the numerical difficulties that arise during the solution. The Pareto sets so generated can be coupled with the surrogate worth trade‐off (SWT) method, which facilitates interaction with a decision maker (DM). The optimal temperature histories obtained for the two problems studied are quite different and suggest that one must solve the three‐dimensional problem in which the vector objective function incorporates all three objective functions. Results from the present study could be used as starting guesses to converge rapidly on the solution of the three‐dimensional problem.
Thermal behavior of hydrostatically extruded polycarbonate and high‐impact polystyrene
Authors: Ariyama Takashi , Nakayama Toshio
Published: May 2005

Effects of hydrostatic extrusion on the thermal properties of polycarbonate (PC) and of high‐impact polystyrene (HIPS) were studied using differential scanning calorimeter (DSC) measurements. A glass transition temperature (Tg) and a peak temperature were determined from the DSC curves for both PC and HIPS extrudates. The Tg values of the PC extrudates, with a percentage reduction in area, R, from 40 to 50%, change appreciably from the value for the as–received PC. The results of the hydrostatic extrusion of the PC billets suggest that a two stage deformation process of molecular chains may be involved. Shear‐banding is observed for HIPS extrudates with R = 30 to 60%; this fact indicates that a sub‐glass transition (β‐transition) occurs at temperatures below Tg. It is suggested that the molecular chains of the HIPS extrudate with R = 70% are oriented in the direction of hydrostatic extrusion. The deformation mechanism of molecular chains caused by the hydrostatic extrusion is discussed.
Effect of grafting degree and side PEO chain length on the ionic conductivities of NBR‐g‐PEO based polymer electrolytes
Authors: Kim Dong‐Won , Park Jung‐Ki , Gong Myoung‐Seon , Song Hae‐Young
Published: May 2005

Comb‐shaped graft polymers were synthesized and complexed with a LiCF3SO3 salt to form a new class of polymer electrolytes. The polymers based on an acrylonitrile‐butadiene copolymer (NBR) have pendant, short‐chain poly(ethylene oxide) (PEO) grafted onto a butadiene unit. The characteristics of these polymer electrolytes were investigated in terms of number of pendant EO groups and grafting degree in the graft copolymer. The maximum conductivity was observed at the optimum side PEO chain length, and the PEO chain length for the maximum conductivity decreased with an increase in the grafting degree. And a solid 7Li NMR relaxation technique was used to study the local environments and dynamics of the ions in the polymer electrolytes. The maximum conductivity value obtained from our study was three orders of magnitude higher than that of classical PEO‐based electrolytes at ambient temperature. These improved low temperature conducting polymers with higher relative mechanical strength are expected to be suitable for practical applications, such as in rechargeable lithium batteries or electrochromic devices.
Viscoelastic‐plastic deformation behavior of polypropylene after cyclic preloadings
Authors: Ariyama Takashi
Published: May 2005

Stress‐relaxation behavior is studied in polypropylene samples subjected to different cyclic preloadings and to simple tension. The relaxation tests are performed under different sets of strain amplitude, number of cycles, and strain rate, using a closed‐loop, electrohydraulic, servocontrolled testing machine. The calculated stress‐strain curves are determined from a constitutive equation based on an overstress theory in which an equilibrium stress and a viscosity function are treated. The calculated results agree well with the experimental ones. It is concluded that the overstress theory explains the nonlinear viscoelastic‐plastic behavior of polypropylene.
Thermal and mechanical properties of injection molded liquid crystalline polymer/amorphous polymer blends
Authors: Engberg K. , Strömberg O. , Martinsson J. , Gedde U. W.
Published: May 2005

