Spin-probe studies. I. Applications to latexes and micelle characterization

The interaction of sodium dodecyl sulfate (NaDS) with styrene—butadiene latexes was investigated by application of the recently developed spin-probe technique. It is possible by this method to detect the presence of micelles in a latex reasonably quantitatively. The effective surface area occupied per molecule of soap was calculated to be 53 Ų. Differences in purity can readily be detected for several NaDS samples. The less pure samples show a lower critical micelle concentration (CMC) and a significantly more ordered micelle structure. The addition of hexane to NaDS solutions above the CMC leads to a greater immobilization of the spin probe. This is interpreted as reflecting a tighter packing of the soap molecules. The addition of ethanol, acetic acid, and acrylic acid leads to a looser association of the probe with the micelles. The micelles catalyze the decomposition of the nitroxide probe in the presence of organic acids. The aggregation of sodium deoxycholate was also conveniently followed by the spin-probe method.     

NMR studies of polymer solutions. II. Polyethylene

The intramolecular structure of polyethylene in solution was studied by a high-resolution nuclear magnetic resonance technique. Highly purified n-alkanes (99.5%) from C₅H₁₂ to C₃₆H₇₄ were used as its oligomers. The NMR spectra of the polyethylenes (oligomers) are very sensitive to the solvents used. The internal methylene protons of all polyethylenes of various chain length resonance at an identical frequency in carbon tetrachloride. A sharp transition in the NMR spectrum of polyethylene in α-chloronaphthalene at 35°C. was observed at n-C₁₇H₃₆, above which there exist two distinguishable NMR peaks for internal methylene protons, and below which (fewer carbons) only a single peak was seen. The NMR spectra of the internal methylene protons of the polyethylenes (oligomers) taken in benzene are very similar to those taken in pyridine. They are not as easily resolved as those NMR spectra taken in α-chloronaphthalene solutions. The effect of the size of the aromatic solvent molecule on the NMR spectra of the internal methylene protons of the polyethylenes (oligomers) in solutions was demonstrated by using aromatic solvents of various sizes, such as chlorobenzene, α-chloronaphthalene, and 9-chloronathracene. The results indicate that the formation of polymeric structure of the internal methylene groups in the polyethylene chain is very sensitive to the size of the solvent used. The interaction of the solvent with the methylene groups of the polyethylenes varies as a function of chain length; it is stronger for those low member n-alkanes and decreases gradually to an asymptotic value.     

Development of gel permeation chromatography for polymer characterization. II. Universal calibration

GPC appearance volumes have been determined for a series of linear polyethylene, polystyrene, and polybutadiene fractions (M_w/M_n < 1.1) in trichlorobenzene at 130°C. and for the latter two series in tetrahydrofuran at 23°C. A polymer-type independent relationship between appearance volumes and the equivalent hydrodynamic radii of the polymer molecules has been demonstrated. The equivalent hydrodynamic radius is calculated from intrinsic viscosity data. It is proposed that this relationship can be used to construct a universal GPC calibration curve for polymers that assume a spherical conformation in solution. Methods for applying the universal curve to the determination of molecular weight averages and molecular weight distribution are described. In addition, a method is outlined by which the universal calibration curve can be empolyed for determining number-average Mark-Houwink constants from polydisperse samples.     

Ultrasonic characterization of polymer viscoelasticity. Application to polystyrene

Ultrasonics is presented as a powerful method for the thermomechanical analysis of polymers. An experiment is described where the specific volume of a polymer is measured in simultaneity with the acoustic parameters. The technique allows full control of the thermal history in the temperature range from — 150°C to 300°C, where the material goes from a glasslike to a liquidlike state. Moreover the technique allows measurements to be performed at different pressures, up to 2 kbar. Results obtained on a typical amorphous polymer (polystyrene) are reported and the propagation of sound is discussed in regards to the well defined thermodynamic state for the material. Also, the results discriminate between the thermodynamic and the relaxational aspects of the glass transition.     

Valency. II. Applications to molecules with first-row atoms

A quantum chemical definition of valency proposed in Part I is used to calculate the valency of carbon, nitrogen, oxygen, lithium, beryllium and boron in a number of compounds with the SINDO1 method. It is demonstrated that consistency of the basis set is necessary for comparable results. The general features of valency and bonding in these molecules are discussed. The π-electron concept of free valence is generalised to sigma systems and atoms in molecules are classified as subvalent, normal or hypervalent. The relation between valency and natural hybrid occupancy is illustrated. The symmetry properties of natural hybrid orbitals are discussed by means of group theory. A preliminary attempt is made to relate covalency and covalent reactivity. Bond indices and the σ, π character of bonds are obtained by a suitable partitioning and projection of valency into bonding and antibonding contributions. Alexander von Humboldt Fellow 1982–83.     

