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Reversible Morphological Evolution of Responsive Giant Vesicles to Nanospheres by the Self‐Assembly of Crystalline‐ b ‐Coil Polyphosphazene Block Copolymers
Author(s) -
SuárezSuárez Silvia,
Carriedo Gabino A.,
Presa Soto Alejandro
Publication year - 2016
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201504733
Subject(s) - vesicle , polyphosphazene , crystallinity , copolymer , micelle , dynamic light scattering , protonation , materials science , crystallization , crystallography , polymer chemistry , chemistry , chemical engineering , polymer , nanoparticle , nanotechnology , membrane , organic chemistry , ion , biochemistry , aqueous solution , engineering
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(OCH 2 CF 3 ) 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(OCH 2 CF 3 ) 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(OCH 2 CF 3 ) 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(OCH 2 CF 3 ) 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 (NEt 3 ), 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.