bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intramolecular cyclization of styrene–p‐divinylbenzene copolymers
Authors: Soper B. , Haward R. N. , White E. F. T. 
Published: April 2003

AbstractStyrene has been copolymerized at low conversion with minor quantities of p‐divinyl‐benzene (p‐DVB) in (10–15%) solution in toluene and cyclohexane. Under these conditions the molecular weight of the polystyrene formed in the absence of p‐DVB was controlled by chain transfer, and the copolymerization coefficients of the styrene and the p‐DVB agreed with previous work. Polymer molecular weights were studied as a function of conversion. At very low conversions the number‐average (2.2 × 105) and the weight‐average (4.4 × 105) molecular weights were unaffected by substituting some of the styrene by p‐DVB, but as the reaction continued M̄n increased slowly and M̄w much faster. On the other hand, even at the lowest conversions the intrinsic viscosity was drastically reduced by the introduction of p‐DVB, and the radius of gyration, as measured by light scattering, fell. Infrared studies on the polymer show that the concentration of pendent double bonds in low‐conversion copolymers is about half of the doubly substituted phenyl groups. It is concluded that the first polymer chains formed are extensively cyclized with the formation of a relatively large number of small rings.
Synthesis of disulfide polymers of low molecular weight by repeated depolymerization
Authors: Tenc‐Popović Mirjana E. , Popov Svetlana , Radosavljević Slobodan D. , Rekalić Vladimir J. 
Published: April 2003

AbstractBy double or triple depolymerization with sodium hydrogen sulfide in the presence of sodium sulfite, polysulfide polymers of a very low molecular weight can be obtained from disulfide polymers prepared from bis‐2‐chloroethyl formal. The products are mixtures consisting chiefly of dimers and trimers with monomers. The effect of depolymerization will be greater when three depolymerization processes, instead of two, are completed with the same total amount of NaHS and Na2SO3. When depolymerization is repeated, the degree of depolymerization will be higher with polymers of a higher molecular weight. If depolymerization is made with sodium dithionite, the same effect will be achieved by either single or double depolymerization, provided that the same total amount of dithionite has been used.
Chromocene catalysts for ethylene polymerization: Scope of the polymerization
Authors: Karol Frederick J. , Karapinka George L. , Wu Chisung , Dow Alan W. , Johnson Robert N. , Carrick Wayne L. 
Published: April 2003

AbstractChromocene deposited on silica supports of high surface area forms a highly active catalyst for polymerization of ethylene. Polymerization is believed to occur by a coordinated anionic mechanism previously outlined. The catalyst formation step liberates cyclopentadiene and leads to a new divalent chromium species containing a cyclopentadienyl ligand. The catalyst has a very high chain‐transfer response to hydrogen which permits facile preparation of a full range of molecular weights. Catalyst activity increases with an increase in silica dehydration temperature, chromium content on silica, and ethylene reaction pressure. The temperature‐activity profile is characterized by a maximum near 60°C, presumably caused by a deactivation mechanism involving silica hydroxyl groups. A value of 72 was estimated for the ethylene–propylene reactivity ratio (r1). Linear, highly saturated polymers are normally prepared below 100°C. By contrast with other commercial polyethylenes, the chromocene catalyst produces polyethylenes of relatively narrow molecular weight distribution. Above 100°C, unsaturated, branched polymers or oligomers are formed by a simultaneous polymerization–isomerization process.
Comparison of number–average molecular weights calculated by GPC and membrane osmometry
Authors: Ambler M. R. , Mate R. D. 
Published: April 2003

AbstractData are presented which show that when a polymer contains an appreciable amount of low molecular weight species below the diffusion limit of the osmometer membrane, the osmotic molecular weight, M̄n, is generally higher than the M̄n calculated from gel‐permeation chromatography (GPC). Experiments were performed on samples of poly(vinyl chloride) (PVC) and high‐cis polybutadiene polymers. Osmotic data were obtained in the usual manner, while GPC data were obtained using the universal calibration approach. It was found that when all polymer species below approximately 10,000 molecular weight were excluded from the calculation of M̄n by GPC, agreement in M̄n was obtained between membrane osmometry and GPC. The data obtained suggest that the choice of M̄n as measured by membrane osmometry in the calibration of the GPC should not be done casually, as the measured M̄n may not reflect the “true” value of that sample, especially when the polymer sample contains an appreciable amount of low molecular weight material.
Solid‐state polymerization of hexamethylcyclotrisiloxane. II
Authors: Chawla A. S. , St. Pierre L. E. 
Published: April 2003

