Gas Transport Properties in Cross-Linked and Vacuum Annealed Poly(oxyindole biphenylylene) Membranes

Abstract

This work studies useful routes to produce cross-linked poly(oxyindole biphenylylene) bearing a crosslinkable propargyl group, PNPr. Thus, the effect of crosslinking temperature and time on gas permeability and ideal selectivity for a non-cross-linked PNPr membrane to produce a cross-linked PNPr membrane is studied in detail in order to learn how more productive membranes, in terms of permeability−selectivity combinations, and membranes resistant to solvent swelling and CO 2 plasticization may be produced. Systematic studies on structure/processing/property relationship assessed by Fourier transform infrared attenuated total reflectance (FTIR-ATR), gel content (GC [%]), swelling degree (SD [%]), specific volume, wide-angle X-ray diffraction (WAXD), and gas permeability measurements reveal that PNPr membranes cross-linked under vacuum (1 mmHg) at 190 °C for 24 h, and further vacuum-annealed for 1584 h, at 35 °C and 10 −3 mmHg, produce membranes that overcome the typical trade-off between permeability and selectivity. In effect, the thermally cross-linked membranes annealed under vacuum for 1584 h, as compared to the non-cross-linked membranes, possess P(H 2 ) and P(CO 2 ) that increase by 2.4 and 2.1 factors while selectivity increases from 25 to 45 for the H 2 / CH 4 pair and from 25 to 39 for the CO 2 /CH 4 pair, whereas P(O 2 ) increases by a 2.4 factor with an associated increase in selectivity from 4.4 to 9.6 for O 2 /N 2 which situates this membrane above Robeson's 2008 upper-bound limit, at least for this pair of gases. The cross-linked membranes are resistant to solvent selling, since their SD [%] in NMP is on the order of 1−3%, and also to CO 2 plasticization since the plasticization pressure was not observed at least up to the 18 bar upstream pressure studied here.

POXINAR Membrane Family for Gas Separation

“…Their high thermal resistances allow the POXINARs to be termed highperformance polymers, and this is an important property for many polymer applications and for further postmodifications (e.g., thermal cross-linking throughout propargyl groups, as has been reported elsewhere). 9,10 The experimental specific volumes and FFVs are comparable to those reported for the well-known polysulfone, 20 polycarbonate, 21,22 and polyarylate 23 families. The chemical structural changes in the repeating units of the polymers affect their packing densities as estimated from FFV.…”

“…More recently, polymer 2aA was used as a model for incorporating thermolabile and cross-linkable groups to illustrate how different thermal treatments lead to POXINAR membranes that not only possess attractive gas permeability and selectivity properties but also are more resistant to aggressive solvents and aging . An unusual and very interesting example of thermal cross-linking of a 2aA membrane followed by long-term annealing under vacuum (10 –3 Torr) was reported; the resulting polymers were resistant to solvent swelling and CO 2 plasticization up to 18 bar, and the selectivity–permeability combinations for O 2 /N 2 overcome the typical trade-off between permeability and selectivity, falling above Robeson’s 2008 upper-bound limit.…”

Mixed Matrix Membranes Based on Fluoropolymers with m- and p-Terphenyl Fragments for Gas Separation Applications

“…In this study, the developed polymeric membranes and MMMs did not display a clear tendency to fracture; this is mainly due to its high thermostability with no significant weight loss below 500 °C (under air) as observed in thermogravimetric analysis (TGA) studies (Figure and Table S1), and glass-transition temperatures were not detected before its decomposition temperature. This behavior is analogous to that of similar polymers. ,− On the other hand, the obtained MMMs withstood harsh conditions during solvent evaporation (up to 200 °C, when NMP was used as a solvent) and gas transport measurements where pressures up to 2 bar were employed. This depicts the good thermal and mechanical stabilities, at least under the conditions studied, of the obtained MMMs.…”

Carbon Molecular Sieve Membranes from Multiring Highly Aromatic Functional Copolymers

“…It has also been shown that it is possible to modify the isatin moiety to obtain polymers with different pendant groups. 18,19 Several reports show that these highly aromatic polymers have glass transition temperatures, T g values, above 400 °C and onset of decomposition temperature, T d , above 450 °C. Furthermore, given their highly aromatic structure they present a high residual char around 75% at 800 °C.…”