Showing papers in "Journal of Polymer Science Part C: Polymer Symposia in 2007"
TL;DR: In this article, a technique was devised for obtaining rate laws and kinetic parameters which describe the thermal degradation of plastics from TGA data, based on the inter-comparison of experiments which were performed at different linear rates of heating.
Abstract: A technique was devised for obtaining rate laws and kinetic parameters which describe the thermal degradation of plastics from TGA data. The method is based on the inter-comparison of experiments which were performed at different linear rates of heating. By this method it is possible to determine the activation energy of certain professes without knowing the form of the kinetic equation. This technique was applied to fiberglass-reinforced CTL 91-LD phenolic resin, where the rate law - (1/we)(dw/dt) = 1018e−55,000/RT [(w - wf)/w0,]5, nr.−1, was found to apply to a major part of the degradation. The equation was successfully tested by several techniques, including a comparison with constant temperature data that were available in the literature. The activation energy was thought to be correct within 10 kcal.
3,002 citations
TL;DR: In this paper, the authors measured and analyzed the complex dielectric behavior of the α-dispersions for five polymers [i.e., polycarbonate and polyisophthalate esters of bisphenol A, isotactic poly-(methyl methacrylate), poly(methyl acrylate) and a copolymer of phenyl methacellitrile] and found that the usual methods of analysis cannot be used to represent the data.
Abstract: The α-dispersion in many polymer systems is the process to be associated with the glass transition temperature where many physical properties undergo drastic changes. We have measured and analyzed the complex dielectric behavior of the α-dispersions for five polymers [i.e., polycarbonate and polyisophthalate esters of bisphenol A, isotactic poly-(methyl methacrylate), poly(methyl acrylate), and a copolymer of phenyl methacrylate and acrylonitrile] and have found that the usual methods of analysis cannot be used to represent the data. However, it is possible to represent the relaxation process as the sum of two dispersions but there is no evidence to support this contention. An empirical expression is proposed to represent the data. This expression which takes the form of
appears to be a general representation for the three known dispersions, i.e., Debye, circular arc, and skewed semicircle. The complex dielectric constants calculated with the aid of this expression and the parameters for each polymer system which was determined graphically were found to be in excellent agreement with the experimental complex dielectric constants. This method of representation was extended to sixteen α-dispersions reported in the literature always with excellent results.
1,503 citations
TL;DR: In this paper, an equation based on reciprocal mean and force additivity was proposed to calculate the interfacial tension between polymers or between a polymer and an ordinary liquid, which can be used to predict accurately the surface tension and polarity of polymers.
Abstract: We propose an equation, based on “reciprocal” mean and force additivity, for calculating the interfacial tension between polymers or between a polymer and an ordinary liquid:
where γ12 is the interfacial tension; γi the surface tension; γ and γ the dispersion and polar components of γi, respectively. This equation is shown to predict accurately the interfacial tension between polymers or between a polymer and an ordinary liquid. Fowkes' equation or Fowkes' equation with a geometric-mean polar term 2(γiPγ2p)1/2 is not applicable to polarlpolar systems. The interfacial tension arises mainly from disparity in the polarities of the two phases. The above equation can also be used to calculate the surface tension and polarity of polymers or organic solids from contact angle data.
960 citations
646 citations
298 citations
TL;DR: In this paper, the authors derived an equation for calculating the strain-optical coefficient of the polymer from those of the non-crystalline and the crystalline phases, respectively.
Abstract: Assuming that the crystalline polymer consists of the crystalline and the non-crystalline phase, a mechanical model for the crystalline polymer is constructed. We introduced into this model such complicated circumstances as some parts of the crystalline phase will be largely deformed under a stress concentration and other parts not so much. The temperature dependence of complex moduli of the crystalline polymers with various degrees of crystallinity is illustrated by using the model. On the basis of the model, we have derived an equation for calculating the strain-optical coefficient of the crystalline polymer from those of the crystalline and the non-crystalline phase. The equation gives a relation among the rheo-optical quantities, the viscoelastic quantities and the parameters representing the fine structure and the crystallinity of the polymer. It is concluded from this equation that the strain optical coefficients cannot be expressed by such a simple additive relation as usually employed.