Injection molded samples of binary blends of Vectra (LCP) and the three amorphous polymers polyethersulfone (PES), polycarbonate (PC), and aromatic poly(ester carbonate) (APEC) have been subjected to morphological and rheological characterization, and coefficients of linear thermal expansion and Young's moduli have been determined. The Young's modulus of the PES/LCP blends exhibited a near lower‐bound behavior that could be predicted by the one‐adjustable‐parameter equations of Halpin‐Tsai (ζ = 0.18) and Takayanaga (b = 0.23), whereas the coefficients of linear thermal expansion followed the Takayanaga equation with a value of b = 0.50. The chain orientation of the LCP component was essentially constant in all PES/LCP blends with a Herman's orientation parameter of 0.39 ± 0.03. Transesterification reactions led to randomization of the constituents of the PC/LCP and APEC/LCP blends. The effect was more pronounced in the PC/LCP blends. The introduction of the LCP into the PC/LCP blends led to no reduction in melt viscosity and no self‐reinforcement. APEC/LCP exhibited self‐reinforcement in blends with a content greater than 27 vol% LCP, and especially the blend with 67 vol% LCP. The self‐reinforcement was caused by the presence of an oriented LCP phase, confirmed by X‐ray diffraction, and by improved interfacial bonding, presumably resulting from the transesterification reactions occurring at the phase boundaries.
Fatigue crack propagation behavior of cellulose esters
Authors: Moskala Eric J. , Pecorini Thomas J.
Published: May 2005

The effect of plasticizer concentration on fatigue crack propagation (FCP) rate in cellulose acetate‐propionate (CAP) was determined. Compact tension specimens were machined from 6.2 mm‐thick injection molded plaques and tested on an MTS servohydraulic testing machine using a sinusoidal waveform with a frequency of 1 Hz. Two FCP mechanisms were identified: a crazing mechanism, which dominated at low values of stress intensity factor range, ΔK, and a shear yielding mechanism, which dominated at high values of ΔK. The value of ΔK at the onset of the transition from the crazing mechanism to the shear yielding mechanism was a function of plasticizer concentration, and therefore yield strength of the CAP. The transition in crack propagation mechanism created a V‐shaped feature on the fracture surface, which could be used to weight the contributions from the two crack propagation mechanisms to the overall FCP rate.
The behavior of bubbles in Bueche model fluids
Authors: Brujan Emil‐Alexandru
Published: May 2005

The nonlinear oscillation of a spherical gas bubble in polymer solutions was theoretically analyzed. Using the rheological equation of Bueche model fluid, the equation of motion and the pressure equation for a bubble are derived. According to the numerical calculations, the effects of rheological properties and initial radius of the bubble on the bubble radius‐time history, pressure at the bubble wall, critical and equilibrium radii of the bubble, as well as pressure distribution in liquid are discussed.
About the existence of a percolation threshold in solid solution of N‐isopropylcarbazole/polycarbonate mixtures
Authors: Santos‐Lémus Simón J.
Published: May 2005

Direct current (DC) dark conductivity, (σ) measurements have been carried out in thin films of N‐isopropylcarbazole/polycarbonate mixtures (NIPC/PC) for relative weight ratio (x) in the range 2 to 80% by weight of NIPC in PC at room temperature. The experimental results suggest a non‐percolative transport in the concentration range explored. In the range 20 to 80%, a hopping character and power law dependence σ ∼ (x − xc)3 is found with xc = 0.16. In the range 2 to 20% these relations are masked by the influence of hops involving polymer matrix which makes such a system not a suitable model for testing percolation ideas.
Characterization of poly(3‐octylthiophene). II: Melt rheological characterization
Authors: Heffner Glenn W. , Rochefort Wille E. , Pearson Dale S.
Published: May 2005

The poly(3‐alkythiophenes) are electrically conducting polymers which are of particular interest due to their melt‐processibility. We have studied the melt properties of poly(3‐octylthiophene) (P3OT) by dynamic rheological measurements at temperatures between 180 and 250°C. The samples investigated have molecular weights in the range Mw = 30,000 to 400,000 and have been carefully characterized by dilute solution techniques, Residual iron chloride, a reagent used in the polymerization of these materials, was found to cause a high degree of crosslinking in the polymer melt. By contrast, samples which had been carefully purified demonstrated a negligible rate of crosslinking in a nitrogen atmosphere; however, the presence of air and higher temperatures were found to increase the rate of crosslinking substantially. The temperature dependence of the viscoelastic properties was characterized according to the principles of time‐temperature superposition, and the influence of molecular weight was also evaluated. Overall, the rheological behavior was determined to be similar to that commonly observed for linear flexible polymers, which is in agreement with the results of our solution characterization of these materials.
Structure and mechanical anisotropy of cold‐rolled ultrahigh molecular weight polypropylene
Authors: Hibi Sadao , Niwa Takahiro , Wang Chi , Kyu Thein , Lin Jar‐Shyong
Published: May 2005

