Showing papers in "Journal of Macromolecular Science, Part B in 1969"
TL;DR: The physical cross-linking effected by secondary valencies is associated with a segregation of the hard segments, whereby statistically defined systems of hydrogen bridges are formed within the segregation areas.
Abstract: The elastomers investigated are cross-linked partly by primary and partly by secondary valencies, i.e., by allophanate, biuret, and cyanurate bonds, on the one hand, and by hydrogen bridges and other intermoiecular interactions, on the other. The so-called physical cross-linking effected by secondary valencies is associated with a segregation of the hard segments, whereby statistically defined systems of hydrogen bridges are formed within the segregation areas. These systems lead to quasiperiodical, paracrystalline arrangements of the hard segments within the segregation areas. Under certain conditions true crystallization of the hard segments can be observed.
184 citations
TL;DR: In this paper, a model for polymer crystallization under stress was proposed and X-ray diffraction patterns recorded while the samples crystallized under stress, at the appropriate elevated temperature, conclusively demonstrated the two-stage nature of the crystallization.
Abstract: A previous paper proposed a model for polymer crystallization under stress [1]. This paper suggested that there could be distinctive crystals which formed under stress at unusually high temperatures to act later as nuclei for the bulk of the crystals. The present paper details definitive evidence for these nucleating crystals. Electron microscope observations are fully consistent with the expected two-phase structure for crystallization under stress, although they are not conclusive. However, X-ray diffraction patterns recorded while the samples crystallized under stress, at the appropriate elevated temperature, conclusively demonstrated the two-stage nature of the crystallization. First, a small number of crystals (type I) form which are highly c-axis oriented, followed by a second group of crystals (type II) having a more complex stress dependence of texture patterns. This is in complete agreement with the model [1] that c-axis-oriented fibers induce transversely growing lamellar crystals. Type...
119 citations
TL;DR: In this article, the authors measured the equilibrium sorption, permeation, and sorption kinetic measurements for water in polydimethylsiloxane rubbers containing various amounts of either sodium chloride or silica filler, and interpreted the results in terms of a model in which a fraction of the water sorbed is immobilized by the filler or by the formation of salt solution.
Abstract: Equilibrium sorption, permeation, and sorption kinetic measurements have been made for water in polydimethylsiloxane rubbers containing various amounts of either sodium chloride or silica filler. In general the addition of filler leads to an increase in the uptake of water by the rubber. On the other hand, the permeability P which is independent of the relative humidity is not affected to the same extent suggesting that the water sorbed by the fillers does riot contribute significantly to the steady-state flux. For the salt-filled polymers the diffusion coefficient D is initially constant and then decreases with the concentration C of sorbed water. Compared with the unfilled rubbers the decrease in D can be orders of magnitude larger. The D vs. C curves for the silica-filled samples exhibit maxima. The results are interpreted in terms of a model in which a fraction of the water sorbed is immobilized by the filler or by the formation of pockets of salt solution.
87 citations
TL;DR: The relationship between crystallization conditions and the formation of a given crystalline phase is discussed in this paper, where it is suggested that the equilibrium crystal form of the polymer is the γ-form rather than the α-form which is ordinarily observed.
Abstract: The conditions under which a given form of any of the three distinct polymorphic crystalline phases of isotactic polypropylene can be obtained have been investigated. The relationship between crystallization conditions and the formation of a given crystalline phase is discussed. Evidence is cited in support of the hypothesis that the β-form of isotactic polypropylene can be produced only when appropriate nucleating materials are present. It is shown that under particular high-pressure crystallization conditions a triclinic γ-phase can be produced that does, not convert to the monoclinic α-phase either by action of heat or mechanical stress. Based on considerations of stability, density, and structure, it is suggested that the equilibrium crystal form of the polymer is the γ-form rather than the α-form which is ordinarily observed.
80 citations
TL;DR: In this article, the viscoelastic relaxation process in polyethylene has been studied over a wide range of frequencies and measurements were made on isotropic and oriented specimens of both low- and high-density polynomials.
