Showing papers in "Journal of Polymer Science in 1958"

Interaction between particles suspended in solutions of macromolecules

Abstract: An attractive force appears between particles suspended in solutions of macromolecules when there is neither direct interaction between two particles nor energetic interaction between particles and solute macromolecules. The magnitude of this force is of the order of the osmotic pressure of the solution of macromolecules and the range is of the order of the diameter of macromolecules. This force is calculated as a function of concentration, shape, and charge of macromolecules, and it is shown that it becomes stronger in solutions of chain macromolecules or of macromolecules of dissymmetrical shape than in solutions of rigid spherical macromolecules at the same net concentration. If macromolecules have charge, the force can be greatly intensified. In every case numerical estimation is made, and it is found that actually this kind of force can have a remarkable influence on the state of suspended particles. Numerical examples of the critical concentration of particles at their macroscopic aggregation are given. Finally a short description is added on the effect of energetic interaction between particles and macromolecules.

La contraction isotherme du volume des polymères amorphes

Abstract: Lorsqu'on trempe un polymere ainorphe a partir d'une temperature T0 > Tg a une temperature T1 < Tg, Tg, btant la temperature de transition vitreuse, on observe une contraction isotherme du volume a T1 qui se poursuit generalement pendant une longue periode. On decrit ce phenombne a partir des observations faites sur des echantillons de polystyrolene, d'acetate de polyvinyle, de polypiperidide et de polymorpholide acrylique. L'expression empirique des isothermes de contraction du volume, v = ƒ(log t′), contient trois paramhtres dont on discute les variations en fonction de la temperature. Dans la region de la transition vitreuse, les isothermes de contraction peuvent se superposer it l'aide d'une translation le long de l'axe de log t′. La variation du parametre de super- position a, en fonction de la temperature est sensiblement la meme que celle deduite par d'autres auteurs, de la variation des paramhtres Blastovisqueux des polymeres amorphes. Ceci sugghre que les processus moleculaires responsables de la relaxation de la contrainte mecanique et ceux qui provoquent la contraction isotherme du volume, sont identiques. La valeur limite de log aT(T − Tg), lorsque T tend vers Tg, s'exprime a partir des paramhtres qui regissent la variation du volume en fonction de la temperature et du temps. La discussion de ces resultats conduit, enfin, a une definition cinetique precise de la temperature Tg qui est compatible avec sa definition usuelle a condition d'adopter un procede experimental adequat. When an amorphous polymer is quenched from a temperature, T0 > Tg, to a temperature, T1, below the glass transition temperature, Tg, an isothermal volume contraction is observed. This phenomenon is described from numerous observations with polystyrene, polyvinylacetate, and polypiperidide and polymorpholide acrylate samples. The volume isotherms can be represented as a function of time by an empirical expression, v = f(log t'), which contains three parameters. The variation of these parameters with temperature is discussed. In the transition region the isotherms can be superposed by shifting them on the abscissa, log t'. The variation of the shift factor, aT, with temperature is essentially the same as that which can be deduced from viscoelastic studies on amorphous polymers. This suggests that similar molecular processes are involved in stress relaxation and isothermal volume contraction of glasses. The limiting value of log aT/(T—Tg), as T approaches Tg, can be related to the constants that control the volume variations with temperature and time. The discussion of these results leads to a precise kinetic definition of Tg which is compatible with that obtained in the usual manner if proper experimental procedures are used.

Sorption and diffusion in ethyl cellulose. Part III. Comparison between ethyl cellulose and rubber

