Novel Bowl-Shaped Morphology of Crew-Cut Aggregates from Amphiphilic Block Copolymers of Styrene and 5-(N,N-Diethylamino)isoprene

Abstract

A new morphology of crew-cut aggregates prepared from highly asymmetric triblock copolymers of 5-(N,N-diethylamino)isoprene and styrene in dilute solution is reported. After quaternization of the polar block, using dimethyl sulfate, the copolymers consist of a long block of polystyrene (PS) with short poly[5-(N,N,N-diethylmethylammonium)isoprene] (PAI) blocks at both chain ends. The aggregates were prepared by first dissolving the copolymers in a common solvent for both blocks and then adding water to induce the segregation of the PS chains. 1,4-Dioxane, THF, or a DMF/THF mixture was used as the common solvent in the preparation of these structures. The bowl-shaped aggregates are essentially highly polydisperse spheres, containing an asymmetrically placed single void space, which has broken through the surface. The continuous phase is composed of an assembly of reverse micelles (PAI core and PS corona) with hydrophilic PAI chains surrounding the structure at the polymer/aqueous solution interface. It is believed that the formation of the bowl-shaped morphology is under kinetic control and does not represent an equilibrium state. A possible mechanism for the formation of this aggregate is proposed, based on two other previously reported crew-cut morphologies from diblock copolymers. This study illustrates the importance of the preparative conditions on the self-assembly of nonequilibrium aggregates from amphiphilic block copolymers.