Abstract: The viscoelastic relaxation processes in polyethylene have been studied over a wide range of frequencies. Measurements were made on isotropic and oriented specimens of both low- and high-density po...
63 citations
TL;DR: Linear high polymer heat capacities by adding contributions from chain segments, deriving table of heat capacity contributions of polymer constituents were derived in this article, where the contributions were extracted from the chain segments.
Abstract: Linear high polymer heat capacities by adding contributions from chain segments, deriving table of heat capacity contributions of polymer constituents
59 citations
TL;DR: In this article, the diffusion constants for water vapor in poly (vinyl chloride) and poly(oxymethylene) have been determined by the time-lag method and the sorption isotherms have been measured by direct weighing.
Abstract: The diffusion constants for water vapor in poly (vinyl chloride) and poly(oxymethylene) have been determined by the time-lag method. In addition the sorption isotherms have been measured by direct weighing. The values of the solubility coefficient obtained gravimetrically have been compared with those calculated from the quotient of the permeability and diffusion constants obtained from the time lags. Quite different patterns of behavior were exhibited by the two polymers. In the case of poly(oxvmethylene) the two sets of values of the solubility coefficients were quite similar and fitted a normal Brunauer—Emmett-Teller (BET) type-III sorption isotherm. With poly(vinyl chloride), however, the solubilities calculated from P/D obeyed Henry's law and were considerably less than those obtained by direct weighing (except at low activities) which again were of the BET type III. These results were compared to those found with other polymers and have been interpreted in terms of the different degrees of ...
54 citations
TL;DR: In this article, an effective temperature is defined, defined as the point at which the glass would have an equilibrium free volume equal to the total free volume of the nonequilibrium glass at temperature T. The treatment assumes that molecular flow is permitted when the free volume increase, resulting from the dilatational component of the applied stress, is sufficient to bring the overall free volume to that characteristic of the polymer liquid.
Abstract: Rigid, glassy polymers show a diversity of tensile behavior-ranging from apparently brittle to ductile. To delineate some of the factors that control the toughness or impact resistance of these polymers, the yielding behavior of poly (methyl methacrylate) (PMMA) was studied. Results of other workers have shown that the cold flow exhibited by many glassy polymers can be explained qualitatively by a free-volume model. The treatment assumes that molecular flow is permitted when the free volume increase, resulting from the dilatational component of the applied stress, is sufficient to bring the total free volume to that characteristic of the polymer liquid. The present study refines this approach by introducing an “effective temperature,” defined as that hypothetical temperature at which the glass would have an equilibrium free volume equal to the total free volume of the nonequilibrium glass at temperature T. Equations are derived which more satisfactorily describe the temperature and strain-rate dependences...
48 citations
47 citations
TL;DR: In this article, the aggregate model for mechanical elastic anisotropy of oriented polymers is extended to a viscoelastic polymer in which one shear modulus is complex.
Abstract: The aggregate model for mechanical elastic anisotropy of oriented polymers is extended to a viscoelastic polymer in which one shear modulus is complex. It is shown that this model predicts the anisotropy of the α relaxation in cold-drawn sheets of low-density polyethylene. This anisotropy relates to the orientation of the crystalline regions of the polymer, determined by wide-angle X-ray diffraction and nuclear magnetic resonance. It is, therefore, concluded that the α relaxation in low-density polyethylene is activated by shear in the c direction in planes containing the c-axis.
34 citations
TL;DR: The structure changes of radiation-polymerized trioxane taking place during annealing have been studied by means of electron microscopy, X-ray small-and wide-angle scattering, and differential thermal analysis.
Abstract: The structure changes of radiation-polymerized trioxane taking place during annealing have been studied by means of electron microscopy, X-ray small- and wide-angle scattering, and differential thermal analysis. The original fibrillar crystals, supposedly consisting of extended chains, change into lamellar crystals due to annealing at temperatures between 150° and 190°C. Lamella formation can be connected with the appearance of a long period of about 200A which is not observed in the unannealed sample. During annealing within the same temperature range the X-ray reflections due to the twin structure of the original polytrioxane disappear, whereas the orientation of the fraction with its c-axis parallel to the c-axis of the parent trioxane remains unaltered. The melting point of the lamellar crystals obtained by annealing is 186°-187°C and, therefore, considerably higher than the melting point (175°C) of crystals grown during cooling of a polytrioxane melt. The equilibrium melting point of an undi...
