The Flory equation-of-state theory, as expressed by Patterson and co-workers, has been applied to two miscible polymer blends: poly(vinyl chloride)/poly(ε-caprolactone) and poly(methyl methacrylate)/poly(vinylidene chloride). For both blends, the variation of the polymer-polymer interaction parameter, χ, as a function of composition, is mostly small and can be accounted for by the Flory theory. However, for poly(vinyl chloride)/poly(ε-caprolactone) blends, at high poly(ε-caprolactone content), the large variation of χ as a function of concentration can be explained by a variation of the surface-to-volume ratio of the polymers in the mixture with blend composition. The variations of the surface-to-volume ratios determined in this study agree with those reported in the literature using small-angle x-ray scattering. 相似文献
FTIR spectra of blends of lightly sulfonated polystyrene (PS-SSA) with polyurethanes (PU) containing a tertiary nitrogen in the chain extender were recorded. These blends exhibit a two-phase behavior, but the individual components are not phase separated. Earlier dynamic mechanical studies suggested the occurrence of proton transfer from the sulfonic acid to the tertiary nitrogen, which enhanced the miscibility via ionic interactions and resulted in the formation of a miscible blend between the PS-SSA and the hard segment of the PU, the soft segment being excluded. FTIR studies of these blends now confirm the proton transfer mechanism. A new absorption band at 3428 cm?1 corresponds to a stretching vibration of an N+?H bond. The 1012 cm?1 band of the SO3H group, which strongly depends on the degree of protonation, shifts to lower frequency. The symmetric stretching vibration of the SO group, which occurred at 1043 cm?1, shifts to lower frequency as well, suggesting a lower polarization of the S? O dipole due to the removal of H+. 相似文献
The formation of superlattices in blends of a series of asymmetric BSV triblock terpolymers and symmetric SV or VC diblock copolymers is investigated with S being polystyrene, B being poly(1,2‐butadiene), V being poly(2‐vinylpyridine), and C being poly(cyclohexyl methacrylate). All of these triblock terpolymers and diblock copolymers by themselves self‐assemble into lamellae. Apart from various core shell morphologies, in these blends some new unexpected superstructures were obtained.
A TEM micrograph of a 50/50 blend of B30S58V with S45V. 相似文献
Rheological and solid‐state physical properties of blends containing high‐density polyethylene (HDPE) and a polyampholyte derivative (PE‐g‐PA) are assessed along with their onium ion‐exchanged montmorillonite clay (NR‐MM) nanocomposites. Strong deviations from the log‐additivity rule of zero‐shear viscosity, combined with synergistic behavior in tensile moduli, are consistent with a multi‐phase blend morphology. While this affects clay dispersion in filled blends, PE‐g‐PA/HDPE based nanocomposites are shown to exhibit a favorable balance between material stiffness and ductility.
The kinetics of the permanganate oxidation of formic acid in aqueous perchloric acid has been studied. The results indicate that this reaction is autocatalyzed by both manganese(II) ion (formed as a reaction product) and colloidal manganese dioxide (formed as an intermediate). The apparent rate constants corresponding to the noncatalytic and autocatalytic reaction pathways are given, respectively, by the following equations The activation energies associated with the true rate constants, ??, ??, ??, ??, ??, and ?? are 37.2, 62.5, 70.9, 52.5, 40.8, and 59.9 kJ mol?1, respectively. The percentage of the total reaction corresponding to each pathway is given for typical experimental conditions. Mechanisms in agreement with the kinetic data are proposed for the six different reaction pathways observed. 相似文献
The crystal structure of the title compound has been determined from three dimensional x-ray data obtained by the multiple film method. The space group is P2l/n and the cell dimensions are: a = 14.90, b = 16.84, c = 8.38 Å; β = 93.5° Z = 4. The structure is formed by discrete Co (en) and Fe(CN) ions, both of which have an octahedral configuration. The Fe(CN) ions are approximately octahedrally surrounded by the Co (en) ions while arrangement of Fe (CN) ions around the Co(en) ions completely differs from an octahedron. The mean Fe? C and Co? C dustances are 1.91 and 2.01 Å, respectively. The water molecules do not play an important role in the structure and all distances between oxygen and other atoms indicate the presence of very weak hydrogen bonds. The salts M (en)3 Q(CN)6 · H2O, where M = Co and Cr and Q = Cr, Mn, Fe and Co, are all isomorphous. 相似文献
The dispersive interaction of nonpolar solutes with nonpolar solvents is investigated in model systems consisting of solutions of dimethyl-tetraacetylene, di-t-butyl-tetraacetylene, dimethyl-pentaacetylene or di-t-butyl-pentaacetylene in binary mixtures of cyclohexane/carbondisulfide or n-pentan/carbondisulfide. For this purpose the 1Σ → 1Σ transition in the electronic spectrum of the solutions has been recorded. With increasing concentration of the more strongly interacting solvent component (i.e. carbondisulfide) bathochromic shifts δν of the transition frequency accompanied by a decrease in oscillator strength fM are observed, which are consistent with calculated values based on a previously proposed exciton model [1]. 相似文献