248 citations
TL;DR: In this article, the dynamic tensile modulus of oriented specimens of polyethylene (PE), polypropylene (PP), polyoxymethylene, polyoxide (polyethylene oxide), and polytetrahydrofuran were measured in sheet form as a function of direction.
Abstract: Complex moduli of oriented specimens of polyethylene (PE), polypropylene (PP), polyoxymethylene, polyethylene oxide), and polytetrahydrofuran were measured in sheet form as a function of direction. The dynamic tensile modulus (E′) along the stretched direction (0° direction) was found to be lower than that perpendicular to the stretched direction (90° direction) above the temperature of primary dispersion (αa) for all polymers cited above. Below the temperature of an dispersion the E′ value of 0° direction is higher than that of 90° direction as expected from the anisotropy of modulus of the crystal. This fact leads us to the model that the crystalline region (C) and this amorphous region (A) are arranged mainly in series along the stretched direction and at the same time the C region should be more or less continuous along the 90° direction. The actual drawn sample is composed of many microfibrils as proved l y the x-ray small-angle scattering. Those conditions imposed on the model should be satisfied even when many microfibrils are bound together into a fiber. This picture agrees with the structural model of hot-drawn PE presented by Hosemann after its slight modification. Effects of cold drawing on the anisotropy of modulus were also surveyed.
211 citations
TL;DR: In this paper, the lattice moduli of high polymers have been studied in terms of the crystal structures of the polymers, pan icularly the skeleton conformation and the cross-sectional bulkiness of the chain molecule in the crystal.
Abstract: Elastic moduli of the crystalline regions in high polymers have been studied. Oriented specimens were used throughout. Lattice strains were measured by an x-ray technique in the direction of the fiber axis as well as in that perpendicular to the fiber axis. The moduli for both directions were calculated on the basis of the assumption that the stress is homogeneous within a specimen held under a load. Remits obtained for various kinds of polymers were discussed in terms of the crystal structures of the polymers, pan icularly the skeleton conformation and the cross-sectional bulkiness of the chain molecule in the crystal. It was shown that the moduli in the direction of the fiber axis are widely different depending upon the polymer. They vary from 240 × 104 kg./cm.2 for polyethylene to 4.1 × 104 kg./cm.2 for isotactic poly (vinyl tert-butyl ether). In the direction perpendicular to the fiber axis, the moduli were shown to take values within a narrow range of magnitude, 3–9 × 104 kg./cm.2. Some of these moduli were compared with the calculated values reported by several authors. To find experimental support for the assumption of the homogeneous stress, measurements were made by using several oriented specimens of different fine textural structures. Inherent values of the lattice moduli were obtained, regardless of the specimens used, which gives a strong support for the assumption.
205 citations
TL;DR: In this article, a new theory of chain twisting is introduced, which connects the data on the n-paraffins and their polar derivatives (n-ketones, esters, ethers) with the results on polymers: the common feature is the chain reorientation and twisting process.
Abstract: Theoretical models for the ac and γe relaxation effects found in chain-folded polymer crystals (single crystal mats and bulk) are presented and compared with the available dielectric and mechanical loss data for polyethylene and polychlorotrifluoroethylene. Details of morphology and crystal structure that can be varied by crystallization and annealing procedures, e.g., roughness of chain-folded surfaces, number of intercrystalline links and cilia, number of chain-end defects and dislocations, and the existence of the extended-chain phase, are brought into the discussion. The αc process, which consists of two overlapping mechanisms, is a result of motions of chain folds and reorientation (with translation) of chains in the interior. (Chain twisting also occurs for long chains.) The theory connects the data on the n-paraffins and their polar derivatives (n-ketones, esters, ethers) with the results on polymers: the common feature is the chain reorientation and twisting process. A new theory of chain twisting is introduced. The β relaxation is a result of reorientation of chains in a “loose” chain-end induced defect (a vacancy row) in the polymer crystal. When the effect of chain twisting is included, the theory successfully predicts the unusually broad and asymmetric loss curve found in the polymer, and is consistent with the experimental activation energies. The β relaxation arising in the amorphous component of PCTFTC is analyzed, and its upward shift in temperature with increasing crystallinity discussed in terms of the Adam-Gibbs theory of relaxation in the glassy state. The γa amorphous relaxation, and the δ relaxation which is found at cryogenic temperatures, are also discussed.