AbstractThe solid‐state polymerization of hexamethylcyclotrisiloxane has been shown, by means of specific ion scavengers, to proceed by a cationic process. The reaction occurs at the crystal surface rather than within the lattice and exhibits a polymerization rate which is inversely proportional to the defect and negative ion concentrations in the crystalline monomer.
Polymerization of pyromellitic dianhydride with 3,3′‐diaminobenzidine in aprotic solvents II. Dilute solution studies
Authors: Johnston Norman J. , Epps Lionel B. 
Published: April 2003

AbstractSolution properties were determined for the poly(amide acid amine) obtained from the room‐temperature polymerization of pyromellitic dianhydride with 3,3,‐diaminobenzidine in aprotic solvents. Membrane osmometry data, viscosity studies, solution aging studies, and pH–viscosity relationships were given. Anomalous upswings in viscosity–concentration plots were attributed to absorption or capillary wall effects and not to polyelectrolyte effects, such as were induced by addition of strong bases. Similar absorption effects were found with polyamic acid solutions, in contrast to earlier reports that these polyimide precursors were polyelectrolytes. Unfavorable storage characteristics of the polymer solutions were explained by aging studies which showed that at 25°C dilute solutions exhibited a rapid drop in viscosity; in concentrated solution a slow increase to gelation was observed.
Stereoelective polymerization of racemic α‐olefins: Influence of conversion and of nature of catalyst components
Authors: Carlini Carlo , Bano Hussan , Chiellini Emo 
Published: April 2003

AbstractThe dependence of stereoelectivity on conversion has been investigated by polymerizing racemic 4‐methyl‐1‐hexene (I) and 3,7‐dimethyl‐1‐octene (II) in the presence of catalysts prepared from TiCl4 and bis[(S)‐2‐methylbutyl]‐zinc(III) or tris [(S)‐2‐methylbutyl]aluminum (IV). The influence of the nature of transition metal halide has also been examined by polymerization of racemic I and II with catalysts obtained from III and transition metal halides as well as from TiCl4 and optically active organometallic compounds containing phenyl groups. Stereoelectivity remains practically constant or increases slightly with increasing conversion, but it is affected by the nature of transition metal halide. Moreover a detectable variation of stereoelectivity was observed by changing the chemical structure of the alkyl group in the optically active organometallic component of the catalyst. In any case, however, stereoelectivity is not higher than 5–10%. Evidence in favor of asymmetric induction by the catalytic complex is reported and discussed.
Domain structure and bulk properties of solvent‐cast films of A–B–A block copolymers of styrene‐isoprene‐styrene
Authors: Uchida Takanori , Soen Toshiichi , Inoue Takashi , Kawai Hiromichi 
Published: April 2003

AbstractDomain structures of solvent‐cast films of A–B–A block copolymers of styrene‐isoprene‐styrene were studied by electron microscopy by use of the OsO4 fixation technique. The effects of varying proportions of the two components and the casting solvent upon the domain structures were examined. It is concluded that the domain formation mechanism can be discussed like that of A–B block copolymers irrespective of sequence arrangements, as Matsuo et al. suggested, by treating A–B–A or B–A–B block copolymers as A–(1/2)B or B–(1/2)A block copolymers. The five types of fundamental domain structures—spherical domains of component A in a matrix of component B, rodlike domains of A in a matrix of B, alternating lamellae of the two components, rodlike domains of B in a matrix of A, and spherical domains of B in a matrix of A—are achieved mainly by the change of the fractional composition of the two components for a given solvent. One of the most significant features of the A–B–A block copolymers in contrast to the A–B block copolymers, i.e., that A–B–A chains can interconnect two A domains, was explored by investigating (1) the swelling behavior in a solvent that is a good one for isoprene but a nonsolvent for styrene and (2) mechanical behavior above the glass transition temperature of the styrene segments.
Comparison of optical and mechanical limits of linear relaxation behavior in glassy polycarbonate
Authors: Yannas I. V. , Doyle M. J. 
Published: April 2003

