Showing papers in "Journal of Macromolecular Science, Part B in 1994"
TL;DR: In this paper, normal modes and their dispersion are obtained for syndiotactic polystyrene (sPS) in the planar zigzag and s(2/1)2 helical conformations.
Abstract: Normal modes and their dispersion are obtained for syndiotactic polystyrene (sPS) in the planar zigzag and s(2/1)2 helical conformations. Comparison is made with the spectra of isotactic polystyrene (ips) to identify the conformation-sensitive modes; for example, the 1221 cm−1 mode is identified as a skeletal mode sensitive to chain structure and it also shows maximum dispersion. Bunching of dispersion curves and their intersection are among the characteristic features which are discussed. A check on the dispersion curves below 400 cm−1 is made from the spectra of polystyrene oligomers.
32 citations
TL;DR: In this article, a study of compatibilization and the mechanism of compatiblization of polypropylene (PP)/thermoplastic polyurethane (TPU) blends with (PP-MA)-g-PEO was conducted.
Abstract: This paper reports a study of compatibilization and the mechanism of compatibilization of polypropylene (PP)/thermoplastic polyurethane (TPU) blends with maleated polypropylene (PP-MA) and its graft copolymer with polyethylene oxide (PEO), (PP-MA)-g-PEO. The results of scanning electron microscope (SEM) and dynamic mechanical analysis showed that (PP-MA)-g-PEO was a very good compatibilizer for PP/TPU blends, while PP-MA also produced some compatibilization. The cocrystallization between bulk PP and PP segments of the compatibilizers was evidenced by differential scanning calorimetry studies. The specific interaction between TPU and polar parts of the compatibilizers was studied with Fourier transform infrared spectroscopy.
21 citations
TL;DR: In this paper, isothermal and nonisothermal crystallization kinetics of different poly(aryl ether ketones) (PAEK) were investigated by means of differential scanning calorimetry (DSC).
Abstract: Isothermal and nonisothermal crystallization kinetics of different poly(aryl ether ketones) (PAEK) were investigated by means of differential scanning calorimetry (DSC). For comparison, a poly(phenylene sulfide) was also included. Systematic relationships between the chemical structure of these materials and their crystallization behavior could be derived. The equilibrium melting temperatures of the different PAEKs were estimated using the extrapolation scheme given by Hoffman and Weeks. Due to the higher flexibility with increasing ether/ketone ratio, the glass transition, crystallization, and melting temperatures decreased, and the melt crystallization was accelerated. The cold crystallization, however, was retarded with more flexible chains relative to that with stiffer chains due to the increased order of stiffer molecules in the quenched amorphous state, which results in a higher nucleation density. Independent of the chemical structure, Avrami exponents of 2.0 ≤ n ≤ 2.8 were found for cold-...
21 citations
TL;DR: In this article, five networks based on a diglycidylether of bisphenol A-dimethacrylate prepolymer of molar mass 1100 g· mol−1 crosslinked with 35, 40, 45, 50, and 55% styrene mass fractions were characterized by Fourier transform infrared spectroscopy, cross-polarization/magic-angle spinning, nuclear magnetic resonance spectroscope, styrene extraction, and rubber elasticity measurements.
Abstract: Five networks based on a diglycidylether of bisphenol A-dimethacrylate prepolymer of molar mass 1100 g· mol−1 crosslinked with 35%, 40%, 45%, 50%, and 55% styrene mass fractions were characterized by Fourier transform infrared spectroscopy, cross-polarization/magic-angle spinning, nuclear magnetic resonance spectroscopy, styrene extraction, and rubber elasticity measurements. Various structural models were built up from the available analytical data, and their crosslink density was compared to the experimental data derived from rubber elastic moduli. Globally, network models based on a purely statistical approach but taking into account the incomplete cure conversion make it possible to predict the trends of modulus variations. The kinetic data on copolymerization show, however, that the material is diphasic, one phase being composed of the vinylester network and the other of practically pure polystyrene. We tried to take this heterogeneity into account in modulus predictions using a simple mixtu...
