Effect of methyl substituents on permeability and permselectivity of gases in polyimides prepared from methyl‐substituted phenylenediamines

Abstract

Permeability and solubility coefficients for H2, CO2, O2, CO, N2, and CH4 in polyimides prepared from 6FDA and methyl‐substituted phenylenediamines were measured to investigate effects of the substituents on gas permeability and permselectivity. The methyl substituents restrict internal rotation around the bonds between the phenyl rings and the imide rings. The rigidity and nonplanar structure of the polymer chain, and the bulkiness of methyl groups make chain packing inefficient, resulting in increases in both diffusion and solubility coefficients of the gases. Polyimides from tetramethyl‐p‐phenylenediamine and trimethyl‐m‐phenylenediamine display very high permeability coefficients and very low permselectivity due to very high diffusion coefficients and very low diffusivity selectivity, as compared with the other polyimides having a similar fraction of free space. This suggests that these polyimides have high fractions of large‐size free spaces.

Intrinsically Microporous Soluble Polyimides Incorporating Tröger’s Base for Membrane Gas Separation

“…The polyimide bearing 6FDA has an expected higher FFV value due to the bulky −C(CF 3 ) 2 − units as compared with the polyimide derived from BTDA. It is interesting to compare the FFVs of PI-TB-1, prepared from 6FDA and DPD and polymerized using the TB method, with a typical polyimide PI-6FDA-DPD (6FDA-pDiMPD 34 ) polymerized in the normal manner from 6FDA and DPD. The PI-TB-1 showed a significantly higher FFV value (FFV = 0.223) induced by the incorporation of TB units compared with that of PI-6FDA-DPD (FFV = 0.175 34 ).…”

“…It is interesting to compare the FFVs of PI-TB-1, prepared from 6FDA and DPD and polymerized using the TB method, with a typical polyimide PI-6FDA-DPD (6FDA-pDiMPD 34 ) polymerized in the normal manner from 6FDA and DPD. The PI-TB-1 showed a significantly higher FFV value (FFV = 0.223) induced by the incorporation of TB units compared with that of PI-6FDA-DPD (FFV = 0.175 34 ). Out-of-plane WAXD measurements were conducted to investigate polymer interchain packing in membranes (Figure 3).…”

“…50 In the case of PI-TB-1, the additional contribution of the large bulky −C(CF 3 ) 2 − units enhances solubility further, rendering it soluble even in acetone. 34,60,61 For many microporous polymers including PIM−PIs, good mechanical properties are difficult to obtain due to high chain rigidity, high porosity and free volume. However, as shown in Table 4, the two polyimides in this study exhibited tensile strengths in the range of 59−64 MPa, initial modulus of 1.38− 1.58 GPa and elongation at break of 5−17%, indicating they have good mechanical properties.…”

“…Gas transport data for the two TB-based polyimide membranes are shown in Figure 5 34 and PIM-6FDA−OH, 47 and even out-performed many other reported non-6FDA PIM− PIs such as PIM−PI-1, 43 PIM−PI-3, 43 PIM−PI-9, 42 PIM−PI-10, 42 and PIM−PI-11 42 (see Figure 5), although the performance data are well below the currently reported KAUST-PI-1. 49 The significant increase in microporosity induced by the incorporation of TB units into PI gives marked gains in the gas separation performance of the membranes.…”

Simulations of gas transport in membranes based on polynorbornenes functionalized with substituted imide side groups

“…It has been found that restriction of both packing efficiency and chain mobility may increase gas permeability with minimum permselectivity losses. Families of polycarbonates [3][4][5][6][7][8][9], polysulfones [4,[10][11][12][13][14][15][16][17], polyimides [18][19][20][21][22][23][24][25], polyoxydiazoles and polytriazoles [26,27], aromatic polyesters [28][29][30][31][32], and methyland phenyl-substituted polyphenylene ethers [33,34], have been optimized using these guidelines. Work has been reported showing that the substitution of hydrogen atoms by methyl groups in the four symmetrical ring positions of bisphenol A leads to polycarbonates, polysulfones and polyarylates that are about four times more permeable to gases than the corresponding unsubstituted materials without losing permselectivity [33].…”