bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polypeptides. VIII. Molecular configurations of poly‐L‐glutamic acid in water‐dioxane solution
Authors: Doty Paul , Wada A. , Yang Jen Tsi , Blout E. R. 
Published: April 2003

AbstractThe configuration of a poly‐L‐glutamic acid sample of 34,000 molecular weight has been studied in 0.2 M NaCl‐dioxane (2:1) as a function of pH and temperature by intrinsic viscosity, optical rotation, optical rotatory dispersion and infrared spectroscopy. The intrinsic viscosity and specific rotation fall sharply in the pH range of 5.4–6.4 reaching values that remain constant at higher pH. The indications that these changes correspond to a reversible helix‐random coil transition are substantiated by the demonstration that the optical rotatory dispersion shifts from the type characteristic of helices to the normal type as the pH is increased through the same region. Further evidence of the transition is found in infrared spectroscopic studies in solutions in which D2O has replaced H2O. The temperature dependence of the specific rotation and infrared spectra shows that within the pH region of 5.4 to 6.4 the equilibrium is shifted toward the coiled configuration by an increase in temperature. The analogy of this behavior with protein denaturation is obvious. It is noted that the transition from the helix to the coil does not begin until about 40% of the residues have become charged. The implications of the ability of the helical configuration to withstand this degree of electrostatic repulsion within its side groups is discussed in relation to the configuration of proteins.
Studies on graft copolymers derived by ionizing radiation
Authors: Chen W. K. W. , Mesrobian R. B. , Ballantine D. S. , Metz D. J. , Glines A. 
Published: April 2003

AbstractStudies are presented on the preparation of graft copolymers by the gamma‐ray irradiation of various polymer‐monomer combinations. The following graft copolymers have been prepared and evaluated for specific applications: (1) vinylcarbazole grafted to polyethylene to produce a higher temperature dielectric material; (2) styrene grafted to polyethylene and sulfonated to produce a cation exchange membrane of high mechanical strength, low resistivity, and high permeaselectivity; (3) surface grafting of styrene to polytetrafluoroethylene for modification of adhesive properties; (4) acrylonitrile grafted to polydimethylsiloxane to increase solvent resistance of the latter.
Alkaline and acid hydrolysis of polyvinylamides
Authors: Moens J. , Smets G. 
Published: April 2003

AbstractThe alkaline and acid hydrolyses of polyvinylamides and their N‐substitution derivatives have been studied and compared to the alkaline and acid hydrolyses of simple homologous substances. The rates of reaction have been followed conductometrically, and the rate constants evaluated at different temperatures in order to determine the energies of activation and the log PZ of the Arrhenius equation. The influence of the polymeric structure on the course of the reactions has been shown. In alkaline medium the increasing negative charges on the polymeric chain exert an electrostatic repulsion effect toward the hydroxyl ion, and, as a consequence, cause a progressive decrease of the rate of reaction. In the case of polyacrylamide (PAA), hydrolysis enhances an uncoiling of the polymeric chain when the degree of conversion reaches about 40%. Therefore the reaction is characterized by two different steps, a first, rapid step analogous to the reaction of aliphatic monoamides (Ea = 13.7 kcal.), and a second, slow step related to the increasing electrostatic effect. This interpretation has been confirmed by hydrolysis measurements on copolymers of acrylamide‐vinylpyrrolidone (42/58) and acrylamide‐acrylic acid (64/36). In the case of polymethacrylamide (PMA), N‐methyl‐PAA, and N,N′‐diethyl‐PAA steric hindrance along the chains confers a stretched configuration on the macromolecules, and reinforces the electrostatic effects; therefore, the rate constants, can be determined only at low degree of conversion. Moreover, the maximum degree of hydrolysis becomes limited and is 72, 55, and 35 for PMA (Ea = 16 kcal.), N‐methyl‐PAA (Ea = 18.3), and N,N′‐diethyl‐PAA (Ea = 22 kcal.), respectively. N,N′‐Diethylpolymethacryamide is completely alkali‐resistant. In acidic medium the hydrolysis of PAA and PMA is characterized by a secondary intramolecular cyclization due to imide formation between amide and acid functional groups. This secondary reaction, which becomes appreciable at 85°C., causes an increase in the overall energy of activation of the hydrolysis, which is consequently 3 to 4 kcal. higher than those of aliphatic low molecular weight compounds. On the other hand, this imidization is absent in the case of the N‐substituted polymers, of which the energies of activation are equal to those of the aliphatic homologous substances (N‐methyl‐PAA = 21.7; N,N′‐diethyl‐PAA = 24.6 kcal.).
Relationships among variously weighted average properties including molecular weights
Authors: Ward Wilfred H. 
Published: April 2003

