(353d) Molecularly Mixed Composite Membranes Based on Triptycene-Isatin Porous Polymer Networks and Carboxylic-Acid Functionalized PIM-1

Porous polymer networks (PPNs) are hyper-crosslinked 3-D networks that have shown promise as sorbents, as well as fillers in mixed-matrix membranes (MMMs) for gas and organic liquid separation. When PPNs are incorporated in glassy polymers to form MMMs, however, a variety of behaviors can be observed, which may lead to either an increase or decrease of permeability. In most cases, a decrease in selectivity is observed with respect to the PPN-free polymer.

To promote an intimate polymer-PPN contact and finely tune the microstructure, porosity and selectivity of the resulting MMMs, in this study we incorporated up to 30%wt triptycene-isatin PPN into carboxylic-acid functionalized PIM-1 (PIM-COOH). PIM-COOH is found to undergo a radical-induced crosslinking reaction typical for acid-containing polymers at 200 C, and convincing evidence is given from SEM, TGA, NMR, and gel fraction analysis that this crosslinking occurs not only among PIM-COOH chains, but also between PIM-COOH and PPN. To systematically study the effect of polymer-PPN mutual crosslinking on the structural and transport properties of the resulting molecularly mixed MMMs, three different batch of materials were prepared, namely neat PIM-COOH, PIM-COOH-PPN MMMs without thermal treatment, and PIM-COOH-PPN MMMs with thermal treatment at 200°C. The resulting materials are mechanically stable and can be easily fabricated as free-standing membranes.

The effect of this low-temperature crosslinking reaction, as well as the presence of PPNs, on the gas transport properties and plasticization characteristics of the resulting MMMs was studied via solid state NMR, microscopy, free volume calculations, as well as gas permeability and solubility measurements and application of the dual mode sorption-partial immobilization model. By doing so, we were able to deconvolute the roles of the PPN in thermally treated and untreated membranes. This study opens new routes to synthesize high performance separation systems for targeted applications by tuning the polymer/filler chemistry and promote an intimate contact between them via the reactive blending.