Wide angle X‐ray diffraction pole figure, small angle X‐ray scattering (SAXS), and refractive index techniques have been employed to investigate structure and deformation mechanisms in unidirectionally cold‐rolled ultrahigh molecular weight polypropylene (UHMWPP) films. All reciprocal lattice vectors (plane normals) of (110), (040), and (130) were found to populate in the film normal (thickness) direction, suggesting that more than one orientation process must be involved in the deformation. SAXS studies on the cold‐rolled UHMWPP reveal an oriented lamellar structure with its long axis perpendicular to the rolled direction, however, the lamellae are somewhat tilted. Refractive index and tensile measurements were undertaken to determine the optical and mechanical anisotropy of the cold‐rolled UHMWPP films. A similar study was undertaken of unidirectionally rolled conventional polypropylene (PP) for comparison.
The leveling of thermosetting waterborne coatings. Part II: Drying of coated wet films
Authors: Kojima Shunji , Moriga Toshinori
Published: May 2005

Evaporation behavior of water/solvent blends was estimated using the universal functional activity coefficient, UNIFAC, method. The evaporation rate from a free surface of a waterborne coating, WBC, containing a co‐solvent was experimentally determined. These results were used to estimate the evaporation rate from wet films of a WBC containing a variety of co‐solvents with a range of initial thickness. Knowing the composition of the WBC during the drying process, the change in the viscosity and the surface tension was determined. The results strongly support the development of a surface tension gradient in the film. It is also suggested that a surface tension gradient would accelerate the leveling of the ribs if a proper co‐solvent were employed.
Effect of casting solvent on the heterogeneity of films of polymer blends
Authors: Lu Shaoxiang , Pearce Eli M. , Kwei T. K.
Published: May 2005

The miscibility window of the 50/50 w/w poly(styrene‐co‐4‐vinylphenyl)‐dimethylsilanol/poly(n‐butyl methacrylate) (ST‐VPDMS/PBMA) blends prepared from toluene was studied and determined to be in the VPDMS composition range of 4 to 18 mole% in the copolymers. The observed miscibility window was to be compared to the range of 9 to 34 mole% found for the blends prepared from methyl ethyl ketone which was capable of competing for hydrogen bonding. The fact that the observed miscibility windows are influenced by the choice of solvents illustrates that an equilibrium state of polymer mixing is not always attained in solvent casting films and that caution needs to be exercised in studying polymer miscibility when solvent cast films are used.
The effect of crystallinity on the light scattering of regenerated cellulose tubular films
Authors: Larena Alcia , Pinot Gabriel
Published: May 2005

An experimental study of the effect of crystallinity on the light scattering of regenerated cellulose tubular films is reported. Several films were prepared by varying manufacturing conditions, so that thickness and surface roughness were maintained approximately constant and the degrees of crystallinity varied between 38 and 66%. The scattered radiation intensity, measured between 220 and 550 nm decreases with the increasing wavelength. It was demonstrated that for the polymeric films studied, there was excellent agreement between crystallinity and scattering radiation intensity for a given wavelength. It was found that for crystallinity values less than around 57%, scattered radiation intensity decreases with increasing crystallinity, the reverse of that for crystallinity values greater than that percentage.
Impact behavior of microcellular foams of polystyrene and styrene‐acrylonitrile copolymer, and single‐edge‐notched tensile toughness of microcellular foams of polystyrene, styrene‐acrylonitrile copolymer, and palycarbonate
Authors: Collias Dimitris I. , Baird Donald G.
Published: May 2005

