bluuebunny/crossref_metadata_2025 huggingface dataset:
Some solution properties of isotactic and atactic polystyrenes
Authors: Danusso Ferdinando , Moraglio Giovanni
Published: April 2003

Results 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

Nuclear 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

A 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

Specific 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

An 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

Intrinsic 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

Vapor 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.
Permeability to liquids of polyethylene and irradiated polyethylene
Authors: Bent Henry A.
Published: April 2003

Permeability constants at four temperatures for twelve organic solvents in three polyethylenes and one electron‐irradiated polyethylene are reported, together with some swelling data, and compared with data on N2, O2, CO2, and CH3Br. Irradiation appears to increase permeability and solubility coefficients for large penetrants at low temperatures, decreases the permeability coefficients of small penetrants at all temperatures, has little effect on the solubility coefficients of small penetrants, and tends to decrease both permeability and solubility coefficients of large penetrants at high temperatures. In almost every case irradiation decreased both Ep and P0 \documentclass{article}\pagestyle{empty}\begin{document}$ (P = P_0 e^{ - E_p /RT} ); $\end{document} and there exists a temperature, T(inversion) = ΔEp/R(Δ ln P0) at which the permeability constants of a penetrant in polyethylene and irradiated polyethylene are equal. These inversion temperatures tend to increase with increasing polarity of the penetrant. To account for these observations, it seems sufficient to assume that irradiation decreases crystallinity and increases crosslinking, that an increase in polymer crystallinity is accompanied by an increase in the quasicrystalline‐like character of amorphous regions, and that small penetrants may dissolve, and diffuse, through the crystalline regions of polyethylene. It is postulated that activated diffusion in polyethylene induces structural changes in the polymer not unlike local melting. An explanation is given for the observation that flexible molecules tend to have small frequency factors compared to rigid molecules of similar activation energy. And a simple, particle‐in‐a‐box model is proposed for diffusion of small penetrants in a crosslinked polymer. This model predicts that irradiation should leave Ep unchanged, and should decrease P0, by nearly the same factor for all penetrants at all temperatures, very much as observed for N2, O2, and CO2.
Pectic substances—water. II. Thermodynamics of water vapor sorption
Authors: Bettelheim Frederick A. , Volman David H.
Published: April 2003

The differential thermodynamic functions of water vapor sorption for the different forms of polygalacturonide chains indicate that in both the acid and sodium salt forms the swelling of polymer during vapor sorption opens new polar groups for further adsorption. In the highly esterified pectin no new polar group will be available through swelling, indicating that the methayl group shields the carboxylic oxygens from hydrogen bonding with water. The differential heat and entropy functions closely follow each other in the investigated systems. The high negative differential entropy values are explained by the contribution of the solid polymer which shows increasing order as indicated by an increase in crystallinity during the water vapor sorption. The mechanisms of water vapor sorption on the different forms of polygalacturonide chain were deduced from the differential thermodynamic functions. The constants of the B.E.T. and of the Hailwood and Horrobin theories of adsorption isotherms are in agreement with the proposed mechanisms.
Graft polymers with preset molecular configurations
Authors: Merrett F. M.
Published: April 2003

It has previously been shown that, when a graft polymer of rubber and polymethyl methacrylate is dissolved in benzene and a limited amount of methanol added, the hydrocarbon rubber chains collapse to form colloid particles stabilized by the still soluble polymethyl methacrylate chains. Similar high solids dispersions of this type and of the complementary type with the vinyl polymer chains collapsed have now been prepared and evaporated down to give dry modified rubbers. Due to the known incompatibility between different polymers the microseparation in the colloid suspension is carried through to the dry polymer. It is shown that the form with rubber chains collapsed, polymethyl methacrylate chains extended, is hard, shows modulus reinforcement, and adheres strongly to glass, while the form with polymethyl methacrylate chains collapsed, rubber chains extended, is soft, shows no modulus reinforcement, and does not adhere to glass. This indicates that the extended chains mainly govern these particular properties. On the other hand, good hot tear strength seems to be conferred by the collapsed rubber chains, the alternative form with extended rubber chains giving poor tear at all temperatures. The possibility of predicting the configuration and hence the mechanical properties given by any particular method of preparation is discussed and examples are given.
Copolymerization of vinyl bromide
Authors: Blauer G. , Goldstein L.
Published: April 2003

