bluuebunny/crossref_metadata_2025_split huggingface dataset:
The SCOPE dynamic model for emulsion polymerization II. Comparison with experiment and applications
Authors: Dougherty Eugene P. 
Published: April 2003

AbstractPaper I provides the underlying theoretical framework for the SCOPE dynamic model of emulsion copolymerization. The present paper compares the model predictions for styrenemethyl methacrylate copolymerizations with experimental measurements made at a variety of polymerization conditions. The SCOPE model predicts conversion–time profiles reasonably well over wide ranges of initiator concentration, monomer concentration and monomer composition. In addition, the model accurately predicts number average molecular weights and copolymer compositions over the entire range of monomer composition. Like previous investigations of this system, the present study suggests that free radical desorption from polymer particles plays a dominant role on the copolymerization kinetics: Simple case II Smith‐Ewart kinetics do not apply. The model for this system was applied to understand how changing reaction conditions could effect polymer properties such as particle size and molecular weight distributions. The power of the SCOPE model is illustrated by using it to predict conversion profiles, temperature profiles and copolymer properties for some large‐scale versions of these recipes.
High‐strength–high‐modulus polyimide fibers I. One‐step synthesis of spinnable polyimides
Authors: Kaneda Takaho , Katsura Toshio , Nakagawa Kanji , Makino Hiroshi , Horio Masao 
Published: April 2003

AbstractPolyimides with aromatic links are synthesized usually in two steps, but a series of aromatic polyimides with large molecular weights sufficient to produce strong fibers were prepared in one step by the reaction of 3,3′, 4,4′‐biphenyltetracarboxylic dianhydride (BPDA) with various aromatic diamines. The one‐step polycondensation was possible even when BPDA was replaced to some extent by pyromellitic dianhydride, which is a basic component in the conventional two‐step method. The copolyimides based on BPDA and mixtures of aromatic diamines were also synthesized in similar manner. For the one‐step polycondensation, phenol and some of its derivatives were found to be suitable solvents, while the typical solvent employed in the two‐step method, such as N‐methyl‐2‐pyrrolidone, could not be used because of the precipitation of low‐molecular weight polyimides. p‐Hydroxybenzoic acid proved to be a very efficient accelerator for the conversion of polyamic acids to polyimides.
Permeation of solutes in water‐swollen poly(vinyl alcohol‐co‐itaconic acid) membranes
Authors: Higuchi Akon , Iijima Toshiro 
Published: April 2003

AbstractPartition and permeability coefficients of urea, NaCl, and saccharose in water‐swollen poly(vinyl alcohol‐co‐itaconic acid) membranes with various water contents (0.25 ⩽ H ⩽ 0.86) were measured. Partition coefficients and permeability ratios in freezing and nonfreezing water were estimated based on a parallel permeation model. It was suggested that at 25°C the permeation of saccharose in the nonfreezing water was nearly zero due to its negligible partition coefficient, while NaCl and urea were found to be able to permeate even the nonfreezing water. The activation energies of diffusion for three solutes were found to increase with the decrease of water content of the membranes. Since the fraction of nonfreezing water increased with the decrease of water content of the membranes, it is assumed that the increased activation energy of diffusion is due to the fact that the diffusion in nonfreezing water needs higher activation energy than in the pure bulk water.
Structure and molecular properties of saponified starch–graft‐polyacrylonitrile
Authors: Rodehed Cenita , Rånby Bengt 
Published: April 2003

AbstractThe Mn3+ initiation system has been used to prepare starch‐g‐polyacrylonitrile copolymers. Both granular native starch and water‐swollen gelatinized starch have been used as substrate. Conversion of monomer, graiting ratio, and percent add‐on tend to increase with increasing amounts of monomer charged. The amount of homopolymer formed is extremely low, a p proximately 1%. The efficiency, measured as conversion, is consistently higher with gelatinized starch as Substrate. The molecular weight of the grafta on gelatinized starch is approximately eight times higher than those on granular starch. Granular starch has a correspondingly higher frequency of grafta. Solubility measurements of starch, polyacrylonitrile, and grafted starch were carried out in dimethylsulfoxide (DMSO) at 348 K. Starch and polyacrylonitrile were totally soluble in DMSO under the chosen conditions. The solubilities of grafted samples were independent of the state of the substrate before grafting and of molecular weights of the grafted chains, but were found to be correlated to percent add‐on. Starch‐g‐polyacrylonitrile samples, with gelatinized starch as substrate, were saponified in aqueous sodium hydroxide eolution. The water retention value increased linearly with increasing add‐on. The saponified polyacrylonitrile, branches alone had a water retention value that was three times higher than that of the original copolymer.
Effect of diethylene glycol content and annealing temperature on the structure and properties of poly(ethylene terephthalate)
Authors: Seganov I. , Schultz J. M. , Fakirov S. 
Published: April 2003