In the first part of this series of papers, the tensile properties of microcellular foams of polystyrene (PS), styrene‐acrylonitrile copolymer (SAN), and polycarbonate (PC) were reported. In this part, the impact properties of unnotched, sharply and bluntly notched samples of microcellularly foamed PS and SAN samples were studied. Furthermore, the effects of the sharpness of the notch as well as of the speed of the test were studied by comparing the impact tests with the single‐edge‐notched (SEN) tensile tests, which were carried out for the PS, SAN, and PC sample. Some limited improvement in impact and SEN tensile properties was exhibited in some experimental conditions. The impact properties of microcellularly foamed PC samples are reported elsewhere.
Compatibility and tensile behavior of polypropylene/ethylene‐propylene rubber blends
Authors: Nomura T. , Nishio T. , Fujii T. , Sakai J. , Yamamoto M. , Uemura A. , Kakugo M.
Published: May 2005

This study clarifies and quantifies factors which increase the ductility of a low‐molecular‐weight propylene homopolymer having an intrinsic viscosity of 0.89 dl/g. The tensile behavior of homopolymer/ethylene‐propylene rubber (EPR) blends was studied from the viewpoint of the associated molecular structure of EPR and its compatibility with the homopolymer. When EPR is “dissolved” in a homopolymer, the glass transition temperature (Tg) of the amorphous phase of a homopolymer was found to shift to a lower temperature, with homopolymer/EPR compatibility being subsequently evaluated using this shift, i.e., Δtg. Results show two conditions are required to improve the ductility of the low‐molecular weight propylene homopolymer: ΔTg must be ≥ 3°C and ≥ 30 wt% EPR must be blended with the homopolymer.
Tension effects on the properties of oxidized polyacrylonitrile and carbon fibers during continuous oxidation
Authors: Tsai Jin‐Shy
Published: May 2005

In this study we used continuous oxidizing equipment to produce carbon fiber. The results show when the stretch of the fiber during continuous oxidation is increased, the orientation and modulus of resultant carbon fiber is unexpectedly decreased. This effect is much different from other published results. In this case, the stretching occurs after the cyclization of the molecular chains in the amorphous region. The stretching leads to the scission of some cyclized molecular chains in the amorphous region and the shrinkage of the crystalline region.
Change of molecular weight distribution of statistical poly(styrene‐co‐acrylonitriles) with compositio of copolymer
Authors: Mencer H. J. , Gomzi Z. , Rogošić M.
Published: May 2005

Statistical poly(styrene‐co‐acrylonitrile) (SAN) copolymes with varying mole fractions of comonomer units have been synthesized in a batch reactor. The intrinsic viscosity and gel permeation chromatography (GPC) patterns of model copolymer samples were the basic experimental results. Chromatographic patterns of SAN copolymer samples were converted into molecular weight distributions and afterwards fitted to the theoretical distribution functions. The correlation between the composition of copolymers and the best fitted model distribution (Schulz's two parameters distribution in this case) was established. The treatment of data shows that parameter α is inversely proportional to the content of acrylonitrile units in the sample and indicates the molecular weight interval. Parameter b shows the invariability of the molecular weight distribution shape.
Magnesium chloride‐supported, high‐mileage catalysts for olefin polymerization. V. BET, porosimetry, and x‐ray diffraction studies
Authors: Chien James C. W. , Wu Jiun‐Chen , Kuo Chi‐I
Published: May 2005

The physical state of the material obtained during the various stages of preparation of a typical MgCl2‐supported, high‐mileage propylene polymerization catalyst was studied by BET, mercury porosimetry, and x‐ray diffraction techniques. The starting MgCl2 and the substance after HCl treatment have negligible BET surface areas. Mercury porosimetry showed that they have large pores with radii > 200 nm which are probably crevices between MgCl2 crystallites. The most pronounced physical changes occur during dry porcelain ball milling in the presence of ethyl benzoate. After 60 h or more of ball milling the material had a 5.1–7.3 m2 g−1 BET surface area, twice the pore surface area, and a smaller pore radius than before ball milling and a large reduction in crystallite sizes to almost ultimate dimensions. The crystallites were probably held together by complexation with ethyl benzoate in the form of large agglomerates. Subsequent reactions with p‐cresol and triethyl aluminum had minor effects in further reduction of the MgCl2 crystallite size but efficiently brokeup the agglomerates. The final refluxing with TiCl4 increased the BET surface area to 110–150 m2 g−1 but may have increased the crystallite size somewhat due to cocrystallization of TiCl3 and AlCl3 with MgCl2. There may have been only 8–10 crystallites in each catalyst particle. The surface structure of the catalyst resembled those of the classical Ziegler‐Natta γ‐TiCl3·0.33 AlCl3 catalyst.
Metal chelates in vinyl polymerization: Kinetics and mechanism of acrylonitrile polymerization initiated by Cu(II) imine complexes
Authors: Marjit D. N. , Kalpagam V. , Nandi U. S.
Published: May 2005