19 citations
TL;DR: In this paper, two nominally equivalent grades of polypropylene designed for similar applications were extruded into sheets, with one surface chilled rapidly, giving a smooth texture; and the other being rougher, with a structure of spherulites separated by crevices formed by retraction of the last traces of molten polymer.
Abstract: Two nominally equivalent grades of polypropylene designed for similar applications were extruded into sheets, with one surface chilled rapidly, giving a smooth texture; and the other being rougher, with a structure of spherulites separated by crevices formed by retraction of the last traces of molten polymer. Differences in the two grades gave rise to differences in spherulitic morphology, in terms of both spatial distribution of spherulites among die lines and the proportions of α- and β-spherulites. The sheets were subjected to three kinds of deformation: unrestricted monoaxial, restricted monoaxial (plane strain), and biaxial. The effects of surface variations persisted right through the drawing process. The morphology of the rough surface in particular was observed (a) to dominate the process of deformation, especially necking as it initiated at surface crevices between spherulites; and (b) to affect the optical quality of the final product, most significantly in the structure and number of h...
19 citations
TL;DR: In this article, the early structure development process in the early stage of crystallization in commercial polyethylene terephthalate (PET) fibers during carefully controlled postspinning annealing treatments has been followed.
Abstract: The fast structure development process in the early stage of crystallization in commercial polyethylene terephthalate (PET) fibers during carefully controlled postspinning annealing treatments has been followed. In addition to conventional structure characterization techniques, transmission electron microscopy (TEM) has been employed to probe the sequence of structural events. In the earliest stage of structural development, direct observation showed an embryonic microfibrillar structure, the microfibril diameter being ca. 5 nm. Upon modest heat treatment, the microfibrils become axially punctuated with crystallites. As further crystallization occurs, the crystallites become more perfect and lateral alignment of crystallites takes place, particularly in extensively crystallized materials, that is, higher temperature and/or longer time of heat treatment. The lateral alignment results finally in a lamellar microstructure.
18 citations
TL;DR: In this paper, a method for the determination of birefringence in thin transparent anisotropic films is proposed, based on the modifications produced by the thin anisotope films in the channeled spectra of a crystal, which are recorded on a spectrophotometer provided with a device developed by the authors.
Abstract: A method is proposed for the determination of birefringence in thin transparent anisotropic films. The modifications produced by the thin anisotropic films in the channeled spectra of an anisotropic crystal are used. The channeled spectra were recorded on a spectrophotometer provided with a device developed by us.
17 citations
TL;DR: In this paper, the authors measured pore size distributions for cationic acrylamide-based hydrogels of different compositions maintained at the same swelling capacity (27.8 ± 0.7 g swollen gel/g dry gel) by varying the ionic strength of the surrounding solution.
Abstract: Pore-size distributions have been measured for cationic acrylamide-based hydrogels of different compositions maintained at the same swelling capacity (27.8 ± 0.7 g swollen gel/g dry gel) by varying the ionic strength of the surrounding solution. Swelling equilibria were measured at about 6°C in pure water and aqueous sodium azide solutions ranging in concentration from to 10−3 to 10−1 M. The mixed-solute-exclusion method (introduced by Kuga) was used to obtain the experimental solute-exclusion curve, which represents the amount of imbibed liquid inside the gel inaccessible to a solute of radius r. The pore-size distribution was obtained by using Casassa's Brownian-motion model and numerically solving the Fredholm integral equation. The modes of the pore radii range from 20.4 to 47.1 A for acrylamide-based hydrogels containing varying amounts of cationic comonomer (1.5 and 4.0 %M), crosslinker (0.3 and 1.0 %C), and initial concentration of total monomer (15 and 35 % T).
14 citations
TL;DR: The degree of crystal perfection in poly(ethy 1ene terephthalate) (PET) fibers and films, produced under different conditions, was estimated in terms of the Ruland-Vonk crystal disorder parameter with the help of x-ray diffraction studies as discussed by the authors.
