bluuebunny/crossref_metadata_2025 huggingface dataset:
Vinyl monomer polymerization mechanism in the presence of trialkylboranes
Authors: Grotewold J. , Lissi E. A. , Villa A. E.
Published: April 2003

The polymerization of methyl methacrylate in the presence and in the absence of triethylborane and different inhibitors was carried out. An ethyl radical displacement reaction between the inhibitor radical (produced through the reaction between a radical chain and the inhibitor) and the triethylborane is postulated. This new chain‐transfer reaction explains the large excess of inhibitor which must be added in the presence of triethylborane in order to suppress the production of high molecular weight polymer. The results are in agreement with a typical free‐radical mechanism.
Thermogravimetric analysis of cellulose
Authors: Chatterjee Pronoy K. , Conrad Carl M.
Published: April 2003

An application of TGA technique to elucidate the chain reaction mechanism of cellulose pyrolysis is discussed. The mathematical expressions for isothermal kinetics are modified for use with temperature‐programmed kinetics. It is shown that in temperature‐programmed kinetics, the initial reaction should theoretically be a pseudo zero‐order type, whereas the latter part should be a pseudo first‐order type. Experimental data from the present study and from the literature are in good agreement with the theory. Energies of activation for the initiation and the propagation steps of cellulose pyrolytic reactions are analyzed from TG data. Various cellulose samples, such as adsorbent cotton, vibratory ball‐milled absorbent cotton, mercerized commercial yarn, mercerized and treated commercial yarn, dewaxed‐kiered cotton, and microcrystalline cellulose are included in this study. A basic problem which is associated with all thermogravimetric kinetic expressions is also discussed.
Polyhydrazides. II. N‐methylated polyhydrazides by direct solution polycondensations of methylated hydrazines and dicarboxylic acid components
Authors: Iwakura Yoshio , Uno Keikichi , Hara Shigeyoshi , Kurosawa Shigeru
Published: April 2003

N‐Methylated polyhydrazides were prepared from methylated hydrazines and terephthalic acid or dimethyl terephthalate, and from terephthalic acid, hydrazine sulfate, and dimethyl sulfate by the solution polycondensation method in fuming sulfuric acid or polyphosphoric acid.
Some studies of the crystallization of polychlorotrifluoroethylene copolymer films
Authors: Adams G. C. , Stein R. S.
Published: April 2003

A fluorocarbon copolymer of chlorotrifluoroethylene (96%) and vinylidene fluoride has been isothermally crystallized and the quenched films analyzed by the light microscope, photographic light‐scattering, and density measurements. Above a supercooling of 79°C., homogeneous nucleation dominates, giving a morphology that appears to be that of a twisted ribbon. At supercoolings below 79°C., heterogeneous nucleation dominates and leads to spherulitic morphology. Sheaf or rodlike morphology occurs at very low supercoolings. Crystallization rates determined from density measurements at room temperature indicate maximum rate due to heterogeneous nucleation occurring at a supercooling greater than 79°C., but the temperature for maximum rate cannot be identified because of the transition to homogeneous nucleation which causes a discontinuity in the rate versus temperature curve. Superposability of crystallization isotherms constructed from density values are inconsistent with the large melting point lowering from that of polychlorotrifluoroethylene for this copolymer. However, this may be explained by the presence of a different crystal system for each monomer in the copolymer.
Molecular weights and molecular weight distribution of polymers by equilibrium ultracentrifugation. Part I. Average molecular weights
Authors: Scholte Th. G.
Published: April 2003

From the sedimentation‐diffusion equilibria of some polymer solutions the average molecular weights M̄n, M̄w, M̄z, and M̄z+1 have been determined in different ways. In particular, the applicability of Fujita's method, which utilizes concentration gradient values at the midpoint of the solution column at a number of rotor speeds, was examined. It appears that if the gradients at some other places in the column are also used, a smaller range of rotor speeds suffices. This method is generally applicable for determining the average molecular weights specified above.
Viscoelasticity of a butadiene–styrene block copolymer
Authors: Canter Nathan H.
Published: April 2003

