The effect of LiNTf₂ on the propagation rate coefficient of methyl methacrylate

Abstract

LiNTf2 catalyses the propagation step of methyl methacrylate radical polymerization but this catalysis hinders stereocontrol.

Photopolymerization of coordinated ionic liquid monomers: Realizing the benefits of structured media using only common reagents

“…56,60,62 Addition of ZnCl 2 to reaction mixtures of MMA in N,N-dimethylformamide (DMF) increased the rate of polymerization relative to the control solution 2.43 at a Lewis acid:monomer ratio of 0.15:1, while the presence of AlBr 3 in similar reaction mixtures at a salt:monomer ratio of 0.35:1 improved the rate of reaction approximately 4.23 in comparison to the control mixture. 62 As mentioned previously, multiple studies have found improvements in the reaction kinetics and product properties for radical polymerizations containing LiOTf and LiTf 2 N. [56][57][58][59][60] The improvements in the radical polymerization kinetics in these reactions have been attributed to both electronic and electrostatic factors. [56][57][58][59][60]62 For the ethylene oxide methacrylate polymerizations, the addition of the salt was associated with a corresponding shift in the position of the CAH vinyl stretching peak to higher wavenumbers.…”

“…62 As mentioned previously, multiple studies have found improvements in the reaction kinetics and product properties for radical polymerizations containing LiOTf and LiTf 2 N. [56][57][58][59][60] The improvements in the radical polymerization kinetics in these reactions have been attributed to both electronic and electrostatic factors. [56][57][58][59][60]62 For the ethylene oxide methacrylate polymerizations, the addition of the salt was associated with a corresponding shift in the position of the CAH vinyl stretching peak to higher wavenumbers. 60 As the presence of similar phenomena in H-bonding systems results in increased monomer reactivity, the increase in the rate of propagation was attributed to favorable electronic redistributions within the vinyl group as a result of interactions between the C@O group and the Li 1 cation.…”

“…57 The use of alkali Tf 2 N salts in the solution polymerization of acrylamide (ACR) and methacrylamide (MACR) monomers has been shown to increase monomer conversion and product molecular weight while also altering the tacticity of the resulting polymers. 58,59 A 2011 study completed by Pedr on and et al, in which several ethylene oxide methacrylate monomers with 1, 2, or 3 ether groups in the side chain were combined with LiOTf, with reported improvements in the reaction kinetics for these solutions compared to bulk reaction mixtures.…”

Mechanistic Perspectives on Stereocontrol in Lewis Acid-Mediated Radical Polymerization

“…87,88 Indeed, it is interesting to note that in the gas phase the interaction energy between the methyl radical and Li þ is over 50 kJ mol À1 . 87 More recent work has confirmed that Li þ exerts a modest stabilizing effect on unimeric MMA radicals, 89 although it is unclear to what extent this stabilization may simply reflect polar effects.…”

“…89 Although LiNTf 2 was found to be ineffective for isotactic control experimentally, these calculations suggest that under normal polymerization conditions, terminal-penultimate chelation infers a modest selectivity preference of around 5 kJ mol À1 for linear pro-meso conformations of the polymer terminus compared with helical pro-racemo configurations. 89 If this level of selectivity was retained in the respective meso and racemo transition states, it would result in a highly isotactic-rich polymer at 25 C (m ¼ 90%).…”