AbstractThe effect of 2,2′‐oxydiethanol (diethylene glycol, DEG) content (ranging from 2 to 15 mol %) and of the annealing temperature (in the range from 100 to 260°C) on the density, calorimetric, dynamic‐ and static‐mechanical and small angle X‐ray scattering (SAXS) behavior of undrawn and drawn samples (granules, films, and bristles) of poly(ethylene terephthalate) (PET) has been studied. The known dependences on the annealing temperature are confirmed. Some discrepancies with earlier investigations of the dependences on the DEG content are established: constant values for the SAXS intensity and long spacing, for the lamellar thickness and for the volume fraction crystallinity ac. These discrepancies are explained by the variation of the glass transition temperature (Tg) and melting temperature (Tm) of the materials with different DEG contents. The previous hypothesis of the segregation of the comonomer (DEG) units into the amorphous regions is confirmed.
The effect of particle concentration on the rheology of polydimethylsiloxane filled with fumed silica
Authors: Kosinski L. E. , Caruthers J. M. 
Published: April 2003

AbstractThe effects of particle concentration on the shear‐rate‐dependent viscosity, stress relaxation, and stress growth function were investigated for various molecular weight polydimethylsiloxane (PDMS) fluids filled with colloidal fumed silica. Shear‐rate‐dependent stress relaxation was observed for all dispersions, and a significant stress growth overshoot was observed when the PDMS molecular weight was just greater than the entanglement molecular weight. The rate of stress—relaxation and the type of stress growth are primarily determined by the previous shear rate history and the PDMS molecular weight, while particle concentration only affects the quantitative details of the filled fluid's rheology. The observed effects of particle concentration are consistent with a molecular deformation process, where the silica particles interact via the entanglements of the polymer adsorbed on the surface of the fumed silica.
Microwave dielectric and mechanical behavior of foams from polystyrene and poly(methyl methacrylate) blends
Authors: Chaki Tapan K. , Bandyopadhyay P. C. 
Published: April 2003

AbstractFoams have been generated from blends of polystyrene and poly(methyl methacrylate) under identical conditions of solvent–nonsolvent ratio, impregnation time, and heating period. Scanning electron micrographs of copper‐coated fractured surfaces of the samples reveal a distinct transition in their structures from a more or less homogeneous cell‐size distribution with prominent grain boundaries to complete lack of foaming and cellularity through random dispersions of spherical poly(methyl methacrylate) inclusions in polystyrene‐foam matrix. Dielectric measurements have been made on test specimens at 9.375 GHz X‐band microwave frequency by the method of Smith and Hippel modified by Dakin and Works. Percent porosity is the least at 20 wt% of polystyrene while foam density linearly decreases with percent porosity. Dielectric constant is linear in foam density on direct and semilog scales (passing through unity and zero, respectively), in blend composition and also in percent porosity. Dielectric constant increases with increase of foam density or weight percent of polymethyl‐methacrylate and decreases with increase of percent porosity. The dielectric constant is, however, nonlinear in volume fraction of polystyrene on both direct and semilog scales, obeying Weiner's inequalities. The logarithmic law of Lichtenecker and Rother with an empirical factor 0.8276 in the index fits the data best. Specific polarization is minimal at 60 wt% of polymethyl methacrylate. The calculated Bottcher‐Bruggleman plot based on the interacting spherical particle model is found to be of limited applicability. This is explained on the basis of long‐range intra‐ and intermolecular dipole–dipole interactions. The pattern of the change of dielectric loss tangent (tan δ), lying in the range 0.150–0.045 and attaining a minimum at 20 wt% polystyrene, has similarly been explained in terms of α and β relaxations due to conformational rearrangements and steric hindrances of rotations. The compressive strength measured as a function of composition shows that the reinforcement depends on an optimization between the degree of cellularity and packing.
Transport of swelling penetrants in glassy polymers: Influence of convection
Authors: Sarti G. C. , Gostoli C. , Riccioli G. , Carbonell R. G. 
Published: April 2003