Abstract: Sorption and diffusion of C4 and C5 hydrocarbons have been studied in thin films of ethyl cellulose in the temperature range 30 to 80°C. Only regions of low penetrant concentration were chosen in order to minimize hysteresis effects associated with slow relaxation of polymer chains. The data have been quantitatively compared with those for the same penetrants in rubber, since ethyl cellulose and rubber are examples of stiff and flexible chain polymers, respectively. In both solution and diffusion some major differences were found between the two types of medium. In rubber the heats of dilution were small and the corresponding positive entropies close to those predicted by the lattice theory of solutions. On the other hand, in ethyl cellulose at low penetrant concentrations the heats of dilution were strongly exothermal and the entropies negative. For both polymers diffusion coefficients of penetrants were dependent upon concentration, but whereas in rubber this concentration dependent decreased rapidly with rising temperature, in ethyl cellulose it was largely independent of temperature. Energy barriers involved in each unit diffusion process were comparable for a given hydrocarbon in rubber and in ethyl cellulose, while the molecular shape of the penetrant molecule substantially influenced the diffusion coefficients in each polymer. Further interpretation of the diffusion coefficients suggested that the involvement of polymer chains in each unit diffusion is much less for ethyl cellulose than for rubber. Explanations are offered, based upon the nature of the chains composing the two media and upon the existence of holes in the ethyl cellulose network, for the essential differences indicated above. The relative efficiency of ethyl cellulose and rubber membranes for gas separation is discussed.

The configurational statistics of polymeric chains

Abstract: A short review of the works of the author and his co-workers in the field of configurational statistics of macromolecules is given. Results are quoted of the calculations relating the dimensions, dipole moments, and optical anisotropies of the chains with the conditions of internal rotation and stereoisomerism. Isotactic and syndiotactic chains are examined. The fundamental ideas of the mathematical methods developed are quoted. The calculations are carried out in usual approximation assuming the independence of the rotations around neighbor bonds, and in the next approximations taking into account the correlation of internal rotations inside monomeric units and between them. Comparison of the theory with experiment, using the rotational-isomeric approximation, has shown in particular that the dimensions and the optical anisotropy of the polyisobutylene molecules can be explained by the examination of their configurations in the crystalline state. The excluded volume effects in the branched chains and their influence on the asymmetry of light scattering are investigated. Some experimental results are explained with the help of this investigation.

Glass transition temperatures of copolymers

Abstract: The Gordon-Taylor equation relating the glass transition temperature θ of a copolymer to the glass transition temperatures θ1 and θ2 of the homopolymers is equivalent to where c1 and c2 are the weight fractions of the constituents and A1 and A2 are constants. It can be recast into the following forms suitable for linear plots and where k = A2/A1. Data from the literature on 10 copolymer systems, including butaciene-styrene copolymers, give linear plots, verifying the equation within experimental error. However, the observed value of k is in most cases significantly smaller than the ratio of the differences of the volume-temperature coefficients for each homopolymer in the rubbery and glassy states, as required by the derivation of Gordon and Taylor. The glass transition temperature (in °C.) for a butadiene-styrene copolymer prepared by emulsion polymerization at 50°C. may be calculated from the weight fraction c2 of bound styrene as and for a similar 5° copolymer as

Infrared spectra of high polymers. VI. Polystyrene

Abstract: The infrared spectrum of polystyrene has been obtained in the region of 70 cm.−1 to 3200 cm.−1. These data, plus Raman scattering data from the literature, are used to make a complete assignment of the normal modes of the polystyrene molecule. The benzene ring modes have been analyzed in detail in terms of C2v symmetry, and a set of normal vibrations has been proposed. On the basis of previous analyses of the benzene and monosubstituted benzenes, and a study of the combination bands, it has been possible to make a fairly satisfactory assignment of all of the benzene ring fundamentals. Assignments of the CH2, CH, and skeletal modes are made on the basis of previous studies of spectra of high polymers. The interpretation of the spectrum is in agreement with other evidence that the chain configuration is a random one, i.e., that the polymer is amorphous.

The X‐ray diffraction, birefringence, and infrared dichroism of stretched polyethylene. II. Generalized uniaxial crystal orientation

Abstract: A general method for describing the crystal orientation in a uniaxially oriented crystalline polymer is presented. It is shown that two orientation functions may be quantitatively evaluated from x-ray diffraction data. The variation of these during mechanical and thermal treatment may be studied. These functions are sufficient to completely characterize the crystal contribution to birefringence and infrared dichrosim. By subtracting the crystal contribution from the total birefringence or dichroism, the amorphous orientation may be characterized.

