title: Reversible Morphological Evolution of Responsive Giant Vesicles to Nanospheres by the Self-Assembly of Crystalline-b-Coil Polyphosphazene Block Copolymers.
abstract: 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.
authors.affiliation: Departmento de Química Orgánica e Inorgánica (IUQOEM), Universidad de Oviedo, Julián Clavería s/n, 33006, Oviedo, Spain.
authors.forename: Silvia
authors.initials: S
authors.lastname: Suárez-Suárez
authors.affiliation: Departmento de Química Orgánica e Inorgánica (IUQOEM), Universidad de Oviedo, Julián Clavería s/n, 33006, Oviedo, Spain.
authors.forename: Gabino A
authors.initials: GA
authors.lastname: Carriedo
authors.affiliation: Departmento de Química Orgánica e Inorgánica (IUQOEM), Universidad de Oviedo, Julián Clavería s/n, 33006, Oviedo, Spain. presaalejandro@uniovi.es.
authors.forename: Alejandro
authors.identifier: http://orcid.org/0000-0003-3565-4672
authors.initials: A
authors.lastname: Presa Soto
mesh_terms: D003460:Crystallization; D054118:Nanospheres / Q000737:chemistry*; D009943:Organophosphorus Compounds / Q000737:chemistry*; D010316:Particle Size; D011108:Polymers / Q000737:chemistry*; D012997:Solvents
chemical_list: D009943:Organophosphorus Compounds; D011108:Polymers; D012997:Solvents; C108974:poly(phosphazene)
keywords: block copolymers; micelles; polyphosphazenes; self-assembly; vesicles