Applications of polymer rism theory to blends

Polymer RISM (reference interaction site model) theory is a theory of polymer systems in the liquid phase in which account for chemical realism can be made. Results are reported here of phase diagrams (spinodals) for blend systems calculated by means of this theory, using the mean spherical approximation as a closure. The systems investigated are an isotopic blend, a set of homopolymer/copolymer blends, and a model blend containing specific interactions.     

Acetal‐functionalized polymer particles useful for immunoassays. II. Surface and colloidal characterization

Monodisperse polymer colloids with dimethyl and diethyl acetal functionalities were synthesized by a two‐step emulsion polymerization process. The first step consisted of a batch emulsion homopolymerization of styrene (St). The dimethyl and diethyl acetal functionalities were obtained by batch emulsion terpolymerization of St, methacrylic acid (MAA), and methacrylamidoacetaldehyde dimethyl acetal (MAAMA) or methacrylamidoacetaldehyde diethyl acetal (MAADA) in the second step, onto the previously formed polystyrene latex particles. The latexes were characterized by TEM and conductimetric titration, in order to obtain the particle size distribution and the amount of carboxyl and acetal groups on the surface, respectively. The chemical stability of the functionalized surface groups during the storage time was analyzed. The hydrophilic character of the surface of the polymer particles was determined by means of nonionic emulsifier titration. The colloidal stability of the synthesized latexes was studied by measuring the critical coagulation concentration (CCC) against KBr electrolyte, and the existence of a hairy layer on the surface of the latex particles was analyzed by measuring the hydrodynamic particle diameter at several electrolyte concentrations. The surface functionalized groups remained stable for 2 years. The relative hydrophilic character and the colloidal stability were affected by the pH of the medium. On the other hand, the higher the surface charge, the larger the thickness of the hairy layer. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 501–511, 1999     

Photopolymerized silver-containing conducting polymer films. Part II. Physico-chemical characterization and mechanism of photopolymerization process

Physico-chemical and mechanical characterizations of nanophase silver-containing polypyrrole films prepared using a new photopolymerization process were performed. In general, the recorded physical, chemical, and mechanical data characteristic of these films was similar to corresponding literature data obtained from electropolymerized or chemically polymerized polypyrrole. However, photopolymerized polypyrrole films possessed an unusually high anion-to-monomer ratio of 0.8:1. Also, the photopolymerized material contained silver nanoparticles, having diameters of 2 μm or less, uniformally distributed throughout the polymer matrix. While the photopolymerization mechanism is complex, it is suggested that a pyrrole–silver cation complex is most likely the key component involved in the photopolymerization initiation step. Paper submitted for inclusion in the special issue of the Journal of Solid State Electrochemistry honoring the 85th birthday of Professor John O’M. Bockris.     

Nanoparticles of a new mercury(II) coordination polymer: synthesis,characterization, thermal and structural studies

Nanoparticles of a new Hg(II) one-dimensional coordination polymer, {[Hg(4-bpdb)I₂] _n , 4-bpdb?=?1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene} were synthesized by reaction of HgI₂ and 4-bpdb by a sonochemical method. The new nanoparticles were characterized by scanning electron microscopy, X-ray powder diffraction (XRD) and FT-IR spectroscopy; [Hg(4-bpdb)I₂] _n was structurally characterized by single crystal X-ray diffraction. This compound consists of one-dimensional polymeric units of [Hg(4-bpdb)I₂]. The thermal stability of [Hg(4-bpdb)I₂] _n was studied by thermal gravimetric (TG) and differential thermal analyses (DTA).     

Zerovalent metal polymer composites. II. Metal–polymer microdispersions

Metallization of water-soluble polymers incorporating metal-binding ligand is achieved by binding palladium ions at substoichiometric quantities, followed by reduction to polymer–zero-valent palladium complex and deposition of transition metal ions by electroless plating solutions. The polymers studied include poly[N,N,N-trimethyl-N-(m- and p-vinylbenzyl)ammonium chloride], poly-L -glutamic acid, poly-L -lysine, and a copolymer of 2-phenylhydroquinone-2-amino-phthalic acid. Noble metal polyelectrolyte solutions were directly reduced with dimethylamineborane to stable microdispersions. The reactive nickel, cobalt and copper microdispersions were coated on KODAK ESTAR filmbase. Scanning electron microscopy (SEM), ESCA, and IR were used for material characterization. Conductivity and magnetic properties were also measured. Hydrophobic materials such as graphite and fluorinated graphite were metallized in organic solvents using hydrophobic trioctylammonium–tetrachloropalladate as the activating noble metal complex. The metallized conductive graphites were evaluated for their electrochemical properties.     

