Ultrasound-Assisted RAFT Polymerization in a Continuous Flow Method

Developments in nanomolecular engineering in the last 20 years have led to the development of technology that uses ultrasonic irradiation in initiating the polymerization process for wider industrial and commercial applications. In this experimental study, ultrasound-assisted reversible addition chain-transfer (Sono-RAFT) polymerization was used to differentiate the effects of the bulk and continuous flow polymerization methods on three parameters─monomer conversion, polymer molar mass, and dispersity─using 2-hydroxyethyl acrylate, N-acryloyl morpholine, and N-dimethylacetamide as monomer substrates. Experimental results indicate that continuous flow polymerization demonstrated higher monomer conversion than polymerizations performed in batch under identical experimental conditions. Furthermore, the increased surface-to-volume ratio inherent to continuous flow reactors enabled Sono-RAFT at a higher monomer concentration than analogous batch reactions due to the higher cavitational intensity accessible in tubular microreactors. The key to continuous flow Sono-RAFT was the observation that stainless-steel microreactors result in increased cavitational intensity and decreased oxygen contamination compared to PFA tubing. We envision that these findings will further advance the field of mechanochemistry in polymer science and provide an approach to make sonochemically regulated polymerization more practical and sustainable.