Room temperature synthesis of block copolymer nano-objects with different morphologies via ultrasound initiated RAFT polymerization-induced self-assembly (sono-RAFT-PISA)

Polymerization-induced self-assembly (PISA), which allows scalable synthesis of nano-objects, has drawn significant research attention in the past decade. However, the initiation methods in most of the current reported PISA are still restricted to thermal or photo processes. Sonolysis of a water molecule by high frequency ultrasound to generate a hydroxyl radical and to initiate polymerization has the potential to be a new "initiator-free" synthesis technique. Despite ultrasound-initiated polymerization-induced self-assembly (sono-PISA) being reported, only spherical micelle morphology was achieved. We demonstrate here the first room temperature synthesis of diblock copolymer nano-objects with different morphologies using ultrasound (990 kHz) initiated reversible addition-fragmentation chain transfer PISA (sono-RAFT-PISA) in an aqueous system. It was found that the morphologies of the block copolymer nano-objects prepared by sono-RAFT-PISA were different from those prepared by conventional thermal-PISA. Furthermore, the impacts of ultrasound and presence of a cross-linker on the nano-object morphology were investigated. It was observed that the stability of worm-like micelles will be affected by ultrasound but could be strengthened via core-cross-linking (CCL). Overall, the externally-regulatable, easily scalable and sustainable "green" features of ultrasound have the potential to promote the application of sono-PISA for the fabrication of nano-objects.