A commercial elastomeric block copolymer of butadiene (B) with styrene (A) is studied. A single chain of the material has the formula A‐B‐A. Differential thermal analysis studies show the presence of two transitions. The lower transformation temperature corresponds to the Tg of the butadiene chain segments, and the upper transformation temperature corresponds to the Tg of the styrene chain segments. The upper transition of the material is also studied by following the variation of the torsional modulus with temperature. This transition is found to be quite unusual. Our experiments show that the upper transformation of unstressed block copolymer samples is broad. The transition sharpens for samples which, prior to the modulus–temperature experiments, are stress‐relaxed at high elongations. These observations (and those of the literature) suggest that the styrene and butadiene chain segments in the block copolymer aggregate in the solid state and give rise to two distinct transition phenomena. Our studies of the upper transformation suggest that stretching of the bulk material enhances the aggregation of the styrene chain segments. Pure polystyrene (A) blocks of the material are recovered by selective cleavage and fractionation experiments. The Tg of the pure polystyrene blocks is found to be similar to the value of the upper transition temperature of the copolymer. The ABA blocks copolymer is found also to undergo a stress‐softening phenomenon analogous to that of reinforced rubber.
Temperature dependence of the growth rate of spherulites
Authors: Mandelkern L. , Jain N. L. , Kim H.
Published: April 2003

The spherulitic growth data that exist in the literature for a wide diversity of polymers have been analyzed according to various possible nucleation mechanisms. It is demonstrated that, if allowed a reasonable choice for the equilibrium melting temperature, no unbiased selection of a unique nucleation process can be made. Moreover, a set of universal parameters exists for each of the allowable nucleation processes which enables the data to be represented by a single straight line which encompasses all the polymers. The only quantities specific to a given polymer are the equilibrium melting temperature and the activation energy for transport. The magnitude of the latter quantity is shown to be dependent on the glass temperature of the polymer.
NMR studies of chlorinated poly(vinyl chloride) and polybutadiene
Authors: Sobajima Shigenobu , Takagi Norio , Watase Hideo
Published: April 2003

Molecular structures of chlorinated poly(vinyl chloride) and polybutadiene have been studied by high resolution NMR. The spectra of the chlorinated polymers give broad signals. New peaks appear in the lower fields of the CH2 and CHCl groups with increasing chlorine content. The chlorination of poly(vinyl chloride) takes place predominantly on CH2 rather than on CHCl, e.g., a 70% chlorinated polymer has about 10 mole‐% of CCl2 groups. Polybutadiene reacts first with chlorine by addition to give a head‐to‐head poly(vinyl chloride), and then the substitution of the hydrogen atom takes place. Chlorinated polybutadiene with 70% Cl has about 18 mole‐% of CCl2. The multiplets characteristic of spin‐spin couplings in the spectrum of the original poly(vinyl chloride) are still observed in that of the highly chlorinated product. This fact shows that a considerable number of poly(vinyl chloride) sequences of certain lengths persist in the highly chlorinated polymer.
Kinetic interpretation of the glass transition: Glass temperatures of n‐alkane liquids and polyethylene
Authors: Miller A. A.
Published: April 2003

On the basis of an isoviscosity criterion for the glass transition (ηg ⋍ 1013 poise) in liquids of low molecular weight, theoretical Tg values were calculated for the n‐alkane series by the equation log η = log A + B/(T − T0), with the use of values reported by Lewis for the parameters. The Tg/T0 ratio reaches a limiting value of 1.25 and ϕg = (Tg − T0)/2.3B = 0.027, a constant. Extrapolation to (CH2)∞ gives Tg = 200°K., T0 = 160°K., and B = 640°K. This Tg is consistent with other estimates for poly‐ethylene, and T0 coincides with the temperature at which the “excess” liquid entropy for (CH2)∞ becomes zero from thermodynamic data. For polymer liquids it is proposed that E0 = 2.3RB is determined by the internal barriers to rotation for the “isolated” polymer chains. Thus, E0 = 2.9 kcal./mole for polyethylene, 3.0 kcal./mole for polystyrene, 5.7 kcal./mole for polyisobutylene, and 1.9 kcal./mole for polydimethylsiloxane.
Change with temperature of the ESR spectra of peroxy radicals trapped in irradiated polytetrafluoroethylene
Authors: Iwasaki Machio , Sakai Yoshiro
Published: April 2003

