Amphiphilic Graft Copolymer in a Selective Solvent: Intramolecular Structures and Conformational Transitions

Abstract

We present a scaling theory for the equilibrium conformations of amphiphilic comblike (graft-) copolymer in dilute solution. We examine intramolecular self-assembly upon inferior solvent strength for the backbone. We demonstrate that at sufficiently dense grafting the backbone collapses via formation of a pearl necklace of intrachain micelles that are stabilized by steric repulsion between coronas. This behavior is reminiscent to the Rayleigh instability in hydrophobic polyelectrolyte, though occurs in a neutral macromolecule. The equilibrium local structure and the persistence length of comblike copolymer are analyzed as a function of solvent strength. Repulsion between micellar coronas leads to swelling of comblike macromolecule on larger scales and ensures the thermodynamic stability of the solution with respect to phase separation. In the case of sparse grafting we predict formation of not only spherical but also cylindrical intramolecular micelles and lamellar mesophases.