Copolymers of vinyl bromide with methyl methacrylate and with styrene were prepared in vacuo either thermally at 28°C. or by UV irradiation at 0°C., using 2,2′‐azobisisobutyronitrile as initiator at 28°C. and as photosensitizer at 0°C. The reactivity ratios of the two systems were determined in bulk for both modes of initiation. They were similar in all four cases. The stability of some of the copolymers was compared at 80°C.
“Monodisperse” polystyrene
Authors: Bianchi J. P. , Price F. P. , Zimm B. H.
Published: April 2003

It has been found possible to control the time of growth of polymerizing styrene radicals by adding overwhelming amounts of free radicals at intervals to an emulsion polymerization system. The styrene chains initiated in one addition are mostly terminated in the next addition, so that their growth time is the interval between additions. Polymers with the molecular weights of most of the molecules very narrowly concentrated around selected values can be prepared in this way. Ultraviolet light plus azoisobutyramide has been found to be a practical initiation system for preparing polystyrenes in this way with molecular weights greater than 500,000. The upper limit of the molecular weight obtainable is determined by the rate of chain transfer. For styrene at 0°C. this upper limit appears to be a few millions.
Models of materials with loss per cycle nearly independent of frequency
Authors: Pelzer H.
Published: April 2003

Based on a continued fraction expansion of the logarithmic function, ladder‐type structures are constructed which exhibit, either approximately or over a limited range of frequencies, a loss behavior that is often encountered in high polymers not only in the dielectric behavior but also in rheology, viz., a loss per cycle that is independent of frequency down to extremely low frequencies. Although such formal models have in general no direct bearing on the actual mechanism, in the present case one of them seems to suggest a molecular model in which groups of molecules are crosslinked into spindleshaped aggregates and immersed in the viscous liquid constituted by the remaining molecules.
Dielectric studies of the methacrylate series. I. Polyethyl methacrylate
Authors: Strella Stephen , Zand Robert
Published: April 2003

The complex dielectric constant of a pure molecular weight fraction of polyethyl methacrylate was determined over a frequency range of 30 to 3 × 105 cps. and a temperature range of −73 to 133°C. The d.c. volume resistivity–temperature behavior was also determined. The data indicate the presence of two transition regions. It is shown empirically that superposition in its present form cannot be applied to these data.
Mastication of rubber. VI. Viscosity and molecular weight relationships for natural rubber after cold mastication
Authors: Angier D. J. , Chambers W. T. , Watson W. F.
Published: April 2003

Values of limiting viscosity number, Huggins' interaction constant, k′, osmotic molecular weight and Flory‐Huggins' constant, μ, of masticated and unmasticated rubber have been compared. A calibration of limiting viscosity against molecular weight has been obtained formasticated rubber, but one is not available for unmasticated rubber due to the occurrence of different extents of branching. A mechanism is advanced of rupture during mastication of molecules above a critical molecular weight.
The oxidative degradation of deuteropolystyrenes
Authors: Beachell Harold C. , Nemphos Spero P.
Published: April 2003

The degradation of polystyrene in the presence of oxygen in the temperature range 175–235°C. and in the presence of ozone between 65 and 154°C. has been studied. The products of the reaction, analyzed by infrared spectra, appear to be low molecular weight polystyrenes containing carbonyl groups upon O2 oxidation, while a peroxidic complex intermediate forms primarily during ozonization. Volumetric studies of the rate of oxygen uptake gave an activation energy of 25 kilocalories per mole, while spectrophotometric studies of the rate of carbonyl formation gave a value of 45 kilocalories. Identical studies on specially synthesized deuterated polystyrenes gave similar results, with rates of oxidation varying approximately in the following order:
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Viscosity of dilute solutions of preparations of deoxyribonucleic acid at low and medium rates of shear
Authors: Eisenberg H.
Published: April 2003