The ESR spectra of peroxy radicals in irradiated powders and oriented samples of polytetrafluoroethylene (PTEE) have been measured with a K‐band spectrometer, and the principal values and directions of the g tensor were determined both at room temperature and at 77°K. In contrast to the spectra of the usual peroxy radicals, those trapped in γ‐irradiated PTFE exhibited an ESR spectrum apparently having a larger principal value for g⊥ than for g∥ when measured at room temperature, although the normal principal values were observed at 77°K. As for the directions of the principal axes, g∥ was directed along the chain axis at room temperature and was perpendicular to the chain axis at 77°K. From the temperature change of the g tensor and the line shapes in the oriented samples, it is shown that the observed temperature change of the spectra is due to rapid rotation at room temperature around the chain axis rather than around the CO bond axis. Assuming this, the apparent principal values of the g tensor at room temperature were calculated from the g tensor obtained at 77°K. for the rigid state, and the results are in good agreement with observations at room temperature. A structure for the peroxy radicals is also proposed. In addition, the spectral line shape function for the uniaxially oriented samples has been derived.
Liquid–liquid phase separation in multicomponent polymer solutions. I. Statement of the problem and description of methods of calculation
Authors: Koningsveld R. , Staverman A. J.
Published: April 2003

Polymers are complex mixtures that may have widely different compositions even if they contain only components having the same chemical constitution. The effect of the chain length distribution on the phase behavior of polymer solutions in a single solvent is described qualitatively. To obtain a quantitative understanding of these phenomena a numerical calculation method is developed which is based on the Flory‐Huggins relation for the free energy of mixing. Some examples are presented, and the accuracy and the reliability of the results are discussed.
Liquid–liquid phase separation in multicomponent polymer solutions. II. The critical state
Authors: Koningsveld R. , Staverman A. J.
Published: April 2003

Theoretical and experimental evidence is put forward to prove that the determination of the phase‐volume ratio as a function of temperature and concentration is a sensitive and simple means of determining the liquid–liquid critical state. Knowledge of the critical conditions permits very accurate calculations of the interaction parameter g in the free‐energy function. In experiments with polystyrene–cyclohexane, g was found to depend on the concentration. The value of g and its concentration dependence agree very well with the results of osmotic measurements by Rehage and Palmen. In experiments with polyethylene–diphenyl ether, g proved to be independent of concentration in the range of measurement. The temperature function was found to be: g = −0.6086 + 482.2/T (at 137–148°C.). Gibbs' expressions for the critical conditions were worked out for a free‐energy relation in the form of an extended Flory‐Huggins function.
Electrical conduction in olefin oxide polymers
Authors: Binks A. E. , Sharples A.
Published: April 2003

The electrical conductivities in vacuo of poly(ethylene oxide) and two higher olefin oxide polymers have been found to be ∼9 orders higher than for other saturated organic polymers. The possibility of ionic transport resulting from the presence of impurities (including water) has been eliminated, and it is proposed that an inherent ionic process is operative, involving the generation of protons and then subsequent transport by a handing‐on process. The two general requirements are the presence of proton‐accepting atoms (in this case oxygen) in the polymer chains; and proximity to the melting point to ensure adequate chain‐mobility. These requirements are met by poly(ethylene oxide), poly(trimethylene oxide), and poly(tetramethylene oxide), which are all close to their melting points at room temperature. poly(methylene oxide), with a melting point of ∼180°C., on the other hand, has the low conductivity of a typical insulator.
Electric properties of macromolecules. XIII. Transient electric birefringence of sodium polyethylenesulfonate solutions
Authors: Yoshioka Koshiro , O'Konski Chester T.
Published: April 2003

The electric birefringence of sodium polyethylenesulfonate in water has been studied. For a low molecular weight fraction, the electric field dependence followed the Kerr law quite closely. For a higher molecular weight fraction, the specific Kerr constant was much larger, and pronounced saturation of the electric birefringence was observed in fields of 15 kv./cm. The specific Kerr constant increased with decreasing polyelectrolyte concentration in pure water. On the other hand, it decreased on isoionic dilution. The saturation effect was the more marked, the lower the polyelectrolyte concentration. The saturation behavior resembled that of permanent dipole orientation, but this mechanism was not supported by the build‐up of the birefringence. The magnitudes of specific Kerr constants of various types of macromolecules in solution are tabulated and discussed.
Nuclear magnetic resonance of poly‐β‐alanine
Authors: Tsutsumi Akihiro , Hikichi Kunio , Kaneko Motozo , Furuichi Jiro
Published: April 2003