Dynamic x-ray diffraction is conducted to explore the structural origin of the α and β mechanical dispersions of a melt-crystallized high-density polyethylene. It is shown that the real component of the strain orientation coefficient for the crystal c axis C decreases with increasing frequency at a rate which decreases with decreasing temperature. Values of C for the c axis are positive, C for the a axis negative, and C for the b axis close to zero, suggesting that the predominant relaxation process is crystal rotation about the b axis. The activation energy found from Arrhenius plots of C corresponds to that of the α1 mechanical dispersion. The dynamic birefringence in this region is dominated by the contribution from crystal orientation changes. At low temperatures, the imaginary component KC of the strain-optical coefficient of the crystal phase approaches zero, while KC of the amorphous phase exhibits a somewhat broad dispersion peak corresponding to the β birefringence dispersion. This suggests that the principal contribution to the β birefringence dispersion arises from the amorphous phase, probably owing to the amorphous orientation process. Contrary to the case of low-density polyethylene, the dynamic crystal lattice deformation and compliance functions reveal distinct frequency dispersions corresponding to the α1 and α2 mechanical processes. The α1 lattice dispersion is thought to be associated with the α1 crystal orientation dispersion, while the α2 lattice dispersion is believed to be the inherent one arising from the onset of intracrystalline chain motions. 相似文献
The crystal structures of four anion cryptates [X? ? BT -6H+] formed by the protonated macrobicyclic receptor BT -6H+ with F?, Cl?, Br? and N have been determined. They provide a homogeneous series of anion coordination patterns with the same ligand. The small F?-ion is tetracoordinated, while Cl? and Br? are bound in an octahedron of H-bonds. The non-complementarity between these spherical anions and the ellipsoïdal cavity of BT -6H+ is reflected in ligand distortions. Structural complementarity is achieved for the linear triatomic substrate N, which is bound by two pyramidal arrays of three H-bonds, each interacting with a terminal N-atom of N. The formation constants of the complexes formed by BT -6H+ with a variety of anions (halides, N, NO, carboxylates, SO, HPO, AMP2?, ADP3?, ATP4?, P2O) have been determined. Very strong complexations are found, as well as marked electrostatic and structural effects on stability and selectivity; in particular the binding of F?, Cl?, Br?, and N may be analyzed in terms of the crystal structure data. The cryptand BT -6H+ is a molecular receptor containing an ellipsoïdal recognition site for linear triatomic substrates of size compatible with the size of the molecular cacity. Further developments of various aspects of anion coordination chemistry are considered. 相似文献
A competitive reaction study for two isoelectronic peroxides (peroxodisulfate S2O and peroxodiphosphate P2O) interacting with the free radical ·Clpar;CH3)2OH is described. The radical formation is initiated by photolysis, the amounts of peroxide remaining analyzed volumetrically. It is found that persulfate reacts with the organic radical over 100 times more rapidly than does perphosphate. Mechanistic consequences in relation to previous work are briefly discussed. 相似文献
Triarylsulfonium salts Ar3S+MX with complex metal halide anions such as BF, AsF, PF, and SbF are a new class of highly efficient photoinitiators for cationic polymerization. In this article we describe several synthetic routes to the preparation of these compounds along with their physical and spectroscopic properties. Mechanistic studies have shown that when these compounds are irradiated at wavelengths of 190–365 nm carbon–sulfur bond cleavage occurs to form radical fragments. At the same time the strong Br??nsted acid HMXn, which is the active initiator of cationic polymerization that takes place in subsequent “dark” steps, is also produced. A study of the parameters that affect the photolysis of triarylsulfonium salts is reported with a measurement of the absolute quantum yields. The cationic polymerizations of four typical monomers—styrene oxide, cyclohexene oxide, tetrahydrofuran, and 2-chloroethyl vinyl ether—with triarylsulfonium salt photoinitiators are described. 相似文献
The radical anions of the compounds N1N, N3N and N5N , in which two naphthalen π-systems are separated by 1, 3 and 5 spirobonded cyclobutane rings, respectively, and tha tof the reference compound N1 , containing one naphthalene π-system and one cyclobutane ring, have been studied by ESR and ENDOR spectroscopy under a variety of experimental conditions. The intramolecular electrons spin transfer between the two π-moieties in N3N and N5N is slow on the hyperfine time-scale, irrespective of the applied conditions. It is also slow in N1N , except for media of high solvating power. In such media, with a slight reduction of N1N to its radical anion, a paramagnetic species is observed, the hyperfine data for which are consistent with N1N to its radical anion, a paramagnetic species is observed, the hyperfine data of which are consistent with N1N , undergoing a fast intramolecular electron spin tansfer. The ESR and ENDOR spectra of this species are superimposed on those characteristic of a slow transfer. It is suggested that the fast and slow transfer involve the syn- and anti-conformations, respectively, since the distance, r, between the two naphthalene π-systems of N1N is considerably shorter in the former than in the latter (r = 740 vs. 880 Pm for the distance between the centres of the π-systems). Glassy solutions of exhaustively reduced N1N display signals of the dianion triplet state, whereas no such signals are found for N3N and N5N . The zero-field splitting parameter, D , is 4.7 mT, corresponding to r ≈ 480 pm. 相似文献