bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal analysis of polyurethane elastomers
Authors: Slade Philip E. , Jenkins Lloyd T. 
Published: June 2010

AbstractDifferential thermal analysis and thermogravimetric analysis were used to evaluate the thermal properties of several types of polyurethane elastomers. The composition of the polymers investigated was changed by varying the substrate, or soft segment, diisocyanate and extender. The data indicated that within the limits of the compositions under study, polyurethanes were thermally stable to their melting points, however, above the melt they were susceptible to oxidation unless stabilized by the addition of an antioxidant. On the differential thermograms the absence of a pronounced endothermic peak at the melting point, characteristic of non‐crystalline polymers, was observed. The decomposition of polymers made with 4,4′‐diphenylmethane diisocyanate (MDI) occurred above 400°C. and was at least a two‐step process, while the decomposition of polymers containing toluene diisocyanate (TDI) occurred below 400°C. and appeared to be a one‐step reaction.
A differential thermal analysis study of the effects of thermal history on polyethylene
Authors: Holden H. W. 
Published: June 2010

AbstractThe melting and crystallization behavior of polyethylene samples has been investigated by differential thermal analysis (DTA), with special emphasis on the effects of thermal conditioning on the crystalline state of the sample. Techniques are outlined for impressing a wide variety of thermal histories on the sample in the DTA cell. In particular, the use of an annealing procedure is shown to provide a significant evaluation of the extrapolated value of the equilibrium melting temperature, combined with a rapidity not possible by the dilatometric method. Theoretical implications of the various procedures and results are briefly discussed. Critical examination of the fine structure observed in the melting thermograms leads to the conclusion that under certain conditions crystallites originating from both heterogeneous and homogeneous nucleation can be detected. The temperature rise associated with very fast crystallization is considered to influence the subsequent melting temperature more significantly than the effects of re‐crystallization during the actual melting cycle. Some illustrations are given of the general usefulness of the conditioning procedures in clarifying phenomena observed with various samples.
Kalorimetrische Messungen von Wärmeeffekten bei Verstreckung
Authors: Müller F. H. , Weimann N. 
Published: June 2010

AbstractHeat effects and the work in stretching a polycarbonate are measured in a wide range of stretching rates and at two different temperatures. Conclusions are drawn on the enthalpy increase during the stretching process. Indirect conclusions on the entropy variation during stretching seem to be possible. The effect of temperature balance is confirmed and the strain relaxation of the stretched material seems also to be coupled with heat production.
Sedimentation velocity determinations of molecular weight distributions
Authors: Blair James E. 
Published: June 2010

AbstractIn the sedimentation velocity experiment, the ultracentrifuge fractionates the molecules according to molecular weight, along the radial axis in the rotating cell. The boundary gradient curve measured during the experiment can be transformed into an apparent distribution of sedimentation coefficients, which can twined to determine the true sediment at ion coefficient distribution by the introduction of a number of corrections. This true distribution can often be converted into the weight distribution of molecular weights. This paper discusses the current views of each of these corrections, which account for the effects of diffusion, hydrostatic pressure, concentration, and the time needed to attain operating speed. The sensitivity of the resultant molecular weight distribution to several parameters is indicated for a polystyrene sample.
Effect of component removal upon the porous structure of the cell wall of wood
Authors: Stone J. E. , Scallan A. M. 
Published: June 2010

AbstractIt has been shown by nitrogen adsorption that the removal of lignin and hemicellulose from the middle lamella and cell wall of spruce wood produces pores with a median size in the 20–40 A. range throughout the dissolution process. During both kraft and sulfite pulping, these pores have a total volume which from 90–100% yield equals, from 55–90% yield exceeds, and below 55% yield is less than, the volume of material removed from the wall. The results therefore indicate a swelling of the wall at intermediate yields followed by a contraction below the initial dimensions towards the end of pulping. In accordance with a previously postulated theory of cell‐wall structure based on a multilamellur model, the pores produced by the dissolution of wood components are the slit‐like spaces between adjacent lamellae. Specific surface measurements show that, on this model, the cell wall of water‐swollen wood consists of about 5 lamellae, which subdivide into a total of about 350 lamellae each 35 A. thick at the point of maximum swelling (65–70% yield). Thereafter, towards lower yields, the lamellae start to reaggregate. This technique applied to groundwood pulp shows that the process of splitting the wall into layers may be accomplished to some extent by purely mechanical action.
A new technique for observing light‐scattering patterns from polymer films
Authors: Moore Robert S. , Gieniewski Chester 
Published: June 2010

