bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electron spin resonance spectra of aged, γ‐irradiated polystyrenes
Authors: Florin R. E. , Wall L. A. , Brown D. W. 
Published: April 2003

AbstractThe electron spin resonance spectrum of polystyrene that has been γ‐irradiated at −196°C. changes gradually with time from a broad three‐peaked structure with outer derivative peaks at ±46 gauss to a much narrower structure with poorly separated outer derivative peaks at ±21–24 gauss. The deuterated polystyrenes behave likewise in general. The aged radicals of α,β,β‐trideuterostyrene and β,β‐dideuterostyrene exhibit only a single peak with derivative maxima at ±7 or 8 gauss from center. The aged spectra are all consistent with the hypothesis of major hyperfine interaction with β hydrogens. During the aging about 80% of the original radicals are lost, but the remainder are very long‐lived. Poorly evacuated samples or those with added benzene decay much more rapidly.
Nuclear radiation effects in polytetrafluoroethylene
Authors: Kline D. E. , Sauer J. A. 
Published: April 2003

AbstractDynamic mechanical studies of polytetrafluoroethylene, subjected to a total reactor radiation dose of about 108 rads, have shown that a decrease occurs in the height of the three damping peaks which are observed in unirradiated samples near 200, 300, and 400°K. Since the 200°K. and 400°K. peaks are associated with configurational changes in the amorphous regions of the material, the experimental observations are compatible with an increased degree of crystallinity. The effects observed in the dynamic modulus–temperature relation upon irradiation are consistent with those found in the internal friction spectrum. The changes that occur in degree of crystallinity upon irradiation have been studied by both infrared and density measurements, and an increase in crystallinity has been found. The changes in the dynamic mechanical properties in the vicinity of room temperature are not well understood, but possible reasons for the observed behavior are given.
Isomorphism in polycarbonates. Copolymers of hydroquinone and substituted hydroquinones
Authors: Rubin Isaac D. 
Published: April 2003

AbstractCopolycarbonates were synthesized by phosgenating various proportions of chlorohydroquinone with hydroquinone, toluhydroquinone, and 4,4′‐dihydroxydiphenylmethane. It was found, by means of x‐ray diffraction diagrams and melting point–composition data, that the copolymers prepared from hydroquinone–chlorohydroquinone and toluhydroquinone–chlorohydroquinone mixtures were isomorphous over their entire composition range. The copolymerizations of 4,4′‐dihydroxydiphenyl with chlorohydroquinone resulted in products characterized by reduced crystallinity. The effect of the monomer structure on changes in the lattice constants of the crystalline copolymers was investigated briefly.
The molecular structure of polyethylene. XII. Intrinsic viscosities of polyethylene solutions
Authors: de la Cuesta M. O. , Billmeyer F. W. 
Published: April 2003

AbstractWhile the intrinsic viscosity of polyethylene solutions is reported in the literature for at least 6 different solvents and 14 different temperatures in 23 combinations, few relations exist for converting from one set of conditions to another. Likewise, intrinsic viscosity–molecular weight relations are reported for several sets of conditions and polymer types, in some cases leading to inappropriate comparisons. The following relations are established between the intrinsic viscosities of branched polyethylene in different solvents:

where α denotes α‐chloronaphthalene at 125°C. d, decahydronaphthalene at 70°C.; t, tetrahydronaphthalene at 125°C.; and x, p‐xylene at 85°C. The relations for linear polyethylene are significantly different from those for branched polyethylene, but have not been established in detail. The literature is examined for the appropriateness and reliability of intrinsic viscosity–molecular weight relationships for polyethylene. Analysis of the experimental data leads to the following relations for linear polyethylene which are proposed as the most consistent, reliable, and appropriate currently obtainable (in‐trinsic viscosities are expressed in deciliters/gram for measurement conditions of decahydronaphthalene at 135°C., within experimental error of those specified in ASTM D 1601–58T). For the number‐average molecular weight of fractions of linear polyethylene, [η] = 2.3 × 10−4 Mn0.82; for the weight‐average molecular weight of whole polymer samples of linear polyethylene, [η] = 2.55 × 10−4 Mw0.74; for the weight‐average molecular weight of fractions of linear polyethylene, [η] = 3.9 × 10−4 Mw0.74
Homogeneous anionic polymerization. IV. Kinetics of butadiene and isoprene polymerization with butyllithium
Authors: Morton Maurice , Bostick E. E. , Livigni R. A. , Fetters L. J. 
Published: April 2003

