ИСТИНА

Up to now only few investigations of dynamics of block copolymer systems have been reported. Mostly copolymers with a hydrophobic block with Tg above room temperature have been investigated (PS-PAA, PS-PMAA,…). Here the dynamic processes of the aqueous solutions are hindered due to the glassy state of the PS core of the micelle. In our case we employ polyisobutylene (PIB) as the core-forming block, that should exist in a liquid-like state (Tg ≈ -55 °C). Therefore changes in the solution parameters (pH, salt concentration) could have an effect not only on the corona, but also on the core of the micelle, i.e. one expects a dynamic behaviour of such aggregates. This should also have an effect on the aggregation number. Also interpolyelectrolyte complexes (IPECs), formed by the polyelectrolyte in the corona of the micelle – poly(methacrylic acid) (PMAA) – with quaternized poly(4-vinylpyridine) (P4VPQ) have been investigated with respect to their kinetics. At pH = 7, water-soluble complexes are formed up to a Z –value (Z = [P4VPQ]/[PMAA], the basemolar concentrations of the cationic polyelectrolyte and ionic block of the copolymer are given in brackets) of 0.4 – 0.5; beyond this value precipitation occurs. Their complexes are stable at low salt concentrations. However, beyond a certain NaCl concentration, the complexes dissolve, thereby reforming the originally present copolymer micelles and molecularly dissolved polyelectrolyte. This can be proven by different types of measurements, including SANS, turbidimetric titration, titration with a sodium-selective electrode and stopped-flow in combination with SAXS. Kinetic investigations of the formation and the dissociation of the complex show an overlay of a fast mixing process, followed by a slower process. The faster one is believed to be the diffusion of individual copolymer molecules coupled to the diffusion of the polycation and the salt into or out of the micelle. The slower one could be a kind of dynamic rearrangement of the block copolymers to form the finally stable aggregates. Thermodynamic investigations on the enthalpy of formation of the IPEC as well as thermodynamic data from titrations are planned to give a deeper insight into the processes occurring during formation and salt-induced dissociation of such complex macromolecular assemblies.