Non-solvent post-modifications with volatile reagents for remarkably porous ketone functionalized polymers of intrinsic microporosity

Chemical modifications of porous materials almost always result in loss of structural integrity, porosity, solubility, or stability. Previous attempts, so far, have not allowed any promising trend to unravel, perhaps because of the complexity of porous network frameworks. But the soluble porous polymers, the polymers of intrinsic microporosity, provide an excellent platform to develop a universal strategy for effective modification of functional groups for current demands in advanced applications. Here, we report complete transformation of PIM-1 nitriles into four previously inaccessible functional groups – ketones, alcohols, imines, and hydrazones – in a single step using volatile reagents and through a counter-intuitive non-solvent approach that enables surface area preservation. The modifications are simple, scalable, reproducible, and give record surface areas for modified PIM-1s despite at times having to pass up to two consecutive post-synthetic transformations. This unconventional dual-mode strategy offers valuable directions for chemical modification of porous materials.


Synthesis of PIM
was gradually added to the system, and then the reaction mixture was stirred for 72 hours. At the end of the reaction, a highly viscous solution was cooled down and poured into water (650 mL). The polymer solid was obtained by filtration. The purification was performed by dissolving the material in chloroform (160 mL) and precipitating from methanol (500 mL) twice. The precipitated PIM-1 was then vacuum filtered and washed with 1,4-dioxane (100 mL), acetone (100 mL), water (100 mL), and an excess amount of methanol. The luminous yellow product was dried in a vacuum oven at 120 °C overnight (Yield: 78.2%, 3.60 g). PIM-1 powder was stored in a tightly sealed container to prevent moisture contact. The high temperature method of PIM-1 was synthesized following the previous report of Huajie Y. et al. The starting materials; 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindane (TTSBI) (4.26 g, 12.5 mmol), tetrafluoroterephthalonitrile (TFTPN) (2.50 g, 12.5 mmol), fine anhydrous potassium carbonate (5.18 g, 37.5 mmol), dimethylacetamide DMAc (25 mL), and toluene (12.5 mL) were placed to a dry three-neck round bottom flask equipped with a Dean-Stark trap and condenser under an atmosphere of argon gas. The reaction mixture was left to stir at ambient temperature until TTSBI and TFTPN were completely dissolved. Then the solution mixture was refluxed at 160°C in an oil-bath with vigorous stirring for 40 min. Subsequently, the viscous solution was poured into methanol to acquire a yellow polymer solid. After filtration, the sample was dissolved in chloroform (100 mL) and re-precipitated from methanol. The final product was further stirred in 1,4-dioxane (50 mL) for 30 min to remove low molecular weight oligomers and cyclic products. The sample was collected and re-washed with acetone. To eliminate K2CO3 residue, the PIM-1 powder was refluxed overnight in deionized water, stirred in methanol for 20 min, and then dried at 120 °C in a vacuum oven overnight. The fluorescent yellow polymer (PIM-1) product yielded 4.31 g (91.5%). To confirm the indispensability of the ketone functional group for chemically anchoring with amine, the identical reaction conditions of amine functionalization of K-PIM-1 was performed by replacing K-PIM-1 with PIM-1. Phenylhydrazine (PhNHNH2) and polyethylenimine (PEI) were used as reagents. In a dry three-neck round bottom flask equipped with a reflux condenser, PIM-1 (0.69 g, 1.5 mmol) was suspended in ethanol (EtOH) (15 mL). The mild acidic condition was induced by adding glacial acetic acid (AcOH) (0.45 mL) and heating up to 80 °C under argon atmosphere. After the temperature reached the setpoint, different amine solutions (0.76 mL of phenylhydrazine reagent or 5.7 mL of polyethylenimine) were added to the solution depending on the targeted final product, and the reaction was refluxed for 48 h. Then the reactions were cooled down to room temperature. The final products were filtered and gradually washed with ethanol (4x50 mL). Additionally, the samples were stirred in ethanol (100 mL) for 20 min before being filtered and dried in the vacuum oven at 105 °C for 12 h. The final products remained fluorescent yellow (Yield: 0.55 g and 0.62 g for the functionalization of PIM-1 with PhNHNH2 and PEI, respectively). 6 3. Processability a) PIM-1 film preparation: PIM-1 powder (0.5 g) was dissolved in chloroform (20 mL) and stirred overnight. After that, the homogenized polymer solution was poured into a flat-bottomed glass petri dish. The solvent was slowly evaporated in the glass cover for 3 days and further dried at 60 °C in a vacuum oven for 24 h. b) K-PIM-1 film preparation: The dried PIM-1 film was cut into a small piece and transferred to the round bottom. Methylmagnesium bromide in diethyl ether (30 mL, non-solvent for PIM-1) was added to the system. The solution was stirred overnight. Then the workup process was performed by placing the round bottom in an ice bath for 15 min. Then 0.5 M HCl in methanol solution (85 mL) was slowly added to the solution. Afterwards 0.5 M HCl in an aqueous solution was slowly added to adjust pH in the range of 4-5. To complete conversion, the solution was additionally stirred at 60 °C for 4 h. The sample was filtered off and washed with an excess amount of water following by methanol. The film was allowed to dry in air overnight, and kept in a vacuum oven at 60 °C for 24 h.

Calculation of Surface Areas 5, 6
To calculate the surface areas from N2 adsorption isotherms at 77 K, we applied following criteria: 1) The linear fit should span at least 5 points.
2) The R 2 should be greater or equal to 0.995.
3) Over the entire fitting range Q(1-P/P0) must continuously increase with P/P0 4) The value of C intercept obtained by linear regression must be positive in the plot of 1/[Q(P0/P-1)] against P/P0 The amount of gas molecules adsorbed in the initial monolayer is The specific surface area was calculated as follows: Where NA is Avogadro's constant, and 16.2 Å 2 is the cross-sectional area of a N2 molecule. 8

Methodology
Well-ground polymer was filled into a stainless-steel column and activated at 120 o C for 5 hours prior to breakthrough adsorption test. Before each experiment, helium reference gas was flushed through the column and the gas flow was then switched to the desired gas mixture at the flow rate of 5 mL min -1 (80.75% N2, 14.25% CO2, 5% He). The test was carried out at 1 bar pressure and

Derivation of adsorption capacity
Adsorption capacity is calculated as the amount of uptake adsorbate per unit mass of the adsorbent. While, Substitute (2), (3) and (4) into (1).
Then total adsorbate will be calculated by Eq. Then adsorption capacity (q) of PEI-PIM-1 is 0.58 mmol g -1 .    Supplementary Figure 9: The mechanism for the ketone formation.      The surface area was measured from powder form. The reported values were obtained from the best conversion, which revealed the surface area data. a The conversion was calculated from elemental analysis. b The ratio between the integration of the -CN stretching vibration peak and the -CH stretching vibration peaks (Characterized from FT-IR) in relation to those for PIM-1 was used to determine the approximate extent of nitrile conversion. c The conversion of nitrile to thioamide was estimated by integrating the 1 H NMR peaks and from the weight percent of sulfur determined by elemental analysis. d The conversion obtained from the combination of amide (2%) and carboxylic acid (92%) contents calculated from 1 H NMR Spectra of hydrolyzed PIMs. e The conversion was calculated from the molar ratio of the tetrazole groups in the TZPIM to the total nitrile groups of PIM-1, which is based on the 1 H NMR calculation of the integration ratio of the methyl signal of a methylated derivative of TZPIM to the methyl signals of the ladder polymer backbone. f The conversion was estimated from IR and NMR data. § The conversion was based on the post-modification of the K-PIM-1 derivative.