Nuclear magnetic resonance of poly‐β‐alanine samples differing in solubility in water was studied over a wide temperature range as part of an investigation of their physical properties. Water‐soluble poly‐β‐alanine has more branches and a lower degree of crystallinity than water‐insoluble poly‐β‐alanine. NMR spectra of poly‐β‐alanine show one component at 77°K. which splits into two components, broad and narrow, at room temperature. Two transition regions were observed in curves for line width and second moment versus temperature. The higher transition temperature, corresponding to the glass transition of the polymer, appears to decrease with increasing water content. The second moment for the water‐soluble polymer differs from that of the water‐insoluble polymer at 77°K. This is interpreted in terms of the difference in the degree of crystallinity of the polymers.
Stochastic model for gel permeation separation of polymers
Authors: Carmichael Jack B.
Published: April 2003

The stochastic theory of chromatography developed by Giddings and Eyring and by McQuarrie is applied to gel permeation chromatography (GPC) by first recasting their assumptions to fit the GPC process and secondly by making specific assumptions about the molecular size dependence of the rate constants λ1 and λ2 for entrapment and elution of a polymer molecule, respectively. The model assumes that: (1) a monodisperse sample is injected; (2) molecules behave independently within the column; (3) no molecular diffusion occurs; (4) the polymer molecules are unperturbed random coils; (5) entrapment sites in the bed are identical; (6) λ1 is proportional to the probability Pe that the square of the polymer end‐to‐end distance is less than the square of the average pore radius in the bed; (7) λ2 is constant. The calculated difference in retention times, tR‐to (where tR is the retention time for a molecule of arbitrary molecular size and to is the retention time for a molecule whose size totally precludes entrance into the pores of the bed), is shown to be proportional to Pe. The model as thus applied is based on only one parameter. The theory is tested by examining the ratio Pe/(tR − to)exp, predicted to be constant, for narrow polystyrene fractions in the molecular weight range 1.1 × 104 – 8.9 × 105. Chromatographs were obtained by Moore and Arrington by using a θ solvent and a single column packed with a porous glass bed having a sharp distribution of pore sizes. Ratio values ranged from 0.046 to 0.073 with an average value of 0.058 ± 0.009. This relative constancy demonstrates semiquantitative utility of the model for gaining insight into the GPC process.
Structure of a novel polyimide
Authors: Reimschuessel H. K. , Roldan L. G. , Sibilia J. P.
Published: April 2003

The product of the thermal polymerization of ß‐carboxymethyl caprolactam has been identified as a poly[(2,6‐dioxo‐1,4‐piperidinediyl)trimethylene]. An indication of various chain conformations has been explained by the possible existence of two different conformations of the dioxopiperidine moiety. One conformation pertains to an equatorial position of the trimethylene moiety with respect to the plane of the imide group. The other is derived from a structural unit in which the trimethylene group is positioned axially to the plane of the ring. While the former conformation has been ascribed to the crystalline modification the latter appears to be the predominant structure of the polymer in formic acid solution as indicated by NMR analysis. In the glassy state the macromolecule is assumed to be composed of segments of either conformation. The unoriented linear polymer crystallizes upon annealing in positively birefringent spherulites. A triclinic unit cell with the following parameters: a = 9.64 A., b = 11.32 A., c = 15.80 A., α = 98°, β = 96°, γ = 114° has been found to contain eight structural units. The calculated density, 1.30 g./cm.3, agrees with experimental data. A crystal structure is proposed on the basis of the x‐ray data.
Fuming nitric acid treatment of polyethylene. IV. Morphology of drawn polyethylene
Authors: Meinel G. , Peterlin A.
Published: April 2003

Drawn PE of different draw ratios (ranging from 1 to 25) and thermal treatment (annealing temperature 80, 100, 110, 120, 127°C.) was treated with fuming nitric acid at 80°C. Weight loss, molecular weight, elastic modulus, and thermograms were measured for annealed and unannealed samples as a function of the treatment time and draw ratio. As a consequence of the preferential oxidation of the noncrystalline portions, there occurs initially a high rate of weight loss and a steep drop in molecular weight, followed by a lower rate of weight loss at nearly constant molecular weight. The elastic modulus stays practically constant up to the moment where the brittleness of the sample prevents further measurement. During the later period the thermograms exhibit one melting peak during the first melting. The remelt of the same sample, however, has two melting peaks with a relative intensity independent of the treatment time. That the two melting peaks are caused by two components of different molecular weights present in the sample is substantiated by fractionation. At very high annealing temperature (127°C.), two peaks appear, not only in the first melting curve of the etched sample, but also in the melting curve of the unetched material. Such an effect is the consequence of partial melting during annealing followed by new crystallization during cooling the sample to room temperature. The findings are related to the morphology of the drawn material under the assumption of preferential scission of chain loops in the amorphous‐crystalline sandwich layer model.
Diffusion in atactic polystyrene above the glass transition point
Authors: Duda J. L. , Vrentas J. S.
Published: April 2003