187 citations
TL;DR: In this article, an overall picture of fiber structure is presented showing how various extreme forms, including continuous crystalline, paracrystalline, and amorphous structures, can be used to define the boundaries of a wide range of intermediate forms which are likely to occur in practice.
Abstract: The “traditional” assumed structures of fibers, such as the fringed micelle and fringed fibril forms, regard the fiber as made up of a mixture of crystalline and noncrystalline regions. This view has been subject to considerable criticism in recent years, but it does, nevertheless, remain the most effective basis for describing many fiber properties. This paper attempts to show how the traditional forms can be modified, for instance by the introduction of chain folding, so that they are entirely compatible with current views on polymer crystallization. An overall picture of fiber structure is presented showing how various extreme forms–including continuous crystalline, paracrystalline, and amorphous structures as well as the two-component forms–can be used to define the boundaries of a wide range of intermediate forms which are likely to occur in practice. The major decision in interpreting fiber properties is the choice of which extreme model–necessarily extreme in order to be susceptible to definition and analysis–is the most useful when studying a particular aspect of the behavior of a particular fiber. The mechanical properties, of wool, plant fibers, rayon, and synthetic fibers are discussed.
135 citations
TL;DR: The force required to stretch a polymer chain by 1% (f value) was calculated from experimental values of elastic moduli E1 in the direction of molecular axis and the cross-sectional area of the molecule of 25 well known polymers as discussed by the authors.
Abstract: The force required to stretch a polymer chain by 1% (f value) was calculated from experimental values of elastic moduli E1 in the direction of molecular axis and the cross-sectional area of the molecule of 25 well known polymers. The f value is mainly dependent on the conformation of a molecule and almost independent of side groups. The f values of polymers of various types of conformation may be summarized as follows: T type, 4−5 × 10−5 dyne; TGTG type, 1.5 × 10−5 dyne; TG(3/1) type, 1 × 10−5 dyne; T′G′ (7/2) type, 0.58 × 10−5 dyne; T′G′ (4/1) type, 0.36 × 10−5 dyne; TTGG type, 0.29 × 10−5 dyne; where T, G, and G mean trans, gauche and minus gauche, respectively, and the numbers in the parentheses denote helical structures. The reason for an anomalous apparent E1 value of nylon 6 (α-form) previously reported was elucidated; it was confirmed that E1 exhibits a value expected for a polymer with a nearly extended zigzag conformation.
TL;DR: In this paper, the authors discuss the geometry of failure surfaces and means for determining them on isotropic bodies, and the scanty information on failure surfaces for polymeric materials is reviewed.
Abstract: Criteria for failure in multiaxial states of stress have associated with them geometrical representations as surfaces in principal stress space. Any combination of stresses is safe if the corresponding point in principal stress space falls within the failure surface. The material will fail if the point lies on or outside of the surface. The geometry of some simple surfaces and means for determining them on isotropic bodies are discussed, and the scanty information on failure surfaces for polymeric materials is reviewed.
TL;DR: In this article, the elastic constants (Cij) of polyethylene (PE) were derived from Born's dynamical theory of long wave method for a model of interatomic interactions representing inter- and intramolecular force fields.
