Gas Transport in a Polymer of Intrinsic Microporosity (PIM-1) Substituted with Pseudo-Ionic Liquid Tetrazole-Type Structures

Abstract

We report a side group modification strategy to tailor the structure of a polymer of intrinsic microporosity (PIM-1). PIM-1 with an average of ∼50% of the repeat units converted to tetrazole is prepared, and a subsequent reaction then introduces three types of pseudo-ionic liquid tetrazole-like structures (PIM-1-IL x ). The presence of pseudo-ionic liquid functional groups in the PIM-1 structure increases gas selectivities for O 2 /N 2 and CO 2 /N 2 , while it decreases pure-gas permeabilities. The overall gas separation performance of PIM-1-IL x is close to the 2008 Robeson upper bound. Since the tetrazoles are versatile groups for building a wide variety of ionic liquids, the modification method can be expanded to explore a broad spectrum of functional groups.

A Review on Ionic Liquid Gas Separation Membranes

“…Pseudo-PILs from post-functionalized PIM-1 were prepared by reacting tetrazole-modified PIM-1 with amines in the presence of MeOH to activate anionic sites in the polymer and introduce amines as anions and bearing a methylammonium, diisopropylamonium, and N , N -diisopropylethylamonium cation [ 123 ]. With increasing cation size, the BET surface area and the gas permeability progressively decreased, while the selectivity increased, maintaining values close to the 2008 upper bound for the CO 2 /N 2 gas pair (selectivity 35.5 at a CO 2 permeability of 817 Barrer) and the O 2 /N 2 gas pair (selectivity 4.5 at an O 2 permeability of 102 Barrer) for the N , N -diisopropylethylamonium cation.…”

“…Only small amounts were added, which were not able to form a gel, but in the case of [BMIM] 2 [Co(NCS) 4 ] it effectively increased the O 2 /N 2 selectivity from 3.77 for pure PIM-1 to 5.3 for the membrane with 2% of the cobalt complex. In an alternative approach, Guiver et al covalently connected the ionic liquid-like tetrazole-type structures as lateral substituents to the PIM-1 backbone [ 123 ], resulting in a PIL.…”

“…This term later spread in the community of groups working on ILs polymerization and was facilitated by works of Mecerreyes et al [116][117][118]. Eventually, the term 'PIL' also started to be associated with the polymers post-modified chemically to mimic the structure of polymerized ILs [119][120][121][122][123][124]. Currently, the term poly(ionic liquids) refers to several variations, such as "polymerized ionic liquids", "polymeric ionic liquids", and "polyionic liquids", that are used interchangeably, and it is widely applied to the broad range of polymeric materials, comprising a similar structure of repeated electrolyte units bound to a shared polymer backbone.…”

“…Although the combination with ionic liquids, which are likely to fill part of this free volume and may also plasticize the polymers, is counter-intuitive, some researchers have nevertheless made for pure PIM-1 to 5.3 for the membrane with 2% of the cobalt complex. In an alternative approach, Guiver et al covalently connected the ionic liquid-like tetrazole-type structures as lateral substituents to the PIM-1 backbone [123], resulting in a PIL.…”

Recent Progress on Polymers of Intrinsic Microporosity and Thermally Modified Analogue Materials for Membrane‐Based Fluid Separations

“…Other types of functional groups that have been recently introduced into PIM structures include ionic liquids (ILs) and sulfonyl groups. [ 130,131 ] Guiver et al (2020) reported a number PIMs containing pseudo‐IL tetrazole‐like functional groups (PIM–1–IL x ) through side‐group modification of PIM‐1. [ 130 ] The gas permeation properties of IL‐modified PIMs approached the 2008 Robeson upper bounds with improved O 2 /N 2 and CO 2 /N 2 pure‐gas selectivities, coupled with lower pure‐gas permeabilities when compared with the original PIM‐1.…”