Aggregation behavior of polystyrene-based amphiphilic diblock copolymers in organic media

Abstract

Two polystyrene (PS)-based amphiphilic diblock copolymers, PS(x)-PV(y) with x/y=3.3−7.7 and PS(x)-PA(y) with x/y=1.2−13.7 (where PS(x)-PV(y) and PS(x)-PA(y) possess poly[(ar-vinylbenzyl)trimethylammonium chloride] and poly(2-acrylamido-2-methylpropanesulfonic acid) blocks, respectively, and x and y are the degrees of polymerization), were prepared by reversible addition-fragmentation chain transfer radical polymerization to investigate the formation of reverse micelles by these copolymers in less polar organic media. The PS(x)-PV(y) samples were more dispersible in halogenated solvents, for example, chloroform and 1,2-dichloroethane (DCE), than the PS(x)-PA(y) samples because of the higher solvophobicity of the PA block. 1H NMR spectra for the PS(x)-PV(y) and PS(x)-PA(y) samples measured in CDCl3 exhibited no signals that corresponded to the PV or PA blocks in the diblock copolymers, which indicated that the PS(x)-PV(y) and PS(x)-PA(y) samples formed reverse micelles in halogenated solvents with the PV or PA blocks in the core. The structures of the reverse micelles formed from the PS(x)-PV(y) samples in DCE were investigated in detail by static and dynamic light scattering. The light scattering data indicated that PS(x)-PV(y) formed star-like micelles at x/y>6 and non-star-like micelles at x/y<6 in DCE. The morphology of the micelles formed from PS(x)-PV(y) with x/y<6 in DCE was most likely brush-like. Two polystyrene-based amphiphilic diblock copolymers, PS(x)-PV(y) and PS(x)-PA(y) (where PS(x)-PV(y) and PS(x)-PA(y) possess poly[(ar-vinylbenzyl)trimethylammonium chloride] and poly(2-acrylamido-2-methylpropanesulfonic acid) blocks, respectively, and x and y are the degrees of polymerization), were prepared by reversible addition-fragmentation chain transfer radical polymerization to investigate their formation of reverse micelles in less polar organic media. Theoretical analysis using light scattering data indicated that PS(x)-PV(y) formed star-like micelles at x/y>6 and brush-like micelle micelles at x/y<6 in DCE.