Multiple Morphologies of PAA-b-PSt Assemblies throughout RAFT Dispersion Polymerization of Styrene with PAA Macro-CTA

The assembly behavior of diblock copolymers in solution can be modulated by block length, block ratio, solvent properties, and preparation route. Different assembly morphologies such as spherical micelles, cylindrical micelles, vesicles, and large compound vesicles have been obtained for diblock copolymers with shorter solvated block, such as poly(acrylic acid)-b-polystyrene (PAA-b-PSt). In the present work, we reported an easy-going route to prepare PAA-b-PSt assemblies with different morphologies through reversible addition fragmentation-transfer (RAFT) dispersion polymerization of styrene in methanol with trithiocarbonated PAA as macromolecular chain transfer agent. Because this RAFT dispersion polymerization exhibited controlled features, the consecutive growth of PSt block led to the successive transition of the obtained PAA-b-PSt assemblies from spherical micelles, cylindrical micelles, vesicles, to large compound vesicles, confirmed by the combination of electron microscopy, laser light scattering, and chemical structural analysis. PAA-b-PSt assembly morphologies and their transition have been adjusted by polymerization conversion, St/PAA feed ratio, and methanol amount, which were elucidated in view of thermodynamic consideration. The mechanisms for the formation of vesicle and the reorganization of vesicles were suggested. This polymerization-induced self-assembly and self-organization provides an efficient way to prepare different nano/microsized polymeric structures.