Abstract: The degree of crystal perfection in semicrystalline poly(ethy1ene terephthalate) (PET) fibers and films, produced under different conditions, was estimated in terms of the Ruland-Vonk crystal disorder parameter with the help of x-ray diffraction studies. Fibers and films which were produced by low-speed melt extrusion followed by drawing in water at low strain rates in a low-temperature environment had the lowest x-ray crystallinity and the most imperfect crystals. Further evidence of greater crystalline imperfection in these samples was provided by their x-ray intensity plots and melting endotherms. The low x-ray crystallinity and high defect density shown by these samples have been attributed to (a) the slow drawing at relatively low temperature, which does not provide the necessary environment for crystallization; and (b) the presence of very small nuclei which may be crystalline remnants that are retained at the low speeds of production and which can act as seed crystals around which crystall...
11 citations
TL;DR: In this article, the roles played by homogeneous and heterogeneous nucleation in the microdomain ordering process are considered through comparison of results from pure samples and samples doped with impurities.
Abstract: Time-resolved small-angle x-ray scattering has been used to study the phase transformation kinetics of a thermally quenched, asymmetric, diblock copolymer. The roles played by homogeneous and heterogeneous nucleation in the microdomain ordering process are considered through comparison of results from pure samples and samples doped with impurities. This crystallization process is unique in that it involves constituent particles (microdomains) that are hundreds of angstroms in size ordering onto a lattice with spacings on a similar length scale. Models derived from classical nucleation and growth theories are used to analyze results from pure and doped samples. Clear experimental evidence of a heterogeneous nucleation process occurring in the doped samples suggests that impurity effects cannot be ignored in these materials. In addition, it is proposed that the late-time coexistence of crystalline and amorphous microdomain structures is due to strain energy effects induced by the volume constraints...
10 citations
TL;DR: The mesomorphic phase was found to be impermeable to dichloromethane vapor at low activity, becoming permeable at higher activities as mentioned in this paper, and its fraction increases greatly going from the δ to the γ form, also characterized by chains in helical conformation but lacking true crystalline order.
Abstract: Sorption and diffusion of dichloromethane vapor in the helical forms—that is, δ and γ—of syndiotactic polystyrene were investigated. The thermal transition from the δ to the γ form occurs through an intermediate mesomorphic form, also characterized by chains in helical conformation but lacking true crystalline order. The mesomorphic phase was found impermeable to the vapor at low activity, becoming permeable at higher activities. The presence of a mesomorphic phase, along with the crystalline and the amorphous forms, was suggested in the crystallized samples, too, and its fraction increases greatly going from the δ to the γ form.
TL;DR: A large number of wholly aromatic and aromatic/aliphatic polyimides have been developed since this class of polymer was first reported in the 1960s as discussed by the authors, and they are one of the important heat-resistant polymers.
Abstract: Polyimides are one of the important heat-resistant polymers. A large number of wholly aromatic and aromatic/aliphatic polyimides have been developed since this class of polymer was first reported in the 1960s. These polyimides are in general either not processable or processable with great difficulty. In most cases, solutions of the corresponding polyamic acid (PAA) in polar solvents are used for processing.
TL;DR: In this article, the degradation of amorphous and semicrystalline PET with different molecular weights by means of hydrolysis at 180°C has been investigated by measuring the weight loss and the x-ray crystallinity as a function of etching time.
Abstract: The degradation of samples of amorphous and semicrystalline PET with different molecular weights by means of hydrolysis at 180°C has been investigated by measuring the weight loss and the x-ray crystallinity as a function of etching time. It is shown that during the first hours of etching, a concurrent crystallization of the amorphous samples takes place. It is found that weight loss values of amorphous samples after long etching times are higher than the weight loss of the crystallized materials. Results also indicate that weight loss depends to some extent on the initial degree of crystallinity of the material. It is emphasized that the lateral size of the crystallites is a major parameter in determining the total amount of etched material. Analysis of results further confirms that mainly the amorphous regions lying outside of the lamellar stacks are removed by hydrolysis. However, the crystals formed during annealing of the amorphous samples at 180°C are less perfect and the lamellar stacks in...