Forms for the stored (strain) energy function for vulcanized rubber

Abstract: Ein numerisches Verfahren zur Behandlung yon axial-symmetrischen Membranproblemen bei endlichen elastischen FormXnderungen wird auf die Verw61bung einer kreisf6rmigen elastischen Membran angewendet. Die zur L6sung notwendige numerische Integration der Gleichgewichtsbedingungen erfolgt bei den gew~Lhlten Beispielen mit Hilfe einer fiir die Berechnung mit Handrechenmaschine gebrguchlichen Differenzmethode. Gestiitzt auf mehrere experimentelle und theoretisehe Arbeiten werden zur Untersuchung der L6sung des Membranproblems verschiedene Formen der Formgnderungsenergie W bei grossen Deformationen betrachtet (10 < 12 < 1000). Eine Verallgemeinerung der logarithmisehen Form ffir W yon GENT und THOMAS erweist sich als ungeeignet ftir die betrachtete Ordnung der Deformation. Durch Anpassung der Parameter in der Drei-Parameter-Gestalt der Formgnderungsenergie yon CARMICHAEL und HOLDAWAY wird eine gute Ubereinstimmung mit dem Experiment erhalten. Fiir diese L6sungen besitzt OW/O 11 einen konstanten Wert bei der Deformation, was eine friihere Feststellung yon RIVLIN und SAUNDERS fiir Werte yon 12 bis 1000 best~tigt. Das Versagen der logarithmisehen Form von W ist auf die starke Abnahme von OW/OI~ im Bereich grosser Dehnungen zuriickzufiihren.

Dependence of the ultimate properties of a GR-S rubber on strain rate and temperature

Abstract: The tensile strength and ultimate elongation of polymeric materials depend on both the temperature and experimental time scale. The mechanical properties of amorphous polymers at temperatures above their glass transition temperature Tg are more amenable to treatment in terms of molecular theories than are their mechanical properties at temperatures below Tg or the mechanical properties of crystalline polymers. For amorphous polymers at temperatures above Tg the viscoelastic properties in small deformations have been studied rather extensively, and several molecular theories—essentially identical—have been published. In contrast, few systematic studies have been made of the effect of time and temperature on the ultimate properties. Consequently, only a limited amount of data is available which can serve as a basis for developing and verifying molecular theories dealing with ultimate properties. A recent theory by F. Bueche treats the time and temperature dependence of tensile strength. According t...

Rupture of rubber. V. Cut growth in natural rubber vulcanizates

Abstract: It has been noted in Part I of this series (referred to hereafter as I), that if a nicked specimen of a natural rubber vulcanizate is slowly stretched, tearing occurs at the tip for quite small applied forces. In the initial stages, this tearing continues only as long as the deformation of the specimen is being increased, and virtually ceases if the deformation is held constant. This tearing is essentially time independent, and is termed “static” cut growth. If, however, the deformation is continued until the cut has grown by a few hundredths of a millimeter the growth becomes time dependent and catastrophic tearing takes place, the cut suddenly increasing in length by perhaps a millimeter or so. If a nicked specimen is alternately stretched and relaxed to the unstrained state, the cut gradually grows even though the applied force is less than that required to produce catastrophic tearing. This phenomenon is termed “dynamic” cut growth. This behavior can be compared to that of gum GR-S vulcanizat...

The fine structure of polytetrafluoroethylene

Abstract: Electron micrographs of highly crystalline PTFE crystallized by slow cooling from temperatures not far above the melting point show well-marked bands, often with striations perpendicular to the bands; optical evidence shows that the chain molecules are parallel to the striations. The structure is in marked contrast to the spherulitic structure of most polymers; it appears that in PTFE the molecules are straight and parallel for much greater distances than in other polymers, and it is suggested that the width of the bands is a measure of molecular length. The unusual structure is attributed to the unusual stiffness of the fluorocarbon chain; the molecules in the liquid are straighter and less tangled than in other polymer melts. Heating to 500°C., followed by slow cooling, gives a modified structure approaching the spherulitic type found in other polymers; it is suggested that this is due to increased molecular tangling in the melt at higher temperatures. One type of polymer shows bands of remarkably uniform thickness, suggesting unexpected uniformity of molecular length. PTFE wax made by thermal or radiation degradation of the high polymer shows well-defined spiral growth steps due to dislocations; the step heights suggest an unexpected uniformity of molecular length.