AbstractThe transport of a solute by diffusion into a glassy polymer can lead to swelling of the material. For certain types of polymers, a sharp interface is formed between the swollen region and the glassy core. When the density of the swollen material is much smaller than the density of the glass, a significant convective mass‐average velocity is generated within the sample. Previous models have neglected the role this convection plays in solute transport and in the proper calculation of the sample dimensions as a function of time. In this paper, we study the contribution of convective terms to the solute transport process, including the motion of the swollen polymer/solution interface. We also compute the eulerian strains that result from the calculated velocity fields and the stresses that would be generated if a linear viscoelastic model is used as a constitutive equation relating the stress to the strain. We show that serious errors can be generated in the calculations if convective terms are neglected. Furthermore, a comparison of the strains and stresses acting on the polymer with those acting on the mixture of solute and polymer shows that they can be significantly different. The stresses and strains acting on the polymer alone offer the most rational physical picture of the material deformation.
Water extraction of polyethyloxazoline from miscible and immiscible polymer blends
Authors: Pfenning J.‐L. G. , Keskkula H. , Paul D. R. 
Published: April 2003

AbstractBlends of water‐soluble polyethyloxazoline (PEOx) with a series of hydrophobic styreneacrylonitrile copolymers (SAN) of varying AN contents were immersed in water to determine the kinetics of water swelling and the extent of PEOx extraction. Copolymers containing 25 and 40% by weight of AN form miscible blends with PEOx; those containing higher and lower amounts of AN form immiscible mixtures with PEOx. A high degree of PEOx extraction was observed for the immiscible blends as expected, whereas surprisingly little PEOx was extracted from the miscible blends over periods up to 2 years in spite of a high degree of water swelling. Similar behavior has been noted for other blends of hydrophobic and hydrophilic polymers. In the present system, thermal analysis revealed that the sorption of large amounts of water induces a microphase separation of the two miscible polymers to form microdomains of SAN in which, evidently, segments of PEOx are entrapped to form physical cross‐links that preclude disintegration of the sample and extraction of the PEOx whose phase is highly swollen by the sorbed water. It is proposed that a similar situation probably occurs for other blend systems exhibiting such behavior.
The gamma‐ray‐induced crosslinking of polyacrylamide
Authors: Burillo S. Guillermina , Ogawa Takeshi 
Published: April 2003

AbstractThe gamma‐ray‐induced crosslinking of polyacrylamide was carried out under various conditions. The molecular weight of the polymer before inrradiation was found to be the most important factor for crosslinking. When polymers have low molecular weights such as 80,000, the intensity of radiation, the external pressure applied, and the water content of the polymer powder became important for crosslinking. Although the polycrylamide hydrogel can be obtained directly by irradiating the monomer, it was obtained more conveniently by the irradiation of monomer—polymer mixtures. The hydrogels obtained by the radiation with a dose of over 50 kgray, absorb water by 1000–1500 wt %.
Miscible ternary blends containing polycarbonate, SAN, and aliphatic polyesters
Authors: Shah V. S. , Keitz J. D. , Paul D. R. , Barlow J. W. 
Published: April 2003

AbstractTernary blends comprising polycarbonate, (PC), poly(styrene‐co‐acrylonitrile) (SAN), and a polyester, either poly(1,4‐butylene adipate) (PBA), poly(1,4‐cyclohexanedimethylene succinate) (PCDS), or poly(ε‐caprolactone) (PCL), were found to be miscible based on the presence of a single glass transition temperature at many compositions. For all systems, the addition of just 1% by weight polyester resulted in a miscible blend for SAN/PC ratios of 1/1 and 3/1, and a region of immiscibility was generally observed for PC‐rich compositions with low polyester content. The melting point depression of PCL in the ternary and in binary mixtures was studied to obtain interaction parameters for the PCL/PC, PCL/SAN, and SAN/PC binaries. These parameters were used to calculate the locus of compositions which mark the boundary between single‐ and multiple‐phase behavior. Agreement between the calculated and experimental boundary was only fair. PCDS was found to be the most efficient of the three polyesters studied for solubilizing PC and SAN. SAN copolymer containing 25% acrylonitrile (AN), was found to be more easily solubilized in PC by PCDS than SAN containing 13% AN.
Reaction and diffusion of reactive disperse dye in nylon 6
Authors: Morita Zenzo , Saito Takayuki , Motomura Hiromi 
Published: April 2003

