bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transfer reactions in radical polymerization of styrene in acetone–chloroform mixture
Authors: Kaloforov N. Ya. , Borsig E. 
Published: April 2003

AbstractThe study of chain‐transfer reactions in thermal and AIBN‐initiated polymerization of styrene is aimed at the determination of transfer constants to the solvents at 60°C. For thermal polymerization the transfer constants Cs to acetone, chloroform, and chloroform mixed with acetone are 3.2 × 10−5, 4.1 × 10−5, and 4.4 × 10−5, respectively. In the case of AIBN‐initiated polymerization, the transfer constant of chloroform in the mixture acetone–chloroform is Cs = 3.3 × 10−4. All these transfer constants are average values. It has been found that neither acetone nor chloroform satisfies the Mayo equation in the presence of transfer agent very well. These anomalies can be explained by assuming a complexation phenomenon. The changes in the polarity and resonance are taken into account. It is considered that in the chain‐transfer reactions under investigation, the association or complex‐forming ability of solvent and monomer or polymer play a role. In studying the chain‐transfer reaction in the acetone–chloroform solvent mixture another phenomenon affecting the determination of the chain transfer constant is assumed. This phenomenon consists in formation of associates in which both solvents participate.
Organometallic polymers. XXIV. Synthesis and copolymerization behavior of h6‐(2‐phenylethyl acrylate) tricarbonylchromium
Authors: Pittman Charles U. , Marlin Gary V. 
Published: April 2003

AbstractThe monomer h6‐(2‐phenylethyl Acrylate) tricarbonylchromium (PEAC) was synthesized and copolymerized in solution at 70°C with styrene, methyl acrylate, acrylonitrile, and 2‐phenylethyl acrylate, azobisisobutyronitrile being used as the initiator. In ethyl acetate solvent the relative reactivity ratios were crudely approximated. The copolymers all exhibited binodal molecular weight distributions, the high molecular weight node probably resulting from branching. The h6‐benzenetricarbonylchromium unit decomposed when exposed to sunlight or ultraviolet light both in air and under N2. In air, Cr2O3 was initially formed within copolymer films. Several unsuccessful attempts were made to prepare h6‐(2‐phenylethyl acrylate)tricarbonylmolybdenum, (III), the molybdenum analog of PEAC, from arenes and both Mo(CO)6 and (CH3CN)3Mo(CO)3. These reactions are described.
Aging and degradation of polyolefins. III. Polyethylene and ethylene–propylene copolymers
Authors: Decker Christian , Mayo Frank R. , Richardson Harold 
Published: April 2003

AbstractRates of oxygen absorption and formation of oxidation products were determined in γ‐initiated oxidations of thin films of high‐ and low‐density polyethylene, atactic and isotactic polypropylene, and of three ethylene–propylene copolymers. Radiation yields G for O2 absorbed and formation of hydroperoxides depend on dose rates and decrease sharply with increasing ethylene content of the copolymers and moderately with increasing crystallinity of any base polymer. G values for dialkyl peroxide and carbonyl formation, and therefore for chain initiation and termination, do not change much with polymer composition and crystallinity and not at all with dose rates. A few experiments with atactic polypropylene and an amorphous ethylene–propylene copolymer, initiated by di‐tert‐butylperoxy oxalate, indicate that 37 mole‐% of ethylene in the polymer increases the efficiency of initiation and the tendency toward crosslinking.
Polymerization of styrene by poly(bisphenol a 4,4′‐azobis‐4‐cyanopentanoate)
Authors: George M. H. , Ward J. R. 
Published: April 2003

AbstractA free radical initiator, poly(bisphenol A 4,4′‐azobis‐4‐cyanopentanoate) (BPA), containing more than one azo group per molecule, was used to polymerize styrene in N,N‐dimethylformamide (DMF) at 60°C. Polymerization rates were measured gravimetrically or dilatometrically, and the molecular weights of the isolated polystyrenes were determined viscometrically, both before and after hydrolysis. BPA has a relatively low initiator efficiency of 0.28. The activation energy and velocity constant at 60°C for decomposition of BPA per azo group in DMF were found spectroscopically to be 105.9 kJ/mole and 2.08 × 10−5 sec−1, respectively. The molecular weights of unhydrolysed polystyrenes increased with increasing conversion and a theory is developed to explain these results.
Mechanism of charge‐transfer polymerization. V. Photopolymerization and photocyclodimerization of N‐vinylcarbazole in the N‐vinylcarbazole–oxygen–solvent system
Authors: Tada Kazuhiro , Shirota Yasuhiko , Mikawa Hiroshi 
Published: April 2003

