Influence of Aliphatic and Aromatic Fluorine Groups on Gas Permeability and Morphology of Fluorinated Polyimide Films

Abstract

Partially fluorinated polymers often exhibit exceptional membrane-based separation performance for a variety of gas pairs. While many gas transport studies focus on the incorporation of aliphatic fluorine groups (e.g., −CF3) on the polymer backbone, few studies have systematically investigated structure–property relationships for aromatic fluorine groups. Here, the effect of aliphatic and aromatic fluorine groups on solid-state morphology and gas transport is compared for structural analogues of 6FDA-based polyimides that contain either hydrogen or fluorine functional groups on the diamine monomer. Both fluorinated analogues displayed higher gas diffusivity compared to their hydrocarbon-based counterparts. However, the aromatic fluorinated analogue displayed a larger decrease in diffusivity selectivity due to weakened secondary interchain forces and a larger increase in interchain spacing, suggesting a greater extent of packing disruption resulting from increased steric hindrance associated with aromatic fluorine groups. This study establishes guiding principles for how carbon–fluorine bonds affect macromolecular packing structure and gas separation performance.

Metal‐Free Multi‐Heteroatom‐Doped Carbon Bifunctional Electrocatalysts Derived from a Covalent Triazine Polymer

“…Figure 2d shows that FP-CTP has excellent thermal durability even at a high temperature of 521 °C, which was mainly due to the existence of a strong polar CF single bond and clotriphosphazene rings in the fully crosslinked structures. [37] The weight retention of FP-CTP was more than 25 wt%, when even heated to 1000 °C under inert atmosphere, indicating that FP-CTP is a promising precursor to prepare versatile carbon materials on a large scale. Nitrogen sorption/desorption isotherms and corresponding pore size distribution curve affirmed coexistence of micropores and mesopores in the resulted CTPs ( Figure S7, Supporting Information).…”

“…The well-maintained microstructure was probably attributed to the strong covalent bond interaction (e.g., CF single bond) in the FP-CTP framework. [37] Notably, compared with the FP-CTP precursor, the optimal NPF-CNS-2 showed a smaller diameter (centered at 360 nm) and rougher surface, owing to weight loss during carbonization. [38] The high-resolution TEM (HRTEM) image manifested that NPF-CNS-2 has no obvious ordered carbon lattice fringes, suggesting that there are abundant defects and amorphous structures in NPF-CNS-2.…”

“…[42] Furthermore, the absorption of the corresponding phosphazene, CF single bond, and phenyl absorptions were located at 1185, 1250, 1152, 1513, and 1465 cm −1 . [37] The existence of strong CF covalent bonds led to the distinct decrease of electron cloud density and the increase of stability, thus greatly improved the carbonization yield and F-doping efficiency. [43] Besides, the obtained CTPs were characterized by 31 P CP/MAS NMR spectra.…”

Functionalized polyimide based on mercaptoacetic acid locking imine reaction: Synthesis and coating application

“…The complete disappearance of the characteristic absorption peaks attributed to amide group indicates the complete imidization of the MPAA. 30 In summary, the analysis of FTIR spectra presents that PAA and PI were successfully prepared.…”

Effect of Direct Fluorination on the Transport Properties and Swelling of Polymeric Materials: A Review

“…Partially fluorinated polymers of different classes have been thoroughly investigated as gas separation membranes [ 12 , 13 , 14 ], although the effects of presence of fluorine in a polymer structure often turned out to be not significant due to its low bulk concentration. Contrarily, amorphous perfluorinated polymers have exhibited outstanding gas transport characteristics, forming upper bonds on Robeson diagrams (i.e., dependence of selectivity on permeability coefficient of the more permeable gas) for He-CH 4 , N 2 -CH 4 , He-H 2 [ 15 , 16 , 17 ] ( Table 1 ).…”