Bromoalkyl ATRP initiator activation by inorganic salts: experiments and computations

Abstract

The bromoalkyl ATRP initiator EBrPA is activated by many alkali, alkaline-earth and ammonium salts, leading to MMA polymerization, but only the iodides yield a controlled process because of a degenerative transfer mechanism contribution.

Ligand- and solvent-free ATRP of MMA with FeBr3 and inorganic salts

“…This agrees with the greater efficiency of KOH as activator for EBrPA relative to KBr. 32 In addition, the same two peaks already observed in the EBrPA/FeBr3/KOH experiment ( Figure S15) at 16.00 and 26.11 min are also observed here. Finally, this GC trace also reveals a very small peak at 11.26 min, the identity of which as methyl 1,2-dibromoisobutyrate was confirmed by the MS, see Figure S18(b).…”

“…Hence, FeBr3 must be converted to the FeBr2 activator by another reduction mechanism, followed by a regular ATRP with FeBr2/EBrPA as activator/initiator pair, as demonstrated in numerous previous contributions. 33 In a recent study, 32 we have shown how inorganic salts (Mt + X -), including alkali metal carbonates and halides, are able to activate EBrPA in the absence of iron complexes to initiate the MMA radical polymerisation, although in an uncontrolled manner. This occurs by atom transfer with formation of the EPA radical and the Mt + (BrX • )radical adduct.…”

“…Table 1 also shows the results of the previously published MMA polymerisation in the presence of initiator and Na2CO3 but without any Fe catalyst (entry 5), which gave a lower yield, even at a much higher temperature, and an uncontrolled polymerisation. 32 The polymerisation of entry 1 follows first-order kinetics ( Figure 1a) in line with a constant radical concentration and is characterised by an induction time, which is related to the need to reduce part of the FeBr3 catalyst to the FeBr2 activator. The good control is demonstrated by the excellent match between observed and calculated molar masses and by the low Đ values (Figure 1b).…”

“…31 We have recently reported that many inorganic salts such as halides, carbonates, sulfates, hydroxide, etc., in the absence of ATRP catalysts, activate EBrPA and promote the radical polymerisation of MMA. 32 These polymerisations proceed without controlled chain growth, except for the iodide salts. However, in combination with FeBr2, excellent control was observed for all those salts, particularly in the presence of a small amount (10%) of FeBr3.…”

“…The same cation effect was previously observed and rationalized in the investigation of the EBrPA activation by MtBr (Mt = Li, Na, K, Rb, Cs) in the absence of iron salt. 32 The anion also has a slight influence on the rate, since the Na and K chlorides (entries 6 and 7) yield slightly lower rates than the corresponding bromides. These trends correspond to those previously observed for the FeBr2/salt-catalysed ATRP.…”