AbstractA number‐average property such as a number‐average diffusion constant Dn cannot be defined in terms of weight‐related weighting factors (such as concentrations in weight per unit volume) without postulating a functional relationship between the molecular weight and that property. Conversely, an analogous statement holds concerning any weight‐average property and number‐related weighting factors such as mole fractions. Ordinarily the molecular weight distribution is not known initially for a given sample under study, so that assignment of any such a relationship under these circumstances would be quite arbitrary. It is proposed that the number average analog [Σci/(Σci/Qi)], which is equal to the true number average Qn only when Qi is directly proportional to the molecular weight Mi within the sample considered, be designated the number‐analogous average Qx to distinguish it from Qn. (In this, ci is a weighting factor proportional to the polymer weight fraction having the value Qi of the intensive physical or chemical property under discussion.) Mn is of course necessarily equal to Mx. However, designation of Dx as the number‐average diffusion constant is particularly unreasonable because it implies direct proportionality between the molecular weight and the diffusion constant. Although such a relation may hold for a specific case, in general, other factors being usual, the diffusion constant is inversely related to molecular weight. Discussion of a specific illustration shows the following: Qx may be the same for heterogeneous systems having different values of Qn. Qn cannot in general be found by analyzing a material distribution by means of a property such as the refractive index that is proportional to the mass concentration rather than to the number of molecules in a given volume. Qx sometimes can be found from such data. Although the sedimentation and diffusion constants, with the partial specific volume, define the molecular weight of a homogeneous sample, the average sedimentation and diffusion constants of a mixture do not uniquely determine its average molecular weights. Values found from weight‐, number‐, or number‐analogous average sedimentation and diffusion constants may be either higher or lower than the weight‐ and number‐average molecular weights, even though these latter have been deduced to be limiting values for certain postulated molecular weight distributions. In a given instance, heterogeneity indexes calculated from true weight‐ and number‐averages of sedimentation and diffusion constants more closely approximate the ratio of the weight‐average to number‐average molecular weights than if the more readily determined number‐analogous averages are used.
Determination of average molecular weight of cellulose acetate by dielectric dispersion in solution
Authors: Scherer Philip C. , Levi David W. , Hawkins Miller C. 
Published: April 2003

AbstractThe capacity of cells containing solutions of 5% cellulose acetate in dioxane was measured from 50 cycles to as high as 5 megacycles by a bridge method. A dispersion region was found between zero and approximately 40 kc. The frequency where the dielectric dispersion was 0.50 was taken as the critical frequency which was found to be related to the viscosity determined degree of polymerization. An empirical correlation enabled the calculation of degrees of polymerization from dielectric dispersion which could be readily duplicated and which agreed reasonably well with those found by the viscosity method. It is suggested that this procedure may develop into a very convenient and rapid method for molecular weights pending the accumulation of further experimental evidence.
Condensation polymers containing fluorine. I. Synthesis of linear polyesters from fluorine‐containing diols
Authors: Schweiker George C. , Robitschek Paul 
Published: April 2003