Abstract: To calculate the elastic constants, (Cij), of the polyethylene (PE), Born's dynamical theory of long wave method has been used for a model of interatomic interactions representing inter- and intramolecular force fields. Among various types of interaction potentials between nonbonded atoms, two sets of H-H, C-H, and C-C interaction potentials have been adopted which give the best results in reasonable agreement with the data of the lattice parameters and the angle between plane of the zigzag chain and crystallographic axis in the PE lattice. It has been also verified that the lattice energy of PE can be calculated successfully by using the present, potentials. In order to calculate the elastic constant, H-H and C-H interactions with close distances have been taken into account for the intermolocular force fields. On the other hand the Urey-Bradley force field has been used for intramolecular interactions. An expression is obtained which relates Horn's force constants to the macroscopic elastic constants in the orthorhombic system. The calculation has been also made on Cij in a rigid model of molecular chain, but it is found that the increments of elastic constants due to the rigid model are at most a few per cent. The elastic moduli along the a, b, and r, axes and also the normal of the (110) plane have been derived from Cij and compared with values experimentally determined by x-ray diffractometry. Furthermore, the space averages for compressional, shear, and Young's moduli of PE polycrystals oriented in all directions, and the T3 low-temperature dependence of heat capacity are discussed.
TL;DR: In this article, the effects of low concentrations of flame retardants on pyrolysis and combustion of α-cellulose were investigated, and it was shown that flame retardant treatment significantly reduced the intensity of combustion and increased the yield of chars.
Abstract: In the combustion of wood, the α-cellulose fraction contributes most of the flaming; the lignin fraction supports the major part of the glowing. In the present study, thermogravimetric and differential thermal analyses were conducted to determine the affect of low concentrations of flame retardants on the kinetics of pyrolysis and phenomena of combustion of α-cellulose. The flame retardants investigated—sodium tetraborate, aluminum chloride, potassium bicarbonate, and ammonium phosphate—were found to lower the active pyrolysis temperatures and increase the yield of chars. The kinetic data obtained by then no gravimetric analysis of the treated -cellulose in vacuum suggest that at least two mechanisms :ire involved. The early stage is controlled by pseudo-zero-order and the late stage is of pseudo-first-order. Sodium tetraborate and aluminum chloride caused little reduction in activation energies. Ammonium phosphate decreased the activation energy mostly in the early stage. Potassium bicarbonate lowered activation energies of both stages. Further thermal analysis in helium and oxygen showed that flaming combustion of α-cellulose was substantially reduced by treatment, and its exothermic peak occurred near the end of pyrolytic volatilization. The heat of pyroiysis was reduced significantly by treatment. The heat of combustion is distributed to a wider temperature range, and the maximum intensity of flaming was much reduced by treatment.
TL;DR: In this article, an equation relating the glass transition temperature (TG) of copolymers to their molecular structure in terms of the mole fractions of the various diad sequences of monomer units combined in the copolymer chain, and temperature parameters (Tij) characteristic of each type of sequence, ij.
Abstract: An equation is proposed relating the glass transition temperature (TG) of copolymers to their molecular structure in terms of the mole fractions of the various diad sequences of monomer units combined in the copolymer chain, and temperature parameters (Tij) characteristic of each type of sequence, ij. The equation, an extension of the Gibbs and DiMarzio copolymer TG theory, accounts for the effect on TG of the different types of bonds between repeating units in different diad sequences, and is in its general form: . In a binary copolymer of structure [(a) × (b)y] n, corresponding to the ij sequences -aa-, -ba-, -ab-, and -bb-. The term n'ij is the mole fraction of ij sequences, nij weighted according to the number of rotatable bonds per sequence, αij, and . The variation in the distribution of sequences with overall composition is obtained from the copolymerization reactivity ratios. The theory, which quantitatively describes the sometimes observed maximum or minimum in TG - composition plots, gives good agreement with published data for 11 copolymer systems. Application of the theory to give homopolymer TG's by extrapolation is demonstrated. Inter-relations are found with other published theories of copolymer TG.
TL;DR: In this article, diffusion and solubility coefficients are presented for He, Ne, Ar, and N2 in three ethylene-propylene copolymers, two styrene-butadiene copolymerg and a cis-poly-butadene for five temperature levels in the range 0-50°C.
