A facile route to well-defined imidazolium-based poly(ionic liquid)s of enhanced conductivity via RAFT

Abstract

The synthesis of well-defined imidazolium-based poly(ionic liquid)s (PILs) by reversible addition–fragmentation chain transfer (RAFT) polymerization is demonstrated. Two specially designed monomeric ionic liquids (MILs), such as 1-methyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide [MVIM][NTf₂] and 1-ethyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide [EVIM][NTf₂] were polymerized with the 2,2′-azobisisobutyronitrile (AIBN) initiator in the presence of a trithiocarbonate RAFT agent. Depending on the varied ratios of the monomer to CTA ([monomer]/[CTA] = 100/1; 400/1; 1000/1) we obtained P[MVIM][NTf₂] and P[EVIM][NTf₂] homopolymers with the number-average molecular weights (M_n) in a broad range M_n = 2.5–340.0 kDa and M_n = 2.1–450.0 kDa, respectively. The controlled character of the polymerization of each ionic monomer was confirmed by the pseudo-first order kinetic, a linear increase in the M_n with conversion and relatively narrow dispersity indices (Đ = 1.09–1.37 for P[MVIM][NTf₂] and Đ = 1.10–1.41 for P[EVIM][NTf₂]). Additionally, the obtained macromolecules are characterized by the enhanced/or comparable conductivity in comparison with those reported in the literature [Wojnarowska et al., Macromolecules, 2014, 47, 4056–4065 and Fan et al., Macromolecules, 2016, 49, 4557–4570], indicating that we are able to produce polymers of high molecular weights characterized by relatively high conductivity (σ_dc ∼ 10⁻⁹ at T_g). Finally, we found quite unexpected evolution of T_gvs. M_n of the produced polymers in the limit of low molecular weight, which seems to correspond to those observed in the case of van der Waals polymers such as polystyrene or polyisobutylene.