AbstractMethods of synthesizing linear polyesters from fluorine‐containing diols have been investigated. The most suitable method consists of reacting the fluorine‐containing diols with dicarboxylic acid chlorides. Number‐average molecular weights in excess of 15,000 have been obtained. The polymers are rubberlike gums or waxy solids, depending on the reactants used. Increasing amounts of fluorine, contained either in a pendent group or on the backbone chain of the polymers, decreases their solubilities in common solvents, and raises their brittle temperatures.
Ionic grafting
Authors: Haas Howard C. , Kamath Pandurang M. , Schuler Norman W. 
Published: April 2003

AbstractCation initiated polymerizations of various monomers were carried out in the presence of several polystyrene derivatives in an effort to obtain graft copolymers. No success was achieved in grafting with vinyl butyl ether, vinyl ethyl ether, isobutylene, N‐vinylpyrrolidone, or pinene under the particular experimental conditions employed. In the experiments involving vinyl n‐butyl ether, the presence of the various polystyrenes appeared to have no effect on the polymerization of this monomer or on the DP of the polyvinylbutyl ethers obtained. However, when styrene was polymerized in the presence of poly‐p‐methoxystyrene (PPMS), graft copolymer was readily obtained. The success of this reaction demonstrates the feasibility of preparing graft copolymers by an ionic mechanism and yields additional proof of an ionic chain transfer reaction with aromatic species in which the latter are incorporated into the chain. Data obtained on the styrene‐PPMS system are discussed in terms of a simple kinetic scheme. The molecular termination constant of PPMS was found to be only 1/67th of that of p‐methylanisole, a low molecular weight analogue. The low chain transfer effectiveness of PPMS is believed to be due to constraints placed on the availability of the transfer sites which are linked in a polymeric chain.
Infrared determination of orientation, orientation distribution, and crystallinity in polyethylene films
Authors: Tobin Marvin C. , Carrano Matthew J. 
Published: April 2003

AbstractThe problem of determining orientation distribution in polymer films from the measurement of infrared dichroism is treated from the theoretical point of view. It is shown that the distribution function cannot be determined from such measurements. However, if an elliptical distribution function is assumed, the axial ratio of the ellipse of planar components may be calculated. The curve for axial ratio as a function of measured dichroic ratio is given. The dichroisms of the 1300, 730, and 719 cm.−1 bands in polyethylene are discussed and interpreted. It is shown that, in extruded films, chain axes in the amorphous areas lie roughly in the extrusion direction. Chain axes in the crystalline areas lie roughly perpendicular to the extrusion direction. In stretched films, all chain axes line up in the stretch direction. The axial ratios calculated from the 730 and 719 cm.−1 bands are given for a cold‐stretched polyethylene film at different degrees of stretch. Axial ratios of over 100:1 may be attained for the crystalline regions of the film. Specific extinction coefficients for the crystalline band at 730 cm.−1 and the amorphous band at 1300 cm.−1 are determined from measurements on polyethylene films of different crystallinities. The latter values is compared with values measured in molten polyethylenes and normal hydrocarbons. The hydrocarbon values do not agree with the polyethylene values. The amorphous contents of a number of polyethylenes as measured by infrared, density, and x‐ray methods are given. Possible reasons for the disagreement between the results are briefly discussed.
Use of the fluorescence technique as an absolute method for obtaining mean relaxation times of globular proteins
Authors: Steiner R. F. , McAlister A. J. 
Published: April 2003

AbstractMeasurements of excited lifetime and of degree of polarization have been combined to yield values for the mean relaxation time of fluorescent conjugates of bovine serum albumin, egg albumin, and lysozyme. Evidence has been presented for the validity of relaxation times thus computed and for the absence of contributions from nonrandomness of fluorescent residue orientation and from internal degrees of rotational freedom.
Viscosity of dilute solutions of polyvinyl alcohol
Authors: Matsumoto Masakazu , Imai Kiyokazu 
Published: April 2003

