Oxygen-Enhanced Atom Transfer Radical Polymerization through the Formation of a Copper Superoxido Complex

Abstract

In controlled radical polymerization, oxygen is typically regarded as an undesirable component resulting in terminated polymer chains, deactivated catalysts, and subsequent cessation of the polymerization. Here, we report an unusual atom transfer radical polymerization whereby oxygen favors the polymerization by triggering the in situ transformation of CuBr/ L to reactive superoxido species at room temperature. Through a superoxido ARGET-ATRP mechanism, an order of magnitude faster polymerization rate and a rapid and complete initiator consumption can be achieved as opposed to when unoxidized CuBr/L was instead employed. Very high end-group fidelity has been demonstrated by mass-spectrometry and one-pot synthesis of block and multiblock copolymers while pushing the reactions to reach near-quantitative conversions in all steps. A high molecular weight polymer could also be targeted (DP n = 6400) without compromising the control over the molar mass distributions (Đ < 1.20), even at an extremely low copper concentration (4.5 ppm). The versatility of the technique was demonstrated by the polymerization of various monomers in a controlled fashion. Notably, the efficiency of our methodology is unaffected by the purity of the starting CuBr, and even a brown highly-oxidized 15-year-old CuBr reagent enabled a rapid and controlled polymerization with a final dispersity of 1.07, thus not only reducing associated costs but also omitting the need for rigorous catalyst purification prior to polymerization.

Influences of nitrogen base excess on ARGET ATRP of styrene with ascorbic acid acetonide and traces of oxygen and water

“…[46][47][48] Furthermore, it has been reported that both oxygen and water might be beneficial to ATRP. 32,45,49 For context, despite oxygen and water traces, ARGET ATRP of styrene with H 2 AA/Na 2 CO 3 , gave fairly good results in terms of Đ and ΔM n (the latter being an index of deviation from the theoretical value of M n ). 17,49 By swapping H 2 AA for its acetonide counterpart, conversion increased at the cost of a slight loss of control (both ΔM n and Đ were higher, compare entries 1 and 2 in Table 1).…”

“…The cuvette contains [base] : [H 2 AAIPI] : [TPMA] : [CuCl 2 ] = 100 : either 16.7 (green) or 0 (red and blue curves) : 2.51 : 1.67 mol% with respect to the base (2.12 mmol L −1 ). Interestingly, a transient peak appears at 450 nm that can be explained by the formation of oxygen-copper-TPMA complexes 39,45. (E) Absorbance at 800 nm vs. time, one acquisition every two minutes.…”

In Situ and Real-Time Visualization of Mechanochemical Damage in Double-Network Hydrogels by Prefluorescent Probe via Oxygen-Relayed Radical Trapping

“…17 However, a very recent work demonstrated the positive role of oxygen as it can promote an unusual atomtransfer radical polymerization. 29 To our surprise, oxygen was also found to play a positive role in promoting the luminescence in our work. To the best of our knowledge, this is the first report utilizing oxygen as a radical relayer for visualizing mechanoradical damages in polymeric materials.…”

“…It has to be noted that, generally, oxygen is considered to have a negative effect as it could terminate radical reactions. − It therefore greatly restricts the usage of mechanoradicals . However, a very recent work demonstrated the positive role of oxygen as it can promote an unusual atom-transfer radical polymerization . To our surprise, oxygen was also found to play a positive role in promoting the luminescence in our work.…”

Cu(0)-RDRP of acrylates using an alkyl iodide initiator

“…In addition, high amounts of catalyst are typically needed for a successful polymerization. To overcome both barriers, a number of alternative ATRP approaches have recently been developed, including eATRP, 11,12 photoATRP, [13][14][15][16] ARGET-ATRP, 17,18 and, (P)ICAR-ATRP. 19,20 A common feature of these methodologies is that they require a stimulus or an additive to in situ re-generate the active catalyst and as a result they can operate at significantly lower catalyst concentrations.…”