Fractionation of polyethylene

Abstract: The relatively rapid Desreux technique for polymer fractionation has been modified and applied to both linear and highly branched polyethylenes. The polymer is precipitated from p-xylene solution onto a sand column by cooling from 127° to room temperature. After removal of solvent, the column temperature is again raised to 127° and fractions are eluted, using p-xylene-ethylene glycol monoethyl ether mixtures of increasing solvent power. Approximately 15 fractions are obtained and polymer recovery is essentially quantitative. The reproducibility of the integral distribution curves is within ±2% for a cumulative weight-% of 85 or higher. In certain cases difficulty has been encountered in resolving the less soluble portion of the sample. The selective nature of the system is indicated by the fact that the reduced specific viscosities of the highest and lowest molecular weight fractions are generally in the ratio of 50 or higher.

Structure and mechanism of dehydrochlorination of polyvinyl chloride

Abstract: Polyvinyl chloride when heated loses HCl, presumably by a “zipper” mechanism. The loss of each molecule of HCl from the polymer results in the formation of a double bond, which activates adjacent chlorine and causes the decomposition reaction to propagate along the resin chain. Virgin and degraded resins were subjected to ozonization in order to ascertain the type and location of the labile structures responsible for initiating the “zipper” HCl loss. The molecular weight decrease and formation of carbonyl structures (detected by infrared) produced by ozone indicate that unsaturated chain ends are primarily responsible for HCl loss. Tertiary chloride chain branches contribute to a lesser degree in the initial stages but become more important as dehydrochlorination proceeds. Stability measurements on simple prototypes of structures presumed to be present in polyvinyl chloride provide additional information which is in essential agreement with this mechanism.

Separation of amylose from amylopectin of starch by an extraction-sedimentation procedure†

Abstract: Corn, wheat, and potato starch were fractionated into their amylose and amylopectin components by selective extraction of amylose in hot water after the starch had been pretreated by heating in aqueous mixtures of glycerol, n-butanol, Pentasol, Cellosolve, or dioxane. About three-fourths of the amylose was leached in relatively pure form from starch in the first extraction at 98°C. The granule residue, sedimented by centrifugation, was separated as relatively pure amylopectin after two or more additional extractions. Retention of the coherent structure of the granule in the extracted residue emphasizes the importance of amylopectin to granule properties. Amylose fractions isolated from successive extractions had progressively lower intrinsic viscosities and absorption coefficients of their iodine complexes indicating that this component was subfractionated according to molecular size and/or structure. X-ray diffraction patterns of the pretreated starches indicated that a complex of amylose and organic solvent was formed which may account for the increased solubility of amylose after pretreatment. Evidence is presented which shows that little, if any, amylose occurs in the crystalline regions of granular starches.

