Wiley
0022-3832
1542-6238
Cơ quản chủ quản: N/A
Lĩnh vực:
Phân tích ảnh hưởng
Thông tin về tạp chí
Các bài báo tiêu biểu
Vapor pressures of polymer solutions. II. Vapor pressure of the poly(vinyl alcohol)‐water system Abstract Vapor pressures were measured for the system, poly(vinyl alcohol)‐water at 30°C. with the apparatus reported in the preceding paper. Fractionated samples were used in the form of thin films, carefully dried under high vacuum at room temperature. The degree of crystallinity of these samples was about 0.2, and the degrees of polymerization were 1530 and 335. The relation between the activity of the water and the composition of the gel phase is discussed. The interaction parameter χ12 is evaluated assuming that the crystalline regions are not affected by the water and correspond to the crosslinks in an amorphous network polymer; also that the chain length between two crosslinks is not changed with the composition of the system. χ12 increases with increasing polymer concentration. This behavior is discussed with the aid of heat of dilution data from the literature. The anomalous concentration dependence of the entropy and energy contributions to χ12 may be explained as resulting from the mutual orientation of water molecules and the hydroxyl groups along the polymer chain.
Tập 35 Số 129 - Trang 497-505 - 1959
Polymerization inhibition by aromatic compounds Abstract A quantiative study of chain transfer and inhibition reactions makes it possible to determine the ratios kx /K p where K p and k x are the rate coefficients for propagation and for chain tranfer, respectively. Since the absolute values of the constants Kp are known for a number of monomers it is possible to determine the absolute values of the constants kx . We have investigated the inhibiting action of some types of aromatic compounds in the polymerization of vinyl acetate, methyl acrylate, acrylonitrile, and methyl methacrylate. In the polymerization of vinyl acetate the inhibiting effect of the aromatic hydrocarbons increases in the order: toluene, diphenyl, naphthalene, phenanthrene, anthracene. The logarithm of kx is linearly related to the logarithm of the methyl affinity. The inhibiting effect increases on incorporating substituents, both electrondonating and electron‐accepting, in the benzene ring. There is no relation, however, between the value of kx and Hammet's σ‐constant. An outstanding position is assumed by nitrobenzene, for which kx is higher by 3–4 orders of magnitude than that of the other substituted benzenes. The incorporation of substitutents in the meta and para positions of the benzene ring follows the Hammet rule, the electron‐donating substituents causing a decrease in the kx values. Similar relations are observed in the polymerization of methyl acrylate, but the absolute values of kx are lower by 3–4 orders of magnitude than in the polymerization of vinyl acetate. Because of this, under the experimental conditions the interaction of the polymethyl acrylate radical with molecules of the transier agent was not revealed (kx < 0.21 1./mole‐sec. at 50°) in the case of many of the substances investigated, for instance of all mono‐substituted benzenes except nitrobenzene. A comparison of the kx values for polyvinyl acetate, polymethyl acrylate, polymethyl methacrylate, and acrylonitrile radicals permits a number of conclusions to be made concerning the influence of the polar factor on radical reactions. The data obtained lead to definite conclusions as to the inhibiting mechanism of aromatic compounds. The primary act is the addition of the polymer radical to the aromatic ring with the formation of a nonreactive radical. In the case of nitro compounds, the polymer radical reacts with the nitro group, probably by transferring to it a β‐hydrogen atom. It has been found that in the polymerization of vinyl acetate in the presence of the inhibitors in question each molecule of the latter terminates two kinetic chains; regeneration of the chains does not take place, and the polymer molecules form as the result of disproportionation between the polymer radical and the radical formed during interaction of the former with the inhibitor molecule.
Tập 52 Số 157 - Trang 31-38 - 1961
Differential thermal analysis of high polymers. II. Effects of diluents on melting behavior of polyethylenes Abstract Studies of the nature and magnitude of the interaction between a polymer and a diluent are of both theoretical and practical importance. The effects of several liquid and solid diluents on the melting behavior of both high‐ and low‐density polyethylene have been studied by differential thermal analysis. The depression of melting point was related by a thermodynamic equation to the type and amount of the diluent. The thermodynamically derived true heat of fusion of polyethylene agrees well with the currently accepted value.
