Gudrun Rother

Amphiphilic cationic block copolymers via controlled free radical polymerization.

N-oxyl terminated vinylbenzyl chloride macromonomers, available via controlled free radical polymerization, were used to synthesize AB-block copolymers of vinylbenzyl chloride and styrene with low polydispersity and different block lengths and block length ratios. The vinylbenzyl chloride blocks were quantitatively converted into cationic polyelectrolytes by reactions with tertiary amines. The micellization of the synthesized amphiphilic cationic block copolymers was investigated using different techniques such as static light scattering, ultracentrifugation and size exclusion chromatography.

The determination of the molecular weight distribution of pectins by calibrated GPC Part I. Calibration by light scattering and membrane osmometry

Abstract Commercial high methoxyl citrus pectin was fractionated on Sepharose 2 B/Sepharose 4 B. Fractions were used to calibrate GPC by light scattering and membrane osmometry. The angular dependence of light scattering of the fractions was interpreted in terms of a two-component system giving reliable M w / M n ratios for the major molecularly dispersed component which forms coils of considerable stiffness in solution. A minor particulate spherical component was identified which was rich in neutral sugars. Structural parameters of this component were determined by comparison of the experimental scattering behavior with master curves. β-Elimination of the fully esterified pectin was carried out to reveal the chemical nature of the particulate component.

Static light scattering technique applied to pectin in dilute solution. 2. The effects of clarification

Abstract The effects of purification/clarification by ultracentrifugation and/or membrane filtration were studied by light scattering, GPC plus off-line capillary viscometry and GLC sugar analysis using a high-methoxyl citrus pectin as model substance. The emphasis of light scattering measurements was put on analysing the angular dependence of the scattered light. For that reason the interpretation of the measured data involved the use of master curves in addition to Zimm or Guinier plots. The benefits and limitations of this method of data treatment for complex systems are discussed both in theory and practice. Due to the natural heterogeneity of pectins, purification or classification modified the original sample by removing the high molecular weight and dense tail, leaving a physically and chemically heterogeneous polysaccharide.

Static light scattering technique applied to pectin in dilute solution. Part I: Reliability of experiments and model calculations

Abstract During static light scattering studies of a commercial high-methoxyl citrus pectin in phosphate buffer, problems arising from sample clarification have been identified. Therefore, the effect of varying the pore size of the membrane filters between 5·0 and 0·2 μm was studied. Also, the effect of repeated filtration was investigated. Data are presented as Zimm and Guinier plots. The lower the pore size of the filter, the lower the average molecular weight, but the higher the negative second virial coefficients found. Results suggest that the negative virial coefficients are due to residual particulate matter. Model calculations suggest that a bimodal system consisting of a molecularly dispersed major component and smaller amounts of a high molecular weight particulate component is an appropriate description of the pectin sample. Dextran sulphate was used to demonstrate the behaviour of a ‘homogeneous’ non-aggregating polysaccharide.

Static Light Scattering of Polyelectrolyte Complex Solutions

The study of highly diluted polyelectrolyte complex (PEC) solutions by physico-chemical methods allows the assessment of the influence of the molecular characteristics of the polyelectrolyte components and of the external parameters of the systems investigated. Especially static light scattering (SLS) has been proved to provide instructive quantitative data about the course of PEC formation and the structural parameters of the generated particles. After a brief survey of the characterization of PEC solutions by SLS an improved algorithm of light scattering curve analysis for higher aggregated structures is described. Its efficiency will be demonstrated by the results of SLS studies on the complex formation between anionically and cationically modified poly(acrylamide) of high molecular weight in comparison with the information obtained by other methods.

Model interpretation in static light scattering

For sufficiently large species, the fit of the experimentally obtained scattering curve with theoretically calculated ones for different basic structure types (sphere, random coil, rod, wormlike chain and others) gives information about the structure type, the polydispersity, the structure density, the molecular parameters Mw and sz, and a characteristic size parameter am, the definition of which depends on the used structure model type. An iterative algorithm is offered to separate bimodal scattering curves into the curves of the components and to characterize the single ones. The theoretical background of such procedures and a corresponding software system will be presented. Application examples demonstrate the efficiency of the procedures.