TL;DR: In this paper, the formal description of penetrant clustering in polymers given by Zimm and Lundberg is applied to systems obeying Flory-Huggins thermodynamics.
Abstract: The formal description of penetrant clustering in polymers given by Zimm and Lundberg is applied to systems obeying Flory-Huggins thermodynamics. Several equivalent procedures for evaluation of the cluster function are suggested including circumstances in which the interaction parameter χ1 varies with composition. An analysis of the cluster function for penetrant and the companion expression for clustering of the polymeric solute is presented for some familiar, special cases of Flory-Huggins' behavior. The utility of the analyses is illustrated by application of these analytical techniques to data taken from the literature.
TL;DR: Minimum energy (vacuum) conformations of proline oligomers and poly-L-proline have been calculated and a third form, not previously described, is found to be almost equally energetically favorable with the trans form of polyproline II.
Abstract: Minimum energy (vacuum) conformations of proline oligomers and poly-L-proline have been calculated. The left-hand helix of trans-polyproline II becomes stable at the tetramer, whereas the right-hand helix of cis-polyproline I is not established until at least the pentamer. The potential minima include values of ψ (ψ = 163° trans, ψ = 56° cis) which yield forms of the polymer that are virtually identical with polyproline I and II in the solid state. Calculated repeat distances and residues per turn for the two forms are 1.90 A and 3.18 (pp I) and 3.11 A and 3.00 (pp II), compared with experimental values of 1.90 A and 3.33 (pp I) and 3.12 A and 3.00 (pp II). A third form, not previously described, is found to be almost equally energetically favorable with the trans form of polyproline II. This form, herein called polyproline III, is a trans left-hand helix with alternating rotation angles of 325° and 170°, and 3.35 residues per turn, which forms a right-hand superhelix. Using collagen II proline c...
TL;DR: In this article, a study has been made on four chain-extended polyurethan (PU) elastomers differing only in the nature of the flexible segment, namely, poly(butylene adipate) (PBA), poly(tetramethvlene oxide) (PTMO), poly-propylene oxide (PPO), and poly-ethylene oxide (PEO), and the saturation water concentration increases from 1.6 to 3% in the first three samples and jumps to 113% in PEO-PU.
Abstract: A study has been made on four chain-extended polyurethan (PU) elastomers differing only in the nature of the flexible segment, namely, poly(butylene adipate) (PBA), poly(tetramethvlene oxide) (PTMO), poly(propylene oxide) (PPO), and poly(ethylene oxide) (PEO). The saturation water concentration increases from 1.6 to 3% in the first three samples and jumps to 113% in PEO-PU. The flux normalized to 1 mil thickness is nearly the same in the first three samples, whereas an increase of 70% is expected in PPO-PU on the basis of the higher water solubility and a 24-fold increase is expected in PTMO-PU on the basis of the 27°C lower glass transition. For PBA-PU, the upward curvature of the isotherm at higher activities, zero heat of mixing, and linear decrease in diffusion constant D with concentration indicate that immobilization of water in clusters plays an important role in the transport mechanism. Nearly identical behavior is observed in PTMO-PU, suggesting that the lower than expected D in this pol...
TL;DR: An interpretive theory applicable to any binary system at sorption equilibrium is given by Zimm's equation relating directly the activity volume behavior and the molecular geometry of the system as discussed by the authors.