Tập 50 Số 153 - Trang 79-86 - 1961
Determination of molecular weight of polyvinylpyrrolidone Abstract The molecular weight of selected polyvinylpyrrolidone samples was determined by light scattering and by osmotic pressure in methanol. The corresponding limiting viscosity numbers were also determined, as well as the limiting viscosity number of the same samples in water. The data relating to the methanolic system conform with theory and the values for K and α in [η] = KM α were determined. The data relating to aqueous solutions do not show such conformity but an unexplained dependence on the degree of homogeneity of the samples. Nevertheless some empirical constants were deduced which may aid in industrial practice in which aqueous viscosity measurements are usual.
Tập 10 Số 4 - Trang 371-378 - 1953
The lactam‐amino acid equilibria for ethylpyrrolidone and polyvinylpyrrolidone Abstract The lactam‐amino acid equilibria of N ‐ethylpyrrolidone and poly‐N ‐vinylpyrrolidone were studied in dilute aqueous solutions and in n ‐butanol at 100°C. and compared with earlier investigations of similar systems. It was found that with in the intermediate p H range the lactam is the predominant form. Below and above certain critical acid and alkaline p H values increasing amounts of amino acid will be formed. It has been shown that these critical p H values are closely related to p K1 and p K2 of the corresponding amino acid. The polymeric lactam PVP is more resistant against hydrolysis than the low molecular lactams. This effect is due to the polyampholyte character of the polymeric amino acid formed in the course of the hydrolysis reaction.
Tập 12 Số 1 - Trang 565-575 - 1954
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.
Tập 28 Số 117 - Trang 365-376 - 1958
Studies on the validity of the Einstein viscosity law and Stokes' law of sedimentation Abstract Ultracentrifugal studies on polystyrene latex particles (PSL) in solutions of different densities prepared either from mixtures of H2 O and D2 O or from various concentrations of sucrose in water yielded a value, by interpolation, of 1.0520 for the density of solution in which the particles neither sediment nor float. Considerations of these results plus the nature of the particles lead to the conclusion that the partial specific volume of the polystyrene latex particles is (1/1.0520) cc./g., a value in agreement with the bulk specific volume of solid polystyrene. Evidence is presented for PSL to support the view that the effective hydrodynamic volume is equal to the partial specific volume, so that volume fractions can be determined from the partial specific volume and the dry weight concentration. Measurements of the viscosity of suspensions of polystyrene latex particles over a broad concentration range showed that the intrinsic viscosity was 2.5, in confirmation of the theory of Einstein. At concentrations above 2% by volume a square term in concentration, with coefficient about 10, and also a cubic term are needed to satisfy the data. From the partial specific volume of the latex particles and the value of the sedimentation coefficient extrapolated to infinite dilution, a value of 2640 ± 12 A. was calculated for the diameter of the particles from Stokes' law. This value is in excellent agreement with values obtained by electron microscopy, light scattering, and low angle x‐ray scattering. This agreement amounts to a satisfactory test of Stokes' law for particles not much larger than some of the viruses. Studies of the dependence of sedimentation coefficient on concentration indicate that existing theories are not completely satisfactory and that the influence of backward flow of liquid during the sedimentation of the solute particles is appreciable.
Tập 16 Số 81 - Trang 19-30 - 1955
Polymethyl methacrylate: Dilute solution properties by viscosity and light scattering Abstract A polymethyl methacrylate polymer, prepared by the emulsion technique, was fractionated three times to obtain essentially homogeneous fractions. The intrinsic viscosities and weight average molecular weights were determined in an ideal solvent at 23°C. and in nonideal solvents at 25°C. The constants K and a in the conventional modified equation [η] = KM a θ = KM 1/2 . Light scattering measurements giving root‐mean‐square distance between ends of a polymer chain were carried out. It was shown that these results support both Kuhn's relation (r̄ 2 )1/2 ≈︁ M 0.50 and Flory's relation (r̄ 2 )3/2 = M [η]/2.1 × 1021 in an ideal solvent. In a nonideal solvent only Flory's relation was found to be in agreement with the experimental results. The values of volume expansion factor α3 ratios A 2 M r̄ 2 )3/2 and A 2 M w M 1/2 in an ideal solvent showed that the polymer molecules were expanded beyond their random flight dimensions in a nonideal solvent.
Tập 17 Số 85 - Trang 391-401 - 1955