Micellization of ω-Functionalized Diblock Copolymers in Selective Solvent. Study on the Effect of Hydrogen Bonds

Abstract

Two series of ω-functionalized diblock copolymers polystyrene-b-polyisoprene, PS−PI, having hydroxyl end groups either at the PS (PI−PS−OH) or at the PI (PS−PI−OH) block were synthesized by living anionic polymerization. The samples had similar molecular weights but different compositions. Employing suitable post-polymerization reactions the hydroxyl groups were transformed to the corresponding 2-ureido-4-pyrimidinone (UPy) functions. The UPy group is known to dimerize strongly in a self-complementary array of four cooperative hydrogen bonds. The micellization properties of the unfunctionalized and the ω-functionalized polymers having either hydroxyl or UPy end groups were studied in n-decane, which is a selective solvent for the PI block, by static and dynamic light scattering and dilute solution viscometry. A distinct micellar behavior was obtained depending on the nature of the end group and their location either at the core-forming or the corona-forming block. To confirm the results regarding the effect of the hydrogen bonds the solid-state properties of the copolymers were studied by differential scanning calorimetry and thermogravimetric analysis. Furthermore, the dilute solution properties were investigated in chloroform, which is a common good solvent for both the PS and PI blocks but nonpolar, thus allowing the formation of hydrogen bonds.