Greener Synthesis\nof the Polymer of Intrinsic Microporosity\nPIM‑1 for Gas Separation

Polymers of intrinsic microporosity (PIMs) are studied\nas membranes\nfor energy-efficient and environmentally friendly separation technologies,\nbut greener polymerization methods are desirable for further scale\nup. This work aimed to synthesize the prototypical PIM (PIM-1) via\na greener synthetic route by changing the solvent system to methyl-5-(dimethylamino)-2,2-dimethyl-5-oxopentanoate\n(MDDOP), a structural analogue of the green solvent Rhodiasolv PolarClean.\nMass-based green metrics analysis was performed on MDDOP, determining\natom economy, complete environmental factor, and total carbon intensity,\ncomparing each to synthetic routes to PolarClean. Green metrics analysis\nfound MDDOP synthesis produced less waste than PolarClean. MDDOP solvent\ncapabilities were exemplified via PIM-1 polymerizations using 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane\n(TTSBI) with either tetrafluoroterephthalonitrile (TFTPN) or tetrachloroterephthalonitrile\n(TCTPN), varying the temperature (120–160 °C) and reaction\nduration (50 min–6 h). Recovery of methanol and MDDOP post\nPIM-1 synthesis reduced solvent waste by 22%. Reactions using TCTPN\nproduced polymers with higher molar masses than those produced using\nTFTPN. All samples showed varied topology, with evidence of branching\nand colloidal network. The polymer from the most successful reaction\nconditions (TCTPN, <i>T</i> = 140 °C, 6 h) was fabricated\ninto thick film membranes and tested with pure gases for CO<sub>2</sub>/CH<sub>4</sub> and CO<sub>2</sub>/N<sub>2</sub> gas pairs, performing\ncomparably with PIM-1 synthesized using conventional solvent systems.