AbstractThe viscosity of dilute solutions of polyvinyl alcohol was measured in aqueous and aqueous phenol systems. In the aqueous solution, Huggins' relation does not hold and a2 = 2.01 × 10−1 [η]2.28 was obtained. In the aqueous phenol solution, Huggins' relation holds very well. The relation between a2 and [η] in both systems is independent of the polymerization conversion of the original polyvinyl acetate. The exponent α of [η] = KMα is greater in the aqueous phenol system than in aqueous solution, showing that the aqueous phenol is a better solvent than water.
Some solution properties of isotactic and atactic polystyrenes
Authors: Danusso Ferdinando , Moraglio Giovanni 
Published: April 2003

AbstractResults of viscometric and osmotic measurements as well as solubility experiments with isotactic and atactic polystyrene fractions are reported. The relation between [η] and M was not found to be different for the two types of polymer. On the contrary, the second virial coefficients B in toluene are appreciably different. Calculated values of the “limiting interaction affinity” φE in toluene and the results of solubility experiments in MEK and in toluene–methanol mixtures show that atactic polystyrene is always more soluble than isotactic polystyrene, regardless of whether the latter is in the crystalline or in amorphous (metastable) state. MEK is shown to be a selective solvent in the separation of the two types of polystyrene. The measure of B or φE is suggested as a possible measure of the isotaxy.
Nuclear magnetic resonance in some fluorine derivatives of polyethylene
Authors: Slichter W. P. 
Published: April 2003

AbstractNuclear magnetic resonance studies have been made of the proton and fluorine absorptions in powder samples of polyvinyl fluoride, polyvinylidene fluoride, polytrifluoroethylene, and polytetrafluoroethylene. Measurements were made over a temperature range of 77 to 300°K., and in some polymers up to 420°K. Narrowing of the absorption curves indicates the onset of motion in the temperature region 280–320°K. The activation energies for the narrowing amount to 2–4 kcal. and frequency factors for the motion are about 106 to 107 sec.−1, values which are much smaller than those reported for other polymers. Second moments of the absorption curves have been calculated for simple models of motionless and rotating molecules, and have been compared with experiment. The onset of motion in polytetrafluoroethylene is related to transitions reported elsewhere in studies of crystallinity, frictional coefficient, specific heat, and density. Nuclear resonance measurements on fibers of this polymer are in keeping with the view that these physical effects are associated with molecular rotations.
Tensile strength of rubbers
Authors: Bueche F. 
Published: April 2003

AbstractA theory for the tensile strength of rubbers is presented. It gives reasonable agreement with the available experimental data for natural and synthetic rubber. One of the basic postulates of the theory is that, in order for the sample to break, conditions must be such that when one chain breaks the extra load thrown onto its near neighbors causes one of them to break. It appears that the effect of crystallites and filler particles is to decrease the additional load forced onto each of its neighbours when a segment breaks. This makes possible the effective use of higher degrees of crosslinking. The resultant increase in effective network chains is apparently responsible for the superior strength of the materials containing small solid particles, either crystallites or filler. It is also pointed out that the low number‐average molecular weight of GRS lowers the maximum strength of the unfilled polymer by about a factor of two. The effect is not nearly so large in the case of filled rubber.
Specific heat of synthetic high polymers. VIII. Low pressure polyethylene
Authors: Wunderlich Bernhard , Dole Malcolm 
Published: April 2003

AbstractSpecific heat measurements have been carried out on granular and annealed Marlex 50, a polyethylene polymerized at relatively low pressures, over the temperature range −25 to 150°C. Calculation of the crystallinity yields maximum values of 82.6 and 93.8% for the granular and annealed Marlex 50, respectively. The specific heat of crystalline Marlex 50 at room temperature is slightly less than that previously predicted for a crystalline paraffinic hydrocarbon of infinite chain length. The maximum melting temperature, 134.8°, is about 1.7° less than that of polymethylene and close to the predicted value for a long chain solid hydrocarbon. 90% of the solid Marlex 50 melts over a 15° range of temperature. The shape of the specific heat‐temperature curve can be well reproduced by application of Flory's theory of crystallization in copolymers by considering branch points and chain ends to be the noncrystallizing copolymer units. Negative temperature drifts just below the melting point and low specific heat values just above have not been explained.
Dependence of mechanical relaxation spectra of linear amorphous polymers on the distribution of molecular weights
Authors: Fujita Hiroshi , Ninomiya Kazuhiko 
Published: April 2003

