Continuous-flow self-supported seATRP using a sonicated microreactor

Continuous-flow simplified electrochemically mediated atom transfer radical polymerization (seATRP) was achieved for the first time without supporting electrolytes (self-supported) using a novel sonicated tubular microreactor. Polymerizations of different acrylic monomers were carried out under different applied currents. The reaction was fast with 75% conversion achieved at ambient temperature in less than 27 minutes. Results also showed good evolution of molecular weight and maintained narrow molecular weight distribution. The reaction rate can be further manipulated by tuning the applied current. Sonication under proper conditions was found to be able to significantly improve both reaction rate and controllability. Self-supported reactions also enable more environmentally friendly and cost-effective operations.

T-junctions (P633 Tee Assembly, ETFE) were purchased from IDEX Health and Science.
Piezorings (SMR837T1411) were purchased from STEMINC. UV glue was purchased from Revell. The tube and rod were both connected electrically to a potentiostat (Stanford Research Systems EC301) via wire soldered on. Coupled piezorings were connected to an E&I 2100 L amplifier, which amplifies the sinusoidal signal generated by a Rigol DG1032 wave generator.
How the piezorings induce acoustic streaming is schematically shown below: Figure S1. Schematic representation how (1) an axially poled piezoelectric actuator vibrates and (2) via Poisson's effect also transmits radial vibrations through the capillary wall. These radial vibrations excite (3) axial resonance modes in the liquid filled channel, which (4) are attenuated in a thin Stokes boundary layer. The attenuation (5) induces a Reynolds stress in this boundary layer, which (6) drags the liquid outside the boundary layer into a steady streaming motion 1 .

Sonication Conditions
Resonance frequencies of solution filled reactor setup were measured using an impedance analyzer (SinePhase 16777k). For each experiment, signal frequency and amplitude were set on the signal generator (1.350MHz, 150mVpp for 1W cases and 210mVpp for 2W cases) and amplified by an E&I 2100 L amplifier. A ventilator was utilized to remove the heat generated by the piezorings.

Rinse Procedure
After each sample was collected, a special rinsing procedure was performed to obtain reproducible results. The procedure includes the following steps: i) 10mL 1M HNO3 was pumped through the reactor at 1mL/min under 5W sonication at 635kHz, then the pump was stopped, and the nitric acid solution was kept in the reactor for 5min. After this ii) flush with 10 mL Milli-Q water at 1mL/min iii) and finally with another 5mL acetonitrile also at 1mL/in.

Dissolved Al 3+ Calculation
The molar concentration of dissolved Al 3+ can be calculated using the equation below: where I is the current applied, t stands for the residence time, V stands for the volume of the reactor, and F is the Faraday constant. As in this research the reactor volume stays unchanged, the equation can be also written as: where Q denotes the applied flow rate.
For instance, when 0.8mA current was applied and the smallest flow rate of 10μL/min (0.1667μL/s) was chosen, the molar concentration can be calculated to be: Hence, a minimum of 16.58mmol/L of excess ligand will be added to compensate for the aluminum dissolution.

Measurements and Analysis
Molecular weights and distributions were measured by GPC (SHIMADZU LC20) equipped with a differential refractive index detector (RID) and with THF eluent at 35°C, 1.0mL/min flowrate.
Agilent PLgel 3μm MIXED-E 300×7.5mm column was used and the column were calibrated using  Figure S2. Polymerization was found to be uncontrollable when (A)630kHz sonication was applied or (B)excess ligand was not added.   Figure S5. Conversion as a function of residence time.  Figure S7. 400MHz 1 H NMR spectrum of purified PMA by continuous-flow self-supported seATRP (in CDCl3). Figure S8. 400MHz 1 H NMR spectrum of purified PBA by continuous-flow self-supported seATRP (in CDCl3). Figure S9.

ESI-MS Data
(1) Full ESI-MS spectrum and (2) zoom-in of one repeating unit of purified PMA by continuous-flow self-supported seATRP.