bluuebunny/crossref_metadata_2025_split huggingface dataset:
Aqueous electropolymerization of polyacrylamide onto AS‐4 graphite fibers
Authors: Iroh J. O. , Bell J. P. , Scola D. A. 
Published: April 2003

AbstractConstant current electropolymerization of acrylamide was initiated on the surfaces of AS‐4 graphite fibers. Electropolymerization was performed using an aqueous solution of acrylamide dissolved in dilute sulfuric acid solution. The progress of electropolymerization was followed by measuring the weight of polyacrylamide deposited onto the surfaces of a unit weight of graphite fiber per unit time. The rate of electropolymerization was obtained from the slope of the linear region of the polymer weight gain vs. electropolymerization time curve. The rate of electropolymerization onto AS‐4 graphite fiber surfaces was found to depend on the initial monomer concentration, sulfuric acid concentration, and current density raised to the powers of 1.67, 0.02, 0.54, respectively. Molecular weight measurements on the electropolymerized polyacrylamide were done by solution viscometry. Number average molecular weights of 430,000, 220,000, and 193,000 were obtained for polyacrylamide, electropolymerized at 1 mA/g, 50 mA/g, and 100 mA/g respectively, consistent with classical radical polymerization kinetics.
Viscoelasticity of thin adhesive layers as a function of cure and service temperature measured by a novel technique
Authors: Challis R. E. , Cocker R. P. , Holmes A. K. , Alper T. 
Published: April 2003

AbstractThis article presents a novel short‐pulse ultrasonic technique for measuring the relaxing planewave modulus in realistically thin films of adhesive polymer over wide‐frequency bandwidths (1 MHz to between 30 and 100 MHz). On‐line computational methods are used to correct for known system distortions, for the estimation of absorption, planewave phase velocity, and complex planewave modulus, all as functions of frequency. Where appropriate it is also possible to fit models of relaxation processes to the measured data. Detailed results are shown for nine structural adhesives designed principally for automotive applications. The changes that occur during cure, as a result of extended cure, and with variation in service temperature are demonstrated. This work concludes that the method provides convenient measures of engineering properties, provides the means to study the effects of cure and service conditions, and provides reliable measures of ultrasonic propagation parameters that can be used to investigate the testability of adhered structures by ultrasonic means.
Environmentally stable conductive polymers from bis(ethynylstyryl) benzene monomers
Authors: Walton Theodore R. , Gratz Roy F. 
Published: April 2003

AbstractSeveral completely conjugated, all‐carbon–hydrogen acetylene‐terminated monomers, bis(ethynylstyryl)benzenes, were synthesized using the Wittig reaction with ethynyl‐benzaldehyde and xylyldiphosphonium salts. These prepolymers were thermally polymerized in the melt phase into thermally stable materials that can be further processed into conductive polymers having high stability to aggressive environments. Conductivity can range from that of an insulator to 10+2 s/cm. The room temperature conductivity is unchanged by extended exposure to boiling water or 500°C in an inert atmosphere. With proper design of the monomers' structures, they will melt sufficiently below the polymerization temperature to provide an adequate time in the liquid state for ease of processing. Once cured into the solid form, the materials are intractable and exhibit high stability to aggressive environments.
Phospholipid liposomes: Preparation, characterization, and uses
Authors: Nordmeier E. , Zeilinger C. , Lechner M. D. 
Published: April 2003

AbstractRhodopsin and cyclic guanosine monophosphat (cGMP)‐dependent channel proteins are isolated from the rod outer segment disk membranes of dark‐adopted bovine retinae and incorporated in liposomes, prepared by the method of detergent removal dialysis. The ion channel does not lose its transport function (release of Ca2+ ions by injection of cGMP) when incorporated in a liposome. Its activity depends on the degree of protein solubilization and the kind of detergent used. The highest activity is obtained by use of the detergent CHAPS. Shape, size, and size distribution of the liposomes are deduced from elastic and quasi‐elastic light scattering, the liposome number density by viscometry, and the photopigment or Ca2+ content by optical absorbance. The liposomes are heterogeneous with respect to size and shape. Small unilamellar liposomes (Rh = 80 nm) and a narrow size distribution (UD = 0.16) are obtained by using the detergent CHAPS. With increasing rhodopsin content per liposome, the hydrodynamic radius Rh increases and at the same time the shape of a liposome converts from a sphere to a prolate ellipsoid. The amount of entrapped Ca2+ per liposome reaches its maximum value when the Rhodopsin nearest‐neighbor distance approaches its minimum value. This suggests an intermembrane protein‐lipid‐protein lattice, which serves as barriere for Ca2+. The influence of temperature or total used Ca2+ content is less profound. Increasing temperature yields slightly smaller liposomes.
Vitrification and further structural relaxation in the isothermal curing of an epoxy resin
Authors: Montserrat S. 
Published: April 2003

