Free Volume and Permeability of Mixed Matrix Membranes Made from a Terbutil-M-terphenyl Polyamide and a Porous Polymer Network

Abstract

A set of thermally rearranged mixed matrix membranes (TR-MMMs) was manufactured and tested for gas separation. These membranes were obtained through the thermal treatment of a precursor MMM with a microporous polymer network and an o-hydroxypolyamide,(HPA) created through a reaction of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane (APAF) and 5′-terbutil-m-terfenilo-3,3″-dicarboxylic acid dichloride (tBTmCl). This HPA was blended with different percentages of a porous polymer network (PPN) filler, which produced gas separation MMMs with enhanced gas permeability but with decreased selectivity. The thermal treatment of these MMMs gave membranes with excellent gas separation properties that did not show the selectivity decreasing trend. It was observed that the use of the PPN load brought about a small decrease in the initial mass losses, which were lower for increasing PPN loads. Regarding the glass transition temperature, it was observed that the use of the filler translated to a slightly lower Tg value. When these MMMs and TR-MMMs were compared with the analogous materials created from the isomeric 5′-terbutil-m-terfenilo-4,4″-dicarboxylic acid dichloride (tBTpCl), the permeability was lower for that of tBTmCl, compared with the one from tBTpCl, although selectivity was quite similar. This fact could be attributed to a lower rigidity as roughly confirmed by the segmental length of the polymer chain as studied by WAXS. A model for FFV calculation was proposed and its predictions compared with those evaluated from density measurements assuming a matrix-filler interaction or ideal independence. It turns out that permeability as a function of FFV for TR-MMMs follows an interaction trend, while those not thermally treated follow the non-interaction trend until relatively high PPN loads were reached.

Thermally Rearranged Mixed Matrix Membranes from Copoly(o-hydroxyamide)s and Copoly(o-hydroxyamide-amide)s with a Porous Polymer Network as a Filler—A Comparison of Their Gas Separation Performances

“…The gas permeability of MMMs and the corresponding neat polymeric matrices of HPA and PAA are shown as a function of the kinetic diameter of the permeated gases, as given by Breck (1975) [ 40 ] for different filler contents, both before and after thermal rearrangement (represented in Figure 9 ). Recently, Soto et al (2022) [ 25 , 41 ] proposed and validated a correlation between permeability and free volume, as: …”

“…The acronyms of the manufactured membranes are shown in Table 1 . Note that we only included up to 30% PPN content, because previous experience revealed that PPN content over 30% strongly decreases the selectivity and worsens the mechanical properties [ 25 ].…”

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

“…The van der Waals volume can be evaluated by using the Bondi's group contribution theory [11] or by molecular modeling of the polymer repeating units, with programs like Hyperchem Molecular Modeling (Hypercube, Gainesville, FL, USA) [20,21] or DS BIOVIA Materials Studio software (2023 v23.1.0.3829) (BioVia Dassault Systémes, San Diego, CA, USA) [8,22].…”

“…We have recently proposed and tested a quantitative correlation of free volume fraction with permeability [ 7 , 8 , 9 , 10 ] that we want to verify here for a homologous series of rather similar polyimides with a wide range of permeabilities. We will test as well whether that quantitative correlation can be applied to d-spacing too.…”

Morphological Study before and after Thermal Treatment of Polymer-Polymer Mixed-Matrix Membranes for Gas Separations

“…However, this technique by itself is not decisive since in many cases, it is difficult to quantify these morphologies in enough detail. The determination of the fractional free volume (FFV) or the density of the MMMs compared to their constituents also informs us about free spaces or the penetration of the polymer into the filler matrix [26,27]. On the other hand, the rigidification of the polymer chains at the interfaces can be studied by analyzing properties such as the glass transition temperature (Tg) or the most probable intersegmental distance as a function of the filler content [14].…”