The free radical polymerization of acrylonitrile (AN) initiated by Cu(II) 4‐anilino 2‐one [Cu(II) ANIPO] Cu(II), 4‐p‐toluedeno 3‐pentene 2‐one [Cu(II) TPO], and Cu(II) 4‐p‐nitroanilino 3‐pentene 2‐one [Cu(II) NAPO] was studied in benzene at 50 and 60°C and in carbon tetrachloride (CCl4), dimethyl sulfoxide (DMSO), and methanol (MeOH) at 60°C. Although the polymerization proceeded in a heterogeneous phase, it followed the kinetics of a homogeneous process. The monomer exponents were ≥2 at two different temperatures and in different solvents. The square‐root dependence of Rp on initiator concentration and higher monomer exponents accounted for a 1:2 complex formation between the chelate and monomer. The complex formation was shown by ultraviolet (UV) study. The activation energies, kinetics, and chain transfer constants were also evaluated.
Electrolytically initiated polymerization of N‐vinylcarbazole
Authors: Mano Eloisa B. , Calafate Bettina A. L.
Published: May 2005

Polymerization of N‐vinylcarbazole was studied systematically using electroinitiation with several quaternary ammonium salts as electrolytes in methylene chloride solution. Polymer was obtained only when the following electrolytes were used: tetraethylammonium perchlorate, tetrabutylammonium perchlorate, and tetrabutylammonium fluoroborate. Polymeric products of molecular weight 104–105 were formed in the anodic compartment of a divided cell. IR and 13C‐NMR spectra showed that the structures of the polymers were similar to those produced by conventional cationic polymerization, which suggests a similar mechanism for the resulting anodic product.
Selective surface modification of polymers by means of hydrogen and oxygen plasmas
Authors: Clark D. T. , Wilson R.
Published: May 2005

An ESCA investigation has been made of the changes in surface functionalization for a series of polymers effected by means of low‐powered inductively coupled rf plasmas excited in hydrogen and oxygen. Reactions in each case are confined to the outermost surfaces of the polymer films and the use of oxygen plasmas leads to extensive oxidative functionalization. Bisphenol‐A polycarbonate and polyethylene terephthalate exhibit similar overall reactivities to both oxygen and hydrogen plasmas, while polystyrene is shown to be substantially more reactive than high‐density polyethylene to the plasma treatments of interest in this work. Comparison has been made of the effects of straight hydrogen and oxygen plasmas and of sequential hydrogen/oxygen and oxygen/hydrogen plasma treatments.
Polymerization of glycidol and its derivatives: A new rearrangement polymerization
Authors: Vandenberg E. J.
Published: May 2005