AbstractIsothermal curing of an epoxy resin based on diglycidyl ether of bisphenol A, using a hardener derived from phthalic anhydride, has been performed at curing temperatures between 30 and 130°C. Samples were cured isothermally at various intervals of time and analyzed by differential scanning calorimetry (DSC), the glass transition temperature Tg, and the conversion degree being determined by the residual enthalpy technique. The vitrification phenomenon and a further structural relaxation process, occurring at curing temperatures (Tc) lower than the maximum Tg (109°C), at which Tg equalizes Tc, have been studied at curing temperatures between 30 and 100°C. The structural relaxation process is analyzed by the endothermic peak that appears superposed on Tg in dynamic DSC scans. The area of this peak (Q) is a measure of the recovery enthalpy, and thus of the extent of the relaxation process. This process begins at higher curing times (tc) when Tc decreases because the vitrification of the system starts later. Both the enthalpy recovery (Q) and the temperature of the endothermic peak (Tm) increase with the annealing time (ta), calculated as the difference between tc and the time in which vitrification occurs, and tend to have a limiting value due to the fact that the system loses mobility when the free volume decreases during its asymptotic approach toward the metastable equilibrium state. Furthermore, the dependence of Q and Tm on ta at different Tc shows that the relaxation process in partially cured resins depends on the conversion degree of the system and consequently on the crosslinking density of the network.
Modification of poly(ethylene ether carbonate) polyols by transesterification
Authors: Harris Robert F. 
Published: April 2003

AbstractPoly(ethylene ether carbonate) polyols are the reaction products of alkylene carbonates or alkylene oxides and CO2 with alcoholic initiators. These polyols can be modified with aliphatic hydroxyl compounds by transesterification reactions. The modifier becomes chemically bound into the polymer during reaction and modifies the properties of the polyol. The extent of reaction is very easy to follow by size exclusion chromatography. Molecular weight is controlled by the molecular weight of the reactants and by their stoichiometry. This transesterification process is compared to the previously described transesterification/advancement process. The transesterification process has the advantage of using milder temperature conditions and runs at ambient pressures. Therefore, modifiers can be used in the transesterification process that are unstable or undergo different chemistry under the reaction conditions of the transesterification/advancement process. Although the modifiers used in the transesterification/advancement process must be less volatile than DEG, more volatile modifiers can be used in the transesterification process. The two processes compliment each other, allowing the preparation of a wide variety of modified poly(ethylene ether carbonate) polyols. These polyols are useful in polyurethane applications.
The synthesis of microgels composed of polyelectrolytes
Authors: Fukutomi Takashi , Imori Yoshihisa , Saito Reiko , Shizu Koji 
Published: April 2003

AbstractMicrogels composed of dimethylaminopropylacryl amide (MAPA) or sodium salt of vinylbenzenesulfonic acid (VBS) were prepared by the crosslinking of primary polymers Poly(MAPA‐co‐acrylamide) or poly(VBS‐co‐acrylamide) with glutaraldehyde in aqueous solutions. Almost mono disperse spheric microgels with the diameter of 120 nm were obtained in the very wide concentration range (up to 5 w/v% for the former and 12 w/v% for the latter). In the copolymerization of MAPA and N‐methyloylacrylamide, microgel with the diameter of 120–140 nm was formed during polymerization.
Electrical properties of poly(butylene terephthalate)
Authors: Sandrolini Franco , Motori Antonio , Saccani Andrea 
Published: April 2003