AbstractPhotochemical reactions of N‐vinylcarbazole (VCZ), studied in various solvents, were profoundly influenced by the atmosphere. In the deaerated system radical polymerization of VCZ occurred in various solvents, e.g., tetrahydrofuran, acetone, ethyl methyl ketone, acetonitrile, methanol, sulfolane, N,N‐dimethylformamide (DMF), or dimethyl sulfoxide (DMSO). By contrast, when dissolved oxygen was present, cyclodimerization of VCZ occurred exclusively to give trans‐1,2‐dicarbazole‐9‐yl‐cyclobutane in such polar, basic solvents as acetone, ethyl methyl ketone, acetonitrile or methanol. In stronger basic solvents, i.e., sulfolane, DMF, or DMSO, simultaneous radical polymerization and cyclodimerization of VCZ proceeded, the ratio of the cyclodimerization to the radical polymerization decreasing in the order, sulfolane > DMF > DMSO. In dichloromethane, on the other hand, cationic polymerization of VCZ occurred irrespective of the atmosphere. It is suggested that oxygen acts as an electron acceptor to the excited VCZ, electron transfer occurring in polar solvents from the excited VCZ to oxygen to give transient VCZ cation radical. The effect of solvent basicity on the photocyclodimerization of VCZ is discussed.
The influence of fine structure on the pyrolysis of cellulose. I. Vacuum pyrolysis
Authors: Basch A. , Lewin M. 
Published: April 2003

AbstractThe effects of crystallinity, orientation and degree of polymerization on the vacuum pyrolysis of cellulose have been investigated. Natural, modified and manmade celluloses were characterized and the kinetics of their pyrolysis at 251°C studied. The high‐temperature pyrolysis of these samples was also investigated by means of DSC and TGA. At 251°C all of the samples showed a rapid, initial weight loss followed by a linear (weight loss)1/2 versus time dependency. Both the initial weight loss and the subsequent reaction rate were dependent upon the crystallinity of the sample. The reaction rate was shown to be inversely proportional to (DP)1/2 and related to the orientation. Effects of crystallinity and orientation could also be seen in the DSC thermograms and in the apparent energies of activation. Results are interpreted in terms of probable mechanisms of the uncatalyzed pyrolysis of cellulose.
Heat‐resistant polymers containing bipyridyl units. II. Polyamide‐imides
Authors: Kurita Keisuke , Williams Roy L. 
Published: April 2003

AbstractPolyamide‐amic acids containing bipyridyl units were prepared by polymerization of various bipyridyl diamines with trimellitic anhydride acid chloride. These polymers were converted to polyamide‐imides by thermal cyclization. The resulting polyamide‐imides exhibited very good solubility in organic solvents.
Polymerization of propadiene. IV. Kinetics and mechanism of polymerization under the influence of rhodium(I) complexes
Authors: Scholten J. P. , Van Der Ploeg H. J. 
Published: April 2003

AbstractThe kinetics and mechanisms of propadiene polymerization under the influence of [Rh(CO)2Cl]2, Rh(CO)2P(C6H5)3Cl, Rh(CO)3Cl are reported. The reaction rates are first‐order in Rh(CO)2P(C6H5)3Cl and Rh(CO)3Cl and half‐order in [Rh(CO)2Cl]2. They are second‐order in the substrate for Rh(CO)3Cl and [Rh(CO)2Cl]2 and first‐order for Rh(CO)2P(C6H5)3Cl. The data are interpreted in terms of a common intermediate mechanism. The formation of this common intermediate is the rate‐determining step. A solvent effect is also discussed.
Thermodynamic interactions in polymer systems by gas–liquid chromatography. III. Polyethylene–hydrocarbons
Authors: Schreiber H. P. , Tewari Y. B. , Patterson D. 
Published: April 2003