The viscosity surfaces of two samples of DNA as a function of rate of shear and concentration of polymer and of NaCl are described. The measurements were performed with a rotation viscometer with electrostatic resorting torque recently described, at rates of shear from 0.13 to 200 sec.−1. The limiting slopes of the viscosity against rate of shear curves are zero in agreement with hydrodynamic theory. The measurements are not amenable to interpretation by the rigid ellipsoid of rotation model but are better described by the Gaussian chain model with high internal viscosity.
Copolymerization of butyl acrylate and vinylpyridine
Authors: Funt B. L. , Ogryzlo E. A.
Published: April 2003

The copolymerization of n‐butyl acrylate with both 2 and 4 vinylpyridine was investigated. Spectrophotometric analysis was employed for determining copolymer compositions utilizing the vinylpyridine absorption at 263 mμ. Reactivity ratios for butyl acrylate/2‐vinylpyridine were r1 = 2.50 ± 0.50 and r2 = 0.10 ± 0.04. For butyl acrylate/4‐vinylpyridine r1 = 5.51 ± 0.09 and r2 = 0.46 ± 0.09. These values were compared with calculated estimates made from the Q–e scheme.
Mechanical properties of natural and synthetic rubbers
Authors: Bueche F.
Published: April 2003

The tensile creep behavior of natural rubber, high and low temperature GRS, polybutadiene, and a synthetic cis‐polyisoprene have been investigated. By combining measurements over the temperature range −70 to +60°C., it has been possible to obtain a composite creep curve covering over 15 decades of time for each of these materials. In addition, similar curves have been obtained for most of these materials at several degrees of cure and containing various amounts of carbon black. All measurements were confined to elongations below about 5%. One can conclude from these data that the synthetic rubbers, except for the cis‐polyisoprene, do not vulcanize to give a mechanically stable network. That is to say, these materials never reach equilibrium elongation under an applied load. It is concluded that the number‐average molecular weights of GRS is so low that excessive degrees of crosslinking are needed in order to form a stable network. Natural rubber and certain synthetic cis‐polyisoprene, do not suffer from this defect. The excessive heat generation found in GRS upon flexure is attributed to the fact that an equilibrium extension is never achieved in these materials. A theoretical relation for the heat production in flexed rubbers is given. It is showed that the theory predicts the relative behavior of the various rubbers in respect to heat generation under flexure.
Methyl ethyl ketone peroxide as an initiator in the polymerization of vinyl monomers
Authors: Gopalan M. R. , Santhappa M.
Published: April 2003

A systematic investigation was undertaken of the kinetics of polymerization of styrene and methyl methacrylate in bulk as well as in solutions of benzene, toluene, methyl ethyl ketone and ethyl acetate and of methyl acrylate in ethyl acetate with methyl ethyl ketone peroxide (MEKP) as initiator at 65–80°C. The decomposition of MEKP in ethyl acetate at 70 and 80°C. was studied and the specific rate constants for spontaneous as well as induced decomposition have been evaluated. Transfer coefficients for the monomer, catalyst, and solvent with their respective activation energies have been determined. The rates of initiation have been evaluated by measuring rates and the degree of polymerization for the monomers under study. The catalyst efficiencies in the polymerization of the monomers have been evaluated from the rates of initiation and the rate of decomposition of the catalyst. It is found that the initiator MEKP is comparable to Bz2O2 and azobisisobutyronitrile in its catalyst efficiency, while its capacity for chain transfer is found to be intermediate between the nontransferring initiators like azobisisobutyronitrile and the highly transferring initiators such as cumene hydroperoxide. That the effect of solvents on the various rate constants such as termination and initiation appears to be of no inconsiderable importance has been inferred.
A simple technique for use with infrared spectroscopy to study the curing of epoxy resins
Authors: Feazel Charles E. , Verchot Edgar A.
Published: April 2003

A simple and rapid method is described in which infrared spectroscopy is used to follow the decrease in the epoxy content of an epoxy resin as it is cured. A film of resin plus curing agent between two disks of potassium bromide is cured by heat and its infrared spectrum is measured as the cure proceeds. The technique is used to compare the activities of diamines as curing agents.
Precision viscometry of polyvinyl acetate in toluene
Authors: Tuijnman C. A. F. , Hermans J. J.
Published: April 2003