AbstractDirect current (dc) and alternating current (ac) electrical properties of semicrystalline poly(butylene terephthalate) (PBT) are investigated as a function of temperature and frequency.Dc electrical conductivity measurements have been performed over the temperature range −75°C to 130°C and point out an essentially ionic mechanism of charge transport. Charge carriers are identified in protons supplied by ionization of carboxyl end‐groups after dissociation of the existing hydrogen bonds.Dielectric constant and loss factor have been measured over the temperature range −100°C to 130°C and over the frequency range 10−6 to 106 Hz. Together with de measurements, they allow the detection of the α glass‐rubber and the β subglass relaxation processes, as well as an interfacial polarization of the Maxwell–Wagner–Sillars type.Finally, the contour map of loss factor, summarizing the overall dielectric behavior of the polymer, is reported and discussed for electrical applications of PBT.
Bulk functionalization of ethylene‐propylene copolymers. IV. A theoretical approach
Authors: Greco R. , Musto P. 
Published: April 2003

AbstractA theroretical model is developed for the bulk functionalization of ethylene–propylene co‐polymers on the basis of the molecular mechanism proposed in previous papers, with certain simplifying assumptions: (1) A steady state regime for all the radical species is hypothesized; (2) a number of termination reaction are neglected; (3) no monomer homopolymerization is allowed to occur. An analytical expression is derived in such a way. A comparison of the theoretical predictions with some experimental data, obtained varying the radical initiator concentration [I]o and the reaction temperature, T, shows satisfactory agreement at low values of [I]o and T. At higher values the molecular mechanism becomes more complex and the model is unable to fit the data.
Pultruded fiber‐reinforced poly(methyl methacrylate) composites. I. Effect of processing parameters on mechanical properties
Authors: Ma Chen‐Chi M. , Chen Chin‐Hsing 
Published: April 2003

AbstractA feasibility study of pultrusion of fiber‐reinforced thermoplastic PMMA composite has been conducted using a proprietary method. Effect of processing parameters, preparation of methyl methacrylate (MMA) prepolymer on the mechanical properties (tensile, flexural strength and modulus, impact strength, etc.) of fiber‐reinforced PMMA composites by pultrusion has been studied. Processing parameters investigated included pulling rate, die temperature, postcure time and temperature, and filler content. From the study of Brookfield viscometer and FTIR spectrum the processing conditions can be defined. It was found from SEM photographs that the wetting out of fibers by PMMA resin was complete, and the fiber bundles were distributed evenly in the PMMA matrix. From the study of 1H‐NMR, GPC, and Brookfield viscometer, the conversion, molecular weight, and viscosity of MMA prepolymer data were obtained. From the DSC diagram, molecular weight measurement, and the rule of polymerization rate, the optimum die temperature was determined. It was found that the mechanical properties increase with increasing filler content and postcure temperature, and with decreasing die temperature and pulling rate.
Kinetic modeling of polymerization of butadiene using cobalt‐based Ziegler–Natta catalyst
Authors: Nitirahardjo Singgih , Lee Sunggyu , Miller Joseph W. 
Published: April 2003

AbstractThe reaction mechanism and subsequent kinetics for polymerization of butadiene using cobalt‐based Ziegler‐Natta catalysts have been investigated by many researchers. Kinetic models developed from these investigations can be used to predict the monomer conversion quite accurately; however, it is difficult to develop models that accurately predict the molecular weight as a function of time or conversion. In this paper, an attempt is made to model the reaction mechanism for the polymerization of butadiene using the cobalt octoate/diethyl aluminum chloride/water catalyst system with data taken from the literature. A dual active site mechanism is proposed and incorporated in a kinetic model. In this case, all reaction steps except the formation of byproducts step have two rate constants. The simulation results predict the molecular weight as a function of conversion and time better than results from previously published models.
Infrared investigations of sulfonated ionomer membranes. I. Water–alcohol compositions and counterions effects
Authors: Kujawski Wojciech , Nguyen Quang Trong , Neel Jean 
Published: April 2003