AbstractThe decay in birefringence of glassy polycarbonate held at constant extension has been studied at 23°C, in the time‐scale range 10–103 sec, up to about 6% strain. The results show that, under these conditions, the birefringence can be validly expressed as a linear hereditary integral of the strain history up to a relatively high strain level which is about 3.4% for an experimental time‐scale of 100 sec. Comparison with previously obtained data on the stress relaxation behavior of the same polymer shows that, other factors remaining constant, mechanical relaxation is linear only up to about 1.1% strain. The earlier onset of mechanical nonlinearity is discussed and it is suggested that the mechanical relaxation spectrum is richer than the optical spectrum in relatively long relaxation times, corresponding to relatively slow molecular motions. It is further suggested that these slow molecular motions are accelerated first as the polymer is extended beyond the limit of linear viscoelastic behavior. The observed nonidentity between strain limits for linear mechanical and linear optical behavior is discussed in the light of current practices in photomechanical stress analysis.
Evaluation of methods for determining the refraction correction for light‐scattering photometers
Authors: Wallace T. P. , Volosin M. T. , Delumyea R. G. , Gingello A. D. 
Published: April 2003

AbstractRecent literature reports from three laboratories have treated the refraction correction for the Sofica and a noncommercial light scattering photometer. Our re‐evaluation of the data contained in these reports, as well as our experiments, indicate that the usually cited n2 refraction correction has not been unquestionably established for these instruments. In some cases, imprecise experimental techniques have been used to support this particular form of the correction. In addition, we find the optical system of the Sofica instrument results in the detector seeing vertically past the horizontal edge of the illuminated volume in violation of a basic assumption in the deduction of the n2 correction. Our experiments, as well as our interpretation of recent literature data, support an exponent of less than 2.0 for the Sofica apparatus, which is consistent with an instrument whose detector views outside the illuminated volume. However, the experimental methods available to evaluate the exponent lack the desired precision.
Crystallization of short aliphatic chains. II. Example of even fold surface with adjacent fold reentry and of a transition to chain extension
Authors: D'ilario L. , Keller A. , Martuscelli E. 
Published: April 2003

AbstractAs a continuation of the preceding study on the folding behavior of short polymer chains, an iodine‐terminated paraffin having 156 Å peak molecular length and a sharp molecular weight distribution was prepared. The paraffin could be crystallized in lamellae of two different thicknesses: (A) thickness close to half the chain length (the most readily obtained); (B) thickness intermediate between half chain length and fully extended chain. Case A corresponds to each chain folding once with equal stems and with ends at the surface. Degradation behavior revealed that the folds must be of closely equal length giving rise to an even fold surface. In case B the situation is more involved: here the chain ends must turn into the lattice. Adjacent reentry is a necessity throughout. In both cases the lamellar thickness could be increased by annealing up to complete chain extension.
Non‐gaussian elasticity of composite and interpenetrating networks
Authors: Smith Jr. K. J. , Gaylord R. J. 
Published: April 2003

AbstractThe elastic behavior of composite and interpenetrating network structures composed of non‐Gaussian chains is investigated. The chain probability density given by Nagai is employed utilizing only the leading correction terms for finite chain extensibility. The independent‐network hypothesis, proven valid in Gaussian statistics, is shown to be erroneous in non‐Gaussian systems. Further, it is found that composite networks composed of monodisperse chains are elastically isotropic, whereas a most probable contourlength distribution yields a large anisotropy but in the direction opposite to that observed experimentally for rubber. On the other hand, retention of the independent‐network hypothesis coupled with a most probable distribution successfully accounts for much of the observed anisotropy. Interpenetrating networks are shown to be substantially anisotropic when a most probable contour‐length distribution is employed.
Lactone polymers. IV. Glass transition temperatures of monomeric lactones and their polymers
Authors: Koleske J. V. , Lundberg R. D. 
Published: April 2003