AbstractThermodynamic interaction parameters have been calculated from gas–liquid chromatographic measurements for linear and branched polyethylene interacting with selected hydrocarbons. The values of the interaction parameter χ are substantial in spite of chemical similarities between the polymer and low molecular weight hydrocarbon species, a fact attributed to significant differences in the respective thermal expansion coefficients. A systematic increase of χ is observed in going from branched to linear polyethylene systems. The thermal expansion coefficients of these polymer homologs therefore may not be identical. The present χ values differ substantially from those reported in earlier literature. The comparison confirms suspicions that some older data, based on equilibrium sorption experiments, were erroneously low because of an underestimate in the reduced melting temperature of polymer in the presence of excess solvent.
Pulsed NMR study of molecular motion in the uncured diglycidyl ether of bisphenol‐A
Authors: Larsen David W. , Strange John H. 
Published: April 2003

AbstractThe diglycidyl ether of bisphenol‐A, an uncured epoxy resin, has been studied by pulsed NMR. Values of the proton relaxation times T1, T1p, and T2 have been measured over the temperature range from −160 to 200°C. The resin was studied in its monomeric form and in two mixtures containing higher oligomers. The relaxation times are interpreted in terms of the molecular motion in the resins. The motion responsible for relaxation in the solid monomer form is thought to be methyl group reorientation at low temperatures and general molecular motion at high temperatures. The motions are characterized by activation energies of 5 kcal/mole and 33 kcal/mole, respectively. The solid mixtures exhibit similar effects to the monomer, but an additional relaxation mechanism is observed which is attributed to segmental motion. This motion is characterized by an activation energy of 12–15 kcal/mole. The self‐diffusion coefficient was measured in the liquid monomer, and the activation energy for self‐diffusion is found to be 11 kcal/mole.
Carbon‐13 NMR of ethylene‐1–olefin copolymers: Extension to the short‐chain branch distribution in a low‐density polyethylene
Authors: Randall James C. 
Published: April 2003

AbstractAs model polymers for isolated short‐chain branches in low‐density polyethylene, a series of ethylene–1‐olefin copolymers was examined by use of 13C NMR at 25.2 MHz. An array of 13C resonances was observed that could be associated independently with methyl through amyl branches. The 13C chemical shifts became insensitive to branch length with hexyl and longer branches. Assignments of the various carbon resonances associated with branching were accomplished by using off‐resonance decoupling techniques and the behavior of alkane chemical shifts previously observed by other investigators. The ratio of certain backbone and branch resonances could be used to establish the short‐chain branch distribution in a low‐density polyethylene.
Statistical thermodynamics of ABA block copolymers. II
Authors: Leary David F. , Williams Michael C. 
Published: April 2003

AbstractA microstructural model for the phase‐separated states of ABA triblock copolymers is proposed. It postulates the simultaneous existence of three phases: pure A, pure B, and a mixed region. Incorporation of the mixed region distinguishes this treatment from all other theories and is responsible for considerable flexibility in the model without increased numbers of parameters. Calculations of free energy changes required to establish specific microstructures permit the prediction of a favored one from among five possibilities: discrete spheres of A (or B), discrete cylinders of A (or B), and lamellae.
Strain‐induced crystallization of natural rubber. III. Reexamination of axial‐stress changes during oriented crystallization of natural rubber vulcanizates
Authors: Luch D. , Yeh G. S. Y. 
Published: April 2003

AbstractIn order critically to evaluate the previous morphological interpretations of stress relaxation during oriented crystallization, a reexamination was made of the relaxation behavior of the same oriented natural rubber material used for the x‐ray investigation in Part II of this series. Our results were found to be in qualitative agreement with previously published reports. Comparison of stress‐relaxation rates at low temperatures for samples with strains of 200% or more with crystallization rates at room temperature by others for similar elongations indicates a dual nature in the strain‐induced crystallization process. This conclusion is in full agreement with the indication of dual crystalline morphologies, namely, fibrillar and lamellar, for both electron microscopy and x‐ray investigations on highly stretched samples reported in Parts I and II. Examination of stress‐relaxation data in light of morphological evidence for oriented crystallization indicates that caution must be exercised in attaching morphological significance to the Avrami exponent n obtained from stress‐relaxation or crystallization data.
Dynamic light scattering of polyethylene. I. Introduction and experimental procedures
Authors: Hashimoto T. , Prud'homme R. E. , Keedy D. A. , Stein R. S. 
Published: April 2003

AbstractAn apparatus and procedures are described for the observation of the light‐scattering changes during the periodic vibration of a polymer film sample. The relationship between static and dynamic scattering experiments is discussed as are the means for interpreting such experiments in terms of spherulite deformation and statistical theories. The performance of the apparatus is illustrated with some experiments on a medium‐density polyethylene sample.
Heat capacity of molten polymers
Authors: Bares Vera , Wunderlich Bernhard 
Published: April 2003

