Formation of genus vesicles in dilute aqueous solution by PtBA(x)-b-PS130-b-PEO90-b-PS130-b-PtBA(x) amphiphilic pentablock terpolymers

A series of linear symmetrical ABCBA pentablock terpolymers, poly(tert-butyl acrylate)-b-polystyrene-b-poly(ethylene oxide)-b-polystyrene-b-poly(tert-butyl acrylate) with constant lengths of PS and PEO blocks but different degree of polymerization x of PtBA block, namely PtBA(x)-b-PS130-b-PEO90-b-PS130-b-PtBA(x) (x = 40, 75, 100, 165, and 200), were found to form various vesicular nanostructures in dilute aqueous solution as observed by conventional transition electron microscopy (TEM), cryogenic transmission electron microscopy (cryo-TEM) and scanning electron microscopy (SEM). Genus vesicles with nanometer sizes and various genus values (g), including individual spherical vesicles, tubular vesicles (g = 0), toroidal vesicles (g = 1) and the vesicles with even larger g values (g > 1) were observed, respectively. The g value of genus vesicles formed by PtBA(x)-b-PS130-b-PEO90-b-PS130-b-PtBA(x) pentablock terpolymers decreased with the increasing length of PtBA block. The formation mechanism of genus vesicles was preliminarily discussed by the combination of membrane bending energy, the area-difference-elasticity and the edge effect.