AbstractGlass transition temperatures were determined for a homologous series of unsubstituted lactone monomers varying in ring size from four to sixteen atoms. Examination of these transitions as a function of ring size shows a maximum in Tg for the seven‐atom ε‐caproalctone ring. This behavior is interpreted on the basis of a conformational change in lactones which occurs in rings containing seven to nine atoms. The Tg values of polylactones derived from these cyclic esters were determined and correlated with Tg values of the monomers. Except for the anomolous ε‐caprolactone and the strained fourmembered lactone, an apparently constant difference between monomer and polymer Tg is observed. Treatment of the polylactones as methylene copolymers permits extrapolations of the Tg values to obtain that of polyethylene. Two values suggesting the γ and β transitions of polyethylene are obtained.
Pressure‐dependent diffusion in velocity sedimentation
Authors: Weiss George H. , Yphantis David A. 
Published: April 2003

AbstractWe have calculated approximate profiles for the concentration gradient in velocity sedimentation of a homogeneous solute when both the diffusion and the sedimentation coefficient depend on pressure. Pressure dependence of the diffusion coefficient narrows the peak but does not seem to shift the maximum appreciably.
Viscoelastic properties of crosslinked solutions of poly(2‐hydroxymethyl methacrylate) in diethylene glycol. VI. Comparison with poly(butyl methacrylate) and poly(butyl acrylate) networks crosslinked to very low degrees
Authors: Janáček J. , Ferry John D. 
Published: April 2003

AbstractOn the basis of our own experimental and some literature data, the contributions of slow relaxation mechanisms to the shear modulus, (GeN — Ge), and the parameter C2 of the Mooney‐Rivlin equation have been examined for lightly crosslinked poly(butyl methacrylate), poly(butyl acrylate), poly(2‐hydroxyethyl methacrylate), and some rubber networks. For the rubbers, increasing degree of crosslinking caused a decrease in GeN — Ge and an increase in C2; for the other networks, both GeN — Ge and C2 diminished with increasing crosslinking. The effectiveness of the crosslinking polymerization, and also the absolute values of the physical crosslinking degree, decreased in the order of poly(2‐hydroxyethyl methacrylate), poly(butyl methacrylate), and poly(butyl acrylate). The values of the equilibrium compliances J of the networks studied, obtained by various methods, have also been compared, and good agreement has been found.
Dielectric behavior of aqueous solutions of sodium carboxymethyl cellulose
Authors: Allen D. J. , Neale S. M. , Tait P. J. T. 
Published: April 2003

AbstractMeasurements are reported for the dielectric loss factor of the SCMC solutions over the frequency range 2 MHz to 50 MHz as a function of concentration of SCMC, concentration of added sodium chloride, molecular weight, and temperature. The results are in general agreement with those of other workers and are interpreted in terms of ionic theories in which motion of the diffuse counterions is the dominant feature.
Kinetics of formation of polybisbenzimidazobenzophenanthroline‐dione (BBB polymer)
Authors: Ammons Vernon G. , Berry Guy C. 
Published: April 2003

AbstractThe kinetics of the polycondensation of 3,3′‐diaminobenzidine with 1,4,5,8‐naphthalenetetracarboxylic acid (NTC) have been investigated. Polymerizations were carried out in solution in either polyphosphoric acid (PPA) or in PPA mixed with some sulfuric acid. The reaction is heterogeneous in PPA owing to partial solubility of NTC, whereas it is homogeneous in the mixed solvent. The rate of disappearance of NTC and of dicarboxylic endgroups on oligomers was followed as a function of time at several reaction temperatures. The results show that NTC is more reactive than oligomers, so that the principle of equal reactivity is not valid for the initial steps in the polycondensation reaction.
Proton spin‐lattice relaxation study of polymer solutions
Authors: Sato Kazuo , Nishioka Atsuo 
Published: April 2003