AbstractHeat capacities of molten polyethylene, polypropylene, poly‐1‐butene, polystyrene, and poly(methyl methacrylate) were measured over a wide range of temperature by using a differential scanning calorimeter. The upper limit of temperature was established for each polymer at about 10°K below the beginning of thermal decomposition. For poly‐1‐butene and poly(methyl methacrylate) the solid‐state heat capacity was also measured starting from room temperature. Several samples of each polymer were used so that average values of heat capacities could be established (reported in 10°K intervals). The data revealed for all polymers a nearly linear increase of heat capacity with increasing temperature over the whole temperature range investigated.
Notes on polymer hydrodynamics
Authors: Fujita Hiroshi 
Published: April 2003

AbstractThe sedimentation of an unperturbed polymer chain in dilute solution is reformulated by using Burgers' method, in which the no‐slip boundary condition on the surface of each chain element is taken into account approximately. It is shown that the forcevelocity proportionality relation employed so far as the basis of theoretical developments in polymer hydrodynamics can be justified as a first approximation to the no‐slip condition. The derived expression for the translational friction coefficient ft is a complex function of n and a/b, where n is the number of chain elements in a single molecule and a/b is the ratio of the Stokes radius of a chain element to the effective bond length. Three special cases corresponding mathematically to b = ∞ (no hydrodynamic interaction), a ≪ b (Kirkwood‐Riseman theory), and b = 2a (touching‐sphere model) are examined in detail. Finally, it is shown that when a/b = 0.2360, our ft varies linearly with n1/2 over the entire range of n.
Approach to generalization of concentration dependence of zero‐shear viscosity in polymer solutions
Authors: Dreval V. E. , Malkin A. Ya. , Botvinnik G. O. 
Published: April 2003

AbstractThe possibility of constructing zero‐shear viscosity master curves valid for the entire range of concentration for a large number of polymer solutions in different solvents independent of molecular weight and the nature of the solvent is considered. The results obtained show that the parameters characterizing the individual macromolecular chain., viz., the dimensions of the polymer coil and the rheological effectiveness of segmental interactions, are significant in determining the viscosity of polymer solutions from very dilute to highly concentrated ones. The relation between the parameter of rheological interaction and characteristics of polymer solutions such as the flexibility of the polymer chain and the Flory‐Huggins parameter is discussed. This permits one to separate the influence of the energy and entropy factors on the concentration dependence of zero‐shear viscosity.
Synthesis and characterization of poly(p‐phenylene pyromellitamic acid)
Authors: Tsimpris C. W. , Mayhan K. G. 
Published: April 2003

AbstractPoly(p‐phenylene pyromellitamic acid)s were synthesized over the weight‐average molecular weight range 8,000 to 22,000. The polymers were recovered as amorphous powders composed of 3–4 × 1–2 μ platelets 0.1–0.2 μ thick containing 20–30% associated solvent. Consumption of reactants and attainment of the ultimate molecular weight of the polymer were found to occur within the first few minutes of reaction. The polymers were characterized by scanning electron microscopy; ultraviolet, visible, near‐infrared, and infrared spectroscopy; x‐ray analysis; viscometry; and light‐scattering photometry. The intrinsic viscosity–molecular weight relation for the polymer in DMF was \documentclass{article}\pagestyle{empty}\begin{document}$ [\eta ] = 25.2 \times 10^{ - 4} \bar M_w^{0.56} $\end{document}.
Mark‐Houwink relations for linear polyethylene in 1‐chloronaphthalene and 1,2,4‐trichlorobenzene
Authors: Wagner Herman L. , Hoeve C. A. J. 
Published: April 2003

AbstractThe parameters in the Mark‐Houwink relationship, [η] = K′M̄va, for linear polyethylene in 1‐chloronaphthalene and 1,2,4‐trichlorobenzene at 130°C have been estimated. They were found by measuring the limiting viscosity numbers of a series of fractions with molecular weights ranging from less than 10,000 to almost 700,000. The results are for 1‐chloronaphthalene, [η] =0.0555 M̄v0.684 (with a standard error of 0.0064 in K′ and 0.010 in a) and for 1,2,4‐trichlorobenzene, [η] = 0.0392M̄v0.725 (with a standard error of 0.00703 in K′ and 0.015 in a), where [η] is expressed in ml/g. The unperturbed end‐to‐end distance calculated from the viscosity‐molecular weight data agrees with the theoretically expected value.
Creep failure in highly oriented nylon 6 fibers
Authors: Narisawa I. , Kondo T. 
Published: April 2003

