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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. 

Abstract Macroscale additive manufacturing has seen significant advances recently, but these advances are not yet realized for the bottom-up formation of nanoscale polymeric features. We describe a platform technology for creating crosslinked polymer features using rapid surface-initiated crosslinking and versatile macrocrosslinkers, delivered by a microfluidic-coupled atomic force microscope known as FluidFM. A crosslinkable polymer containing norbornene moieties is delivered to a catalyzed substrate where polymerization occurs, resulting in extremely rapid chemical curing of the delivered material. Due to the living crosslinking reaction, construction of lines and patterns with multiple layers is possible, showing quantitative material addition from each deposition in a method analogous to fused filament fabrication, but at the nanoscale. Print parameters influenced printed line dimensions, with the smallest lines being 450 nm across with a vertical layer resolution of 2 nm. This nanoscale 3D printing platform of reactive polymer materials has applications for device fabrication, optical systems and biotechnology.