Formation of Amphiphilic Block Copolymer Micelles in Nonaqueous Solution

Abstract

In contrast to aqueous solution, the nature of non-aqueous solvents for amphiphilic block copolymers can vary from organic solvents to supercritical fluids, and even homopolymers. The driving force of micellization of an amphiphilic block copolymer in both aqueous and non-aqueous solution is the solvent selectivity for different blocks. However, the micellization of a block copolymer in an organic solvent with hydrogen bonding properties is usually enthalpy-driven. Moreover, the variation in organic solvents leads to diversity in the association behavior. In this chapter, the micellization behavior of amphiphilic block copolymers in selective organic solvents is reviewed. Supercritical fluids, especially supercritical CO2, are becoming increasingly more attractive as environmentally benign solvents. The investigation of supramolecular formation of block copolymers in supercritical CO2 has potential, because it is closely related to the development of new routes for polymer synthesis. In dilute solution, the micellization of amphiphilic block copolymers in supercritical CO can be quite different when compared with regular solvents because of the unique properties of supercritical fluids. For example, the solvent quality for supercritical fluid is pressure dependent, while it is much less so for aqueous or nonaqueous organic solvents. A brief introduction to the micellization of amphiphilic block copolymers in dilute low molecular weight homopolymer solutions is also included in this chapter to show the similarity of micelle formation of a block copolymer in polymer blends to the more conventional nonaqueous solutions.