Preparation and characterization of core-shell latexes

Polymeric dispersions with a concentric core-shell structure of the latex particles were obtained by a two-stage emulsion polymerization technique. Conditions for the formation of shells on polymeric seeds are discussed. SANS and SAXS investigations were carried out in order to verify the core-shell structure of the particles. DSC and IR measurements indicate the existence of an interfacial layer between core and shell polymers. The results are transferred to emulsion polymers containing inorganic filler particles.     

Two new xanthones from Hypericum japonicum

Two new xanthones, 1,6-dihydroxyisojacereubin-5-O-beta-D-glucoside (1) and 3,6,7-tri-hydroxy-1-methoxy-xanthone (2), were isolated from Hypericum japonicum. The structural elucidation of the isolated compounds were primarily based on HREIMS, EIMS, UV, IR, 1D-, and 2D-NMR analyses, including COSY, HMQC, HMBC, and NOESY correlations.     

Anisotropic effects in the optical spectra of magic metal clusters: the role of ionic structure

The effect of the ionic positions on the optical spectra of magic metal clusters is studied via pseudopotential perturbation theory. Electronic many-body effects are considered within perturbed time-dependent local-density-approximation. Quantitative agreement with recent experiments by Reiners et al. is obtained. In this way a natural explanation is obtained for the temperature dependence of the optical absorption of magic metal clusters.     

Modeling of configurations and third-order nonlinear optical properties of methyl silsesquioxanes

Configuration optimizations, excited state properties, and the frequency-dependent third-order nonlinear optical polarizabilities have been investigated on a series of methyl-silsesquioxane (MeT) cages [CH(3)SiO(1.5)](n) (n=4, 6, 8, and 10) using ab initio quantum mechanical methods coupled with the sum-over-states methods. The obtained electronic absorption spectra show a redshift as the cage size increases, and the absorption spectra are assigned as charge transfers from oxygen p type to silicon s type atomic orbitals. The calculated average third-order polarizabilities of in the three optical physical processes (third-harmonic generation, the electric-field-induced second-harmonic generation, and degenerate four-wave mixing) have wide nonresonance regions. For all the considered species, the values of gamma decrease in the order of [MeT](4)>[MeT](8)(C(2v))=[MeT](10)>[MeT](6)>[MeT](8)(O(h)).     

SAXS study of core-shell colloids

Polymeric core-shell systems were produced by a two-stage emulsion polymerization technique under fixed conditions: i) monodisperse seed latex with a sufficiently high particle number; ii) starved monomer-II addition; iii) water-soluble initiator; iv) incompatibility of core and shell polymer. From electron micrographs, it is not possible to determine where the second polymer is located within these two-stage emulsion polymers. The internal structure of the particles can be detected by small-angle x-ray scattering. The results indicate that; i) the emulsion polymerization process takes place in a small surface layer region of the seed particles, and ii) a small interfacial layer exists between the core and shell polymer.Part 6 of Polymerizations in the Presence of Seeds     

On the molecular mechanism of clouding in aqueous solution of poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) triblock copolymers

The physical aspects of the clouding phenomenon in the aqueous solution of a poly(oxyethylene)(POE) – poly(oxypropylene)(POP) – poly(oxyethylene)(POE) triblock copolymer were investigated by applying various experimental methods: viscometry, ultrasonic technique, light scattering, infrared and Raman spectroscopy. The ultrasonic absorption studies hint at a critical behaviour. In order to understand the spectroscopic findings, conformational energies of model POE molecules as well as interaction energies between oxyethylene (OE) units and water molecules were calculated by the use of the quantum chemical PCILO method. It is suggested that the clouding is connected with conformational changes of POE segments.     

A DSC study of PVAC-PMMA two-stage emulsion polymers

Core-shell polymer colloids were produced by a two-stage emulsion polymerization technique. The polymers thus formed were investigated by means of differential scanning calorimetry (DSC). The DSC thermograms show two separate glass transition regions of the core and the shell component with positions unchanged regardless of chemical composition. Increases in specific heat capacity at the glass transition temperature of both components are lower than theoretical values calculated from the net chemical composition. From these results, it is possible to estimate i) the chemical composition of the interfacial layer and ii) the interfacial layer thickness. This interfacial layer thickness is in the order of 2–7 nm.Part 7 of Polymerizations in the Presence of Seeds     

Study of 3d – 4f and 3d – 5f quartet and doublet transitions of doubly excited three-electron ions

We present the first observation of optical transitions between doubly excited doublet states in the term systems N V, O VI and F VII. The spectra were produced by foil excitation of fast ion beams. The assignment of the spectral lines was made by comparison with the results of MCDF calculations along the isoelectronic sequence. The same method also led to the identification of two 3d – 4f quartet transitions in Mg X.     

Industrial Polymerization Monitoring

Summary: Monitoring and control of polymerization reactions is essential for high process safety, high product quality and competitive production costs. Ideally the entire process chain is regarded, starting with raw material analysis and the polymerization reaction up to the measurement of polymer- and application- properties. Process data like temperatures and pressures can be used to monitor reaction trajectories in a cost effective way, e.g. using calorimetric evaluations. Additional sensors can provide chemical or morphological information but must be robust and inexpensive for commercial applications (e.g. NIR- or Raman spectroscopy). Data from these different sources can be used for multivariate data analysis, delivering additional insights that might not be obtained by direct measurement.