The viscosity of dilute solutions of PVA in toluene is investigated as a function of shearing stress in an Ubbelohde precision viscometer which permits determining the efflux time to within 3 × 10−3 sec. Various sources of error in capillary viscometry are discussed. Correction for drainage is made on the basis of a newly developed theory. In a first series of measurements uncorrected values of (t − t0)/t0c are shown to give an anomalous curve when plotted against c. In this series the effect of changes in concentration as a result of adsorption onto the walls of the dilution vessels is studied. The anomaly disappears when corrections are made for various sources of error and for non‐Newtonian behavior in particular (second series). The thickness of the adsorption layer on the wall of the capillary is estimated from results in two viscometers with different bore. A comparison with direct measurements of adsorption on glass beads reveals that the average density of the polymer adsorbed is about 0.17 g./ml. The viscosity at low shearing stress is an even function of the shearing stress. The intrinsic viscosity is markedly dependent on shear rate, its value at high shear rates being about 40% of that of zero shear rate.
Effect of pH on homopolymerization of N‐isopropylacrylamide
Authors: Wooten W. C. , Blanton R. B. , Coover H. W.
Published: April 2003

The polymerization of N‐isopropylacrylamide in aqueous solution was studied using a redox catalyst consisting of ammonium persulfate and sodium bisulfite. The purpose of the study was to relate the rate of polymerization and the molecular weight of the resulting polymer to the pH of the system and the catalyst concentration. It was observed that the rate of polymerization was very sensitive to the pH of the system. A plot of rate versus pH for a given catalyst concentration showed a maximum rate at a pH of 6.5. For a given catalyst concentration, the viscosity (molecular weight) of the polymer formed was independent of the rate of polymerization when the pH was 6.5 or less. Above a pH of 6.5 the viscosity was inversely proportional to the rate of polymerization. These results, together with data obtained on polymerization rates and polymer viscosities as functions of catalyst concentration at various pH values, indicate that the viscosity of the polymer formed is primarily a function of bisulfite ion concentration.
Poly‐n‐Hexyl methacrylate. IV. Dilute solution properties by viscosity and light scattering
Authors: Chinai Suresh N.
Published: April 2003

Poly‐n‐hexyl methacrylate prepared by the emulsion technique was fractionated three times by the fractional precipitation procedure to obtain eight fractions. Relationships between viscosity‐ and weight‐average molecular weight were obtained in both an ideal solvent, isopropanol, and a nonideal solvent, methyl ethyl ketone. These relationships are represented by equations:

The effect of the size of the pendant groups (‐methyl, ‐ethyl, n‐butyl and ‐n‐hexyl ester) on the degree of extension of macromolecules in ideal solvents is discussed. It was found that initially as we progress from polymethyl to poly‐n‐butyl methacrylate the degree of flexibility of the macromolecule increases as the size of the pendant group increases. These results are believed to be due to the short‐range interference effect of the solvent molecule on the degree of free rotation of the macromolecule. However, it was found that poly‐n‐bexyl methacrylate chains have considerably greater chain extension than any of the other three polymers. This expansion of poly‐n‐hexyl methacrylate chains ia a result of the steric effect of large pendant units.
Osmotic pressures of moderately concentrated polymer solutions
Authors: Flory P. J. , Daoust H.
Published: April 2003

An osmometer is described which is applicable to highly viscous concentrated polymer solutions. Results are presented for polyisobutylene (MW = 90,000) in cyclohexane at 30 and at 8°, and in benzene at 24.5° (the theta point) and at 50°. Concentrations ranging up to 20% (w/v) and 29%, respectively, were used. The results are compared with the semiempirical formulation of the chemical potential:

