Noncovalently connected polymeric micelles based on a homopolymer pair in solutions

The intermolecular complexes with poly(4-vinylpyridine) (PVPy) as the backb one and carboxyl-terminated polybutadiene (CPB) as the grafts were formed d ue to hydrogen bonding in their common solvent chloroform. Two solvent pair s, i.e., n-hexane/chloroform and nitromethane/chloroform, were found select ive for CPB and PVPy, respectively. Thus, the stable micelles with PVPy bei ng the core and CPB being the shell, denoted as (PVPy)-CPB, and the ones wi th CPB core and PVPy shell, denoted as (CPB)-PVPy, were formed in the corre sponding selective solvent pairs. Differing from the conventional micelles made of block or graft copolymers, the present micelles possess hydrogen bo nds instead of covalent bonds connecting the core and shell and their compo sition; i.e., the weight ratio of the core to shell is readily adjustable. Dynamic light scattering study demonstrated that the average hydrodynamic d iameters <D-h> of the micelles were mostly in the range from 100 to 300 nm depending on the solvent composition, polymer concentration, and the chain number ratio of CPB to PVPy, etc. (PVPy)-CPB were found more stable against dilution than (CPB)-PVPy. The two kinds of micelles differ in their diamet er-composition dependence; namely, with increasing the ratio of CPB/PVPy, < D-h> of (PVPy)-CPB decreases monotonically while that of (CPB)-PVPy increas es at the low ratio range but decreases at the high ratio range. Besides, t he core-shell structure of both micelles was clearly visualized by transmis sion electronic microscopy using staining techniques.