AbstractFT‐IR spectra of Nafion 117, Raipore 1010, and PESS membranes loaded with different alkaline counterions and equilibrated with different liquid media were recorded by means of the attenuated total reflectance technique. The antisymmetric (vas) and especially the symmetric stretching vibrations (vs) of the sulfonate groups are affected by the presence of solvents in its local chemical environment. In the dry membrane the smaller the bare counterion, the higher the frequency of the symmetric vibration and the stronger the sulfonate‐counterion interactions in the contacting ion pair. After equilibration with pure water, ethanol, and 2‐propanol, the vs vibration shifts to a constant value corresponding to the solvated sulfonic grouping in the case of Nafion‐Li+ membrane. In the cases of PESS‐Li+ and Raipore‐Li+ membrane only water can cause a similar shift. The greater affinity of the Nafion membrane to alcohols can be attributed to the stronger acidity of the corresponding sulfonic acid. In water‐alcohol mixtures the variation of vs with water content indicates that the ion pairs in the PESS‐Li+ membrane are progressively dissociated and solvated by increasing amounts of water in 2‐propanol. Complete dissociation occurs at about 9 wt % water. Smaller shifts are observed with bigger cations, due to the weaker sulfonate‐cation interactions.
Hydrophilic and adhesive properties of methacrylic acid‐grafted polyethylene plates
Authors: Yamada Kazunori , Kimura Tomohiro , Tsutaya Hideyo , Hirata Mitsuo 
Published: April 2003

AbstractMethacrylic acid (MAA) was grafted onto polyethylene (PE) surfaces by simultaneous irradiation with UV rays in the liquid phase to estimate hydrophilic and mechanical properties for MAA‐grafted PE plates. The amount of grafted MAA increased sigmoidally with UV irradiation time, and the higher grafted amount was obtained at higher monomer concentrations. With an increase in grafting of MAA, the wettabilities from the contact angles of water were enhanced and the refractive indices from the ellipsometry decreased. Though the contact angles remained constant above the grafted amount of 0.02 mmol/cm2, the refractive indices approached the value of PMAA around 0.009 mmol/cm2, indicating that the PE surfaces were fully covered with grafted PMAA chains. Then, at a fixed grafted amount, the grafted layer can absorb more water and the grafted PE plates possessed higher tensile shear adhesive strength, in case grafting was carried out at lower monomer concentrations. Surface properties depended on the density of carboxyl group at the surfaces of grafted layers, whereas adhesive properties depended on the structural properties of grafted chains as well as on the density of carboxyl group of the whole grafted layers.
Structure–property relationship of modified polypropylene–polycaproamide fiber
Authors: Grof I. , Sain M. M. , Durc̆ova Olga 
Published: April 2003

AbstractThe effect of the addition of polyamide on the structure and properties of polypropylene fiber has been studied. Although a good fiber is obtained with a composition containing only a very low concentration of polycaproamide in polypropylene, the increase in polyamide content decreases the drawing strength of the mixed polymer melt due to sudden lowering of melt viscosity and strength. The poor melt strength of the studied polymer mixture is attributed to increased heterogeneity induced in the system with increased concentration of polyamide. Use of an effective interphase modifier, maleic anhydride‐grafted polypropylene, however, was found to improve fiber properties of the studied polymer mixtures even with a very high concentration of polyamide as the dispersed phase. Thus, addition of a 1–4 wt % interphase modifier facilitates the formation of good fiber even with 30 wt % polycaproamide in the blend. This improvement is attributed to the improved dispersity of polyamide in the polypropylene matrix as well as improved phase compatibility due to the formation of a chemically modified polyamide during melt extrusion in the presence of maleic anhydride‐grafted polypropylene.
Synthesis of model latices for the study of coalescence mechanisms
Authors: Dobler F. , Pith T. , Holl Y. , Lambla M. 
Published: April 2003

AbstractThis work describes the synthesis of model latices devoted to the study of the influence of particle‐water and particle‐air interfacial energies on coalescence mechanisms. Core‐shell particles with the same diameter (≃ 2600 Å) and narrow size distributions were prepared. The core is a poly(styrene‐co‐butyl acrylate) (60/40 wt %) copolymer; it represents 90% of the volume of the particle. The shell is a poly(St‐BuA‐methacrylic acid) terpolymer with 10, 15, or 25 wt % MAA. The St‐BuA weight ratio in the shell is also 60/40. The amount of MAA in the shell determines the particle‐water or air interfacial energies. In order to limit the use of an emulsifier and to ensure a homogeneous particle surface layer, an inverted core‐shell synthesis was performed. The hydrophilic shell was prepared first and used as a seed for the synthesis of the hydrophobic core. For all three core‐shell latices, about 45% of the introduced MAA was found at the surface of the particles, which indicates that the core‐shell inversion was successful. The synthesis of the latices with 10 or 15 wt % MAA was relatively easy, whereas the particle size was difficult to control in the 25 wt % MAA latex synthesis.
Effects on properties of varying the cis/trans isomer distribution in polyurethane elastomers made with 1,4‐cyclohexane diisocyanate
Authors: Joseph Michael D. , Savina Michael R. , Harris Robert F. 
Published: April 2003

