Reversible Morphological Evolution of Responsive Giant Vesicles to Nanospheres by the Self‐Assembly of Crystalline‐b‐Coil Polyphosphazene Block Copolymers

The preparation of long‐term‐stable giant unilamellar vesicles (GUVs, diameter ≥1000 nm) and large vesicles (diameter ≥500 nm) by self‐assembly in THF of the crystalline‐b‐coil polyphosphazene block copolymers N=P(OCH₂CF₃)₂]_n‐b‐N=PMePh]_m ( 4 a : n=30, m=20; 4 b : n=90, m=20; 4 c : n=200, m=85), which combine crystalline N=P(OCH₂CF₃)₂] and amorphous N=PMePh] blocks, both of which are flexible, is reported. SEM, TEM, and wide‐angle X‐ray scattering experiments demonstrated that the stability of these GUVs is induced by crystallization of the N=P(OCH₂CF₃)₂] blocks at the capsule wall of the GUVS, with the N=PMePh] blocks at the corona. Higher degrees of crystallinity of the capsule wall are found in the bigger vesicles, which suggests that the crystallinity of the N=P(OCH₂CF₃)₂] block facilitates the formation of large vesicles. The GUVs are responsive to strong acids (HOTf) and, after selective protonation of the N=PMePh] block, they undergo a morphological evolution to smaller spherical micelles in which the core and corona roles have been inverted. This morphological evolution is totally reversible by neutralization with a base (NEt₃), which regenerates the original GUVs. The monitoring of this process by dynamic light scattering allowed a mechanism to to be proposed for this reversible morphological evolution in which the block copolymer 4 a and its protonated form 4 a⁺ are intermediates. This opens a route to the design of reversibly responsive polymeric systems in organic solvents. This is the first reversibly responsive vesicle system to operate in organic media.