AbstractCreep failure in oriented nylon 6 fibers has been studied. The results suggest that the variations in the lifetime under various loading histories are inherent, but statistical, characteristics of the material itself. The treatment of experimental data by a stochastic theory shows that the creep failure can be regarded as a nucleation process. An interpretative analysis of the structural changes during creep indicates that the nucleation is brought about by bond rupture in the amorphous regions of the fiber structures.
Electrical properties of carbon black in an SBR–wax matrix
Authors: Bueche F. 
Published: April 2003

AbstractThe resistivity and dielectric constant for carbon black (5–12 vol‐%) in a nonconducting matrix have been measured over the range 20–90°C and dc to 2–105 Hz. Styrene–butadiene rubber dissolved in tetracosane (22 parts SBR to about 70 parts wax) constituted the matrix. Wide variations in resistivity and dielectric constant with temperature and/or frequency were observed. A theory is presented to explain the experimental observations. It correctly predicts the qualitative features of the experimental results but its predictions are not quantitatively accurate.
Interpretation of boundaries in the pressure–temperature diagram for liquid tellurium and their relationship to the melting‐curve maximum
Authors: Vezzoli G. C. 
Published: April 2003

AbstractResearch on liquid tellurium is reviewed and interpreted in an effort to obtain a consistent picture of the effect of pressure and temperature on the structure and properties of tellurium in the liquid state. Electrical resistance experiments on liquid tellurium support the existence of reaction boundaries in the p–T diagram. The boundaries are believed to identify stages in the reaction whereby the 2‐coordinate covalent chain structure transforms to a 3‐coordinate covalent network structure which eventually dissociates with pressure and temperature into a metallic system. The increasing liquid density associated with the molecular reaction is given as the cause of the maximum on the P–T melting curve. The melting curve maximum in tellurium is shown to be related to maxima in selenium and sulfur. Quenching tellurium from different liquid fields, delineated by reaction boundaries, resulted in materials with different x‐ray spectra.
Random‐coil dimensions and dipole moments of propylene–vinyl chloride copolymers
Authors: Mark J. E. 
Published: April 2003

AbstractMean‐square unperturbed dimensions 〈r2〉0 and dipole moments 〈μ2〉 have been calculated for propylene–vinyl chloride copolymers by means of rotational isomeric state theory. The calculations indicate that for these chain molecules 〈mu;2〉 is much more sensitive to chemical sequence distribution than is 〈r2〉0, a conclusion in agreement with results of previous studies of ethylene–propylene copolymers and styrene‐substituted styrene copolymers. In the case of propylene–vinyl chloride chains, both 〈r2〉0 and 〈μ2〉 are most strongly dependent on chemical sequence distribution in the case of copolymers which are significantly syndiotactic in stereochemical structure. At equimolar chemical composition, increase in average chemical sequence length generally increases 〈r2〉0 but decreases 〈μ2〉. Under some conditions, values of these statistical properties go through a minimum with increase in the reactivity ratio product r1r2, thus complicating the use of experimental values of these properties in the characterization of chemical sequence distributions in these copolymers.
Diglycidyl ether of bisphenol‐A with 4,4′‐methylenedianiline: A pulsed NMR study of the curing process
Authors: Larsen David W. , Strange John H. 
Published: April 2003

AbstractThe curing process, during which the monomeric diglycidyl ether of bisphenol‐A is cured with 4,4′‐methylenedianiline, has been studied by pulsed NMR. Values of the proton relaxation times T1, T1ρ, and T2 have been measured as a function of time as the resin system cures at constant temperature. The relaxation times are interpreted in terms of the decrease in general molecular motion which results from the cure. Plots of correlation frequency versus time for the constant‐temperature cure were constructed for three temperatures. It is shown that these three plots can be represented by a reduced curve. With certain simplifying assumptions, the shape of this reduced curve. With certain simplifying assumptions, the shape of this reduced curve can be accounted for in terms of the chemical rate constant and an exponent relating molecular weight to viscosity. The activation energy for the cure is estimated to be 11.7 kcal/mole.