Abstract: Diffusion and solubility coefficients are presented for He, Ne, Ar, and N2 in three ethylene-propylene copolymers, two styrene-butadiene copolymerg and a cis-poly-butadiene for five temperature levels in the range 0–50°C. The data were obtained by using a slightly modified Dow Gas Transmission Cell and analyzed by a new modified time-lag technique which properly accounts for the increase in pressure on the downstream side of the cell. Activation energies were calculated for the twenty-four diffusion systems and correlated with the polymer intermolecular forces and the gas molecule sizes by using ii cell theory for amorphous polymers which employs a potential energy depth parameter, ϵ*, a range parameter, p*, the number of degrees of freedom per structural unit (center), 3Cm, and the number of centers per unit cell, n. The first three parameters were evaluated from thermodynamic data, while n was evaluated from the diffusion data. It is believed that n is an indication of the number of backbone carbon atoms active in polymer segmental motion. The values obtained here (5–9) agree well with existing values estimated from polymer viscous flow data. A correlation for the solubility data is shown and a linear free energy relationship is discussed.
TL;DR: The effect of increasing the substitution of water-soluble hydroxyethyl cellulose and hydroxypropyl cellulose is to decrease their affinities for water as discussed by the authors, consistent with data given on the cloud point, salt tolerance, surface tension of aqueous solutions, and solubility in organic solvents, all as functions of MS.
Abstract: The effect of increasing the substitution of water-soluble hydroxyethyl cellulose (HEC) and hydroxypropyl cellulose (HPC) is to decrease their affinities for water. This is consistent with data given on the cloud point, salt tolerance, surface tension of aqueous solutions, and solubility in organic solvents, all as functions of MS.
Ionizable substances have a great influence on temperature-solubility behavior of the hydroxyalkyl celluloses. If the ions are present as inorganic salts in solution, they cause hydration of the polymer to decrease with some loss in solubility. In the case of HPC, ions derived from substituent groups, present in small amounts, improve hot water solubility and impart unusual viscosity-temperature behavior.
Mechanical properties of HEC film and thermoplasticity of HPC are functions of the extent of substitution rather than the hydrophilicity.
TL;DR: In this paper, it was shown that the growth rate of spherulites and the overall crystallization rates at any fixed supercooling essentially depend upon molecular weight, and that the minimum in the crystallization rate which occurs at molecular weight 4000 is a consequence of transition from extended chain crystallization to folded-chain crystallization.
Abstract: The temperature dependence of the isothermal growth rate of spherulites and overall crystallization kinetics of different fractions of poly (ethylene oxide) over the range of molecular weight from 300 to 20,000 were studied by calorimetry, dilatometry, and polarized light microscopy, in order to establish the dependence of the kinetic parameters upon molecular weight. The morphology of crystallites was studied by small-angle x-ray scattering. In the course of this study it has been established that the growth rates of spherulites and the overall crystallization rates at any fixed supercooling essentially depend upon molecular weight. The minimum in the crystallization rate which occurs at molecular weight 4000 is a consequence of transition from extended-chain crystallization to folded-chain crystallization. Small-angle x-ray scattering study of the morphological features confirmed this conclusion. This minimum depends very strongly on the degree of supercooling, increasing rather sharply at small supercooling. The temperature and molecular weight dependence of the growth rates of spherulites and the overall crystallization rates has been analyzed by means of the theoretical expression given by Hoffman and Lauritzen. The product of the lateral and basal surface free energies of the crystallites σσe increases with molecular weight and reaches a limiting value at molecular weight 6000. Such behavior is in agreement with morphological transformations.
TL;DR: Star-shaped macromolecules have been obtained by anionic block copolymerization of a monofunctional monomer and a divinyl compound with cumylpotassium or butyllithium as initiator as discussed by the authors.