Diffusivities and solubilities in the system n‐pentane‐polystyrene were measured for low penetrant concentrations at several temperatures above the glass transition temperature. The relatively sharp changes in the activation energy of diffusion and the heat of solution near 150°C. are interpreted tentatively as indicating that a second‐order transition exists in atactic polystyrene above the glass transition temperature. Evidence indicating the existence of this transition has been obtained by other techniques and the effects observed in this study should also be present in the diffusion of other penetrants in polystyrene. Correlation of these and other available data for diffusion in polystyrene as a function of the molecular size of the penetrant indicates that specific thermodynamic interactions between polymer and penetrant have little influence on the diffusion process.
Isochronal temperature–concentration diagram for a polymer–diluent system
Authors: Yannas Ioannis
Published: April 2003

The results of an investigation of the viscoelastic and thermal properties of the gelatin–glycerol system are presented in the form of a complete temperature–composition diagram. This diagram shows the isochronal (10‐sec.) mechanical behavior of the system along lines of constant modulus and thereby affords a convenient assessment of variation in viscoelastic behavior along any isotherm or isopleth of interest. Comparison of the results with previously obtained limited sets of data on a number of other polymer–dilent systems indicates the applicability and utility of such a presentation.
Ductile behavior of single crystal mats of an ethylene–propylene copolymer
Authors: Holdsworth P. J. , Keller A.
Published: April 2003

It is reported that mats formed by the sedimentation of single crystals of methyl‐ and ethyl‐branched polyethylene exhibit strength and ductility comparable with that of melt‐crystallized films. In fact, in the case of methyl‐branched polymers, extensions of up to 50× were obtained on cold drawing. Observations on separate crystals suggest that this extension is due to the pulling out of individual lamellae. In view of the magnitude of the extension, this implies unfolding of the molecules. That considerable coherence can be obtained without original molecular ties between crystals is of significance as regards the molecular interpretation of the strength and ductility of crystalline polymers.
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

When 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

Two 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

The 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

The 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

The 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

A 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

The 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

Conformations 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

The thermodynamic properties of crystalline and amorphous poly(2,6‐dimethyl‐1,4‐phenylene ether) (PPO

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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

A 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

The 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

At 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

Infrared 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

The 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

The 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

GPC 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

An 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

Fibrous 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

The 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

The 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.
Rapid stress‐induced crystallization in natural rubber
Authors: Mitchell J. C. , Meier D. J.
Published: April 2003

Stress‐induced crystallization in a rapidly stretched natural rubber gum vulcanizate has been studied using thermal techniques to follow the development of crystallinity. A special‐purpose analog computer has been assembled and used on‐line to process the thermal and mechanical data obtained in high speed tensile testing. Roughly first‐order room temperature crystallization kinetics curves were obtained having time constants of 50–60 msec in the range of 400–540% extension. While the rate of this rapid, presumably primary crystallization appears rather insensitive to elongation in this limited range, the extent of crystallization at 400 msec increases smoothly from zero at 340% elongation to around 18% at 540% elongation. It is shown that our high‐speed tensile tester can stretch this vulcanizate fast enough that most of the crystallization takes place after extension has been completed. Stress‐strain curves obtained at this high rate are compared with those obtained at lower rates where crystallization takes place during the stretching.
Birefringence of semicrystalline polymeric networks
Authors: Smith K. J.
Published: April 2003

A simple theoretical development is proposed to explain the variation of birefringence with degree of crystallization for crosslinked, stretched polymer networks. The model adopted for the calculations is one proposed by Flory in order to calculate the thermodynamic properties of such systems and hence is restricted to the special case of network orientation prior to the onset of crystallization. Our findings are briefly discussed and possible applications of the results are considered.