Anionic (KOH) polymerization of glycidol, or its trimethylsilyl ether (TMSGE) followed by hydrolysis, gives a low molecular weight, largely amorphous polymer that is not the reported 1,3‐polyglycidol but, based on 13C‐NMR, largely a 1,4‐poly(3‐hydroxyoxetane) with much branching. This result is achieved by a simple rearrangement of the usual, propagating secondary oxyanion to a primary one. Substantial amounts of four dimers (5–10%), four trimers, and some tetramers were also found. One dimer was isolated and shown to be glycidyl glycerin, the usual thermal dimer from glycidol. Possible structures of the other dimers are proposed. The polymerization appears to begin with the rapid formation of the glycidoxy anion , formed by base abstraction of a proton from glycidol and by nucleophilic displacement of the SiMe3 group from TMSGE. Other bases such as KOtert‐Bu give similar 1,4 polymer for glycidol but, with TMSGE, there is considerable 1,3 polymerization. Detailed mechanisms are proposed. The polymer perpared from R‐TMSGE with KOH was highly crystalline, high melting (166°C), H2O soluble, isotactic poly(3‐hydroxyoxetane). The cationic polymerization of tert‐butyl glycidyl ether (TBGE) and TMSGE gave low molecular weight 1,3 polyethers. The TBGE polymer was all head‐to‐tail whereas the polyglycidol from TMSGE contained extensive head‐to‐head chain units with considerable branching. Mechanisms for these interesting differences are proposed.
A study of molecular weight of methyl methacrylate–styrene copolymer
Authors: Bataille Pierre F. , Granger Francois
Published: May 2005

An alternating copolymer of methyl methacrylate and styrene was obtained by the reaction of these two monomers in the aqueous phase and in presence of zinc chloride acting as complexing agent. It was found that the optimum conditions were obtained when the monomer concentrations are equal. The molecular weight and the molecular weight distribution were obtained by gel permeation chromatography (GPC). The polymers obtained have a very narrow molecular weight distribution. A model which takes into account the various parameters is proposed.
Analysis of some phenolic copolymer mixtures by electrometric titration techniques
Authors: Chatterjee S. K. , Katyal Anita
Published: May 2005

Some two‐, three‐ and four‐component phenolic copolymers have been characterized, and mixed in definite stoichiometric proportions. The total amount of acidic and basic functional groups in a given weight of the copolymer mixture have been calculated from the characteristic parameters of the polymer components. Analysis of these copolymer mixtures by electrometric titration techniques revealed an excellent correlation between the calculated and observed values of functional groups.
Thermal polymerization of N‐tert‐butylacrylamide in 1,4‐dioxane
Authors: Aşikoğlu Bi̇lge , Kiliç Soner , Baysal Bahatti̇n M.
Published: May 2005

The kinetics of the thermal polymerization of N‐tert‐butylacrylamide were investigated in 1,4‐dioxane as solvent, in the 65–80°C temperature range. It was found that the overall rate of polymerization which was determined by a gravimetric method is proportional to the 1.9 power of monomer concentration at 70°C. The rate of initiation was determined by ESR spectroscopy using DPPH as an inhibitor, and it was found that the order of initiation rate is 1.8 with respect to monomer concentration at 70°C. The overall activation energy for the thermal polymerization of N‐tert‐butylacrylamide was found to be 64 ± 9 kJ mol−1 in the 65–80°C temperature range. The activation energy for the rate of initiation was also determined and it was found to be 90 ± 23 kJ mol‐1.
The effect of molecular weight on the behavior of hydrophobic polyacids
Authors: Strauss U. P. , Andrechak J. A.
Published: May 2005

The effect of the degree of polymerization on the potentiometric titration behavior of alternating copolymers of maleic anhydride and alkyl vinyl ethers was investigated. Apparent abnormalities in the titration curves of the lower oligomers were attributable to endgroups. After accounting for these effects, the potential was found to decrease with diminishing molecular weight. However, the decreases were much more pronounced with the butyl, pentyl, and decyl copolymers which have compact conformations at low degrees of deprotonation, than with the propyl copolymer which shows random coil behavior over its whole ionization range. The standard free energy of complete deprotonation, ΔG°, generally increased with the degree of polymerization, but this increase was relatively small compared to the difference between ΔG° of the monomer and ΔG° of the lowest oligomer investigated.
Direct mass spectrometry of polymers. XII. Thermal fragmentation processes in poly‐α‐aminoacids
Authors: Ballistreri Alberto , Giuffrida Mario , Maravigna Pietro , Montaudo Giorgio
Published: May 2005