AbstractA now, extremely Simple, technique for visually observing light scattering from polymer films is presented. The technique employs a polychromatic divergent light source, in some cases with no polarizers, as the entire apparatus. It is shown that patterns characteristic of scattering from the spherulites and the rings, including multi‐ple‐Order scattering from the latter, can be observed by this method. Applications to monitoring of spherulite size during polymer processing are briefly discussed. It is shown that by simple collimation the method can be extended to photographic recording of scattering patterns and that after determination of the effective wavelength of the source the patterns can be quantitatively analyzed. It is demonstrated that wide angle scattering patterns comparable to those obtained with a laser can be obtained in comparatively short exposure times.
Approximate theory for diffuse first‐order phase transitions
Authors: Tobolsky A. V. , Canter N. H. 
Published: June 2010

AbstractThe phenomenon of diffuse phase transitions occurs widely in simple inorganic and organic systems, such as the solid‐solid transitions in ammonium chloride and in methane. It is known that in a finite temperature interval centered around the transition temperature, both the low temperature phase A and the high temperature phase B coexist. The most renowned manifestations of this phenomenon are the unusual specific heat curve (the lambda point anomaly); the appearance of x‐ray lines of two distinct phases, A and B, in the temperature interval of transition; and a gradual rather than a discontinuous change of volume in the transition interval. A statistical thermodynamic model of the Ising type was developed which describes all of these seemingly diverse phenomena in a unified and quantitative manner. The central feature of the theory is that it postulates the existence of a geometrically simple boundary phase which coexists with phase A and phase B. The theory introduces only a simple constant to describe a diversity of experimental results, the constant being the free energy of formation of the boundary phase, denoted as ΔGk. The theory was applied to the diffuse phase transitions in such solids as (NH4)2SiF6, Ag2H3IO6, KH2AsO4, KH2PO4, NH4Cl, and CH4, as well as to the diffuse melting of polymers, such as polyethylene, and to the helix‐coil transition in polypeptides and in polynucleotides. By use of a single constant, ΔGk, for each substance a very good fit of the experimental heat capacities versus temperature is generated for (NH4)2SiF6, Ag2H3IO6, KH2PO4, KH2Aso4, NH4Cl, and CH4. For diffuse solid‐solid transitions, the width of the x‐ray lines in the coexistence regions was predicted‐ Since such experimental data are not yet available, this prediction is offered as a very severe experimental test of the theory. In this paper we present very simple approximate equations of the Gaussian form which represent an excellent fit to the exact theory and to experiment.
A complex plane analysis of α‐dispersions in some polymer systems
Authors: Havriliak S. , Negami S. 
Published: June 2010

AbstractThe α‐dispersion in many polymer systems is the process to be associated with the glass transition temperature where many physical properties undergo drastic changes. We have measured and analyzed the complex dielectric behavior of the α‐dispersions for five polymers [i.e., polycarbonate and polyisophthalate esters of bisphenol A, isotactic poly‐(methyl methacrylate), poly(methyl acrylate), and a copolymer of phenyl methacrylate and acrylonitrile] and have found that the usual methods of analysis cannot be used to represent the data. However, it is possible to represent the relaxation process as the sum of two dispersions but there is no evidence to support this contention. An empirical expression is proposed to represent the data. This expression which takes the form of

appears to be a general representation for the three known dispersions, i.e., Debye, circular arc, and skewed semicircle. The complex dielectric constants calculated with the aid of this expression and the parameters for each polymer system which was determined graphically were found to be in excellent agreement with the experimental complex dielectric constants. This method of representation was extended to sixteen α‐dispersions reported in the literature always with excellent results.
Multiple transitions in polycarbonate
Authors: Matsuoka S. , Ishida Y. 
Published: June 2010

