bluuebunny/crossref_metadata_2025_split huggingface dataset:
Acetylation of cellulose I and II studied by limiting viscosity and X‐ray diffraction
Authors: Glegg R. E. , Ingerick D. , Parmerter R. R. , Salzer J. S. T. , Warburton R. S. 
Published: April 2003

AbstractWhen cellulose triacetates and some hydrolyzed acetates are boiled in 2.5Nhydrochloric acid there is no residue. Under the same conditions cellulose is hydrolyzed, and a residue is obtained with a limiting viscosity that is related to the average length of the cellulose crystallites. These findings are combined to develop a method for studying the progress of acetylation through the amorphous portion of cellulose and into the crystallites, and to investigate the relative reactivities of cellulose I and cellulose II. Acetates were made from cotton and wood cellulose by a “fibrous” (heterogeneous) esterification involving sulfoacetic acid or perchloric acid catalyst in acetic acid‐acetic anhydride; the final acetyl contents (10–41%) were attained by stopping the reaction at various points short of the triester (rather than by hydrolyzing a triester). When these acetates were boiled in 2.5NHCI they did not disappear completely, and the residues were cellulose I, indicating that cellulose acetate had been removed. With increasing acetyl the yield of residue decreased, and beyond about 33% acetyl the viscosity and x‐ray measurements showed that the length and width of the crystallites decreased. However, when a nonsolvent such as toluene was added to the acetylation medium, the limiting viscosity did not change over the same acetyl range (up to 40%). Samples of varying acetyl values were taken during a regular acetylation of cotton linters in a mixer with sulfuric acid catalyst. X‐ray studies of the residues obtained by boiling the acetates in 2.5NHCI revealed the presence of unreacted cellulose I even after 40% acetyl had been reached. This explains why the manufacture of cellulose esters from cellulose I requires complete esterification before they are hydrolyzed to the desired acetyl level. It was shown that there is a distinct difference between the acetylation reactivity of cellulose I and cellulose II. This indicates the importance of avoiding cellulose II formation during the refinement of cellulose for the manufacture of cellulose acetate in a process involving activation with acetic acid.
Infrared spectrum of poly(vinylidene fluoride)
Authors: Enomoto S. , Kawai Y. , Sugita M. 
Published: April 2003

AbstractTwo crystalline forms (α and β) of poly(vinylidene fluoride) were studied by infrared spectroscopy. The spectral differences permitted the study of the transformation and the ratio of the two forms. The ordinary \documentclass{article}\pagestyle{empty}\begin{document}$ \vec G,\vec F $\end{document} matrix method was used to calculate the fundamental mode with a Urey‐Bradley type potential field, and a preferred set of the force constants was obtained.
Hydrogen bonding in butadiene copolymers. I. Network formation
Authors: Otocka E. P. , Eirich F. R. 
Published: April 2003

AbstractThe incorporation of comonomers bearing functional groups yields butadiene copolymers capable of hydrogen bonding. Three such butadiene‐based materials were studied: methacrylic acid copolymers, 2‐methyl‐5‐vinylpyridine copolymers, and stoichiometric mixtures of the acidic and basic copolymers. The elastic effects of intermolecular hydrogen bonding were determined by comparing the simple weighted average of the moduli of the parent copolymers with the observed modulus of their stoichiometric mixture. The results show that measurable increases in the moduli of the mixtures persist even above the glass temperature Tg, which is itself elevated in the mixtures. These increases may be treated as temperature‐dependent temporary crosslinks.
Ionic bonding in butadiene copolymers. I. Network formation
Authors: Otocka E. P. , Eirich F. R. 
Published: April 2003

AbstractThe mechanical effects of association between pendant ionic groups are investigated in series of butadiene–lithium methacrylate copolymers, butadiene–methyl (2‐methyl‐5‐vinyl)‐pyridinium iodide copolymers, and mixtures of these polyelectrolytes. Thermal and mechanical tests reveal a new transition above Tg in the pyridinium copolymers, designated Tt*. Below this temperature the materials behave like covalently crosslinked elastomers. The complex between the metal carboxylates appears thermally dissociable at all temperatures. The mixing of the oppositely charged polyelectrolytes leads to the formation of more stable intermolecular pyridinium carboxylate links.
Nuclear magnetic resonance study of low molecular weight polychlorotrifluoroethylene
Authors: Hara T. , Okamoto A. , Hama Y. , Okamoto S. 
Published: April 2003

