Journal of Polymer Science: Polymer Symposia最新文献

In an effort to elucidate the nature of ionic aggregation and its effect on the primary relaxation (α process) in the Nafion polymers (EW = 1200), underwater and undermethanol stress relaxation tests were conducted at various temperatures (20–70°C). Both semicrystalline and amorphous Nafion-Na relax faster in the presence of water than in the dry state. In marked contrast to the behavior observed for Nafions in the dry condition, the kind of countercations is insignificant in the underwater stress relaxation. The great similarity in the underwater stress relaxation curves for different cations is attributable to the reduction of ionic interaction between the bound anions and unbound cations, probably associated with the water shielding around the ionic species. This leads to the suggestion that the primary α relaxation may be relevant to the ionic groups rather than to the matrix T_g, representing a reversal of the original assignment of the mechanical α and β relaxations. Increased swelling in methanol shows a modulus being one order of magnitude lower than that in the underwater runs. However, little or no difference is seen in the rates of stress relaxation in the underwater and undermethanol stress relaxation experiments. It is postulated that methanol also interacts with the interracial regions or with the fluorocarbon matrix in the Nafions, not just with the ionic regions.

Light-scattering and viscosity measurements are reported for fractions of poly(decamethylene perfluorosebacate). Intrinsic viscosity (dL/g) relationships at 25°C are [η] = 1.55 × 10⁻⁴M_v^0.70 in chloroform and (η) = 8.8 × 10⁻⁴M_v^0.50 in s-tetrachloroethane. From these data the characteristic ratio is found to be C_θ = 6.3 ± 0.5, indicating that the perfluoroalkane chain is not much more extended than an alkane chain. The solid semicrystalline polymer melts at 45°C, and its x-ray powder pattern suggests a structure different from that of poly(decamethylene sebacate).

The transitions and melting behavior of thermally crystallized poly(ethylene terephthalate) (PET) are studied using a computerized differential scanning calorimeter (DSC). A transition occurs from a structural stage characterized by a strong glass transition and an exothermic crystallization peak to a stage with a barely perceptible glass transition and an endothermic low melting (LM) peak in the DSC thermograms. This transition corresponds to the change from the primary to secondary crystallization process of PET. The exothermic crystallization peak is only observed within the primary crystallization stage. The maximum temperature of the LM peak is a function of annealing temperature and time, and depends on the microstructure of the imperfectly formed crystallites. The high melting peak is the melting of crystallites of higher perfection and is influenced by the recrystallization process of the sample during the scan.

The structures of crystallites formed from a dilute solution of linear polyethylene and of an ethylene-butene copolymer (hydrogenated polybutadiene) have been studied using several different methods. In addition to the conventional thermodynamic methods, small-angle x-ray scattering measurements and analysis of the low-frequency Raman longitudinal acoustic mode (LAM) were also carried out. The major objectives were to establish the level of crystallinity and to determine the thickness of the crystallite core. The results of these studies were also applied to the analysis of the literature data for isotactic polystyrene crystallites formed from dilute solution. For the linear chains and the isothermally crystallized copolymer the different methods gave essentially the same results. The thickness of the amorphous overlayer for the lamellas formed by the homopolymers was found to be about 25 Å, in agreement with previous conclusions. It represents about 20–30% of the lamellar thickness. For the isothermally crystallized copolymers, the overlayer thickness increases to as much as 60 Å and the level of crystallinity is reduced to about 50%. For the rapidly crystallized, small crystallite size copolymer there is a discrepancy in the sizes obtained by the different methods. Possible reasons for the differences are pointed out However, a rather large overlayer is still deduced. When examined in perspective, it becomes clear that the lamellar-like crystallites, typical of crystallization from dilute solution, contain a significant disordered overlayer. The relative extent of this overlayer depends on the chain structure.

The data of isothermal stretching calorimetry on rubbers at different temperatures above room temperature are presented. Based upon the van der Waals equation of state for rubbers calculations can be fitted to the experimental data obtained by simple elongation whereby the thermoelastic behavior is related to a constant thermal expansion coefficient in the unstrained state and to an invariant temperature coefficient of the end-to-end distance of the equivalent freely jointed chain.

An optically clear sample of undiluted poly(vinyl acetate) (PVAc) has been prepared by UV-initiated bulk polymerization of monomer at 42°C. Measurements of light-scattering intensities in the temperature range T_g − 30°C > T > T_g + 50°C have been carried out. Photon correlation spectroscopy has been performed in the temperature range T_g + 5°C > T > T_g + 23°C. Intensity data for T < T_g are in agreement with the Einstein–Smoluchowski expression for density fluctuations, >δρ²; below T_g statistical thermodynamic formulation of >δρ², evaluated using experimental equation-of-state information, is found to be in accord with the light-scattering results. Photon correlation functions are well described by a single Williams–Watts function. Mean relaxation times and associated activation energies are compared with results of other relaxational studies of PVAc. Discrepancies observed are interpreted to be due in part to variability of sample histories as well as to problems in analytical treatment of the pertinent relaxation spectra.

A copolymer of vinylidene chloride and vinyl chloride containing 13.5% of the latter has been found to form completely miscible blends with atactic and isotactic poly(methyl methacrylate). poly(ethyl methacrylate), poly(n-propyl methacrylate), and poly(cyclohexyl methacrylate). All but the latter of these blends were shown to exhibit lower critical solution temperature behavior at temperatures below that at which the copolymer rapidly degrades. The copolymer was found to be only partially miscible with poly(isopropyl methacrylate), while no detectable level of miscibility was observed with poly(methyl acrylate), poly(ethyl acrylate), poly(vinyl acetate), poly(vinyl methyl ether), or poly(vinyl methyl ketone). Information about interactions between components in the miscible blends was estimated from melting point data and is discussed.

The adsorption of poly(vinyl butyral) (PVB) at the γ-Fe₂O₃–benzene interface and the air–water interface was investigated by means of the adsorbance on γ-Fe₂O₃ and surface pressure (π)–area (A) curves. The adsorption isotherms of PVB on γ-Fe₂O₃ from the various solvents are of the Langmuir type and can be explained by competitive adsorption between PVB and the solvents. From the π–A curves of monolayers and the adsorbance on γ-Fe₂O₃, it was confirmed that the adsorbed PVB on γ-Fe₂O₃ is in a train-loop conformation with the hydroxyl groups and the butyral segments directed toward the solution phase. The packing density of γ-Fe₂O₃, particles in the magnetic coatings preferentially depends on the conformation of polymers on the particle surface. The PVB–solvent system which gives the most compact train-loop conformation gives the highest dispersion and packing of γ-Fe₂O₃ in the magnetic coatings.

This article presents a systematic investigation into the influence of dose rate on the results of irradiation of Nylon-6 in air.