Effect of solvent composition on transformation of micelles to vesicles of rod-coil poly(n-hexyl isocyanate-block-2-vinylpyridine) diblock copolymers.

The self-aggregation behavior of an amphiphilic rod-coil block copolymer of poly(n-hexyl isocyanate-block-2-vinylpyridine) (PHIC(189)-b-P2VP(228)) (f(P2VP) = 0.78, M(n) = 24.5K) in a tetrahydrofuran (THF)/water system was examined using dynamic light scattering (DLS), transmission electron microscopy (TEM), and field emission scanning electron microscopy (FE-SEM). The presence of a certain amount of water in the THF-based polymer solution induced a morphological transition from spherical solid micelles to open mouth platelike vesicles. The size of the aggregates increased with an increase in water content in the mixed solvent of THF/water. In the range of 30-40% water, the polymer formed vesicles with an interdigitated architecture of poly(n-hexyl isocyanate) (PHIC) at the center of the membrane and with the poly(2-vinylpyridine) (P2VP) block forming the outer layers and pointing toward the solvent. However, at higher water contents, the thickness of the bilayer increased due to the rearrangement of the vesicle membrane from a flip-flop to a lamellar architecture. After the degradation of the PHIC from the vesicles at basic pH, hollow spherical aggregates remained stable. After removing the THF from the mixed solvent using dialysis, large-sized compound vesicles were formed.