Copolyampholytes Produced from RAFT Polymerization of Protic Ionic Liquids

Polyampholytic copolymers have been synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization of protic ionic liquid monomers. The monomers were prepared by acid-base proton exchange between acid and basic precursor conjugates, each containing one or more vinyl pendant groups. The polymerization, which was carried out without additional solvents present, led to high molecular weight glassy polymers, which were stable in the form of bulk viscous liquid ionic complexes. Various polyampholytes belonging to both linear and cross-linked families were prepared by judiciously varying the molecular structure of the acid precursor. Furthermore, by using solid-state NMR, the molecular arrangement of the polymeric backbone was identified, highlighting the presence of copolymers with both random and alternating copolymer chains which in the latter case involves a regularly alternating acid monomer, whereas the base occurs as a random sequence with the average and most probable number of monomers dictated by the stoichiometry used. The structural and mechanical properties of the resulting copolyampholytes were characterized by atomic force microscopy, peak-force quantitative nanomechanical analysis, differential scanning calorimetry, and small-angle X-ray scattering. These showed that the final polymers were essentially glassy and amorphous, with weak compositional fluctuations of the order of a few monomers and Young moduli in the range 1-3 GPa.