AbstractThe diffusion of a reactive disperse dye with a vinylsulfonyl group accompanied by simultaneous reaction with the amino end groups in nylon 6 was examined by the method of cylindrical film roll at 70°C and pH 2.2–8.0. The experimental diffusion profiles of the active and fixed species of the dye in nylon 6 were confirmed to be described by the diffusion equation accompanied by the chemical reaction with substrate taking the limited amount of the end groups into account, where the active species of dye were assumed to react only with the free base of amino end groups. The completion of the reaction with the amino end groups was observed in the first layer from the surface at pH 6.0–8.0. The value of diffusion coefficient was constant (8.0 × 10−10 cm2/s) at all the pH's. The product of the second‐order rate constant, k2, of reaction of the dye and the dissociation constant, Ka, of the amino end groups was constant (k2Ka = 4.0 × 10−9 s−1) at pH 2.2–8.0. The k2 values of the reaction with various substrates for vinylsulfonyl and monochlorotriazinyl‐reactive dyes were compared and the practical dyeing conditions were discussed.
Hydrolytic stability of single‐package silicone sealant
Authors: Gan L. M. , Ong H. W. K. , Tan T. L. , Chan S. O. 
Published: April 2003

AbstractStability of a commercially available single‐package silicone sealant has been investigated under different water immersion temperatures. The study involved water sorption, weight loss, thermal stability, and strength reduction. It is believed that the deterioration of silicone sealant was due to the combined effects of leaching, water swelling, and hydrolysis. Water uptake of about 2% was crucial for its hydrolytic degradation, especially at higher temperatures.
Effect of water on the strength of filled polychloroprene vulcanizates
Authors: Hinkley Jeffrey A. , Holmes Brenda S. 
Published: April 2003

AbstractThree commercial rubber compounds used in marine applications were immersed in water or in 3.5% NaCl solution for up to 250 days. Tear strengths, measured with the “trousers” test piece, decreased in the order dry > salt water exposed > fresh water exposed, and changes of up to 50% were seen. Tensile strengths also decreased, but not always in the same proportion, suggesting a possible change in structure of the voids which initiate fracture. Results are discussed in terms of osmotic swelling and extraction of rubber components.
Preparation of new hydrophilic poly‐vinylpyridine beads and their application to immobilization of urease
Authors: Sugii A. , Ogawa N. , Matsumoto M. 
Published: April 2003

AbstractMacroporous hydrophilic poly‐vinylpyridine beads were prepared by suspension copolymerization of 4‐ (or 2‐)vinylpyridine and hydrophilic cross‐linking agents, such as ethylene glycol dimethacrylate (1EG) and tetraethylene glycol dimethacrylate (4EG), and their physical properties were studied. Immobilized enzymes were obtained by adsorption of urease on vinylpyridine polymers and commercially available hydrophobic polymers. The poly‐4‐vinylpyridine resin crosslinked with 4EG (degree of crosslinkage, 25%) showed higher water regain, larger average pore radius, and the highest adsorption of urease. Leakage of urease from immobilized urease was scarcely observed in the buffer solution used. The hydrophilicity and hydrophobicity of support affected markedly the enzymatic reaction of the immobilized enzyme. As one of the applications of the polymer‐supported urease, blood urea nitrogen in human sera was determined.
Diffusion of a volatile liquid in polychloroprene rubber
Authors: Lawandy S. N. , Helaly F. H. 
Published: April 2003