Nanoparticles of a new zinc(II) coordination polymer: synthesis,characterization, thermal,and structural studies

Nanoparticles of a Zn(II) coordination polymer {[Zn(DADMBTZ)(CH₃COO)₂] _n , DADMBTZ?=?2,2′-diamino-5,5′-dimethyl-4,4′-bithiazole} were synthesized by reaction of Zn(NO₃)₂?·?4H₂O, CH₃COONH₄ and DADMBTZ by a sonochemical method. The nanoparticles were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy. [Zn(DADMBTZ)(CH₃COO)₂] _n was structurally characterized by single-crystal X-ray diffraction. In this four-coordinate compound with nearly C₂ symmetry, DADMBTZ is bidentate. The metal lies in a pseudo-tetrahedral environment and is ligated by the two bithiazole ring nitrogen atoms and an oxygen from each of the two monodentate acetates; 2-D networks are formed via N–H···O hydrogen bonds. Thermal stability of [Zn(DADMBTZ)(CH₃COO)₂] _n was studied by thermal gravimetric and differential thermal analyses. A ZnO nanostructure was obtained by direct thermolyses at 500°C under air. The ZnO nanostructure was characterized by SEM, XRD, and FT-IR spectroscopy.     

Space-time contours to treat intense field-dressed molecular states. II. Applications

This second article in the two back-to-back articles presents a numerical application to support and strengthen two theoretical findings extensively discussed in the previous article (article I). In I, we found that introducing the space-time contours enables to distinguish between N, the number of nuclear Schrodinger equations to be solved, and L, the number of field-free states that become populated by the external field (in the ordinary, perturbative approaches this distinction is not apparent). In the numerical study we show, employing the electronic transition probability matrix P(s,t) [which closely is related to the transformation matrix omega(s,t)--see Eqs. (21) and (25) in I], that the N=L case is rare and in most cases we have N相似文献   

Application to polymer characterization by thermal analysis

The measured results of thermal analysis depend on experimental conditions. The international and national organizations have constituted a series of methods to characterize the physical and chemical properties for substances. The applications to physical transition, chemical reaction, and characteristic parameters of substances are given in the article as examples.     

NMR Approach to the kinetics of polymer crystallization. II. Polydimethylsiloxane solutions

The dilution effect on the crystallization kinetics of PDMS/toluene solutions, ranging from a polymer volume fraction of ? = 1.00 (pure PDMS) to ? = 0.32, was studied using ¹H high-power NMR. Spin-spin magnetic response was analyzed into relaxation components, arising from the different phases of the semicrystalline sample, through a spin-echo technique. The intensity and shape of the amorphous component provide relevant information concerning (1) the global crystallization process and (2) the state of hindrance of the amorphous chains induced by the growing crystalline domains. It was shown that, in solutions, the main effect on the crystallization kinetics of changing concentration is to depress the equilibrium melting temperature of the system. However, a radically distinct crystallization rate between the pure and the more concentrated system must be explained in terms of the activation energy for interphase chain transport. Thermodynamic parameters of PDMS crystallites were also deduced from a model. Comparison between the isothermal development of the overall crystallinity and the variation of a characteristic relaxation time of the amorphous PDMS proton response gives an insight into the relative predominance of nucleation or growth rates in the crystallization mechanisms.     

Photocurrents in simple polymer systems. II

Large photocurrents have been observed in films of some simple polymers (containing no π-orbitals), of which poly(vinyl fluoride) is a typical example. Not only are the currents large (up to 10^?5 A/cm²) but also they are capable of being excited by light in the visible wavelength region where absorption by the polymer is too low to be detectable. The results indicate that the effects are electronic, rather than ionic, in nature.     

Algorithm to evaluate rate constants for polyatomic chemical reactions. II. Applications

A new implementation of the classical reaction path-Liouville algorithm, as developed by the authors in the preceding paper, is tested with several chemical reactions. It results in a simple algorithm, which may be used straightforwardly for the calculation of rate constants, as well as to extract dynamical information of the reactive process. Results for the rate constant have been compared to transition state calculations, confirming that it provides a new lower bound than traditional transition state estimates. In addition, the time-dependence of the kinetic energy stored in vibrational modes has been studied, as a means of characterizing the importance of each normal mode inside the reaction mechanism.     

Multireference perturbation theory with optimized partitioning. II. Applications to molecular systems

The second‐order multireference perturbation theory using an optimized partitioning, denoted as MROPT(2), is applied to calculations of various molecular properties—excitation energies, spectroscopic parameters, and potential energy curves—for five molecules: ethylene, butadiene, benzene, N₂, and O₂. The calculated results are compared with those obtained with second‐ and third‐order multireference perturbation theory using the traditional partitioning techniques. We also give results from computations using the multireference configuration interaction (MRCI) method. The presented results show very close resemblance between the new method and MRCI with renormalized Davidson correction. The accuracy of the new method is good and is comparable to that of second‐order multireference perturbation theory using Møller‐Plesset partitioning. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1390–1400, 2003