Comparative Study of Solution Properties of Amphiphilic 8-Shaped Cyclic-(Polystyrene-b-Poly(acrylic acid))2 and Its Linear Precursor

Abstract

Amphiphilic 8-shaped cyclic-(polystyrene-b-poly(acrylic acid))2 with two rings and its linear precursor, i.e., 8-shaped cyclic- and linear-(PS–PAA)2, were successfully prepared by a combination of atom transfer radical polymerization (ATRP) and “click” chemistry. Using various methods, we characterized those intermediates and resultant copolymers and studied their association properties in solutions. As expected, the average aggregation number (⟨Nagg⟩) increases with the molar fraction of styrene for a given overall degree of polymerization. Our results reveal that the cyclization leads to a smaller ⟨Nagg⟩ but slightly larger and looser aggregates, presumably due to the topological constraint of the two rings (8-shaped). Using these amphiphilic chains as emulsifying agents, we found that 8-shaped cyclic-(PS–PAA)2 chains are less effective in stabilizing latex particles in emulsion polymerization because each cyclic chain occupies a smaller interfacial surface area than its linear counterpart. Further, using pyrene as a model hydrophobic molecule, we investigated their solubilization powers. Our results reveal that 8-shaped cyclic- and linear-(PS–PAA)2 chains have a similar ability in loading hydrophobic pyrene molecules, different from our original expectation, presumably because the hydrophobic PS block is too short and the hydrophilic PAA rings are too small. The current study provides a better understanding of the complicated topological constraint on the solution properties of 8-shaped cyclic amphiphilic copolymers.