In cyclohexane χ1 = 0.429 at 30°, and 0.434 at 8°; higher parameters may be neglected. These observations stand in excellent agreement with results of vapor pressure measurements on more concentrated solutions, with parameters derived from intrinsic viscosities, and with the second virial coefficient observed at higher dilutions. The results in benzene at 24.5° lead to χ1 = 0.500 and x2 = 0.31; at 50°, χ1 = 0.485 and x2 = 0.29. The values of χ1 are compared with deductions from instrinsic viscosities and from second virial coefficients. The fact that the critical miscibility point for M = ∞ occurs at v2 = 0 for this system requires x2 < 1/3.
Some considerations of fractionation, viscometry, and the molecular weights of linear and branched polymers
Authors: Carlo Mussa I. V.
Published: April 2003

The procedures which have been followed in previous work to estimate the molecular weight distribution of some high‐pressure polyethylenes are examined here from a more general point of view. In keeping with these considerations, some equations have been obtained for the cases in which a relationship of the type [η] = KMα is valid, and when some particular weight distribution formulae may be foreseen. These equations and the procedures connected with them may be helpful when one has to check whether the data on fractionation, viscometry, and of absolute determinations of molecular weights are consistent with each other and with the supposed distribution function and viscosity law.
Multicomponent polymers. I. Three‐component systems
Authors: Slocombe R. J.
Published: April 2003

Terpolymer systems which form two azeotropic copolymers frequently give clear terpolymers when the ratio of monomers charged is taken from a line joining the azeotropic copolymer compositions (designated the azeotropic line) as shown when the system is plotted on triangular coordinates. Two terpolymer systems which form three azeotropic copolymers gave clear terpolymers from compositions lying within the area bounded by the three azeotropic lines and in one of the external triangular areas. In the 44 terpolymer systems reported, those containing styrene, various substituted styrenes, acrylic acid, acrylonitrile, methacrylonitrile, methacrylic acid and esters (methyl through butyl), maleic and fumaric esters (methyl and ethyl), vinyl methyl ketone, butadiene, isoprene, and vinyl acetate largely conformed to this behavior. Systems consisting of either two styrene monomers and one methacrylic ester or one styrene monomer and two methacrylic esters are unusual in that clear terpolymers were obtained from all compositions tested. Systems containing acrylic esters, vinylidene chloride, maleic anhydride, and trans‐dichloroethylene did not conform to this behavior. A number of corresponding monomer and polymer compositions, obtained by solution of the terpolymer equations, were plotted on triangular coordinates. The graph showed that, during polymerization, the composition of the polymer species formed and the composition of the residual monomers migrate toward that of one of the pure monomers. Clarity of films cast from solutions containing two or more different polymers was used as an indication of compatibility. High compatibility was found with polymers having compositions on the azeotropic line. Incompatibility was found with polymers having compositions not on the azeotropic line. Incompatibility increased as the distance between these compositions (shown by a triangular graph) increased.
Diffusion in ethylene polymers. I. Desorption kinetics for a thin slab
Authors: McCall D. W.
Published: April 2003

Theory and experiments are described for the determination of diffusion coefficients liquids in solids from desorption data. Experimentally the desorption is followed by weighing the solid specimens. The mathematical process of extracting diffusion coefficients from desorption data is examined and a numerical procedure is described which may be employed in systems in which the diffusion coefficient is concentration‐dependent. Data and analysis are presented for the diffusion of benzene and n‐hexane in two ethylene polymers. The two polymers are representative of highly branched high pressure material and low pressure highly crystalline material. A discussion of the molecular significance of the results is given. The desorption curves obtained by numerical analysis are applicable to other systems which exhibit a similar dependence of the diffusion coefficient upon concentration.
Anomalous viscosity behavior of polymer solutions at very low concentrations
Authors: Kawai Tōru , Saito Kazuhisa , Krigbaum W. R.
Published: April 2003

