Synthesis and properties of highly processable asymmetric polyimides with bulky phenoxy groups

Abstract

A series of new aromatic polyimides (PIs) and co-PIs containing bulky tert-butyl phenoxy group was synthesized by one-step high-temperature polycondensation of 1,3-diamino-4-(4′- tert-butylphenoxy)benzene ( tBuPDAB) with different commercially available aromatic dianhydrides. The polymers were obtained in quantitative yields with inherent viscosities of 0.40–0.70 dL g−1. They exhibited high thermal stability with 10% weight loss above 480°C and were cast in films with good mechanical properties capable to be tested as gas separation membranes. These PIs were compared with analogs bearing phenoxy group (PDAB). The incorporation of tBu improved the solubility of the PIs, their free volume fraction, d-spacing, and gas permeability coefficients in comparison with their analogs obtained from PDAB. The permeability enhancement was from 2.5 to 8 times depended on the gas tested. The PI, based on tBuPDAB and 4,4’-(hexafluoroisopropylidene)diphtalic anhydride and, thus, containing two different bulky pendant groups, showed the highest gas permeability coefficient for CO2 (58.3 Barrer) and moderate ideal selectivity to the gas pair CO2/CH4 ( α = 18.0).

Gas Permeability through Polyimides: Unraveling the Influence of Free Volume, Intersegmental Distance and Glass Transition Temperature

“…Note that, in Figure 7, the ordinates correspond to the slope of versus which is proportional to 𝛼 = 𝑎 + 𝑏𝑑 𝑘 + 𝑐𝑑 𝑘 2 , in accordance with Equations ( 5) and (7). The constant appears in order to pass from log 𝑃 to ln 𝑃 because log 𝑃 = CO 2 permeability as a function of the fraction of free volume for several data extracted from the literature [6,[41][42][43][44] is shown in Figure 6.…”

“…Some data from the literature [42,44,45,[50][51][52][53] on the free volume fraction versus dspacing are shown in Figure 13, where it is seen that there is an average linear trend according to Equation ( 14). spacing are shown in Figure 13, where it is seen that there is an average linear trend according to Equation ( 14).…”

“…Given that Bondi's group contributions are not kept truly updated [6,11,40], it seems preferable to use molecular simulations to obtain more accurate estimations of FFV. CO2 permeability as a function of the fraction of free volume for several data extracted from the literature [6,[41][42][43][44] is shown in Figure 6.…”

“…In Figure 10, the permeability of CO2, for the membranes we studied here, as a function of 𝑑 𝑆 showing the fitted straight line corresponding to Equation ( 9), is shown. Some data from the literature [42][43][44][45][46][47][48][49] on CO2 permeability versus d-spacing are described in Figure 11.…”

“…3. Some data from the literature [42][43][44][45][46][47][48][49] on CO 2 permeability versus d-spacing are described in Figure 11. Note that, although in a somehow diffuse way, a certainly linear dependence of P on d S with some divergences could be due to the possible non-homologous series of membranes shown in Figure 11.…”