AbstractAn expression is obtained in the form of an integral equation of the Fredholm type which correlates the mechanical relaxation distribution of a linear amorphous polymer with its molecular weight distribution. A method of approximate solution of this integral equation is given on the basis of the assumptions that: (1) the relaxation spectrum of a monodisperse sample in the rubbery region is approximated by a box‐shaped function; (2) the steady‐flow viscosity of a monodisperse sample increases with the 3.4 power of molecular weight above a certain critical molecular weight M̄c; and (3) the relaxation modulus (or the real part of the complex dynamic elasticity), Ē, in the initial zone of the rubbery region is independent of molecular weight and may be calculated in terms of Alfrey's approximation. The method permits predicting the molecular weight distribution from experimental relaxation data obtained over the entire region of rubbery timescale, provided the values of Mc, Ē, and M̄z (z‐average molecular weight) of the given sample are known. Stress‐relaxation data on unfractionated samples of polystyrene and polyvinyl acetate are analyzed in terms of this method, and it is found that the predicted molecular weight distributions agree quite satisfactorily with the observed data for both polymers, except in regions of low molecular weight where the theory gives rise to a fictitious maximum and minimum, neither of which is observed in the experimental data. This anomaly is attributed to the effect of the transition region on the initial zone of the rubbery region which is neglected in the present theory. The experimental data on polyvinyl acetate used for the tests are taken from our previous study, and those on polystyrene are newly obtained for this work. Since no complete stressrelaxation data covering the entire region from glassy state to rubbery flow are yet available on polystyrene, those obtained in this work are presented in rather great detail. The relaxation spectrum in the transition region is compared with that of Grandine and Ferry and of Becker from dynamic mechanical measurements in an audiofrequency range, with a fair agreement with the former of the two. The shift factor aT determined over the temperature range from about 80 to 150°C. follows a similar curve to that found previously for polyvinyl acetate when reduced to an appropriate reference temperature, and yields a maximum activation energy for relaxation processes of 210 kcal. mole−1 at a temperature of 92 ± 1°C. This temperature is in the middle of the reported second order transition temperatures on polystyrene of high molecular weight.
Dimensions of linear polystyrene molecules in solution: Molecular weight dependence for low molecular weights
Authors: Notley N. T. , Debye P. 
Published: April 2003

AbstractIntrinsic viscosities were measured for sharply fractionated polymer in a good solvent and in a poor solvent at several temperatures. They increased with specific volume of the solute, [η] = ΦL3/M. Φ was considered as an empirical constant depending on solute and solvent. Values were determined for polystyrene/toluene and polystyrene/cyclohexane, using light‐scattering measurements for derivation of molecular weights and dimensions. The equation was assumed valid for extrapolation to lower molecular weights and used to estimate molecular dimensions from viscosity/molecular weight data in a range not directly measurable. The results were compared with theoretical calculations of the random coil problem.
The interaction parameter for solutions of nitrocellulose in acetone
Authors: Takenaka H. 
Published: April 2003

AbstractVapor pressures of solutions of nitrocellulose in acetone were measured in all‐glass systems over the complete range of concentration, at temperatures from 20 to 60°C. Applying Flory's theory, the interaction parameter, χ1, was calculated. From its temperature‐dependence, the free energy of interaction between polymer and solvent was separated into interaction heat and interaction entropy components. A graph in which the heat terms are plotted against the corresponding entropy terms shows a straightline relation, with the line going through the origin.