Synthesis of Well‐Defined Block Copolymers of Hyperbranched Polyamide and Polystyrene and Their Micelle‐to‐Vesicle Transformation in Organic Solvents

Abstract

AbstractWell‐defined block copolymers consisting of hyperbranched polyamide (HBPA) and polystyrene (PSt) are synthesized, and their self‐assembled structures in solutions are investigated. Atom transfer radical polymerization (ATRP) of styrene initiated from an HBPA macroinitiator, prepared by the chain‐growth condensation polymerization of an AB2 monomer, followed by introduction of an ATRP initiator unit at the focal point, gives the desired block copolymers, PSt‐b‐HBPAs, with well‐defined molecular weight and narrow molecular weight distribution. The block copolymer (PSt/HBPA = 84/16) undergoes self‐assembly in toluene to form spherical micelles (≈10–20 nm), but upon addition of methanol to the toluene solution (toluene/methanol = 0.97/0.03), the morphology changes to vesicles. Further addition of methanol (toluene/methanol = 0.90/0.10) leads to an increase in vesicle size (200–300 nm) and the morphology further transforms from vesicles to large aggregates (>100 nm) at toluene/methanol = 0.80/0.20. In the case of PSt‐b‐HBPA with shorter PSt segments (PSt/HBPA = 76/24 and 60/40), spherical micelles are formed in toluene, but the micelle morphology remains unchanged when 10 wt% methanol is added, though large aggregates (>100 nm) are still formed in toluene/methanol = 0.80/0.20. Interestingly, the morphological transformations of linear/hyperbranched block copolymers are different from those of their double linear block copolymer counterparts.