AbstractTwo kinds of dielectric absorptions due to motion of carbonate groups in polycarbonate were observed. In the primary transition region near 150°C, the shape of e′ versus log frequency curve is little affected by a temperature change, while it becomes more widely spread when the polymer is partially crystallized. In contrast, in the secondary transition region near −120°C., the shape of e′ versus log frequency curve is greatly affected by a temperature change, but it is not sensitive to the crystallinity. By using a conclusion drawn from a separate study that an increase in width of the loss curve is a manifestation of segments that are constrained, it is suggested here that the secondary transition involves local motions which persist in a highly restricted framework of glassy polymer chains and that such restriction becomes more pronounced at lower temperatures. Results from the PVT and x‐ray studies are consistent with the above concept, i.e., glassy polymers in general contain enough space so that limited local motions arc allowed that give rise to the low temperature transition.
The high temperature (T > Tg) amorphous transition in atactic polystyrene
Authors: Boyer Raymond F. 
Published: June 2010

AbstractWe first summarize available experimental evidence indicating the existence of a second‐order transition or relaxation region in atactic polystyrene at 60 to 100°C. above Tg. It increases from 137°C. at a molecular weight of 3000 to 192°C. at a molecular weight of 392,000. It appears in such diverse measurements as thermal expansion, heat capacity, x‐ray studies, deformation‐temperature plots, dynamic mechanical loss, stress relaxation, melt viscosity, and DTA. It may not appear if the test method is a very slow one, presumably because it merges with Tg. We ascribe this phenomenon to an ability of the entire polymer chain to act as a unit because of the available free volume and enhanced chain mobility at elevated temperatures. This is consistent with the fact that this transition shows up in melt viscosity studies and is completely suppressed by crosslinking. Since this represents a change from one liquid state to another, we designate this transition as Tl,l.
Nuclear magnetic resonance study of molecular motions in some crystalline polymers
Authors: Iwayanagi Shigeo , Sakurai Ikuko 
Published: June 2010

AbstractNuclear magnetic resonance linewidth studies are made concerning the molecular motions in crystalline polymers moh as polyethylene, polytetrafluoroethylene, and trans‐1,4‐polybutadiene. (1) The γ (local mode) relaxation of polyethylene is studied based on the temperature variation of mobile fraction. The range of the β (primary) dispersion of linear polyethylene is shown to spread far wider than that of branched polyethylene, whereas its lower limit (Tg−) is the same for the two. (2) Concerning polytetrafluoroethylene, a third NMR component is found in addition to narrow and broad‐line components, and the third phase of molecular aggregation is assumed to be intermediate between the amorphous and crystalline phases. The notion of the intermediate phase (an array of rodlike molecules) is instrumental in clarifying the complicated viscoelastie behavior by admitting two glass transitions in the polymer. (3) At the solid‐phase transition of trans‐1,4‐polybutadiene, a huge‐scale motional narrowing of the NMR absorption line takes place, indicating the onset of rodlike rotation of the molecules belonging to the crystalline phase. Above the phase transition temperature, the polymer crystal is “plastic”.
Rheo‐optical studies of the deformation of crystalline polymers
Authors: Stein R. S. 
Published: June 2010

AbstractThe deformation of a polycrystalline polymer must be examined in terms of the changes in morphology, texture, crystalline structure, and chain conformation. The understanding of the dynamic mechanical properties requires the specification of the rates of these changes. Optical techniques may be employed for this purpose. Dynamic x‐ray and dynamic infrared dichroism diffraction serve to define the rate of crystal orientation. Dynamic light scattering characterizes changes in the crystalline superstructure while dynamic birefringence characterizes the total orientation of crystalline and amorphous regions. A direct measure of amorphous orientation rate may be attempted by introducing a dye or chromophoric group into the amorphous regions and measuring its dynamic dichroism. In general, each of these dynamic observables may be resolved into a real and imaginary part (in and out‐of‐phase with strain). The results of measurements of these along with dynamic modulus measurements are discussed in an effort to present a consistent molecular and structural interpretation of mechanical behavior.
Effects of molecular weight and concentration on flow properties of concentrated polymer solutions
Authors: Onogi Shigeharu , Kimura Shigezo , Kato Takashi , Masuda Toshiro , Miyanaga Nobuyuki 
Published: June 2010