Recently, it was reported by many authors that polymer solutions display a peculiar anomaly in their viscosity behavior at very low concentrations. In order to explain this phenomenon, the expansion of the polymer coils with dilution has been taken into account. Krigbaum, in his fine calculation of molecular sizes at finite polymer concentrations, indicated that the unperturbed configuration is rapidly approached as the concentration is increased. His result is utilized in this paper to obtain the theoretical ηsp/c vs. c curve. It is assumed that a modified Huggins' formula is valid for a conveniently defined [η], which varies with concentration in accordance with the Krigbaum theory. The upswing of the ηsp/c vs. c curves, observed frequently at very low concentrations, can be predicted from theory. Moreover, this treatment seems capable of accounting for the influence of molecular weight of the polymer and of the solvent type upon the observed viscosity behavior. Before a conclusion is drawn, however, the experimental difficulties in working with very dilute solutions must be carefully considered. Several points which still require clarification are also discussed briefly.
Osmotic pressure measurements with solute‐permeable membranes
Authors: Gardon J. L. , Mason S. G.
Published: April 2003

A method of determining the osmotic pressure of a solute which can diffuse through the membrane is described. It is shown theoretically that after a certain time interval a plot of the logarithm of the indicated osmotic pressure against time yields a straight line which can be extrapolated to zero time. The true value of the initial osmotic pressure is calculated by correcting the extrapolated value for the rate of transfer of solute and solvent through the membrane and for the partition coefficient of the solute between the membrane and the solvent. The various correction factors are calculated from experimentally determined quantities. By the use of cellophane membranes, osmotic pressures of lignin sulfonates with molecular weights as low as 4,300 have been evaluated.
Crystallinity and orientation in silicone rubber. I. X‐ray studies
Authors: Ohlberg Stanley M. , Alexander Leroy E. , Warrick E. L.
Published: April 2003

A technique is described for quantitatively examining the diffraction pattern of polydimethylsiloxane at and below room temperature with the x‐ray diffractometer. The crystalline fraction of the unstretched material is determined by the classical method developed for natural rubber. In the case of the stretched elastomer, a modified procedure is required which takes into account the extent of preferred orientation of the molecular chains. As the extension ratio is increased, the crystallization temperature rises and preferential orientation of the crystallites with respect to the extension axis increases. The crystallinity increases with decreasing temperature and appears to be independent of the extension ratio below −60°C. An over‐all crystalline fraction of 0.42 was measured for a silicone rubber specimen at −60°C. and an extension ratio of 6.3.
Crystallinity and orientation in silicone rubber. II. Physical measurements
Authors: Warrick E. L.
Published: April 2003

Density data for a silica‐filled dimethylpolysiloxane rubber define incipient crystallization conditions and indicate the forms of crystalline growth for the unstressed rubber and for a sample at 200% elongation. Temperature—tension data for the same silicafilled rubber show incipient crystallinity temperatures as a function of extension. While stress relaxed filled silicone rubber samples show a tension decrease with falling temperatures, they are far from ideal rubbers. The change in polymer filler interaction links with temperature may account for this nonideality. Both the filled and unfilled rubbers show a thermoelastic inversion. The comparison with x‐ray data yields good evidence that crystallization is responsible for the tension rise at low temperatures. This rise may stem from the tendency of silicone rubber to crystallize without altering the orientation of chain segments. The ability to crystallize chain elements in all states of orientation may be founded upon a much greater chain segment mobility for silicone rubber than found with natural rubber. Normal stress—strain curves taken at low temperatures qualitatively show the effects of crystallization.
Reactivity ratios of vinyl esters of aliphatic acids and some common vinyl monomers
Authors: Marvel C. S. , DePierri W. G.
Published: April 2003

The copolymerization reaction of five vinyl esters of aliphatic acids with vinyl chloride, vinylidene chloride, acrylonitrile, butadiene, styrene, and methyl acrylate have been studied. The reactivity ratios have been determined and the Q and e values for the esters have been calculated. The results clearly show that the nature of the acyl residue in a vinyl ester has little influence on its reactivity ratio in a copolymerization reaction or on the Q or e value.
Nuclear spin resonance line width measurements of polyethylene
Authors: Collins R. L.
Published: April 2003