AbstractThe molecular motion of low molecular weight polychlorotrifluroethylene of different molecular weights between 500 and 1300 was investigated by means of broad‐line nuclear magnetic resonance measurements. The line width and second moment of the resonant absorption lines were obtained at temperatures from 77 to 300°K. The line narrowing for low molecular weight samples takes place in one step. In samples higher than 900 in molecular weight, however, there appears to be a glass transition process, and the line narrowing tends to occur in three steps. The line narrowing due to local molecular motion becomes observable with increasing molecular weight.
Thermoelasticity of networks in swelling equilibrium
Authors: Bashaw J. , Smith K. J. 
Published: April 2003

AbstractA theoretical analysis of the thermoelastic behavior of polymeric networks in swelling equilibrium with excess diluent, using both the kinetic theory of elasticity and the Flory‐Huggins theory of mixing, is presented. Our calculations are restricted to the special case of diluents composed of a single constituent. The results are used to obtain the ratio of the energy component of the force fe to the total force f of rubber networks swollen in excess n‐decane, and we find fe/f to be 0.17, which compares favorably with the value 0.18 reported for the unswollen network. Furthermore, fe/f is independent of elongation, in accordance with theory. The kinetic theory of elasticity is reasonably well obeyed in this highly swollen system although there remains a small contribution to the force from the C2 term of the Mooney‐Rivlin phenomenological elasticity equation. It is not believed that this has an appreciable effect on fe/f.
Thermoelastic properties of networks in swelling equilibrium: Poly(vinyl alcohol)
Authors: Bashaw J. , Smith K. J. 
Published: April 2003

AbstractThe energy component of the stress has been determined for poly(vinyl alcohol) networks in swelling equilibrium with a series of water–ethylene glycol compositions. The data are analyzed by using the equations describing the thermoelasticity of networks in swelling equilibrium. The ratio fe/f of the energy component to the total force, as calculated from these equations, varies systematically with diluent composition but is independent of elongation in a given diluent. For a network crosslinked by terephthalaldehyde, fe/f varied from −0.33 to −0.42 as the diluent composition was changed from pure water to 20% ethylene glycol. Similar effects were found in a network crosslinked by formaldehyde. It is not yet certain whether this effect represents a real solvent dependence of fe/f or a failure of the equation of state to account for the effect of composition changes on the force.
Poly(γ‐alkyl L‐glutamates). II. Optical rotatory dispersion studies in organic solvents
Authors: Sugai S. , Kamashima K. , Nitta K. 
Published: April 2003

AbstractConformations of a series of poly(γ‐alkyl L‐glutamates) (ethyl, n‐propyl, n‐butyl, isobutyl, and isoamyl) were studied by ORD and infrared absorption methods. All except the n‐propyl ester were found to be in helical form in nonpolar non‐aromatic solvents such as ethyl acetate, chloroform, ethylene dichloride, methylene chloride, carbon tetrachloride, 2‐chloroethanol, dimethylformamide, and dioxane. In such cases, the Cotton effects due to the n–π* transition of peptide bonds occurred near 234 mμ and were of a magnitude similar to those found for poly(γ‐benzyl L‐glutamate) and poly‐L‐methionine in nonpolar non‐aromatic organic solvents. These four polypeptides in aromatic nonpolar solvents, such as benzene, benzyl alcohol, pyridine, and m‐cresol, were also found to be in helical form, although the ORD parameters differed considerably from the values in non‐aromatic solvents. An essential cause seems to be the interaction of π electrons on peptide bonds with π electrons in the solvents. Helix‐coil transitions of these esters in chloroform‐dichloroacetic acid mixtures (dichloroacetic acid seems to be a random coil‐forming solvent) were expressed by the Shechter‐Blout formulation. This was not true, however, for helix–coil transitions in benzyl alcohol–dichloroacetic acid mixtures. The dependence of the helical stability of these polypeptides in chloroform solution upon the side‐chain length and upon temperature is discussed.
Thermodynamic properties of poly(2,6‐dimethyl‐1,4‐phenylene ether)
Authors: Karasz F. E. , Bair H. E. , O'Reilly J. M. 
Published: April 2003