Abstract: Star-shaped macromolecules have been obtained by anionic block copolymerization of a monofunctional monomer and a divinyl compound with cumylpotassium or butyllithium as initiator The polymer molecule is a crosslinked nodulus, to which n linear, solvated chains are attached The shielding effect of these chains is such that more than 40% difunctional monomer is necessary to induce gel formation in the reaction medium Star-shaped polystyrenes, polyisoprenes, polyvinylpyridines and poly(methyl methacrylate) were obtained by this method, the crosslinking agent being divinylbenzene or glycol dimethacrylate The individual branches of the star molecules may be considered identical, but a polydispersity arises from the fact that within a sample the number of branches of the star molecules fluctuates appreciably Fractionation remains possible, though it is not very easy to get monodispersed samples The molecular dimensions of the star-shaped polymers, as determined from their intrinsic viscosities or from their radii of gyration, are smaller than those of the corresponding linear polymers, and this may be considered a proof of their highly branched structure
TL;DR: A general treatment of time-temperature superposition in thermorheologically complex materials is developed and a model is proposed from which, for a two-phase material, the amount of shift can be calculated which is necessary to bring a point on a mechanical response curve obtained at a given temperature and time or frequency into superposition at another temperature as discussed by the authors.
Abstract: Two-phase polymeric materials such as polymer blends, block copolymers, and graft copolymers, are thermorheologically complex. Mechanical response curves obtained on such materials at different temperatures cannot, in principle, be brought into superposition by a simple shift along the logarithmic time or frequency axis. The shift factors become functions of time or frequency in addition to temperature.
A general treatment of time-temperature superposition in thermorheologically complex materials is developed and a model is proposed from which, for a two-phase material, the amount of shift can be calculated which is necessary to bring a point on a mechanical response curve obtained at a given temperature and time or frequency into superposition at another temperature. The mechanical responses of the constituent homopolymers and their temperature functions must be known.
TL;DR: In this article, the diffusion of water through slightly volatile hydrocarbon liquids can be described by dm/dt = -DA(dc/dx) where dm is the rate of mass transport, A the area, dc/dx the concentration gradient, and D the diffusion coefficient.
Abstract: Diffusion of water through slightly volatile hydrocarbon liquids can be described by dm/dt = –DA(dc/dx) where dm/dt is the rate of mass transport, A the area, dc/dx the concentration gradient, and D the diffusion coefficient. For dilute systems, D can be determined from an experimental evaluation of dm/dt, A, and dc/dx. In the experimental arrangement used, water diffuses through a layer of hydrocarbon lying fiat on a layer of water in a small beaker which is attached to a recording microbalance. The system is closed and maintained anhydrous with MgClO4. When steady-state diffusion is attained, dm/dt is measured directly by the microbalance. Water diffuses from maximum concentration (water-hydrocarbon interface) to zero concentration (hydrocarbon-anhydrous air interface). Thus, the gradient dc/dx becomes –s/l where s is the solubility of water in the hydrocarbon, and l is the layer thickness. Therefore D = (dm/dt)l/(sA). Diffusion coefficients have been determined for water diffusing through n-hexadecane and 2, 6, 10, 15, 19, 23-hexamethyl tetracusane at five temperatures from 25–45°C. Results give a good fit in an Arrhenius plot. Diffusion activation energies are calculated as well as entropies of activation based on the Eyring absolute rate theory. Results are compared with data for the diffusion of water through polyethylene and polypropylene.
TL;DR: In this paper, the authors studied the solution and diffusion of He, Ne, Ar, Kr, Xe, H2, N2, O2, and n-C4H10 elastomers at temperatures between 0 and −37°C for all penetrants, and down to −78°C. for some.
Abstract: Solution and diffusion of He, Ne, Ar, Kr, Xe, H2, N2, O2, and n-C4H10 have been studied in filled dimethylpolysiloxane elastomers, at temperatures between 0 and −37°C. for all penetrants, and down to −78°C. for some. Crystallization of the rubber, commencing at about −50°C. resulted in large decreases in permeability and diffusion coefficients and smaller decreases in solubility. Diffusion coefficients were measured in three different ways and solubility coefficients in two. Above the crystallization temperature, the results by all methods agreed for a lightly filled rubber but for a rubber with a high filler content especially when partially crystalline (i.e., below −50°C.) differences were observed between solubility coefficients measured directly and those derived from permeation and diffusion. These differences arc related to the heterogeneity of the medium and to consequent differences in diffusion coefficients obtained by the time-lag and steady-state methods. Diffusion and solubility coefficients both show relationships with other physical properties. Permeabilities of the silicone rubbers to gases are high, and selectivity can be good as between appropriate pairs of molecules.
