Solvent-Induced Transition of Hollow Sphere to Giant-Tube from Amphiphilic Rod-Coil-Rod Triblock Copolymers of 2-Vinylpyridine and n-Hexyl Isocyanate

The effect of solvent compositions on the micellization behaviors of amphiphilic poly(n-hexyl isocyanate)-b-poly(2-vinylpyridine)-b-poly(n-hexyl isocyanate) (PHIC-b-P2VP-b-PHIC) rod-coil-rod triblock copolymer was studied. In absolute methanol the block copolymer formed hollow spherical micelles. These micelles transformed into giant-tubes by simply changing the solvent composition. With 20% THF in CH₃OH hollow spheres got interconnected and formed species that are precursors of the giant tubes. When the composition of THF reached 50–70%, long giant tubes are formed. Further increasing THF content in the mixed solvent, fragmentation of the wall of the tubes was observed. In absolute THF, which is the common solvent for both the blocks, the usual phase separation occurred. TEM image of the giant tubes stained with iodine showed that the core of the tubes is made from PHIC rod block.