Cold‐drawing of glass‐like and crystalline polymers

Abstract: Solid polymers—both glass-like and crystalline—can be cold-drawn. In addition to studies of the specific aspects of this process in individual cases, as governed by structural features, the development of a theory of cold-drawing requires an investigation of the general laws of this process. According to the experimental conditions used, cold-drawing may be carried out either isothermally (at low rates of drawing and with good heat dispersion) or non-isothermally. A number of specific features of the non-isothermal process may be explained by a temperature increase in the stressed region; this has in fact been done in published work on this subject. However, the basic features of this phenomenon persist, as has been shown experimentally, in the isothermal cold-drawing of both glass-like and crystalline polymers. These features include: (a) the possibility of cold-drawing, with large residual deformations; (b) the character of the stress—deformation curves; (c) a displacement at the beginning, and a homogeneous or inhomogeneous stretching over the further course of the cold-drawing (both possibilities being realized in either type of polymer—glass-like or crystalline); (d) the effect of temperature and the rate of drawing on the initial stress σB. These phenomena must be interpreted in a way which does not involve the assumption of a temperature rise. The values of σB depends on the rate of drawing v, this dependence being expressed by the relation σB = A + B log v, valid for both glass-like and crystalline polymers. The two types differ only in the value of the constant B, which is lower for crystalline polymers (polyethylene, polyamide, crystalline silicone rubber) than for glass-like polymers (polyvinyl chloride, amorphous silicone rubber, polymethyl methacrylate, butadiene-acrylonitrile copolymer, etc.). Crystalline and glass-like polymers differ in their mechanisms of cold-drawing. Crystalline polymers, as is well known, undergo recrystallization on deformation; in either type, however, there is a rupture of intermolecular bonds by stresses. Hence follows the kinetic, relaxational character of cold-drawing. The dependence of σB on the temperature and rate of drawing may be explained on the assumption that the activation energy of the molecular rearrangement is decreased with increasing stresses. Uniform isothermal stretchig is, generally speaking, unstable. The fact that it may be realized in practice, and also the stabilization of the block in non-uniform drawing, makes it necessary to assume that the mechanical relaxation properties of the polymer change on orientation.

Effect of physical state during the electron irradiation of hydrocarbon polymers. Part I. The influence of physical state on reactions occurring in polyethylene during and following the irradiation

Abstract: Measurements of crosslinking, trans-vinylene formation, and hydrogen evolution have been made on high- and low-density polyethylenes irradiated at temperatures from about −170 to +240°C. Crosslinking produced during irradiation is mainly in the amorphous areas of the polymer; whereas trans-vinylene unsaturation is produced as readily in the crystalline areas as in the amorphous areas. Radicals are trapped in the crystalline regions. These can react with oxygen to form carbonyl groups, rather than crosslinks. Thus, in Marlex-50 irradiation in the crystalline state at 25°C. followed by a 7 day storage in air prior to the crosslinking measurements, was only about one-sixth as effective in producing crosslinks as irradiation in the amorphous state at 150°C. In the low-density polyethylene where less trapping occurs the factor is about one-half for the same conditions of irradiation and storage. The lifetime of radicals trapped in Marlex-50 when stored in oxygen can be thousands of hours compared with a few hours in low density polyethylene. Both the low-density polyethylene and Marlex-50 irradiated in the crystalline state at 25°C. (in nitrogen) could be further crosslinked by quickheating them to the amorphous state at 150°C.—delayed carbonyl formation does not occur in this case. Delayed crosslinking resulting from the quick-heating of irradiated Marlex-50 gave only about one-half of the crosslinks for the same irradiation as when irradiated in the amorphous state. Hydrogen evolution as a function of irradiation temperature for Marlex-50 is discussed; a satisfactory material balance was obtained in which the radiation yield (G value) for total hydrogen produced nearly equaled the sum of G for crosslinking and G for trans-vinylene formation. Hydrogen yield was found to be nearly constant in the temperature range −170 to +34°C. where crystallinity is also nearly constant, indicating hydrogen production to be nearly independent of temperature. Therefore, the main change in crosslinking yield in the +34 to +150°C. range is considered to be due almost entirely to change in crystallinity. A comparison method for determining relative values of the degree of crosslinking fom the gel measurements is described.

Irradiation effects in plexiglas

Abstract: Samples of methyl methacrylate were irradiated with 2-mev 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

A study of the elastic modulus and extensibility of the crystalline regions in highly oriented polymers

Abstract: The elastic modulus of highly oriented crystalline polymers is discussed in terms of a series model. As has been shown previously, if a polymer has fully extended chain configurations within the crystalline regions, the modulus of this phase may be expected to be high. In this case the macroscopic elastic modulus is limited primarily by the characteristics of the amorphous phase and the degree of crystallinity. Where the fiber identity period (FIP) indicates a contracted chain configuration, the crystalline regions, themselves, may be extensible and their modulus may not be much greater than that of the unoriented amorphous phase. In this case the macroscopic elastic modulus is much less dependent upon orientation and crystallinity. The elastic moduli of eight chemically different polymers have been determined from measurements of their macroscopic moduli and the extensions of their FIP when subjected to small strains. Where the degree of crystallinity could also be determined the modulus of the amorphous phases were also determined from these same measurements. The moduli of some of these systems are discussed in terms of their structure as deduced from birefringence measurements and x-ray diffraction patterns.