AbstractThe penetration rate of chloroform (highly volatile solvent) in chloroprene rubber vulcanizate, based on different carbon black type and loading, has been studied. The results relevent to carbon black loading have shown an increase in the penetration rate with the increase in loading percentage. Other factors affecting the penetration rate, such as particle size and aggregate structures of carbon black, have shown some confusing results, such as the decrease in penetration rate with the increase of particle size and the decrease in penetration rate at a higher degree of equilibrium volume swelling. These results were attributed to the wrinkles formed at the surface of the rubber at these high equilibrium swellings.
Application of statistical experimental design in Ziegler–Natta polymerization of butadiene
Authors: Ho F. K. W. , Hsu C. C. , Bacon D. W. 
Published: April 2003

AbstractThe results of butadiene polymerization initiated with CoCl2· 4Py/Et2AlCl/H2O are presented. The effectiveness of statistical experimental design techniques is demonstrated in identifying the individual and joint effects of polymerization variables on rate constants, molecular weights, and polydispersity. The proposed conversion model, representing polymerization with instantaneous initiation and bimolecular termination, was found to provide an adequate representation of experimental conversion data. Evidence indicates that water is not only directly involved in the initiation reaction but also plays an important role in the chain transfer reaction.
Kinetics of 1‐hexene polymerization
Authors: Dandge D. K. , Heller J. P. , Lien C. , Wilson K. V. 
Published: April 2003

AbstractKinetics of 1‐hexene polymerization was studied by following the amount of unreacted monomer using gas chromatography. The Ziegler‐Natta catalyst system used was comprised of TiCl4‐AlEt3 with Al: Ti ratio of 0.85. The sampling and monomer analysis techniques developed can be applied to study the kinetics of higher α‐olefins polymerizations, in general. Also, with minor modifications in this technique, a precise profile of molecular weight can be obtained during polymerization.
Peroxide‐initiated crosslinking of polypropylene in the presence of p‐benzoquinone
Authors: Chodák I. , Lazár M. 
Published: April 2003

AbstractCrosslinking of polypropylene was investigated when initiated by thermal decomposition of organic peroxides. p‐Benzoquinone was found to be an effective coagent of crosslinking. The efficiency of benzoquinone is about 5 times higher than that of polyfunctional monomers. Almost complete crosslinking of polypropylene can be reached at proper conditions.
Cocrystallization and miscibility studies of blends of ultrahigh molecular weight polyethylene with conventional polyethylenes
Authors: Kyu Thein , Vadhar Parimal 
Published: April 2003

AbstractUltrahigh molecular weight polyethylene (UHMWPE) was mechanically mixed with conventional polyethylenes (LLDPE, HDPE, and LLDPE) using an internal mixer. Rheological studies of these blends suggest that UHMWPE seems to be miscible with LLDPE, HDPE, and LDPE in the melt state. Yield characteristics are observed in all blend systems, particularly in high UHMWPE blend compositions. Differential scanning calorimetry and small‐angle light scattering studies show that cocrystallization takes place in the blends of UHMWPE/LLDPE and UHMWPE/HDPE blends. However, separate crystals are formed in UHMWPE/LDPE. The formation of separate crystals may be attributed to long chain branching of conventional low‐density polyethylene. Tensile properties of the former two blends vary almost linearly with blend compositions, while deviations are seen in the latter UHMWPE/LDPE blends.
Graft copolymerization with new class of acidic peroxo salts as initiators. I. Grafting of acrylamide onto cotton–cellulose using potassium monopersulfate, catalyzed by co(II)
Authors: Sahoo Prafulla K. , Samantaray Himansu S. , Samal Rajani K. 
Published: April 2003

AbstractGraft copolymerization of acrylamide (AM) onto cotton–cellulose has been studied using a new class of acidic peroxo‐salt “potassium monopersulfate” as initiator catalyzed by Co(II). It is observed that the graft yield is influenced by the reaction time, temperature, and concentrations of the monomer, catalyst, initiator, at fixed weight of the polymer. Maximum graft yield (30.8%) is obtained at 40°C under nitrogen atmosphere for the concentrations of monomer 1.2M; initiator 4.83 × 10−3M; Co(II) 5 × 10−4M for 4 h of reaction time. The graft copolymers after proper purification have been subjected to IR analysis, testing of their water‐retention properties, rot resistance, tensile properties, and behavior towards acids and alkalies. The results of such analysis are compared with the base. Suitable mechanism for the graft copolymerization is suggested and grafting rate has been evaluated.