Covalent vs. metallo-supramolecular block copolymer micelles

An amphiphilic metallo-supramol. polystyrene-block-poly(ethylene oxide) diblock copolymer contg. a bis(2,2':6',2''-terpyridine)ruthenium(II) complex (PS20-[Ru]-PEO70) as supramol. connector between the two blocks was compared to (PS22-b-PEO70). The two different copolymers were used to prep. kinetically frozen aq. micelles that consist of a glassy polystyrene core surrounded by a poly(ethylene oxide) corona. The micelles were characterized by dynamic light scattering (DLS). In the case of the PS22-b-PEO70, micelles with a hydrodynamic diam. (Dh) of 18 nm were obsd. while stable micelles with a Dh of 65 nm and larger aggregates are formed by PS20-[Ru]-PEO70. Addn. of different salts during the initial stage of micelle formation has a deep effect on the final micellar characteristic features; in the case of PS20-[Ru]-PEO70, the micelles become quite similar to those of PS22-b-PEO70. This effect is attributed to decreased electrostatic repulsions between the charged bis(2,2':6',2''-terpyridine)ruthenium(II) complexes at the interface of immiscible polystyrene and poly(ethylene oxide) blocks. Addn. of different salts to solns. of the PS20-[Ru]-PEO70 micelles, initially prepd. in the absence of salt, caused a decrease in size, although the packing of the charged bis(2,2':6',2''-terpyridine)ruthenium(II) complexes did not change in these kinetically frozen micelles. A decrease in micelle size was obsd. as temp. increased. These effects were not obsd. in PS22-b-PEO70 and are attributed to stretched poly(ethylene oxide) chain segments. A model for metallo-supramol. micelles is proposed based on exptl. observations