Abstract: An interpretive theory applicable to any binary system at sorption equilibrium is given by Zimm's equation relating directly the activity-volume behavior and the molecular geometry of the system. A clustering function, G11/V 1, a monotone, increasing function of the probability of finding molecules of the same kind close to one another is given by Where Values of G11/V 1 -1 increases with increasing tendency of like molecules to cluster. Diverse sorption behavior is easily interpreted in terms of this equation. For example, in water-protein systems the range of behavior from strong-binding, site adsorption to diffuse swelling as water concentration increases can be explained. The almost athermal, Langmuir-type adsorption found for methane in hydrocarbon polymer me...
TL;DR: In this article, a polymer crystal with a non-crystalline surface layer formed by chain loops of different lengths is considered, where the length of each loop can be changed by longitudinal diffusion of the molecule through the crystal lattice.
Abstract: A polymer crystal with a noncrystalline surface layer formed by chain loops of different lengths is considered. It is assumed that the length of each loop can be changed by longitudinal diffusion of the molecule through the crystal lattice. From the condition that the free energy of the system is minimum, the loop length distribution and the average loop length as function of temperature are calculated. In contrast to the results for loops of equal length, for the present model, a substantial thickness of the noncrystalline surface layer and a broad melting range is obtained also for the case of adjacent reentry. In order to get this result one has to take into account that even an “ideal fold” consists of at least four rigidly arranged CH2 groups in energetically unfavored conformation.
TL;DR: The morphology of polyethylene single crystals prepared isothermally in solution was found to be independent of molecular weight as mentioned in this paper, and the enthalpy of fusion, lamellar fold period, and optical appearance was found independent of the molecular weight.
Abstract: The morphology of polyethylene single crystals prepared isothermally in solution was found to be independent of molecular weight. The enthalpy of fusion, lamellar fold period, and optical appearanc...
TL;DR: In this article, the assignment of the infrared fold bands to modes of vibration of the repeat unit is discussed with reference to the spectra of films with varying extents of N deuteration (normal 6.6, disordered regions deuterated, N deutero 6.5, hydrogenated).
Abstract: Following the assignment of the 1329 and 1224 cm−1 infrared bands to chain-folded conformations in nylon 6.6 by Koenig et al. examination of the infrared spectra of positively birefringent and negatively birefringent spherulitic films has been made. The spectra indicate extensive regular folding in negative spherulites but fewer folds or less regular folding in the positive spherulite structure. The assignment of the infrared fold bands to modes of vibration of the repeat unit is discussed with reference to the spectra of films with varying extents of N deuteration (normal 6.6, disordered regions deuterated, N deutero 6.6, disordered regions hydrogenated). Electron micrographs of negative spherulites are analyzed with the infrared and previous evidence. We suggest they are built up of single-crystal lamellae of 0.2 to 0.3 μ lateral dimensions packed with a preferential orientation of the lamellae planes parallel to the radial direction but otherwise randomly oriented.
TL;DR: In this article, the dynamic shear behavior of poly (ethylene terephthalate) (PET) was investigated in the 4.2-300°K temperature region using a freely oscillating torsion pendulum at frequencies of 0.4 to 2 cp.
Abstract: The dynamic shear behavior of poly (ethylene terephthalate) (PET) has been investigated in the 4.2—300°K temperature region using a freely oscillating torsion pendulum at frequencies of 0.4 to 2 cp...
TL;DR: In this paper, the plastic deformation modes of single polypropylene have been studied as a function of applied uniaxial strain and the orientation of the lathlike crystals relative to the draw direction.
Abstract: The plastic deformation modes of single crystals of polypropylene have been studied as a function of applied uniaxial strain and as a function of orientation of the lathlike crystals relative to the draw direction. The crystals were drawn on a Mylar substrate and the morphology of the drawn crystals was observed by electron microscopy for various imposed uniaxial strains varying from nominal values of 3 to 100%. For crystals oriented in, or close to, the direction of draw, microcracks developed at low strains and grew progressively larger as the draw ratio increased. Fibrils, about 50 A in diameter, were found to extend across the apparent cracks. The fibril diameter appeared to be independent of the imposed strain but the fibril length was found to be proportional to the strain. For crystals oriented at an appreciable angle to the strain, additional modes of plastic deformation were found to occur. These included simple and multiple shear, slip, and buckling. Crystallographic twinning also appea...
