ABSTRACT
I. INTRODUCTION Because they are both polymers and electrolytes, polyelectrolytes represent a special class of materials with interesting properties and high practical relevance. One of their particular features is the ability to form interpolymer complexes between oppositely charged species, polyanions and polycations, driven by the attractive Coloumb interaction. This phenomenon has been well known for a long time from the mutual precipitation of proteins [1,2]. The first systematic studies with synthetic polyelectrolytes were carried out by Michaels and Miekka [3], dealing especially with the stoichiometry of the polyelectrolyte complexes (PEC). Michaels realized already the practical relevance of the principle of PEC formation for the production of membranes with special separation properties. At present, PECs are used for such largescale industrial applications as flocculants, coatings, and binders and for special purposes in biotechnology and medicine. Promising fields under the latter aspect are the PEC-microencapsulation of drugs, enzymes, cells, mi croorganisms up to subjects such as Langerhans islets [4-7], poly electrolyte multilayers as biosensors [8,9], immobilization of proteins by complex for mation [10-13], and polycation complexes with polynucleotides or oligo nucleotides as vectors in gene therapy [14-17].
