Sonochemically Initiated RAFT Polymerization in Organic Solvents

Sonochemically initiated RAFT polymerization (sonoRAFT) in organic solvents is presented for the first time. Acoustic cavitation, induced by high frequency ultrasound (US) (490 kHz), caused pyrolysis of organic solvent molecules providing a source of initiating radicals. In this way, polymers could be prepared without conventional radical initiators (e.g., AIBN) or additives (e.g., piezoelectric nanoparticles). The polymerization of acrylates and acrylamides was well controlled with the prepared polymers displaying good agreement between theoretical and experimental molecular weights with low dispersities. Methacrylates were found to be less controlled. Several factors were found to influence the final monomer conversion (25-92%) and the upper limit of molecular weight (20-30 kDa) such as the monomer vapor pressure and solubility, solvent choice, and polymer type. No polymerization occurred in the absence of US demonstrating excellent temporal control, and the polymer products were found to possess high chain-end fidelity via chain extension and MALDI-TOF mass spectroscopy.