TL;DR: In this paper, a combination of structural and physical properties measurements: wide and small angle x-ray diffraction, broad and narrow line nuclear magnetic resonance, sonic modulus, density, shrinkage, and tensile properties.
Abstract: When heated to high temperatures under zero tension, some of the molecules in oriented nylon 66 filters change from the elongated to the folded conformation, with no change in crystal orientation. This transformation is shown by a combination of structural and physical property measurements: wide and small angle x-ray diffraction, broad and narrow line nuclear magnetic resonance, sonic modulus, density, shrinkage, and tensile properties. A fortyfold increase of the intensity of the discrete small angle x-ray diffraction is obtained for treatments between 160-and 255°C. as well as an increase of the length of the long period and a change from a smeared four-point to a sharp two-point diagram. Wide angle x-ray measurements show little change in crystallite orientation for treatments up to 250°C. even though much shrinkage occurs. Disruption of some type is observed by sonic measurements, as would be expected if new folds occurred. An increase of density and x-ray crystallinity confirms that heating causes much additional crystallization. The high temperature NMR spectra for these more crystalline yarns show a much larger proportion of fluidlike segments. Shrinkage of the yarns during the heating appears to be governed by the number of folds which are introduced. Tensile strength is reduced by this introduction of folded chains.
TL;DR: In this article, an investigation of the kinetics of the emulsion polymerization of vinyl chloride has been performed, and the effect on the rate of reaction of such variables as concentration of initiator (K2S2O8), amount and type of emulsifier and number of latex particles has been investigated at 50°C.
Abstract: An investigation of the kinetics of the emulsion polymerization of vinyl chloride has been performed. The effect on the rate of reaction of such variables as concentration of initiator (K2S2O8), amount and type of emulsifier and number of latex particles has been investigated at 50°C. The order of reaction with respect to initiator was found to be 0.5. The rate of reaction was found to increase with increasing conversion. The number of latex particles was found to be constant during the polymerization, between 10 and 90% conversion, and also found to be independent of the concentration of initiator. The order of reaction with respect to the number of particles was found to increase from 0.05 to 0.15 in the range investigated (Nw = 1016-1019 per liter H2O). The order decreases slightly with increasing conversion. A mechanism involving a rapid desorption and reabsorption of radicals in the latex particles is proposed. A marked increase in rate was observed at about 70–80% conversion. A closer investigation of this phenomenon was performed by a continuous addition of vinyl chloride at a pressure below the saturation pressure of vinyl chloride corresponding to the reaction temperature. It appeared that under such conditions reaction rates of about twice those of the ordinary runs might be obtained. No change in the number of particles was observed, either during the polymerization or compared to the ordinary run at the same concentrations of emulsifier and initiator. The effect of the degree of reduction in the pressure of vinyl chloride was also investigated. It was found that the rate of reaction passed through a maximum at a pressure of about 6.75 atm, as compared to 7.75 atm in an ordinary run (Saturation pressure of vinyl chloride at 50°C).
TL;DR: In this article, the wetting properties of wood polysaccharides were characterized by Zisman's empirical parameter, the critical surface tension of wetting, γc, and the effect of moisture on contact angle measurements was discussed.
Abstract: The wetting properties of wood polysaccharides were characterized by Zisman's empirical parameter, the critical surface tension of wetting, γc. Cellulose was tested in the form of cellulose films regenerated from viscose and cellulose acetate. It was found that the source of cellulose (cotton, wood and hydrolyzed cellulose), the method of film preparation (single-bath, two-bath, dry-cast, orientation), and consequently the physical state of the cellulose surface, influenced the wettability of the samples. Contact angles were also measured on hemicellulose films derived from hardwoods and softwoods. The critical surface tension γc ranged from 35.5 to 49.0 erg cm−2 for cellulose and from 33 to 36.5 erg cm−2 for hemicellulose films. The hemicellulose samples showed the smallest hysteresis effects which may be related to its energetically more uniform surface or lower porosity. The effect of moisture on contact angle measurements is discussed. Finally, the wetting of cellulose is evaluated in terms of recent theories relating surface energies and intermolecular forces.