TL;DR: In this paper, the role of water at the molecular level is investigated using two different experimental techniques, dynamic mechanical relaxation spectroscopy in monodirectional stretching, and low-resolution solid-state nuclear magnetic resonance (NMR) analysis.
Abstract: The dynamic mechanical spectrum of PEEK at low temperature shows a relaxation band which is affected by the presence of water. A mechanism based on the interaction between water and oxygen atoms present in the polymer chain was previously suggested. In the present paper, direct evidence of the role of the water at the molecular level is reported. The analysis was carried out using two different experimental techniques, dynamic mechanical relaxation spectroscopy in monodirectional stretching, and low-resolution solid-state nuclear magnetic resonance (NMR) spectroscopy. Both techniques give information on molecular mobility phenomena. The comparison between data obtained using the two techniques, and the analysis of samples with a controlled water content, supports a model in which the motions of the water molecules play a relevant role in the relaxation mechanism involving the polymer chains.
TL;DR: In this paper, solution blends of a modified polyacrylonitrile (PAN) with polyurethane (PU) ionomers were prepared in N,N-dimethylformamide.
Abstract: Solution blends of a modified polyacrylonitrile (PAN) with polyurethane (PU) ionomers were prepared in N,N-dimethylformamide. PU anionomer (PUAn20) blends showed phase separation of up to several micrometers, whereas almost homogeneous morphology was obtained with PU ca-tionomer blends. In PU cationomer blends, the tan δ peaks of the soft segments of PU and PAN moved toward lower and higher temperature, respectively. Notably, the tensile strength of PU cationomer blend at 30/70 (PU/PAN by weight) increased to over 2.5 times that of PAN; for this blend the concentration of PU cation approximately matched that of the sulfonate anion of the modified PAN. The synergistic effect was interpreted in terms of ionic interactions between the main chains of the polymers.
TL;DR: In this paper, the authors investigated the dynamic mechnical properties of liquid crystal polyester (LCP) composites in the temperature range from -100° to 250°C and observed two transitions, at T g and T β, where T g is the glass transition of the samples.
Abstract: Dynamic mechnical properties of unfilled and glass fiber filled liquid crystal polyester (LCP) have been investigated in the temperature range from -100° to 250°C. Two transitions, at T g and T β, were observed with decreasing temperature, where T g is the glass transition of the samples; however, the origin of T β is unknown. Both LCP and LCP composites exhibit strong dynamic mechanical anisotropy with respect to the molding flow direction. As the glass fiber content increases, the reinforcing effect is improved due to the increase in the effective storage modulus, while the modulus anisotropy is reduced.
TL;DR: In this article, the properties of styrene-co-acrylonitrile (SAN) with phenoxy were evaluated in terms of morphological, rheological, thermal, and mechanical properties.
Abstract: Melt blends of styrene-co-acrylonitrile (SAN) with phenoxy were prepared over a full range of compositions and were evaluated in terms of morphological, rheological, thermal, and mechanical properties. Viscosity-composition plots showed a crossover with the additivity line at 50/50 (SAN/phenoxy by weight), and deviations from semicircles in Cole‐Cole plots were seen for 70/30, 50/50, and 30/70 blends. Scanning electron micrographs (SEM) of the blends showed a two-phase morphology with a finer dispersion and well-elongated fibrils seen when SAN formed the dispersed phase. The glass transition temperature (T g) of SAN was almost unchanged in the blends, whereas T g of phenoxy was increased over 5°C. Tensile modulus and strength generally showed synergistic effects in phenoxy-rich blends. In the 10/90 blend, the ultimate elongation was greater than for pure phenoxy, and a dramatic drop of Izod impact strength was observed.
TL;DR: In this paper, the thermal properties of polyvinyl alcohol (PVA)-Cu(II) and PVA-Cr(III) complexes with different concentrations of CuC12 and Cr(NO3)3 salts were investigated using UV spectroscopy and x-ray analysis.
