Synthesis and self-assembly studies of amphiphilic poly(n-hexyl isocyanate)-block-poly(2-vinylpyridine)-block-poly(n-hexyl isocyanate) rod-coil-rod triblock copolymer

Rod-coil-rod triblock copolymers of 2-vinylpyridine (2VP) and n-hexyl isocyanate (HIC) were synthesized by living anionic polymerization. The homopolymerization of 2VP was carried out at -78 degrees C in THF by using bidirectional initiators sodium naphthalenide (Na-Naph) and potassium naphthalenide (K-Naph). Block copolymerization with HIC was performed at -98 degrees C in the presence of sodium tetraphenylborate additive. While K-Naph yields copolymers of broad molecular weight distribution, Na-Naph was quite effective in facilitating a high degree of control over the copolymerization. The block copolymers containing higher rod volume fraction showed lamellar microphase separation in THF, a common solvent for both the rod and the coil blocks. The self-organization of the copolymer in solvents selective for one block was quite fascinating in that in CHCl3 solid micelles of similar to 20 nm were formed, whereas large hollow micelles of similar to 200 nm were generated in CH3OH.