TL;DR: In this article, the isomorphism of copolymers is discussed and the folded-chain crystals of the solution-grown crystals are changed to extended chain crystals by hydrolysis.
Abstract: Hydrolysis of solution-grown crystals and X-ray crystal structures were investigated in some Copolyesters. The isomorphism of the copolymers is discussed. The folded-chain crystals of the solution-grown crystals are changed to extended-chain crystals by hydrolysis. The changes of the counit content indicate that ethylene is-ophthalate units can coexist, but ethylene orthophthalate and sebacate units can coexist only to a limited extent, with ethylene terephthalate units in the central portions of the lamellae. These results agree well with the X-ray studies of the fiber structures. Two types of constitution diagrams are proposed for the copolymer.
TL;DR: The dependence on temperature of the tensile modulus in the machine and transverse directions was examined for specimens which were dry, conditioned to 50% R.H., and saturated with water.
Abstract: Samples of 66 nylon were oriented by rolling to produce structures in which the polymer chains are preferentially in the machine direction and the hydrogen bonds are in the transverse direction. Conditioning to 50 or 100% relative humidity (R.H.) produces anisotropic swelling with the transverse direction expanding much less than the other two directions. The dependence on temperature of the tensile modulus in the machine and transverse directions was examined for specimens which were dry, conditioned to 50% R.H., and saturated with water. At high temperatures, the modulus was larger in the transverse direction. At-40°C, it was larger in the machine direction and increased with increasing moisture. The data are interpreted in terms of crystals which have their largest dimension in the hydrogen bond direction.
TL;DR: In this article, steady state permeation rates and equilibrium sorption measurements were made as a function of temperature for a series of alcohols in a polybutylene adipate polyurethan.
Abstract: Steady-state permeation rates and equilibrium sorption measurements were made as a function of temperature for a series of alcohols in a polybutylene adipate polyurethan. The alcohol series included methanol; ethanol; n-propanol; n-, iso-, sec-, and t-butanol; n-pentanol, n-hexanol, and n-heptanol (all at unit activity). Calculated integral diffusivities of the various penetrants correlated well with effective penetrant size. The solubility coefficients for the various alcohols increased as the difference between the solubility parameters of the polymer and penetrant decreased for the normal alcohol series. The solubility coefficients for the branched alcohol isomers were characterized by values lower than those predicted by the correlation for the normal alcohols; possibly steric hindrance limits sorption on specific polymer sites. A detailed analysis of the system ethanol/poly(butylene adipate-polyurethan) revealed a sigmoidal increase of the diffusion coefficient with increasing penetrant conc...
TL;DR: In this article, the effect of microstructure on the glass temperature T(g) of poly(alpha-methyl styrene) has been investigated, and it has been observed that T increases as the syndiotacticity of the molecule increases.
Abstract: : The effect of microstructure on the glass temperature T(g) of poly(alpha-methyl styrene) has been investigated. It has been observed that T(g) increases as the syndiotacticity of the molecule increases-thus T(g) = 446K for polymer with 67% syndiotactic placements, while a value of T(g) = 453K is found for a sample with 95% syndiotactic placements. Coefficients of expansion for the liquid and glassy states have been calculated and from these a chain stiffness parameter has been estimated using the Gibbs-DiMarzio theory. The result indicates that the flex energy of the alpha-methyl styrene chain is about 20% larger than for the polystyrene chain. (Author)
TL;DR: In this article, the authors proposed the two-phase concept of single crystal structure assuming a very nearly ideal lattice core and two amorphous layers on the fold-containing surfaces.
Abstract: Polyethylene single crystals from dilute solutions usually have a density ρ which is less than that of the ideal crystal lattice (ρc = 1.000 g/cm3). This density defect can be formally assigned to an “amorphous” component (1-α) = (ρc-ρ)/(ρc-ρa) and may be caused by vacancies in the crystal lattice and/or by the surface disorder connected with chain folds. The two-phase concept of single crystal structure assumes a very nearly ideal lattice core and two amorphous layers on the fold-containing surfaces. It is supported by density and heat content data of annealed samples, by small-angle X-ray scattering, by wide-line NMR investigations, and by the results of fuming nitric acid treatment. The maximum thickness of the amorphous surface layer as a function of temperature may be estimated from the free energy requirement of such a layer. With regular chain folds one has a high concentration of gauche conformations yielding a high surface energy. The need for such a concentration disappears in the amorp...