Abstract: Polyvinyl alcohol (PVA)-Cu(II) and PVA-Cr(III) complexes were prepared with different concentrations of CuC12 and Cr(NO3)3 salts. The structures of the obtained complexes were investigated using UV spectroscopy and x-ray analysis. The thermal properties (volumetric heat capacity, thermal diffusivity, and thermal conductivity) of aqueous solutions of PVA-metal complexes have been measured using the hot-wire (and strip) technique as a function of temperature (20°-80°C). The results show that the values of the thermal properties depend on the type and the concentration of metal ions bound to the polymeric chains of PVA and the temperatures. However, a considerable increase in the values of the thermal properties was observed for PVA-Cu(II) complex. The type of metal salt under investigation affects the structure of PVA. The complex of PVA-Cr(III) is more thermally stable than the complex of PVA with Cum. However, both polymer-metal complexes showed good properties which may make them acceptable for ...
TL;DR: In this paper, the effect of different fluid environments on the properties of poly(ether sulfone) has been studied and it has been found that ortho-dichlorobenzene greatly affects the ductility of the polymer, producing a catastrophic embrittlement.
Abstract: The effect of different fluid environments on the properties of poly(ether sulfone) has been studied. It has been found that, among the solvents studied, ortho-dichlorobenzene greatly affects the ductility of the polymer, producing a catastrophic embrittlement. This results even after short sorption times at 20°C. Among the possibilities of solvent-induced crystallization, antiplasticization, chemical attack, and surface cavitation, the last seems to be the most responsible for the observed embrittlement.
TL;DR: In this paper, a simple technique is developed for predicting the dynamic viscosity from the steady shear visco-ity data of polyelectrolyte solutions, which is based on the Carreau-type equation.
Abstract: A simple technique is developed for predicting the dynamic viscosity from the steady shear viscosity data of polyelectrolyte solutions. The Carreau-type viscosity equation is used to represent both the steady shear and dynamic viscosity data. A shift factor β, defined as the ratio of the dynamic time constant to the steady shear time constant, is introduced. This dimensionless parameter enables all the dynamic viscosity data to be shifted onto the steady shear viscosity curve. The parameter β correlates well with the zero shear viscosity and has the following form:
TL;DR: In this article, the authors studied the complexation behavior of deoxycholic acid for poly(oxy-ethylene), poly(propylene oxide, poly(tetrahydrofuran) derivatives with various chain lengths.
Abstract: Complexation behavior of deoxycholic acid was studied for poly(oxy-ethylene), poly(propylene oxide), poly(tetrahydrofuran), and several poly(oxyethylene) derivatives with various chain lengths. The complexes were obtained for poly(oxyethylene) with an average molecular weight greater than 200 (average degree of polymerization n = 4). In spite of very short ethylene oxide chains, poly(oxyethylene) monostearate and poly(oxyethylene) mono-p-nonylphenyl ether with n = 2 formed the complexes. The unit cells of all complexes corresponded to the orthorhombic crystal which is most commonly observed for the complexes with low molecular weight compounds. Dimension a in the complexes of poly(propylene oxide) and poly(oxyethylene) mono-p-nonylphenyl ether with n = 2 and 5 was larger than those in other complexes, while b and c did not differ much. Most of the complexes exhibited an increase in the melting points with increasing length of the polymer chains, while the melting points of poly(oxyethylene) monos...
TL;DR: In this article, a numerical method is presented for the accurate determination of the viscoelastic spectra from dynamic response function data, which is validated by application of the method to dynamic data for a hypothetical polymer with an assumed relaxation spectrum.
Abstract: A numerical method is presented for the accurate determination of the viscoelastic spectra from dynamic response function data. First, the technique is validated by application of the method to dynamic data for a hypothetical polymer with an assumed relaxation spectrum. It is shown that the method produces a single retardation spectrum which when used in viscoelastic integral equations yields excellent agreement with the functions from which the spectrum was determined in the first place. Also, upon applying computed transient functions to the linear viscoelastic convolution integral, excellent agreement is obtained. Finally, the method is applied to dynamic mechanical data for a vinyl ester resin system. It is shown that a single retardation spectrum can be generated that upon integration in appropriate integral equations yields response functions in excellent agreement with experiment.