AbstractThe thermodynamic properties of crystalline and amorphous poly(2,6‐dimethyl‐1,4‐phenylene ether) (PPORegistered trademark of General Electric Company.
polymer, General Electric Co.) have been studied calorimetrically between 80 and 570°K. The calculated configurational entropy of this polymer, of similar magnitude to other glass‐forming liquids, is consistent with the combination of an unusually high ratio of Tg/Tm, and a low melting entropy.
Dynamic analysis of branching in radical polymerization
Authors: Saidel Gerald M. , Katz Stanley 
Published: April 2003

AbstractA method for the theoretical analysis of branching in radical polymerization is presented which includes the dynamics of the process. In particular, the method is applied to a polymerization that occurs by decomposition of initiator, propagation, termination by radical combination, and chain transfer with polymer. By a numerical solution of the kinetic equations (suitably transformed), the time dependence of the number‐average degree of polymerization (DP), the weight‐average DP, the mean number of branches, and the monomer conversion are obtained. The parameters of the process, that is the rate coefficients and initial concentrations, have the following effects: (1) An increase in the chain transfer coefficient increases the ratio of weight‐average to number‐average Xw/Xn and the mean number of branches Xb, but does not change the number‐average Xn. (2) For a given value of the chain transfer coefficient, a change in the parameters of the process such that Xn increases, causes Xw/Xn and Xb to increase also. (3) Chain transfer with polymer seems to produce relatively few polymer molecules having many branches and a large number of smaller polymer molecules having no branches; consequently, the polymer size (or molecular weight) distribution broadens.
Analysis of the melt viscosity and glass transition of polystyrene
Authors: Miller A. A. 
Published: April 2003

AbstractThe melt viscosity, the glass transition, and the effect of pressure on these are analyzed for polystyrene on the basis of the Tammann‐Hesse viscosity equation: log η = log A + B/(T − T0). Evidence that the glass transition is an isoviscosity state (log ηg ≃ 13) for lower molecular weight fractions (M < Mc) is reviewed. For a polystyrene fraction of intermediate molecular weight (M ≃ 19,000; tg = 89°C.), it is shown that B is independent of the p–v–T state of the polymer liquid and that dT0/dP = dTg/dP. This is consistent with the postulate that B is determined by the internal barriers to rotation in the isolated polymer chain. Relationships are derived for flow “activation energies” at constant pressure and at constant volume, and for the “activation volume.” Values for polystyrene along the zero‐pressure isobar and along the constant viscosity, glasstransition line are reported. For the latter, ΔVg* is constant and corresponds to about 10 styrene units. The “free volume” viscosity equation: log η = log A + b/2.3ϕ, is reexamined. For polystyrene and polyisobutylene, ϕg/b = 0.03, but ϕg and b themselves differ appreciably in these polymers. The parameter b is the product of an equilibrium term Δα and the kinetic term B, and none of these is a “universal” constant for different polymers. The physical significance of the free volume parameter ϕ, particularly with regard to the “excess” liquid volume, remains undefined. Two new relationships for dTg/dP, one an exact derivation and the other an empirical correlation, are presented.
Damped torsional oscillator model for polymer molecules
Authors: Tobolsky Arthur V. , Dupré Donald B. 
Published: April 2003

AbstractAt present the widely used model for explaining viscoelastic and dielectric properties of polymer solutions is that of Rouse and Bueche. Here the polymer molecule is considered as an array of Gaussian subunits, each of which acts as an entropy spring. The motion of these segments is damped by the viscous drag of the surrounding solvent (RB model). An alternative model is presented, in which the segments are torsional oscillators consisting of two or three backbone links, and the damping is due to hindered internal rotation (DTO model). The mathematical treatment of these two models is essentially identical, but the physical interpretation of the constants used is very different. The DTO model has previously been applied by one of us to the interpretation of viscoelastic data. It is here applied to the interpretation of dielectric loss data. It is shown that dielectric measurements in dilute solution should very readily discriminate between the two approaches. Finally it is shown that the relaxation time computed from the DTO model is in closer agreement with published NMR data on poly(propylene oxide) 2025, than is the RB relaxation time. The postulates of the DTO model appear to be confirmed for this low molecular weight polymer. An even more sensitive distinction should be available by studies of the relaxation time as a function of polymer concentration.
Skeletal deformation vibrations and rotational isomerism of methylbutenes and methylpentenes as model compounds of 1,4‐polyisoprene
Authors: Shimanouchi T. , Abe Y. 
Published: April 2003