AbstractMolecular weight (M) and concentration (c) dependencies of the viscosity were measured over wide ranges of M and c for concentrated solutions of linear and branched Poly(vinyl acetate) (PVAc) as well as of polystyrene (PS) in good and poor solvents, and the effect of branching and solvent on the flow properties was studied. The log η versus log M and log η versus log c curves for a given system can be superposed by the shift along the abscissa, giving smooth master curves. From the shift factors the ratio of the two exponents α and β, which appears in the following viscosity equation, can be evaluated:

where η is the viscosity, p is the density of the solution, and K is a constant at constant temperature. The evaluated values of β/α for the several systems studied here ranged from 0.54 to 0.72. The log η versus log M curves cannot always be approximated by two straight lines, and therefore it was proposed to determine this critical molecular weight Mc an the lowest molecular weight above which the viscosity becomes proportional to M3.4 or M3.5. Then, the viscosity at Mc is constant independent of c, and the relation between Mc and c is given by (cp)Mβ/α = constant. The experimental values of β/α were compared with the theoretical values given by Bueche and Onogi et al.
Secondary (β) Relaxation Process of Alkaline Polycaprolactam Swollen by Low Molecular Weight Substances
Authors: Kolařík J. , Janáček J. 
Published: June 2010

AbstractBy using the method of free torsion vibrations, a detailed dependence was determined of the temperature position and the height of the secondary (β) loss maximum of alkali‐polymerized polycaprolactam upon the concentration of water in the range of 0 < PA < 1.3, where PA is the number of moles of water per mole of monomer units of the portions accessible to the sorption of water. The increase in the secondary loss maximum and the decrease in the height of the low‐temperature loss maximum due to the effect of water in the concentration range 0 < PA < 0.5 is interpreted as consequence of a transformation of the corresponding relaxation processes; subsequent increase in the water content then exhibits only little influence on the height of both the maxima. The β relaxation process is attributed to kinetic units containing amide groups which, owing to interaction with molecules of water, are more firmly bonded to neighboring molecules than the amide groups of a dry polymer. The secondary loss maximum arises also because of the effect of caprolactam monomer and of some low molecular weight amides, being markedly shifted to higher temperatures with the decreasing molecular weight of the amide.
A light‐scattering study of the molecular parameters of polycaprolactam
Authors: Tuzar Z. , Kratochvíl P. , Bohdanecký M. 
Published: June 2010

AbstractThis paper describes a study of dilute solutions of polycaprolactam in mixed solvents TFP‐H2O‐LiCl with the objective of finding the most convenient solvent for determining the molecular weight of polyamides by the light‐scattering method. Selective adsorption of both TFP and LiCl on the polyamide has been proved and quantitatively determined. The adsorption of TFP decreases the measured value of molecular weight, whereas that of LiCl increases it. A composition has been found (TFP‐10% H2O‐0.1M LiCl) in which the two effects exactly compensate. In this mixed solvent 24 fractions of hydrolytic and alkaline polycaprolactams were measured in a range Mw = 9 × 1033 to 3.5 × 105. The same solvent and m‐cresol have also been selected for measuring the intrinsic viscosities and determining the constants of the Mark‐Houwink equation.
Specific polymerization of vinylpyridinium salts. Polymerization on macromolecular “matrices”
Authors: Kabanov V. A. , Aliev K. V. , Kargina O. V. , Patrikeeva T. I. , Kargin V. A. 
Published: June 2010

