Unusual Aggregation Behavior of a Novel Tertiary Amine Methacrylate-Based Diblock Copolymer: Formation of Micelles and Reverse Micelles in Aqueous Solution

Abstract

It is well-known that AB diblock copolymers aggregate to form micelles in solvents which are selective for either the A block or the B block.1-5 Provided that the block ratio is not too asymmetric, it is also possible to obtain micelles or reverse (inverted) micelles from the same block copolymer by choosing appropriate selective solvents. For example, Oranli and co-workers reported6 that styrene-butadiene diblock copolymers can form micelles with either polystyrene cores (in n-alkanes) or polybutadiene cores (in DMF or MEK, respectively). Similarly, it is well-known that small molecule surfactants can form micelles or reverse micelles in aqueous and nonaqueous media, respectively. However, as far as we are aware, there are no literature examples of block copolymers or surfactants which are capable of forming both micelles (A block in core) and reverse micelles (B block in core) solely in aqueous media. At first sight this might appear impossible, but in this paper we describe a novel water-soluble AB diblock copolymer which exhibits this highly unusual behavior at room temperature at around neutral pH (see Figure 1). The critical parameters which affect the solvency and, hence, govern the formation of micelles or reverse micelles are the solution pH, electrolyte concentration, temperature, and block symmetry.