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Mar 24, 2017 - INTRODUCTION. In the past decade, polymers of intrinsic microporosity (PIMs) have attracted much interest as versatile platform materia...
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A Critical Update on the Synthesis of Carboxylated Polymers of Intrinsic Microporosity (C-PIMs) Bagus Santoso, Paam Yanaranop, Hong Kang, Ivanhoe K. H. Leung, and Jianyong Jin* School of Chemical Sciences, The University of Auckland, Auckland 1142, New Zealand S Supporting Information *

1. INTRODUCTION In the past decade, polymers of intrinsic microporosity (PIMs) have attracted much interest as versatile platform materials for applications such as gas separation membrane,1−4 gas storage,5,6 solvent nanofiltration,7,8 and fuel cell catalyst support.9 The well-studied polymer of its class is the original PIM-1, first synthesized by Budd and McKeown in 2004.10 Ever since, in parallel to synthesis progress, postsynthesis modification has also been explored extensively. Specifically, the nitrile group in PIM-1 has been the most convenient reaction site and has been converted to various functional groups.5,6,11−15Among those, the carboxylic acid is a highly desirable functionality to be installed into the PIM backbone due to its ability to undergo decarboxylation,16 polymer alloying,17−19 and ionomer formation.20,21 For example, the “carboxylated” PIM-1 (C-PIMs) were cross-linked via thermally induced decarboxylation.16 The proposed reaction mechanism proceeded through similar fashion to Koros’ carboxylic acid-containing polyimide work.22 Furthermore, C-PIMs have also been modified by blending with Torlon,17 Matrimid,18 and P8419 in attempts to improve the overall gas separation performance. In these studies, the significantly improved properties of the blended membranes were connected to the hydrogen bonding between C-PIMs and the other polymers. Most recently, the ionomers of C-PIMs with various metal ions Ag+, Ca2+, Mg2+, Zn2+, Al3+, and Fe3+ have been reported.20,21 Notably, in comparison to the parent PIM-1 membrane, the metal ion treated membranes successfully enhanced the CO2/CH4 and olefin/paraffin separation performance, this being above the upper bound lines under both pure and mixed gas conditions.20 Lastly, the “assumed” C-PIMs exhibited the selective removal of various heavy metal ions and organic dyes for wastewater treatment.23 Originally in 2009, the preparation of C-PIMs through the conversion from nitrile to carboxylic acid was reported via a rapid 5 h base hydrolysis process.11 The hydrolyzed products with various levels of carboxylation were obtained by subjecting PIM-1 to a basic medium between 1 and 5 h duration. Since then, this method has become the “standard” procedure to obtain C-PIMs as it is considered to be a “simple and efficient” route. To date, it has collected more than 100 citations. The original paper proposed that the resulting product contained the combination of pure PIM-1 (nitrile group only), a mixture of PIM-1 and C-PIMs (nitrile and carboxylic acid groups), and pure C-PIMs (carboxylic acid group only), as demonstrated in Scheme 1a.11 There was no mention of the primary amide as portion of hydrolysis products. © XXXX American Chemical Society

Lately, the actual chemical structure of the base-hydrolyzed PIM-1 material was revisited by Satilmis and co-workers in 2014.24 On the basis of their characterization and calculation, the authors pointed out their important findings that the hydrolyzed materials contained various ratios of amide, carboxylates, ammonium carboxylate, and sodium carboxylate (Scheme 1b). The amide content was significant even under extensively hydrolyzed conditions.24 Interestingly, Satilmis’ claims appeared to have been overlooked in recent C-PIMs related literatures.18−21,23 In this Note, to further support Satilmis’ statement,24 a more thorough investigation on the alkaline PIM-1 hydrolysis reaction in the powder form was carried out with extended reaction time. Furthermore, three model compounds were synthesized and characterized for assisting the identification of hydrolyzed PIM-1 products. Specifically, here we report (1) the peaks between 7.5 and 8.5 ppm in 1H NMR do not belong to the carboxylic acid signal, (2) the amide and carboxylic acid functionalities are distinguishable by spectroscopic assessments including FT-IR, 1H NMR, and 13C NMR, and (3) the 5 h base-hydrolyzed product is essentially the amide-functionalized PIM-1.