AbstractInfrared spectra of methylbutenes and methylpentenes in the skeletal deformation region have been measured. The force constants for the skeletal deformation vibrations are determined from the frequencies of isobutylene, isobutylene‐d6, and methylbutenes. The frequencies of methylpentenes are calculated for the various conformations, and the stable rotational isomers determined. The energy differences between the isomers are determined from the temperature dependence of the spectra. These results are correlated with the conformations of cis‐and trans‐1,4‐polyisoprene chains, and possible conformations are suggested.
Solvent‐induced crack growth in rubbery block polymers
Authors: Gent A. N. , Hirakawa H. 
Published: April 2003

AbstractThe rapid cracking of lightly stressed rubbery block polymers of styrene and isoprene in certain liquids and vapors has been examined experimentally, by using model test pieces containing a single crack. Solvents which preferentially dissolve the rigid molecular end blocks rather than the rubbery center blocks are efficient cracking agents. The stress required for crack growth to occur is shown to be in accord with a simple energy criterion: the stored elastic energy must be sufficient to provide a characteristic energy for the newly formed surface. This characteristic energy ranges from values close to the surface energy of simple liquids up to about 100 times this value for thicker test pieces or slowly diffusing vapors, when some tearing of an incompletely swollen core is inferred. “Induction times,” before the initial crack starts to grow, are shown to be due to a progressive increase in stored energy under a constant stress as the material absorbs solvent and softens until the critical energy criterion is met. Thus, a timedependent fracture process is shown to be in accord with a constant energy criterion. Above the critical condition the rate of crack growth depends strongly upon stress, like tearing of amorphous elastomers, and the crack then accelerates rapidly.
Structure of poly(ethylene oxide) complexes. II. Poly(ethylene oxide)–mercuric chloride complex
Authors: Iwamoto Reikichi , Saito Yasushi , Ishihara Hideaki , Tadokoro Hiroyuki 
Published: April 2003

AbstractThe structure of the crystalline complex of poly(ethylene oxide) with mercuric chloride, whose composition is (CH2CH2O)4 · HgCl2, has been determined by x‐ray diffraction. The unit cell is orthorhombic with the dimensions of a = 13.55 Å, b = 8.58 Å, and c (fiber axis) = 11.75 Å, and the unit cell contains 4 HgCl2 molecules and 16 CH2CH2O units. Four chains pass through the lattice and four monomeric units are contained in the fiber identity period. The space group is Ccmm–D2h17, Ccm21–C2v12, Cc2m–C2v16 or C2221–D25. The positions of Hg and Cl atoms have been determined by the Patterson function synthesized by the use of intensity data of the fiber sample, and the molecular conformation of poly(ethylene oxide) has been determined by examining the space not occupied by mercuric chloride molecules in the crystal lattice. The conformation of polyethylene oxide in the complex has been found to be the form of T5GT5G; that is, magnified image where G and G mean the right‐ and left‐handed gauche forms, respectively. This molecular structure has been confirmed further by the results of the Fourier syntheses by using the more accurate data refined by the intensity measurements with a diffractometer on the powder sample. The bond length between Hg and Cl in the complex (2.30 Å) is a little longer than that of HgCl2 in the crystal (2.25 Å). This is consistent with the fact that the infrared absorption band associated with the antisymmetric stretching vibration of HgCl2 shifts to 353 cm−1 in the complex from 367 cm−1 in the crystal. It was also found that another type of complex, giving a different infrared spectrum and x‐ray diffraction pattern, was obtained when the original complex was soaked much longer in a saturated ether solution of HgCl2.
Development of gel permeation chromatography for polymer characterization. II. Universal calibration
Authors: Boni K. A. , Sliemers F. A. , Stickney P. B. 
Published: April 2003