Abstract4‐Vinylpyridinium salts could be spontaneously polymerized in organic and water media by unusual ionic mechanism. The growing active species were characterized with high chemical specificity. The growing chain end being intramolecular ionic pair (zwitterion) was able to add only the molecules of monomeric vinylpyridinium salt and does not react with other vinyl monomers, including vinylpyridine. The reaction described was used for polymerization of 4‐vinylpyridine on macromolecules of polystyrene sulfonic acid in water and in organic solvent. The chains of strong polyacid were operating as activating “matrices,” which adsorbed, neutralized, and polymerized strictly stoichiometric amount of monomer molecules. The morphology of polymerization products was studied with electron microscopy.
Cyclo‐ and cyclized diene polymers. VIII. Cyclization of polybutadienes and ir spectra of cyclized polybutadiene
Authors: Kössler I. , Vodehnal J. , Štolka M. , Kálal J. , Hartlová E. 
Published: June 2010

AbstractCyclization of cis‐1, 4 and trans‐1, 4‐polybutadiene as of poly (2,3‐dimethyl butadiene‐1,3) was carried out with H2S4 as the cyclization agent. The decrease of the original unsaturation as well as of total unsaturation were measured with IR spectroscopy and the iodine monochloride method, respectively. The kinetics of cyclization were measured and evaluated with an analog computer. Both methods indicate the length of cyclic segments as 25–45 cycles. In the case of poly(2,3‐dimethyl butadiene‐1,3) only monocycles are formed. Some indications of secondary reactions, including isomerization, accompanying the eyclization were given by analyses of IR spectra and chemical analysis.
Growth reaction in the radical polymerization of chloroprene
Authors: Hrabàk F. , Bezděk M. , Hynkovà V. , Pelzbauer Z. 
Published: June 2010

AbstractThe effects of solvent, molecular weight regulator, and concentration of initiator and emulsifier on the polymerization rate of chloroprene in the latex particle was studied. By a modification in the method for the determination of the latex particle size by means of soap sorption, errors of conductometric titration due to the liberation of hydrochloric acid and dilution of latex were reduced. The found data were used to calculate the velocity constant of the growth reaction of chloroprene and its temperature dependence in the range of 10–35°C.
Study of the solution properties of linear and grafted polyurethanes
Authors: Beachell H. C. , Blumstein Rita 
Published: June 2010

AbstractA high molecular weight linear polyurethane was prepared by condensation of tolylene‐2,4‐diisocyanate with ethylene glycol. Variable amounts of reactive side‐groups, such as the acrylyl and the ethylacrylate groups were introduced and the partially substituted N‐acrylyl and N‐ethyl acrylate polyurethanes were copolymerized in solution with methyl methacrylate, methyl acrylate, and styrene, using benzoyl peroxide as free‐radical initiator. The copolymers obtained had variable amounts of branches grafted onto the linear polyurethane backbone chain. These were isolated from the copolymer‐homopolymer mixtures by fractional precipitation. After fractionation the initial polyurethane was characterized by viscosity and light scattering. The configuration of the copolymers poly(urethane‐g‐methyl methacrylate) was found to depend on the number and molecular weight of the branches, the influence of the latter being particularly striking.
Polymerization of α‐methacrolein and the structure of the polymers
Authors: Andreeva I. V. , Koton M. M. , Getmanchuk Yu. P. , Madorsikaya L. Ya. , Pokrovskii E. I. , Koltsov A. I. 
Published: June 2010

AbstractA high molecular weight poly(α‐methylacrolein) was obtaiiied with a yield of about 100% in the presence of a redox system and its strncture was investigated. It was established that the intrinsic viscosity of the polymers increases during the polymerization. It was shown that high molecular weight. poly(α‐methylacrolein) obtained with K2S2‐O2/AgNO3 contains not only free aldehyde groups but also the seniiacetal‐ether ones. The polymerization of α‐methyl‐ and α‐ethylacrolein was conducted with sodium naphthalene and trityl sodium. The structure of the polymers obtained was investigated by the following methods: oxinlation, ozonization, hydrogenation, oxidation with perbenzoic acid, and by PAIR and infrared spectroscopy. The dependence of the resulting structure on the temperature of the polymerization was established. It was shown that when the polymerization was conducted below 0°C. the polymers contained mainly coildensed tetrahydropyran cycles. At 0°C. and above the polymerization rate is changed, and the structure of the polymers is changed according to the data of chemical analysis, the formation of lactone structure being observed. Some considerations on the mechanism of the polymerization are given.