The proton spin resonance spectrum of polyethylene consists of two superimposed lines. The narrow line is attributed to the amorphous phase, and the broad line to the crystalline phase. The width of the narrow line was measured at various temperatures from 25−130°C. for Alathon 10, Alathon 14, DYNH, and Marlex 50 polyethylene and it was found to vary with temperature. The results have been interpreted using the theory of motional narrowing, which indicates that the product of temperature and line width is proportional to the viscosity. A plot of log of line width times temperature versus reciprocal temperature is linear for Marlex 50 polyethylene, and is curved for the other three. The linearity is believed due to the simple structure of the material, and the slope yields an activation energy of 8200 cal./mole. The curvature of the other data is believed due to extensive branching which causes a change of composition of the amorphous phase upon cooling, and the apparent activation energy varies from 11,800 cal./mole at 130°C. to 4900 cal./mole at 25°C.
Crystalline recovery of quenched polyethylene
Authors: Collins R. L.
Published: April 2003

The effect of time and temperature on the crystalline recovery of quenched Marlex 50 polyethylene has been investigated. Quenching thin films in ice water reduced the room temperature crystallinity from a normal value of 93 to 82%. These specimens were maintained at 25, 66.2, and 106.4°C., and the time variation of crystallinity was followed by nuclear spin resonance. The crystalline recovery appears to follow the empirical formula, X = A + B log t, where X is the percentage crystallinity and t, is the time in hours. The rate, X, increases with temperature. The temperature‐dependence of B was computed by assuming the rate to be controlled by diffusion in the amorphous phase. The temperature‐dependence of diffusion is determined by nuclear spin resonance line width measurements to be exp {−8700/RT}. The rate is then X = C/t exp {−8700/RT}, and C, evaluated at 25, 66.2, and 106.4°C., is 2.2 ± 1.9, 1.7 ± 0.5, and 2.1 ±0.2 × 105. This agreement is within the probable error, and justifies the assumption of diffusion as the rate‐controlling factor. The result is X = 2.04 × 105(1/t) exp { −8700/RT} and X = A + 4.70 × 105 log t exp {−8700/RT}.
The scattering of light from thin polymer films. IV. Scattering from oriented polymers
Authors: Norris Forrest H. , Stein Richard S.
Published: April 2003

The scattering of both unpolarized and polarized light by a series of stretched polyethylene films has been studied. The radiation envelope of the scattered light loses its cylindrical symmetry upon stretching. The dissymmetry depends upon the orientation of the stretching direction of the film as does the intensity of scattered light. The results imply a scattering unit which is anisotropic both in shape and in polarizability. The largest dimension and highest polarizability lie in the stretching direction. The Debye‐Bueche theory has been generalized to describe oriented anisotropic systems. The single parameter, a, describing the size of the heterogeneity is replaced by two parameters, a and c. The mean‐square dielectric constant fluctuation η2 depends upon the principal polarizabilities of the scattering unit and upon its orientation. The parameters are evaluated for the series of polyethylene samples. A model is proposed which accounts for the variation of the parameters as well as the changes occuring during melting and crystallizing the polymer.
Molecular weight of ethyl cellulose by dielectric dispersion of solutions in dioxane
Authors: Scherer Philip C. , Hawkins M. C. , Levi D. W.
Published: April 2003

The dielectric dispersion of dilute solutions of ethyl cellulose in dioxane was studied using a “differential” bridge method for the range from 200 cycles to 300 kilocycles. The frequency where the dispersion was 0.50 was recorded as the “critical” frequency. The critical frequency is related to the intrinsic viscosity of the samples as log 100[η] = 2.97 − 0.59 (vc). Since the determination of critical frequency is very rapid this method apparently is satisfactory for molecular weight determinations in the systems studied.
Irradiation effects in plexiglas
Authors: Gross Bernhard
Published: April 2003

Samples of methyl methacrylate were irradiated with 2‐m.e.v. electrons. Stopping and trapping of the incident electrons in the dielectric leads to the formation of a negative space charge. Under proper conditions the electric field of this charge can produce breakdown accompanied by the appearance of a characteristic discharge pattern. The nature of this effect is discussed. It is shown that the bulk of the space charge is concentrated in a narrow layer at a depth corresponding to the effective range of the electron beam. The quantity of charge released during breakdown is measured for various doses and compared with the value of the intercepted charge.