Manfred Dieter Lechner

Synthesis and characterisation of dextran and pullulan sulphate

Dextrans and pullulans of different molar masses in the range of 10(4)-10(5) g/mol were sulphated via a SO3-pyridine complex. The degree of substitution achieved was DS = 2.4 and DS = 1.4 for dextran sulphate and DS = 2.0 and DS = 1.4 for pullulan sulphate, respectively. Confirmation of sulphation was given by FTIR spectroscopy. Asymmetrical S=O and symmetrical C-O-S stretching vibrations were detected at 1260 and 820 cm(-1). Reactivity of the polysaccharide C-atoms was determined by 13C NMR spectroscopy: For dextran this was C-3 > C-2 > C-4, while for pullulan it was C-6 > C-3 > C-2 > C-4.

Pressure Dependence of Thickness and Refractive Index of Thin PMMA-Films Investigated by Surface Plasmon and Optical Waveguide Spectroscopy

Total internal reflection (TIR) and attenuated total reflection (ATR) measurements in the Kretschmann configuration have been performed at 25 °C with poly(methyl methacrylate) (PMMA) films (of ca. 2.5 μm thickness) spincoated on top of a 50 nm thick gold layer, as a function of the applied hydrostatic pressure, ranging from p = 1. 10 5 to 1 050. 10 5 Pa. The analysis of guided optical modes allows for the separate determination of the refractive index n and the thickness d of the polymer films as a function of pressure. The pressure media in contact with the PMMA films were water, ethanol, and methanol. Thermodynamic theories for the density of solids and fluids in combination with the Lorentz-Lorenz equation for their optical properties fit the experimental data quite well.

Photoisomerization of Disperse Red One in Films of Poly(methyl-methacrylate) at High Pressure

Abstract Evanescent wave optics under high pressure is developed for the optical and mechanical characterization of thin films. Both the attenuated total reflection in the Kretschmann configuration and the grating coupling techniques are implemented. We apply total internal reflection and surface optical wave, e.g. surface plasmon spectroscopy, in order to gain information about the pressure dependence of the optical and mechanical properties of the pressure medium and the metal coupling layer. Optical modes guided in thin films allow us to characterize the pressure effects on these films. We show that hydrostatic pressure applied to thin polymer films increases their refractive index and decreases their thickness. The pressure increases the density of these films by a reduction of the free volume. As far as microscopic environments are concerned, we show that the molecular movement induced by photo- and thermal isomerization of an azo chromophore flexibly tethered to a poly(methyl-methacrylate) polymer is hindered by increasing the pressure.

Thermal properties of poly(styrene-block-ϵ-caprolactone) in blends with poly(vinyl methyl ether)

Abstract The thermal characteristics of a styrene-ϵ-caprolactone diblock copolymer, P(S- b -CL), in blends with poly(vinyl methyl ether) (PVME) were studied by DSC. The glass transition temperatures show that PVME is only dissolved in the PCL block. It segregates from the PCL block at low temperatures. The addition of PVME leads to increasing crystallinity of the PCL block in a certain range of composition. However, degrees of crystallinity do not change significantly with crystallization temperature. Optical inspection revealed that the PCL block does not form spherulites. The crystallization kinetics of the PCL block has been systematically studied. The rate constants of crystallization for different blends decrease exponentially with crystallization temperature, whereas the rates of crystallization are scarcely affected by PVME content. The Avrami exponents were found close to two.