TL;DR: In this paper, the deformation relationship between temperature, stress, strain, and stress rate in polyethylene terephthalate (PET) near the glass transition temperature was analyzed.
Abstract: Analyzed in this paper are the deformation relationships between temperature; stress, strain; and stress rate in polyethylene terephthalate (PET) near the glass transition temperature. The uniaxial stress rate of inelastic deformation was found to be proportional to the square of the effective stress. A physical model of two simultaneous rate-activated processes with a general activation energy barrier is utilized. We call this “second-order kinetics.” Experimental data obtained by measuring load rate versus load point displacement were analyzed to describe stress relaxation of thin uniaxial strips. The activation enthalpy and activation volume show that the rate-controlling process is second-order.
TL;DR: In this article, the authors synthesized and characterized monocyclopentyl and moncyclohexyl itaconates and the corresponding polymers, poly(monocyclopeentyl, itaconate) (PMCPI) and poly(poly(mono-cyclo,hexyl,itaconate), (PMCHI), by fractional precipitation, using methanol-water as solvent-precipitant pair.
Abstract: Monocyclopentyl and monocyclohexyl itaconates and the corresponding polymers, poly(monocyclopentyl itaconate) (PMCPI) and poly(mono-cyclohexyl itaconate) (PMCHI), were synthesized and characterized. Polymers were fractionated, by fractional precipitation, using methanol-water as solvent-precipitant pair. Fractions were characterized by membrane osmometry in 2-propanol at 298 K, vapor pressure osmometry in methanol at 318 K, size exclusion chromatography in THF, and by viscometry in THF and methanol. The Kuhn-Mark-Houwink-Sakurada equations were established to determine the viscometric parameters. By using the Stockmayer-Fixman equation, the conformational parameter K θ was determined in both solvents. The rigidity index, σ, and the characteristic ratio, C∞, were calculated. These polymers show high rigidity values but they are comparable with those reported for other poly (itaconates).
TL;DR: In this paper, the authors extended the Debye-Huckel method to evaluate the electrostatic field caused by charged groups, dipoles, and multipoles, in globular molecules.
Abstract: The method of Debye-Huckel is extended so as to be applicable for the purposes of evaluating the electrostatic field caused by charged groups, dipoles, and multipoles, in globular molecules. Charged groups and dipoles may be situated arbitrarily in the protein molecule. The problem is solved using the spherical coordinate system. General expressions for the potential are given. In the case of a protein molecule having a strong dipole moment, the general problem is approximately solved presuming that the potential is caused by an effective dipole moment. The numerical simulation of electrostatic interaction between two molecules with strong dipoles is provided.
TL;DR: In this paper, the structural relaxation of polystyrene under sub-T g annealing at 50°C and at 70°C was investigated by the radial distribution function (RDF) derived from its wide-angle x-ray scattering (WAXS).
Abstract: The structural relaxation of an atactic polystyrene under sub-T g annealing at 50°C and at 70°C was investigated by the radial distribution function (RDF) derived from its wide-angle x-ray scattering (WAXS). By recording the changes in RDF (i.e., ΔH(r), where r is the radial distance from an arbitrary reference atom) after it had been annealed for a certain period of days, and taking the integration of ΔAH(r) 2dr, we found that the atom density within structural domains in a size below 15 A was changed dramatically, but that the tendency leveled off as annealing proceeded. However, the atom density outside the domains is barely changed by sub-T g annealing. The size of the domain is similar to the statistical segment length reported in the literature. The behavior of the domains—that the segmental relaxation inside the domains in the initial sub-T g annealing is unconstrained by their neighbors outside the domains—is also similar to the behavior of the statistical segments. The domains are believ...