AbstractThe kinetics of polymerization of butadiene and isoprene with butyllithium initiator have been studied both in n‐hexane and tetrahydrofuran solution. The overall polymerization rates were much faster in the THF solutions than in n‐hexane, and the latter also exhibited relatively slow initiation rates compared to propagation. By use of a preinitiation technique, where necessary, it was possible to study the propagation kinetics without any interference by initiation. The propagation reaction was found to be first‐order with respect to monomer in both solvents, but much faster in THF. Furthermore, it was first‐order with respect to growing chain concentration in the THF system, but only half‐order in the n‐hexane system. This was taken to indicate the existence, in n‐hexane solution, of an association equilibrium between active single chains and inactive chain pairs. The activation energy for propagation was found to be 6–7 kg. cal. in THF and about 22 kg. cal. in n‐hexane for both monomers, but the latter value obviously includes the heat of dissociation of the associated chain pairs. The Arrhenius expression for the propagation rate in THF contains a very low frequency factor (∼︁104) and leads to a propagation rate constant at least two orders of magnitude less than the corresponding value for free radical propagation.
Anisotropic properties of strained viscoelastic fluids. III. Birefringence of polystyrene solutions
Authors: Toggenburger Robert , Gill Stanley J. 
Published: April 2003

AbstractBirefringence relaxation has been studied in concentrated polystyrene solutions. The birefringent state is induced by a sudden application of strains and the subsequent relaxation effect is observed by photoelectric monitoring. The effect of temperature concentration on the decay of induced birefringence follows the general patterns observed for stress relaxation. Samples of different molecular weights and different molecular weight distributions have been studied. A particularly simple empirical result was found to express the relaxation behavior of highly fractionated materials. In such instances the birefringence decays with exponential dependence upon the square root of time. The results for samples with broad distributions show curvature when plotted in a similar fashion. This simple relaxation behavior has a simple LaPlace transform, so that a comparison of the exact relaxation distribution function with approximate methods can be made. The general behavior of birefringence relaxation distribution functions is similar to that noted for stress relaxation functions. The method of reduced variables likewise is applicable to bring the birefringence relaxation results into correspondence at different temperatures.
Theoretical calculations of stress relaxation in concentrated solutions
Authors: Toggenburger R. , Beck K. , Gill S. J. 
Published: April 2003

AbstractThe Mooney theory for stress relaxation of polymer materials has been numerically evaluated in unmodified and modified forms. The modified expressions include such effects as molecular weight distributions and entanglement or polymer interaction distributions. The relaxation behavior was found to be highly dependent upon the number of interaction points per chain molecule particularly for small numbers. The distributions in molecular sizes and in the number of interaction points have a much smaller effect on the shapes of the relaxation curves. A comparison of the theoretical stress relaxation behavior is made with birefringence relaxation data. The region of correlation indicates a number of five interaction points per molecule of polystyrene at 10 wt. % in benzene.
Olefin polymerizations and polyolefin molecular weight distribution
Authors: Chien James C. W. 
Published: April 2003

