Vesicular and tubular structures prepared from self-assembly of novel amphiphilic ABA triblock copolymers in aqueous solutions

A kind of novel soft amphiphilic ABA triblock copolymers, poly(L-lysine)b-poly(tetrahydrofuran)-b-poly(L-lysine), was synthesized by the anionic ring-opening polymerization of ε-benzyloxycarbonyl-L-lysine N-carboxyanhydride using amine-terminated poly(tetrahydrofuran) as a macroinitiator and subsequent removal of the protecting group. The resulting copolymers possessing a nearly symmetrical and narrow molecular weight distribution were dissolved in water at an appropriate concentration range at room temperature to yield vesicles as confirmed by using negative stain TEM and DLS. Meanwhile, nanotubes were obtained as the result of the conjunction of vesicles by reducing the medium temperature as evidenced by TEM. The effect of pH and salt concentration variations on the self-assembly behavior was also examined.