The thermal fragmentation processes in poly‐α‐aminoacids have been investigated by direct pyrolysis–Mass Spectrometry. The mass spectral data show that the pyrolytic breakdown of polyglycine, polysarcosine, and polyproline leads to the formation of cyclic oligomers. Polyalanine, polyphenylalanine, and polytyrosine decompose yielding compounds with olefin and nitrile end‐groups. Finally, in the case of poly‐α‐methylglutamate, the primary thermal process is the loss of methanol with consequent formation, along the polymer chain, of pyroglutamic units, which yield cyclic dimer as main pyrolysis product.
Particle Growth by Coalescence and Agglomeration
Authors: Koch Wolfgang , Friedlander Sheldon K.
Published: May 2005

A dispersed system is considered which will form its condensed phase at high temperatures and is characterized by a high density of very small supercritical nuclei. It is assumed that particle growth is determined by coagulation and (viscous flow) coalescence. The morphology of the final particles depends on the temperature history of the formation process. Compact spherical particles and agglomerates may be formed. Agglomerates result when the process temperature decreases to an extent that coalescence is quenched in the course of the growth process. The average size of the primary particles in the agglomerates is calculated by using the analysis and the approximations described in a previous paper. The growth kinetics of the primary particles are presented in a dimensionless form. The results show that the dimensionless size of the primary particles depends only on the ratio of two characteristic lengths of the system. For small values of this ratio, the size of the primary particles composing the agglomerates, although much greater than the initially formed nuclei, is independent of the volume fraction of the condensed aerosol. For large values of this parameter, the theory merges into the classical theory of perfectly coalescing spheres.
Development of an Automatic System for Measuring Particle Charge and Size distributions in a clean room
Authors: Adachi Motoaki , Liu Benjamin Y. H. , Pui David Y. H.
Published: May 2005

An automatic measuring system was developed to perform simultaneous measurements of particle size and charge distributions in a clean room and other aerosol sources. The system consists of an electrostatic condenser (EC) and an optical particle counter (OPC), which are controlled by a personal computer (PC). The PC automatically varies the voltage on the EC and converts the corresponding OPC counts to charge distributions. The reliabilities of the data inversion method and the automatic measuring system were confirmed by theoretical and experimental examinations, respectively. In the theoretical examination, inverted charge distributions were tested and compared with various assumed input distributions. In the experiment where monodisperse aerosols neutralized by a 85Kr neutralizer were used, the measurement results agreed well with the theoretical Boltzmann charge distribution. The application of this technique is demonstrated by the measurement of charge and size distributions of aerosols in a clean room.
Top‐Hat Beam Technique: Improvements and application to bubble measurements
Authors: Corbin Frédéric , Gréhan Gérard , Gouesbet Gérard
Published: May 2005

A new‐generation velocimeter/sizemeter is described. Size measurement is based on the top‐hat beam technique. Velocity measurement is carried out by using laser Doppler velocimetry. Advantages and limitations of the top‐hat beam technique are discussed and compared with other techniques (pedestal, visibility, phase Doppler). Bubble diagnosis in a turbulent pipe flow is reported.
Design Data for Cyclones
Authors: König Christine , Büttner Helmut , Ebert Fritz
Published: May 2005

For many years efforts have been made to describe the complex process of particle separation in cyclones, and a multitude of separation models have been set up. A comparison of such separation models fails because insufficient usable test results are available and systematic and precise investigations are missing.

It is important for the design of cyclones to rate their separation properties by means of the fractional collection efficiency. On account of the known measuring problems, the data supply of reliable fractional efficiency curves of cyclones is still too small. Fractional efficiency as a function of the entrance velocity was measured with a high‐speed optical measuring technique. Measurements of low dust concentrations are presented. Geometrically similar cyclones of four different sizes were investigated. The fractional efficiency curves are plotted versus dimensionless parameters and the validity of the design criteria gained in this way is shown. The influence of particle shape on the fractional efficiency curves is discussed.
Contribution à l'Etude de la Thermolyse de la Nitroglycérine
Authors: Caire‐Maurisier M. , Tranchant J.
Published: May 2005