AbstractA method for rapid determination of the nonuniformity coefficient, Mw/Mn, of linear polyethylenes and crystalline polypropylenes is described. The number‐average molecular weight Mn was determined by counting the number of C14‐labeled alkyl groups introduced into the polymers during the initiation step. The weight‐average molecular weight Mw was calculated from viscometric data. The errors in these calculations were estimated. The values of Mw/Mn thus obtained for eleven samples of linear polyethylenes and three samples of crystalline polypropylenes are compared with the corresponding results obtained by polymer fractionations. The agreement was good for all the polyethylene and polypropylene samples studied except for three high viscosity polyethylene samples with high Mw values and low Mn values from fractionation data. The Mw/Mn values were determined for polymer samples taken during ethylene polymerizations initiated by the (C5H5)2TiCl2–(CH3)2AlCl system. This ratio at first decreased with the polymerization time, then reached a minimum as the concentration of growing chains reached a maximum. Comparison of polyethylene produced at various temperatures reveals that the width of polymer distribution decreases with rising polymerization temperatures. This decrease is attributed to the increase in the rates of initiation and termination and the higher activation energy for the termination processes. High catalyst concentrations yielded polyethylenes of broad distributions. At high catalyst concentrations, the concentrations of growing chains are also high. Consequently, more low molecular weight chains terminate early to give products with large Mw/Mn. On the other hand, increase of the Al/Ti ratio increases chain transfers giving polyethylenes having a low Mw/Mn. An additional effect of increasing the Al/Ti ratio is the decreased variation of Mw/Mn with t. The Mw/Mn values of crystalline polypropylene samples taken during polymerizations initiated by α‐TiCl3‐(C2H5)2AlCl are also presented. They were high at the beginning of the polymerizations and decreased gradually to a lower constant value. At higher temperatures, this variation was less pronounced; and the Mw/Mn values were lower than those for the polymers obtained at lower temperatures. The Mw/Mn values were insensitive to experimental variables such as the catalyst concentrations, the Al/Ti ratios, and the monomer pressures in agreement with the kinetic results. The Mw/Mn values of amorphous polypropylene samples taken during propylene polymerizations did not vary with t or with the other polymerization conditions. These results support the earlier kinetic interpretation that extensive chain transfers occur during the formation of amorphous polypropylenes.
The reference point for liquid relaxation processes. I. Melt viscosity of polystyrene
Authors: Miller A. A. 
Published: April 2003

AbstractRecent theories have suggested or implied that below the experimental glass temperature, Tg, there exists a temperature, T0, which governs the temperature dependence of relaxation processes in a liquid. In the “free‐volume” approach, T0 should be associated with an “occupied” volume, v0. In the present paper, published melt viscosity—temperature data for a series of polystyrene fractions (M = 1675–134,000) are shown to conform to a “modified” Arrhenius equation: η = A exp {B/(T ‐ T0)}. From this and from a previous free‐volume treatment of the same data, the reference point (T0, v0) is derived. Either or both of these approaches indicate that this reference point is situated on the liquid specific volume—temperature curve, extrapolated linearly into the glass region. In the series of polystyrene fractions for which Tg increases from 40 to 100°C., the corresponding T0 values increase from 5 to 50°C. Further relationships between the parameters in the modified Arrhenius, the Doolittle free‐volume, and the Williams‐Landel‐Ferry (WLF) equations, are expressed.
Hydrolysis of cellulose triacetate crystals
Authors: Manley R. St. John 
Published: April 2003

AbstractCrystals of cellulose triacetate were hydrolyzed in an attempt to obtain single crystals of cellulose. The hydrolyzed material retains the morphology of the triacetate crystals, but its crystalline state depends upon the method of hydrolysis. In an aqueous medium, polycrystalline cellulose is formed, while a nonaqueous medium gives an amorphous cellulose. The results suggest that the hydrolysis is accompanied by a disruption of the lattice and that recrystallization of the resulting amorphous cellulose is caused by the water.
Polymerization studies on allylic compounds. I
Authors: Baldwin M. G. , Reed Samuel F. 
Published: April 2003

AbstractThe polymerization of a series of α‐(substituted methyl) acrylates was investigated. Polymerization rate measurements showed that each of the monomers, though containing allylic hydrogen atoms, polymerizes readily. Polymer viscosity data were obtained which indicate that appreciable nondegradative chain transfer occurs with several of the monomers. An explanation for the rapid polymerization of the monomers was proposed.
Polymerization of vinyl ethers with magnesium compounds. I. Catalytic reactivity of magnesium halides
Authors: Iwasaki K. , Fukutani H. , Nakano S. 
Published: April 2003

