Solution Behavior of Cascade Polymers.

Abstract

This thesis consists of four chapters. In the first, a general introduction is presented. Chapter 2 deals with the characterization of polyamidoamine (PAMAM) cascade polymers. Diffusion coefficients of four different generations (generation 3, 5, 7, and 9) of PAMAMs were measured in aqueous solutions by dynamic light scattering. Generation 3 and 5 were characterized again, after labeling with fluorescein isothiocyanate, by fluorescence photobleaching recovery. The dynamic light scattering results depended on the concentration of added salt in the low salt limit, while the fluorescence values were almost independent of salt concentration. The polyelectrolyte effects, or solution nonidealities, strongly affected light scattering, and were observed in the lower generations of PAMAMs at zero added salt. Nevertheless, PAMAMs should make suitable markers and diffusion probes unless they are studied at low salt with dynamic light scattering. In Chapter 3, the interaction between positively charged PAMAM and negatively charged Sodium Polystyrene Sulfonate (NaPSS) is considered. The complex formation between oppositely charged polyelectrolytes was confirmed, and its dependence upon added salt and pH values was studied. At low ionic strength, all PAMAM molecules were bound to NaPSS, and only one diffusion mode corresponding to LPAMAM-5/NaPSS complex was observed. However, two diffusion modes, slow and fast, appeared as the ionic strength was increased. The slow one is interpreted as the diffusion of LPAMAM-5/NaPSS complex while the fast one is not explained yet. At low pH, LPAMAM-5/NaPSS complex made a precipitate, while no complex was formed at high pH. Two diffusion modes were observed at pH 9. Chapter 4 concerns the gelation of arborols, another family of cascade polymers that makes aggregation in appropriate solvent. Several two directional dumbbell shaped arborols with hydrophilic terminal hydroxy groups and lipophilic hydrocarbon skeleton were investigated. Gelation was first confirmed with tilting test and intensity measurement by light scattering. The transition point from gel to fluid was measured by Small Angle Light Scattering and Differential Scanning Calorimeter. The cross section radius of gyration and average distance between neighboring particles were determined with Small Angle X-ray Scattering. The structure of arborols was pictured by Freeze Fracture Electron Microscope.