TL;DR: In this paper, the X-ray diffraction patterns of polysiloxane (R2SiO)n.n. where R= n-propyl, has been characterized through high-resolution Xray diffract patterns of the polycrystalline material and selected-area electron-beam diffraction pattern of single crystals.
Abstract: The crystalline polysiloxane (—R2SiO—)n. where R= n-propyl, has been characterized through high-resolution X-ray diffraction patterns of the polycrystalline material and selected-area electron-beam diffraction patterns of single crystals. The smallest unit cell consistent with the diffraction data is tetragonal, with dimensions a = 9.52 • 0.01 and c = 9.40 ± 0.05 . The probable space group is P41 (or P43).
TL;DR: In this paper, the authors measured reverse osmotic water permeabilities, equilibrium water sorption levels, and rates of approach to sorption equilibrium for a series of polymers, including HEMA, copolymers of HEMA and ethyl methacrylate (EMA), cellulose acetate, cellulose nitrate, and poly(urethans).
Abstract: Reverse-osmotic water permeabilities, equilibrium water sorption levels, and rates of approach to sorption equilibrium were measured for a series of polymers, including hydroxyethyl methacrylate (HEMA), copolymers of HEMA and ethyl methacrylate (EMA), cellulose acetate, cellulose nitrate, and poly(urethans). Pronounced equilibrium solvent clustering behavior was observed for these systems as vapor saturation was approached in sorption experiments. However, clustering tendency was not found to be a function of total membrane water content at saturation but rather appears to be a function of the chemical nature of the polymer in question. Moreover, clustering of water molecules in (relatively) hydrophobic membranes resulted in low effective diffusivities (reverse osmotic permeability divided by equilibrium water content) whereas clustering in hydrophilic membranes led to higher effective water diffusivities. Clustering tendency was not as strong in the case of the weakly interacting membranes (i.e....
TL;DR: In this article, a discussion of the problems involved in transport studies with water vapor is presented and various practical solutions are offered. But the authors focus on the case of hydrophilic polymers where nonsteady-state direct sorption methods can be used and the large amount of heat liberated during the sorption process again causes considerable difficulty.
Abstract: Water presents special and unique difficulties in diffusion and sorption measurements because of its high cohesive energy and hydrogen-bonding capacity. In the case of transport measurements in hydrophilic polymers the time-lag method is complicated by the tendency of the water vapor to be adsorbed onto the glass receiving sections of the equipment. On the other hand, with more hydrophilic polymers where nonsteady-state direct sorption methods can be used the large amount of heat liberated during the sorption process again causes considerable difficulty. A discussion of these and other problems concerned with transport studies with water vapor is presented and various practical solutions are offered.
TL;DR: The 1224 and 1323 cm−1 infrared bands in nylon 66 have previously been assigned to a unique conformation in a tightly folded chain with adjacent reentry as mentioned in this paper, which is a nitrogen-methylene bond that is between cis and trans.
Abstract: The 1224 and 1323 cm−1 infrared bands in nylon 66 have previously been assigned to a unique conformation in a tightly folded chain with adjacent reentry. The unique conformation in the fold giving rise to these bands is a nitrogen-methylene bond that is between cis and trans. Models of the cyclic monomer and dimer of Nylon 66 indicate that this type of nitrogen-methylene bond exists in these compounds also. Since these cyclic oligomers must exhibit “adjacent reentry,” the fact that the 1224 and 1323cm−1 bands appear with greatly enhanced intensity in the infrared spectra of these compounds strongly supports the original assignment of these bands. It should be noted that in the infrared spectra of the linear oligomers these bands are absent.