TL;DR: In this paper, it was shown that in the homogeneous catalytic system (C5H5)2TiCl2 + Al(CH3)2Cl the catalytic activity is due to the presence of free ions.
Abstract: It was found that in the homogeneous catalytic system (C5H5)2TiCl2 + Al(CH3)2Cl the catalytic activity is due to the presence of free ions, presumably (C5H5)TiCH3 formed in the equilibrium: (C5H5)2TiCH3Cl. AlCH3Cl2 ⇄ (C5H5)2Ti+CH3 + Al(CH3) Cl3 - Further evidence for the suggested mechanism has been found. By means of electrodialysis the formation of positive ions containing Ti was shown. Catalytic activity appears only in the presense of the latter. The increased cataivtiy activity in comparatively polar solvents (CH2Cl2, C2H4Cl2) is connected with the increased number of the ions. The linear dependence of log k (k is the rate constant of the reaction of free ion with an olefin) with 1/D (D is the dielectric constant) was found in five different solvents and their mixtures.
TL;DR: Princen's modification of Vonnegut's rotating drop procedure for measuring inter-facial tension between low viscosity liquids has been adapted for use with pairs of liquid polymers with viscosities up to 5000 poise as mentioned in this paper.
Abstract: Princen's modification of Vonnegut's rotating drop procedure for measuring inter-facial tension between low viscosity liquids has been adapted for use with pairs of liquid polymers with viscosities up to 5000 poise. Extrapolation to infinite time of results obtained with 10–20 min of rotation provided steady state data as indicated by its corre-spondence with results reported from other techniques. An adaptation of this procedure was also found useful for determining surface tension values of molten polymers at temperatures up to 290°C. Reductions of 60–70% in interfacial tension between viscous samples of a polydimethylsiloxane and a copolyether were accomplished by addition of 1–2% of amphi-pathic or polar compounds such as polydimethylsiloxane-polyoxyethylene copolymers and carboxyl-substituted polydimethylsiloxanes. A linear reduction in interfacial tension with a logarithmic increase of additive concentration was noted.
TL;DR: In this article, a study was carried out on block polymers of the A-B-A type, the thermoplastic elastomers, where A represents polystyrene and B polybutadiene or polyisoprene.
Abstract: A study has been carried out on block polymers of the A-B-A type, the thermoplastic elastomers, where A represents polystyrene and B polybutadiene or polyisoprene. The objective was to relate the mechanical properties of these elastomers to their molecular architecture. For this purpose a series of styrene-butadiene and styrene-isoprene block polymers were synthesized by means of organolithium initiators, in which the block lengths of the polystyrene and polydiene were varied. It was found that the stress-strain properties of styrene-butadiene polymers are mainly dependent on the polystyrene content, regardless of the block sizes, and that the center, elastic block does not appear to behave as the “molecular weight between crosslinks” of these networks. However, the monodispersity of the chain length of these elastic blocks does appear to contribute substantially to higher tensile strengths. The polystyrene appears to be aggregated in small domains, of the order of several hundred angstrom units, and these undergo an irreversible deformation under stress, which is, however, completely recoverable above the Tg of the polystyrene. At high polystyrene contents (∼40%) these elastomers exhibit an irreversible yield point at very low elongations, and this is ascribed to the presence of a continuous phase of connected polystyrene domains, which can be re-formed by raising the temperature above the Tg of the polystyrene. Although the stress-strain curves are not affected by the thermal history of the sample, the tensile strength, especially at high styrene contents, is strongly dependent on “annealing” of any frozen stresses in the polystyrene phase. The useful range of block molecular weights is about 10,000–20,000 for polystyrene and 40,000–80,000, respectively, for polybutadiene. The lower limit is probably governed by the minimum polystyrene chain length required to insure the formation of a heterogeneous phase; while the upper limit is set by the high viscosity of both blocks, which might seriously hamper domain formation.