Poly(ether ether ketone) Ionenes: Ultrahigh-Performance Polymers Meet Ionic Liquids

Abstract

This work presents the first example of an imidazolium ionene containing aromatic ether-ketone-ether linkages inspired by poly(ether ether ketone) (PEEK), a well-known ultrahigh-performance (UHP) engineering polymer. The requisite starting materials for this “PEEK ionene” were efficiently synthesized in good yields and then polymerized through condensation (Menshutkin reaction), followed by anion metathesis to form the final polymer product, which had a number-average molecular weight (M n) of ∼90 kDa. The properties of the PEEK-ionene were thoroughly characterized, and its potential utility was demonstrated by analyzing this material as a gas separation membrane and 3D-printing this ionic UHP polymer. Thin films of this material and composites containing “free” ionic liquids (ILs) were also tested as membranes, to evaluate the gas/permeation behaviors. While the addition of [C4mim][Tf2N] IL to the PEEK-ionene enhanced membrane performance, the ether-functionalized [PEG1mim][Tf2N] IL exhibited notably different interactions with the PEEK-ionene, resulting in diminished selectivity and irregular ordering due to partial exfoliation and dissolution of the polymer. To better understand the range of processability and morphological effects with ILs, the PEEK-ionene was extruded into fibers and was 3D-printed through fused deposition modeling (FDM) techniques, to demonstrate how the PEEK-ionene is more readily processable than conventional PEEK. Compared to neutral PEEK, the PEEK-ionene with bistriflimide (Tf2N) counterions exhibited reduced glass-transition temperature (T g) and melting point (T m) and increased permeability to gases, as well as the ability to hold ILs within their structures. This approach to the design of ionenes and PEEK-containing materials can provide great opportunities to create tailored materials for a variety of applications.

Precisely segmented PEEK–ionene + ionic liquid composite membranes for CO2 separation

“…IL composite membrane showed good permselectivity of 35.7 and 24.7 for CO 2 /N 2 and CO 2 /CH 4 , respectively. Here, the IL content is higher than the previously reported PEEK-ionene values 37 and can reach as high as 3 eq., and a substantial increase in gas permeabilities and selectivities is observed. Similarly, an enhanced permeabilities and selectivity (CO 2 /N 2 ) Fig.…”

“…Data take from neat PEEK, 10,11 modified-PEEK, 20,29,50,51 poly(IL)-IL composites, 48,52 supported based ILs, 53 imidazoliumbased ionenes, 36,49,54 and PEEK-ionene + composites. 37 and reduced selectivity for CO 2 /CH 4 is observed when compared to the pristine PEEK polymer. 9 Although, it is difficult to compare the CO 2 performances of newly developed PEEK ionene-IL composites with those from the literature data due to the difference in the polymeric backbone.…”

“…Towards this, we reported new class of imidazolium PEEK ionenes for gas separation membranes. 37 The CO 2 permeability was enhanced 4× when compared to neutral PEEK membrane indicating the inuence of ionic groups within the polymeric backbone. Further, incorporation of distinct kinds of free IL into the PEEK ionene matrix resulted in different gas transport properties, suggesting the IL impregnation greatly impacts the molecular interactions with the ionenes.…”

Enhancing CO2 Transport Across a PEEK‐Ionene Membrane and Water‐Lean Solvent Interface

“…The interaction of CO 2 with the membrane was examined by collecting 13 C MAS NMR spectra of the membrane with 13 CO 2 gas. A previous study explored the selectivity and gas permeability of this membrane, and in comparison to neutral PEEK polymer [5c] . Figure 3A shows the results under pressure and after pressure was released.…”

“…The polyether ether ketone (PEEK) membrane was synthesized as detailed in our previous publication [5c] …”