AbstractAn attempt was made to summarize the activity of magnesium halides in the polymerization of vinyl ethers. Bulk polymerization was carried out at temperatures of 0–80°C. Methyl, ethyl, isopropyl, and isobutyl vinyl ethers were used as monomers, and the relative reactivities of these monomers were compared. Except for the fluoride, magnesium halides had mild activity. Within a given group, the overall activation energies of polymerization decrease with increasing weight of halogen. On the other hand, the molecular weight of polyvinyl ethers obtained from this group of catalysts increases with decreasing weight of halogen. In addition, some differences were observed between the diethyl ether complex and the dioxane complex of magnesium bromide.
Bulk copolymerization of methyl methacrylate with phenyldichlorophosphine
Authors: Boryniec Atanazy , Łaszkiewicz Bogumił 
Published: April 2003

AbstractCopolymers of methyl methacrylate with phenyldichlorophosphine were isolated as compact, incombustible, and colorless thermoplastic resins. The copolymerization was carried out at 60°C. by the standard bulk method, azobisisobutyronitrile being used as catalyst. The experiments indicate that in the investigated reaction there are concurrent processes which lead to degradation. The effect of duration of the copolymerization process and the content of phenyldichlorophosphine in the methyl methacrylate copolymer on the extent of reaction and on the intrinsic viscosity of copolymer has been investigated.
Enthalpy and free energy changes in some simple polymerization processes
Authors: Parks George S. , Mosher Helene P. 
Published: April 2003

AbstractThe heats of combustion of four polymers, viz., polyoxymethylene (Delrin), polymethylene, polyethylene (Marlex), and polypropylene, have been accurately measured. From these results the changes in enthalpy and free energy have been calculated for (a) the process of forming the respective polymer units from the elements and (b) the process of forming these polymers from their monomer building blocks.
Copolymerization of styrene and aliphatic olefins
Authors: Overberger C. G. , Miyamichi Kazuo 
Published: April 2003

AbstractAn attempt has been made to study the composition of the products resulting from polymerization of equal molar amounts of styrene and 4‐methyl‐1‐pentene and styrene and 3‐methyl‐1‐butene with vanadium oxytrichloride and aluminum triisobutyl as the catalyst system. Fractionation of the products has revealed that some copolymers can be obtained with both olefins—a larger amount of copolymer being obtained with 4‐methyl‐1‐pentene. Homopolymerization of both styrene and the α‐olefin also occur. Qualitatively, in this catalyst system, the order of the polymerization rate is 4‐methyl‐1‐pentene‐1 > styrene > 3‐methyl‐1‐butene. The results again collaborate the authors' early work that the copolymers obtained are not of uniform composition.
Mechanism of secondary crystallization in polymers
Authors: Rybnik´ř F. 
Published: April 2003

AbstractIn isothermal crystallization of polymers, where the fusion preceding the crystallization process is conducted at relative low temperatures or in samples subjected to γ‐radiation, there is extensive secondary crystallization. Secondary crystallization, which has been found to start stepwise at a time equal to two half‐times of primary crystallization, represents a new process of crystallization following the Avrami equation with n = 1. In addition to this crystallization process a further slow increase of crystallinity with time takes place.
Some anomalous brittleness temperatures of polyethylene
Authors: Rudin A. , Mackie J. S. 
Published: April 2003

AbstractRabesiaka and Kovacs have reported experiments in which the shapes of crystallization isotherms of several polyethylenes depended on the sample history as well as the intrinsic properties of the polymers. The suggestion was made that, in general, molten polyethylene is not in a true thermodynamic equilibrium and includes some quasi‐indestructible clusters, which act as heterogeneous nuclei in the crystallization process. This paper reports anomalous brittleness temperature experiments on polyethylenes, the results of which are explainable in terms of quasi‐indestructible clusters. The data are consistent with the supposition that the crystalline embryos responsible for the observed behavior result from strong entanglements or cross‐linking in natural polyethylene and from binding to carbon black surfaces in black compounds. At the low, nonuniform shear rates in compression molding these clusters may survive relatively intact. If subsequent remelting is performed in the absence of shear, any ordered structure between entanglement points will expand but not break. Such configurations can contract to form crystalline embryos as the polymer is cooled.
Polycondensation of xylylene dibromides by transition metals in water suspension
Authors: Sisido Keiiti , Kusano Nobuo , Noyori Ryôzi , Nozaki Yôko , Simosaka Masatosi , Nozaki Hitosi 
Published: April 2003