Par l'utilisation de méthodes analytiques modernes, telles que la résonance paramagnétique électronique, la spectrophotométrie infrarouge avec étude des déplacements de masse, la spectrométrie de masse et la fragmentométrie, combinées avec des analyses de gaz et des couplages chromatographie‐spectrométrie de masse, on a pu mettre en évidence le caractère radicalaire de la décomposition thermolytique de la nitroglycérine, puis proposer une série de réactions secondaires aboutissant aux produits de réaction observés.
A Unique Failure Criterion for Characterizing the Fracture of Propellants
Authors: Gledhill R. A. , Kinloch A. J.
Published: May 2005

The problem of crack growth in a nitrocellulose/nitroglycerin propellant has been studied employing a continuum fracture mechanics approach. Values of the stress‐intensity factor, Kc, at the onset of crack propagation have been ascertained and found to be dependent upon both the thickness of the specimen and the test temperature. By proposing that the value of Kc arises from the sum of a plane‐strain and a plane‐stress component a unique failure criterion, which is constant over a wide temperature range, has been identified. Namely, that crack propagation in the propellant occurs when the plane‐stress plastic‐zone at the crack tip attains a critical size.
Separation and quantitation of nitrocellulose, nitroglycerin, diethylphthalate, and centralite in double‐base powder
Authors: Sjöbom R. A. , Oresten H. G.
Published: May 2005

A method is described which makes possible a direct determination of nitrocellulose in double‐base powder and powder paste after separation from low‐molecular components by gel permeation chromatography and subsequent integration of the nitrocellulose peak. It is also possible to determine nitroglycerin and stabilizers in the same sample by collecting the components in the low‐molecular peak and subsequent injection into a reversed‐phase chromatography system. The procedure is exemplified on a powder paste containing nitrocellulose, nitroglycerin, centralite I, and diethylphthalate. The whole quantitation procedure will take less than an hour.
Free Radicales of TATB
Authors: Britt A. D. , Moniz W. B. , Chingas G. C. , Moore D. W. , Heller C. A. , Ko C. L.
Published: May 2005

TATB (1,3,5‐triamino‐2,4,6‐trinitrobenzene) forms an unusually stable free radical upon irradiation with ultraviolet light. Extraction with dimethylsulfoxide yields a liquid solution ESR spectrum which is, apparently, due to a TATB‐H adduct. The g‐values, spectral widths, and hyperfine assignments for the solution radical are given.
Some Observations on Sublimation and Decomposition of Ammonium Perchlorate
Authors: Pai Verneker V. R. , Kishore K. , Chaturvedi B. K. , Ramanath M.
Published: May 2005

Ammoniumperchlorate (AP) was aged at 100 °C and 150 °C. Depending on the aging time, AP shows different decomposition characteristics. By a special experimental arrangement sublimation and thermal decomposition could be separated.
Effect of Lead and Copper Methylene Disalicylates on the combustion rates of double‐base rocket propellants
Authors: Singh H. , Rao K.
Published: May 2005

The effect of lead and copper methylene disalicylates and their mixtures was studied on the burning rates (35 kg/cm2‐140 kg/cm2), heat of explosion, stability and thermal decomposition of double‐base propelants. The results indicate that these salts are very effective catalyst and their mixtures produce super‐rate burning (140% increase) with a uniform pressure index value in the entire pressure range. These additives lower “n” value to about 0.2–0.3 in some of the pressure regions. Results of DTA study suggest that these additives decompose in an exothermic mode in the temperature range close to the surface temperature of double base propellants.
Quelques propriétés physico‐chimiques des Solutions aqueuses de perchlorate d'ammonium
Authors: Hiquily N. , Laguerie C.
Published: May 2005

La solubilité du perchlorate d'ammonium dans l'eau, la masse volumique, la viscosité, I'indice de réraction et la conductivité électrique des solutions aqueuses ont été mesurés et comparés à d'autres valeurs de la bibliographie.
The Detonation Properties of Explosive‐Water Mixtures
Authors: Zygmunt B.
Published: May 2005

Mixtures of crystalline explosive and water have as a rule detonation properties different from the dry material. It has been shown that the character of those changes is closely related to the structure of the particles (crystals, granules) of the explosives. The critical diameters and detonation velocities have been measured for a range of explosive‐water mixtures, and the results are interpreted in terms of the hotspot theory.