AbstractProton spin‐lattice relaxation times of solvent molecules were measured on ternary mixtures of a polymer and two solvents by the adiabatic rapid‐passage method. The selective adsorption of a good solvent was verified by this experimental technique for the systems benzene—cyclohexane—polystyrene(PS), benzene—carbon tetrachloride—poly(methyl methacrylate)(PMMA), and chloroform—carbon tetrachloride—PMMA. The number of molecules of adsorbed benzene per monomeric unit of PS was estimated to be about four, which is almost identical with that determined previously by thermodynamic measurements. The number of molecules of benzene and chloroform adsorbed on PMMA were also determined to be about five and four, respectively. It was found that the interaction between chloroform and PMMA has the greatest effect on the molecular motion of the solvent, whereas the benzene—PS interaction is weak.
Thermal healing of scratches and determination of solid surface tension of selenium
Authors: Harris Lee B. , Vernon J. Peter 
Published: April 2003

AbstractThe healing of scratches on the surface of vitreous selenium was observed over a period of nine weeks, and from the data the solid surface tension of vitreous Se is estimated to be (100 ± 20) dyne/cm at 38.8°C, about the same as that of the liquid at the melting point. This value is three times as large as the critical surface tension determined from contact angle measurements, which indicates that for vitreous Se in contact with organic liquids, the solid—liquid interfacial tension is about two‐thirds as much as the solid surface tension. The present method of measurement can probably be used to determine the solid surface tension of other polymers, and by measuring the healing of scratches on a solid immersed in a liquid the method could be used to determine the solid—liquid interfacial tension.
Effects of melting on dielectric relaxation in poly(hexamethylene sebacamide) (nylon 610)
Authors: Boyd Richard H. , Porter Christopher H. 
Published: April 2003

AbstractIn order to investigate the role of solid morphology on molecular relaxation in crystaline polymers, the effect of melting on the α relaxation in poly(hexamethylene sebacamide) (nylon 610) was measured dielectrically. It was found that the α loss peak was continuous into the melt with respect to location in the frequency‐temperature domain and with respect to the shape of the peak. However, the strength of the process, as measured by the difference in the relaxed and unrelaxed dielectric constants, was discontinuous on melting, the process being much stronger in the melt. These observations are consistent with a two‐phase model of discrete crystalline and amorphous regions. The relaxation takes place in the amorphous regions, and melting creates more of this material but does not greatly after its nature. The correlation of the amount of amorphous material as measured by dielectric relaxation with that infrared from density measurements is discussed for nylon610, polyoxymethylene, and poly(ethylene oxide).
Extension and compression behavior of rubbery polymer networks
Authors: De Candia F. , Amelino L. 
Published: April 2003

AbstractThe elastic behavior of different types of rubbery polymers (natural rubber, polybutadiene, silicone, and polyisoprene) networks at various degrees of vulcanization and swelling was examined in extension and compression. The data are represented by the Mooney‐Rivlin equation. In compression, although C2 is zero, C1 decreases strongly with increasing swelling to a limiting value which, in some cases, may be correlated with the value of C1 found in extension and hence related to the theoretical modulus for highly swollen networks. A possible explanation is presented in terms of supramolecular order in the amorphous materials.
Membrane selectivity for an aqueous system by dynamic osmometry
Authors: Sheffer Howard , Sumner Paul 
Published: April 2003

AbstractCommercial and fractionated samples of poly(ethylene glycol) and a sample of Dextran were used as standards to show the limitation of a cellulose acetate membrane for osmotic pressure determination of molecular weight in an aqueous system. The leakage of this membrane was much greater in the aqueous system than in organic solvents.
Quantitative structural characterization of the mechanical properties of poly(ethylene terephthalate)
Authors: Samuels Robert J. 
Published: April 2003

AbstractThe mechanical properties of poly(ethylene terephthalate) are examined to see if the quantitative morphological criteria previously used to define the structural state of isotactic polypropylene will lead to similar quantitative structure‐property correlations when applied to PET. Tenacity, thermal shrinkage in oil and air, tensile modulus, dynamic loss modulus, long spacings, and small‐angle x‐ray intensities are included in the study. All of the data were obtained from the open literature. In all cases the physical properties correlate simply and quantitatively with the internal structure of the PET, and the character of the correlations leads to new insights into the nature of the internal mechanisms controlling the observed properties. The study shows that only by considering the structural state of a polymer, and not its fabrication parameters, can general, simplifying, quantitative, structure‐property correlations be achieved.