Ionic liquid functionalized polylactides: the effect of anions on catalytic activity and carbon nanotube dispersion

Abstract

Some hydroxylated imidazolium-based ionic liquids with different anions ([ILs-OH]⁺[X]⁻) were synthesized using an anion exchange reaction. A series of novel polylactides bearing an imidazolium group with different anions (PLLA-ILs[X]⁻) at one chain extremity were synthesized at 25 °C by ring-opening of L-lactide, which was initiated by the hydroxylated imidazolium-based ILs ([ILs-OH]⁺[X]⁻) in the presence of organocatalysts. Nuclear magnetic resonance (NMR) and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS) confirmed the structures of the PLLA-ILs[X]⁻. The results showed that the hydroxylated ionic liquid is an efficient initiator for the ring-opening polymerization (ROP) of L-lactide. Carbon nanotubes (CNTs) were dispersed in a solution of PLLA-ILs[X]⁻ in 1,4-dioxane and a significant improvement in the stability of suspension was observed by measurements of suspension absorbance. The absorbance of suspension between CNTs and PLLA-ILs[X]⁻ followed the order: [TFSI]⁻ > [H₂PO₄]⁻ > [Cl]⁻ > [NO₃]⁻, and was much higher than that of untreated CNTs, indicating that the anions have an obvious effect on the interaction between CNTs and PLLA-ILs[X]⁻. In the scanning electron microscopy (SEM) images, it was also clearly visible that the globular aggregates of PLLA-IL[Cl]⁻ were bound to CNTs, which was consistent with the results of absorbance.