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Insights into the relationship between structure and properties of Spirobichroman-based polyimides: Effects of substituents on molecular structure and gas separation
- Source :
- Materials & Design, Vol 194, Iss , Pp 108933- (2020)
- Publication Year :
- 2020
- Publisher :
- Elsevier, 2020.
-
Abstract
- Four spirobichroman-based polyimides (6FDA-F, 6FDA-O, 6FDA-P, and 6FDA-M) were successfully obtained via polyreaction between diamines of different substituents (-H, -OCH3, -N, and -CH3) and 4,4′-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA). The molecular weights, thermophysical, dihedral angle of the molecules, fractional free volume, d-spacing, Brunauer–Emmett–Teller surface area, and gas separation performance were studied through a combination of experiments and molecular dynamics simulations. These polymers show high molecular weights, with number-average molecular weights (Mn) in the range of 5.0–15.3 × 104, and excellent thermal stability, with weight loss temperatures (T5%) of over 420 °C. The pure-gas (O2, N2, CO2, and CH4) permeation results indicated that the four polymers selectivity of CO2/CH4 over 31 and that 6FDA-F had the highest gas permeability among the four tested gases. Importantly, the dihedral angle from molecular simulation was used to clarify the phenomenon wherein the 6FDA-P gas permeability lower than 6FDA-F. A detailed analysis indicates that -CH3 increased the gas permeability of the polyimides, while the turnstile-like rotary thermal motion of -OCH3 formed channel obstacles and improved the gas selectivity. The polymers containing pyridine ring and those containing benzene ring follows different gas separation mechanisms, based on the gas solution-diffusion behaviour.
Details
- Language :
- English
- ISSN :
- 02641275
- Volume :
- 194
- Issue :
- 108933-
- Database :
- Directory of Open Access Journals
- Journal :
- Materials & Design
- Publication Type :
- Academic Journal
- Accession number :
- edsdoj.50934d2cddf44f3d9e5e0b9b4e860c60
- Document Type :
- article
- Full Text :
- https://doi.org/10.1016/j.matdes.2020.108933