Aromatic polyanhydrides, a new class of high melting fiber‐forming polymers

Abstract: Contrary to the aliphatic polyanhydrides prepared by Carothers, polyanhydrides containing aromatic nuclei in the main chain possess high melting points and good hydrolytic stability. A number of different aromatic polyanhydrides were prepared. Their preparation and properties, such as fiber-forming properties, melting points, glass transition temperatures, and crystallinity, are described. An effort has been made to correlate some selected physical properties, such as melting points and crystallizability, with the chemical structure of the particular polyanhydride. The influence of p-phenylene, m-phenylene, carbonyl, ether, thioether groups, etc. on the properties of the polymers is discussed.

Infrared spectra of high polymers. VII. Polyacrylonitrile

Abstract: The infrared spectrum of polyacrylonitrile has been obtained in the extended region of 70 to 3200 cm.−1 Polarized measurements were made on stretched and rolled specimens in the range of 350 to 3200 cm.−1. An analysis of the spectrum has been made on the basis of an atactic chain configuration, and has been shown to be in agreement with the observed data. Detailed assignments are proposed for all of the absorption bands in the spectrum, being aided by previous studies of high polymer spectra and by approximate normal frequency calculations for the nitrile group.

Diffusion‐controlled stress relaxation in polymers. III. Stress relaxation in a swelling polymer

Abstract: An approximate theory of the relaxation of stress in amorphous linear polymers accompanying sorption of a low molecular weight penetrant is worked out on the assumption that the relaxation time of each Maxwellian relaxation mechanism involved is changed in the presence of penetrant by a factor dependent on penetrant concentration. A method is derived from the theory which permits approximate evaluation of the integral diffusion coefficient D of the penetrant in the polymer from stress-relaxation data on swelling systems. The theory is checked on experimental data for the systems polymethyl acrylate-water and polymethyl acrylate-methanol at 40°C., and it is found that, for both systems studied, the values of D computed from mechanical data agree reasonably with those evaluated directly from usual sorption experiments. The theory described presents only a first attempt to the quantitative interpretation of the phenomenon discussed. Further improvement and modification of it is apparently desirable, in view of some drastic approximations incorporated in its mathematical development.

The Flory constants for poly‐4‐vinylpyridine in ethanol

Abstract: Vinylpyridine was polymerized in suspension, using azobis-iso-butyronitrile as initiator. The polymer was fractionated by partial precipitation from methanol solutions by addition of toluene to cloud point in chilled solution and then raising the temperature. Viscosities of four fractions were determined at 25, 50, and 70° in absolute ethanol. Rayleigh ratios and scattering asymmetry were determined for eight fractions; from the corresponding Zimm plots, molecular weights, coil diameters, and virial coefficients were determined. Addition of ammonia was found necessary at low concentrations to suppress ionization due to traces of acid impurities. Addition of water (a nonsolvent) lowers the second virial coefficient. Molecular weights were determined for two fractions by osmotic pressure. In absolute ethanol, the results are summarized by the equation [η] = 2.5 × 10−4M0.68; experimental range 0.102 ⩽ 106M ⩽ 1.85. The second virial coefficient from light scattering was 4.2 ± 0.3 × 10−4, independent of molecular weight; the osmotic values agreed within experimental error. The Flory constant was found to be 2.1 ± 0.3 × 1021. Extrapolation for the θ-point leads to the rough estimate θ ≈ −50°C. Evidence is presented which shows that polyvinylpyridine degrades slowly in solution.