AbstractPolyurethane elastomers have been made using 1,4‐cyclohexane diisocyanate (CHDI), 1,4‐butanediol (BDO) and a 2000 Mn polyether diol soft segment. The cis/trans isomer distribution of the CHDI was varied between 23% and 100% trans. This variation in isomer distribution had significant effects on the polyurethane's thermal and physical properties.Decreasidng the trans CHDI content gives polyurethanes with lower hardness, lower thermal stability, higher Coefficient of Linear Thermal Expension (C.L.T.E.) values and decreased modulus values. Morphology studies showed good phase separation between the hard and soft segment blocks as well as a block copolymer morphology between the cis and trans CHDI/BDO blocks in the hard segment. The polyurethanes made were compared to polyurethanes made with MDI and H12MDI, the leading aromatic and aliphatic diisocyanates respectively.
Transport phenomena into and out of plasticized PVC sheets: The influence of sample history
Authors: Papaspyrides Constantine D. 
Published: April 2003

AbstractDiffusional exchanges in plasticized PVC applications comprise a critical aspect of much of the published work, which has been intended to study plasticizer migration into simpler extractants, enabling the various parameters involved in migration to be studied in isolation. In this study the migration of dioctyl phthalate into petroleum oils is investigated with emphasis on prior sample history. Simultaneously, the penetration of the liquid environment into the sheets is monitored. Plasticized PVC samples were prepared containing different amounts of plasticizer. The samples are immersed in paraffin oil until the plasticizer concentration reaches a predetermined value. Afterwards the samples are immersed in white spirit and their migration behavior is compared with that of new samples containing this predetermined plasticizer content, i.e., excluding the prior desorption cycle. Under these experimental conditions the parameters studied include immersion time, immersion temperature, initial plasticizer content and specimen thickness. The results obtained, suggesting considerable restriction of the migration activity for the two‐stages specimens, are discussed in terms of surface‐depleted concentration profiles and structure rearrangement mechanisms.
Kinetics of silane grafting and moisture crosslinking of polyethylene and ethylene propylene rubber
Authors: Sen Achintya Kumar , Mukherjee Bibha , Bhattacharyya A. S. , De P. P. , Bhowmick Anil K. 
Published: April 2003

AbstractPeroxide initiated graft copolymerization of vinyl trimethoxy silane (VTMO) and vinyl triethoxy silane (VTEO) onto polyethylene (PE) and ethylene propylene copolymer (EPR) was studied. The kinetics of grafting, studied by differential scanning calorimetry, are the same for all the systems and the activation energy for VTMO is 170 ± 4 KJ/mol. Activation energy for VTEO is 185 ± 5 KJ/mol. The VTMO and VTEO graft copolymers of PE and EPR were prepared by reactive processing in a Brabender extruder in the temperature range of 150–200°C. Moisture catalyzed crosslinking of the silane grafted copolymer was also studied. The influence of the structure of the catalyst, its concentration, moisture concentration, temperature, and time on degree and rate of crosslinking has been evaluated. Crosslinking reactions follow first order kinetics with respect to both catalyst and moisture concentration. Activation energy (Ea) of the crosslinking reaction has been determined as 65 KJ mol−1. The mechanism of grafting and crosslinking is discussed.
Copolymers of N‐vinylcarbazole with monomers containing carboxylic acid groups or carboxylic anhydride groups. II. Photoconductivity and composition
Authors: Wainwright M. , Griffiths J. , Guthrie J. T. , Gates A. P. , Murray D. E. 
Published: April 2003

AbstractCopolymers of N‐vinylcarbazole containing olefinic monomers that possess carboxylic acid or anhydride functionality have been produced. The photoconductive properties of the copolymers were measured. Fluorimetry has been used to relate this photoconductivity to the copolymer composition. Photoconductivity was greatest in copolymers containing high percentages of vinylcarbazole. It is suggested that this is due to block copolymer formation, since the development of such blocks allows greater interchromophore overlap than would be possible with alternating copolymers, which exhibit low photoconductivity.