AbstractTreatment of benzyl chloride with iron powder in water suspension results in the formation of benzyl radicals, which are subsequently dimerized into bibenzyl. This reaction has now been extended to p‐xylylene dibromide under a set of conditions as summarized in Table I. High yields (70–80%) of poly‐p‐xylylene, which was identified by infrared spectrum, x‐ray diffraction pattern, and other properties, were obtained with reduced iron suspended in a mixture of xylene and water (50:50) or in dimethylformamide. Zinc powder coated with nickel (Urushibara nickel CB) gave comparable yields of poly‐p‐xylylene, while cobalt powder or zinc—cobalt couple afforded inferior yields. Similar reaction of o‐ and m‐xylylene dibromides gave soluble polymers. The presence of o‐xylylene as an unstable intermediate of the polymerization of o‐xylylene dibromide has been indicated by trapping this transitory hydrocarbon with acrylonitrile and with methyl acrylate as diene adducts.
Elektronenspinresonanz‐untersuchungen an peroxydradikalen in bestrahltem polypropylen
Authors: Fischer H. , Hellwege K.‐H. , Neudörfl P. 
Published: April 2003

AbstractPeroxide radicals are formed by oxidation of carbon radicals in irradiated isotactic polypropylene. An interpretation of their ESR‐spectra is given. The recombination of the peroxide radicals follows a chain reaction mechanism, which is derived from the reversibility of formation of peroxide radicals, the time dependence of their concentration, and from the oxygen consumption of samples containing peroxide radicals. The reactions are discussed in view of the radiation induced oxidative degradation of polypropylene.
Crystallinity in ethylene—propylene copolymers
Authors: Jackson J. F. 
Published: April 2003

AbstractA mathematical expression has been developed which treats crystalline content of ethylene—propylene copolymers as a function of monomer sequence length distribution in the copolymer chains. The model is based on the Goldfinger‐Kane mathematical relationship for sequence length distributions derived from the conventional copolymer equation. Use of the general Flory theory for depression of the crystalline melting point by copolymerization provides independent evidence in substantiation of the model.
Irradiation of polyethylene oxide and polypropylene
Authors: Salovey R. , Dammont F. R. 
Published: April 2003

AbstractThe solubility behavior of electron‐irradiated (in vacuo) polyethylene oxide indicates a ratio of main‐chain scission density to the density of crosslinked units of 0.6, independent of molecular weight. This value, derived from measurements at high doses, correlates well with the observed increase in intrinsic viscosity and invariance of number‐average molecular weight at low irradiation doses. Analogous measurements on polypropylene indicate a linear dependence of S + S1/2 (where S is the sol fraction of the irradiated polymer) on the reciprocal irradiation dose. This treatment leads to a ratio of scission‐to‐crosslinking of 0.8. Increased scission in polypropylene as compared to polyethylene oxide is evidenced by a gradual decrease in the intrinsic viscosity as a function of dose. This decrease is not indicative of an initial irradiation degradation of the polymer, because the number‐average molecular weight is relatively unaffected by irradiation until quite close to the gel point. The intrinsic viscosity of the progressively crosslinked polymer is apparently depressed by branching. Direct comparison of the results on polypropylene with theory is uncertain because of a nonrandom initial molecular weight distribution. It is reemphasized that the intrinsic viscosity is not a simple indication of molecular weight changes in crosslinking polymers.
The role of metal chelates in polymerization initiation. I. Chromous chelates
Authors: Bond Joan , Hobson D. B. 
Published: April 2003

AbstractThe polyaminocarboxylic acids, ethylenediaminetetraacetic acid (EDTA), cyclohexanediaminetetraacetic acid (CDTA), and diethylenetriaminepentaacetic acid (DTPA) have been used to chelate the chromous and chromic ions when the system chromous ion—hydrogen peroxide is being used as an initiator for the emulsion polymerization of styrene. With CDTA and DTPA the zero‐order rates of polymerization increase continuously with increasing pH but with EDTA the zero‐order rate is constant over the range pH 5–7 and increases rapidly above pH 7. These results are to be anticipated from the variation of the redox potential of the chromous ion‐chromic ion‐chelating agent system with pH, since with CDTA and DTPA the redox potential decreases continuously with pH while with EDTA the redox potential varies only slightly over the range pH 5–7.