Syndiotactic- and heterotactic-specific radical polymerization of N-n-propylmethacrylamide complexed with alkali metal ions

Abstract

We investigated the radical polymerization of N-n-propylmethacrylamide (NNPMAAm) in the presence of alkali metal bis(trifluoromethanesulfonyl)imides (MNTf 2 ), in particular LiNTf 2 . The addition of MNTf 2 led to a significant improvement in the yield and molecular weight of the resulting poly(NNPMAAm)s. Furthermore, the solvent employed influenced stereospecificity in the presence of LiNTf 2 . The stoichiometry of the NNPMAAm-Li + complex appeared to be critical for determining the stereospecificity in the NNPMAAm polymerization. The 1 : 1-complexed monomer in protic polar solvents provided syndiotacticrich polymers, whereas the 2 : 1-complexed monomer in aprotic solvents gave heterotactic-rich polymers. Stereochemical analyses revealed that m-addition by an r-ended radical was the key step in the induction of heterotactic specificity in the aprotic solvents. Spectroscopic analyses suggested that the Li + cation played a dual role in the polymerization process, with Li + stabilizing the propagating radical species and also activating the incoming monomer. Kinetic studies with the aid of electron spin resonance spectroscopy revealed that the addition of LiNTf 2 caused a significant increase in the k p value and a decrease in the k t value. The stereoregularity of poly(NNPMAAm)s was found to influence the phase transition behavior of their aqueous solutions. In a series of syndiotactic-rich polymers, the phase-transition temperature decreased gradually with increase in the rr triad content. Furthermore, heterotactic-rich poly-(NNPMAAm) exhibited high hysteresis, which increased in magnitude with increasing mr triad content. † Electronic supplementary information (ESI) available: 13 C NMR spectra of the CvO group of NNPMAAm in the presence of MNTf 2 , changes in the chemical shifts of 1 H NMR spectra of the vinylidene group of NNPMAAm in the presence of LiNTf 2 , relationship between the radical concentration and time, additional ESR spectra and relationship between the ΔT c and n r values. See

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

“…53,54 Indeed, in spectroscopic investigations of vinyl monomers and Li 1 salts, cation complexation has been detected using IR as well as 1 H and 13 C NMR spectroscopy. 55,56,[58][59][60] Based on similar evidence, it can be confirmed that these species are also formed in our study. As displayed in Figure 9, the C@O stretching peaks of MMA undergo shifts to lower wavenumbers following the addition of LiTf 2 N at monomer:salt ratios of 1:1 and 2:1.…”

“…60,63,64 Likewise, the increase in the rate of polymerization of ACR and MACR monomers in the presence of alkai Tf 2 N salts was partly attributed to the decrease in the difference in the 13 C and 1 H NMR shifts of vinylidene carbon and H atoms that have been previously associated with favorable propagation kinetics. 58,59,65 The presence of these salts also affects the termination kinetics of these reactions, resulting in substantial increases in the radical concentrations of the reaction mixtures as determined by electron paramagnetic spectroscopy. 56,58,59 The mechanism of the reduction in the rate of termination in these reactions has been assigned to a variety of factors including radical stabilization and single electron-alkali metal interactions as well as electrostatic repulsion between complexed macroradicals.…”

“…58,59,65 The presence of these salts also affects the termination kinetics of these reactions, resulting in substantial increases in the radical concentrations of the reaction mixtures as determined by electron paramagnetic spectroscopy. 56,58,59 The mechanism of the reduction in the rate of termination in these reactions has been assigned to a variety of factors including radical stabilization and single electron-alkali metal interactions as well as electrostatic repulsion between complexed macroradicals. 56,58,59,62 The improvements in the reaction kinetics of the polar vinyl monomers in this study may be due, in part, to these effects.…”

“…56,58,59 The mechanism of the reduction in the rate of termination in these reactions has been assigned to a variety of factors including radical stabilization and single electron-alkali metal interactions as well as electrostatic repulsion between complexed macroradicals. 56,58,59,62 The improvements in the reaction kinetics of the polar vinyl monomers in this study may be due, in part, to these effects. We attribute improvements in overall monomer conversions to structuring of the monomers about the Li 1 cation (Fig.…”

“…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. 60 However, LiOTf would be expected to have different kinetic effects than a more weakly coordinating Li 1 salt such as LiTf 2 N. Based on our experiences, LiOTf does not sufficiently dissolve in non-ether-containing monomers to form coordinated ILs, while LiTf 2 N is capable of dissolving at up to 1:1 (mol:mol) in monomers without ethers such as MMA without cosolvent.…”