AbstractGPC appearance volumes have been determined for a series of linear polyethylene, polystyrene, and polybutadiene fractions (Mw/Mn < 1.1) in trichlorobenzene at 130°C. and for the latter two series in tetrahydrofuran at 23°C. A polymer‐type independent relationship between appearance volumes and the equivalent hydrodynamic radii of the polymer molecules has been demonstrated. The equivalent hydrodynamic radius is calculated from intrinsic viscosity data. It is proposed that this relationship can be used to construct a universal GPC calibration curve for polymers that assume a spherical conformation in solution. Methods for applying the universal curve to the determination of molecular weight averages and molecular weight distribution are described. In addition, a method is outlined by which the universal calibration curve can be empolyed for determining number‐average Mark‐Houwink constants from polydisperse samples.
Excluded volume effect of linear polymer molecules
Authors: Kurata Michio 
Published: April 2003

AbstractAn approximate closed expression for the excluded volume effect of linear polymer molecules is developed with the aid of a uniform expansion model of perturbed chains. The linear expansion factor α for the end‐to‐end distance is given by (α3 − 1) + (3/8) (α5 − α3) = (5/2)z where z is the excluded volume parameter. This equation is numerically close to the Ptitsyn equation in the ordinary range of α; i.e., for 1 ≤ α ≤ 2.
Gel permeation chromatographic studies of the degradation of polyethylene with fuming nitric acid. III. Fibrous stirring‐induced crystals
Authors: Willmouth F. M. , Keller A. , Ward I. M. , Williams T. 
Published: April 2003

AbstractFibrous crystals of polyethylene are produced by crystallization from agitated solutions in xylene. If crystallization temperature is maintained between 97°C and 108°C these fibers are free from overgrowth effects and are seen to consist of flat, striated ribbons. This material was treated with fuming nitric acid, and the molecular weight distribution of the degradation product was analyzed by gel permeation chromatography. This distribution was found to consist of a low molecular weight peak and an exceptionally resistant high molecular weight tail over a wide range of degradation times in quantitative agreement with the serrations developed during the nitric acid attack. This is consistent with the fibers possessing a composite folded and extended chain structure. The lateral pulling out of smooth fibrils from the original fibers in the course of certain electron microscope sample preparation methods is consistent with the presence of chain‐folded material and might account for the structureless fibrils reported in the literature. Partially successful attempts to obtain the extended chain portion in pure form by selective dissolution are mentioned together with some low‐angle x‐ray results.
Electrical transport through polystyrene films
Authors: Burmester A. F. , Caldecourt V. J. 
Published: April 2003

AbstractThe steady‐state current density versus applied electric field characteristics have been measured for two types of polystyrene films. Measurements were made on 1‐mil biaxially oriented film and on films produced by casting from solution. The cast films ranged from 5 to 0.5 μ in thickness. The measurements of the steady‐state current flowing through the films were done by two different methods. The first was the direct observation of current flowing in a circuit connected to the film which was under a potential stress. The second involved the observation of the decay of a static charge placed on the surface of a film. Both methods are handicapped by the fact that large transient currents flow for extended periods after any change is made in the experimental set up. The results indicate that at 25°C the current increases as the 3.5 power of the applied electric field when the field is greater than 8 × 104 V/cm. At fields less than 8 × 104 V/cm the current decreases more rapidly and tends to become zero.
Infrared study of substrate effects in the surface region of polyethylene
Authors: Luongo J. P. , Schonhorn H. 
Published: April 2003

AbstractThe surface of thin polyethylene films (ca. 1 mil) nucleated on high‐ and low‐energy surfaces was studied. It was found that the degree of crystallinity in the surface region, as determined by transmission and reflection infrared spectroscopy, was dependent on the nature of the substrate. Relatively small and randomly oriented spherulites were observed in the surface region of thin polyethylene films nucleated on gold, a high‐energy surface. The surface region of a thin polythylene film nucleated on polytetrafluoroethylene, a low‐energy substrate, was observed to have considerably fewer spherulites, but much larger in size, with orientation restricted, in general, to the plane of the film. The relative intensity of the 720 cm−1 to the 730 cm−1 band in the reflectance spectra (ATR) indicates that the surface region of a polyethylene film nucleated on a high surface energy substrate is more crystalline than the surface region of a film nucleated on a low surface energy substrate.