Synthesis, characterization of a novel high heat-resistant soluble fluorinated sulfur-containing polyimide for gas separation

Abstract

A novel sulfur-and fluorine-containing dianhydride monomer 2,2-bis[4-(3,4-dicarboxyphenylthio)phenyl]hexafluoropropane dianhydride (6FDAPSA) was synthesized by molecular design, and a series of random co-polyimides were prepared from 6FDAPSA, 4,4-(hexafluoroisopropene)diphthalic anhydride (6FDA) and 4-(3-fluoro-4-(trifluoromethyl)phenyl)-2,6-bis(4-aminophenyl)pyridine (FTPPA). The obtained co-polyimides exhibited excellent thermal properties (T_g > 288 °C, T_{5 %} > 504 °C, T_10 % > 536 °C), good optical properties (λ_cut-off > 342 nm, λ_80 % > 410 nm), commendable mechanical properties (tensile strength >75 MPa) and outstanding hydrophobic properties (contact angle >90.0°). They also showed excellent solubility in both high and low boiling point organic solvents. Besides, Wide-angle X-ray diffraction test and molecular simulation confirmed that the prepared co-polyimides possess a large molecular chain spacing, with d-spacing values ranging from 5.59 to 5.84 Å and fractional free volume from 0.237 to 0.280. Consequently, polyimide membranes exhibited commendable gas permeability values of He (up to 49.5 barrer) and CO₂ (up to 34.2 barrer), and good ideal gas selectivity values of He/N₂ (up to 34.2) and CO₂/N₂ (up to 22.2). These results indicate that polyimide matrix materials have potential application prospects in the field of gas separation.