Controlling Micellar Structure of Amphiphilic Charged Triblock Copolymers in Dilute Solution via Coassembly with Organic Counterions of Different Spacer Lengths

Abstract

Micelle structures from the assembly of poly(acrylic acid)-block-poly(methyl acrylate)-block-polystyrene (PAA-b-PMA-b-PS) triblock copolymers in mixed tetrahydrofuran (THF)/water solution, including disks, toroids, cylinders, and spheres, were targeted by coassembling with different diamines. At constant solution composition (THF:H2O, polymer concentration, and diamine concentration), the interfacial curvature of the assembled structures was determined primarily by diamine chain structure. It was found that interchain binding from the interaction of the two amine end groups of diamines with acid groups from different PAA corona blocks governs the final assembled structures. Diamines with hydrophilic spacers induced the formation of micelles with larger interfacial curvature as the spacer length increased. Disklike micelles, cylindrical micelles, or spherical micelles were observed with the gradual increase of hydrophilic spacer length. Diamines with variable hydrophobic spacers showed a similar effect when the spacer length was less than six methylene units. Application of longer hydrophobic diamines had a reverse effect on the interfacial curvature. This effect was attributed to the interaction of hydrophobic diamine hydrocarbon linking chains with the PMA-b-PS hydrophobic core. These findings indicate an easy method to tune micelle structure with multivalent organic counterions. Assembled morphologies were characterized by means of transmission electron microscopy, and the interaction of diamines with acidic units of the PAA block segments was studied by solution-state nuclear magnetic resonance spectroscopy.