2. EXPERIMENTAL SECTION Materials and Instruments. All chemicals were purchased from Sigma-Aldrich and used as received without further treatment, except tetrafluoroterephthalonitrile (TFTPN) which purchased from Manchester Organics and recrystallized twice from ethyl acetate before use. 5,5′,6,6′-Tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane (TTSBI) was recrystallized twice from tetrahydrofuran (THF) and n-hexane mixed solvent before use. Dimethyl 2,3,5,6-tetrafluoroterephthalate25 was prepared as described previously. The single master batch of PIM-1 is the polycondensation product of ultrahigh purity monomers of TTSBI and TFTPN and was synthesized in-house following established procedures developed by Budd and McKeown.10 GPC of PIM-1: Mn = 70 596 g mol−1; Mw = 266 345 g mol−1 in THF solvent. NMR spectra were recorded on a Bruker Avance III 400 MHz spectrometer. Chemical shifts are reported in parts per million (ppm) referenced to δ 7.26 and 77.0 ppm from chloroform (CDCl3) or δ 2.50 and 39.5 ppm from dimethyl sulfoxide (DMSO-d6) for 1H and 13C nuclei, respectively. All 13C NMR spectra were acquired using broadband decoupled mode. 1 H−15N HSQC was measured using the Bruker pulse program hsqcetf 3gp on a Bruker Avance III HD 500 MHz spectrometer equipped with a BBFO probe. The size of the FID for the 1H dimension was 2048 points and for the 15N dimension was set as 80 points. Received: February 16, 2017

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Macromolecules Scheme 1. (a) The Originally Proposed Structure of Base Hydrolyzed PIM-1 Containing a Combination of Nitrile and Carboxylic Acid;11 (b) Satilmis’ Proposed Chemical Components of the Resulting Hydrolyzed PIM-124

Scheme 2. Synthetic Routes of the Model Compounds for Bis(nitrile) (1), Bis(amide) (2), and Bis(acid) (3)a

Reagents and conditions: (i) K2CO3, DMF 65 °C, 24 h; (ii) 30% H2O2, NaOH, DMSO, 70 °C, 2 h; (iii) K2CO3, DMF, 65 °C, 24 h; (iv) DMSO, KOH, 100 °C, 24 h.

a

The spectral width was set as 20 ppm (1H) and 250 ppm (15N), and the center of the spectrum was set to 4.7 and 125 ppm. 1JNH (cnst4) was set to 90 Hz. 15N decoupling was achieved using a 240 μs 90° GARP sequence, and the high power 15N 90°pulse was achieved using a 15 μs GARP sequence. The number of transients was 384. The relaxation delay was 2 s, and the temperature was 300 K. Infrared spectra were recorded on a Nicolet iS50 FT-IR spectrometer using a diamond ATR sampling accessory. Each sample was scanned 32 times at a resolution of 4 cm−1. UV−vis spectra were collected by Shimadzu UV-2700 spectrophotometer. The PIM-1, model compounds, and hydrolyzed PIM-1 samples were dissolved in chloroform, DMSO, and DMF with 0.1 mg/mL concentration, respectively. Pure solvents were employed as a blank for baseline correction. Elemental analysis was carried out at the Campbell Microanalytical Laboratory, The University of Otago. All measured microanalysis results had an uncertainty of ±0.4%. Synthesis of the Bis(nitrile) Model Compound (1). The bis(nitrile) model compound was prepared as described previously in the thioamide PIM-1 paper.14 Anhydrous DMF (60 mL) was added to 1,2-dihydroxybenzene (2.242 g, 20.36 mmol), tetrafluoroterephthalonitrile (1.863 g, 9.31 mmol), and potassium carbonate (7.990 g, 57.81 mmol) under an inert atmosphere. The reaction was heated to 65 °C and kept at this temperature for 24 h. The reaction was cooled, and then the solid was collected via vacuum filtration. The crude product was then stirred in water (150 mL) for 1 h and acetone (150 mL) for 1 h before being dried in an oven at 110 °C overnight. Compound 1 was obtained as a yellow solid (2.875 g, 90% yield). 1H NMR (400 MHz, DMSO-d6) δ ppm: 7.25−7.00 (m, 8H, Ar). FT-IR (ATR; cm−1): 2240, 1607, 1498, 1446, 1099, 1029. Synthesis of the Bis(amide) Model Compound (2). A 30% H2O2 solution (3 mL) was added to a suspension of bis(nitrile) model compound (1) (1.057 g, 3.10 mmol) and NaOH (0.902 g, 5.13 mmol) in DMSO (30 mL). The mixture was then heated to 70 °C and left to stir for 2 h. After the reaction had cooled down, it was then diluted with water (100 mL), and the solid was filtered out. The crude product

was washed with water (100 mL) before being collected and dried in the oven at 110 °C overnight. The bis(amide) model compound (2) was obtained as a yellowish-brown solid (0.733 g, 70% yield). 1H NMR (400 MHz, DMSO-d6) δ ppm: 8.07 (s, 2H, CONH2), 7.77 (s, 2H, CONH2), 7.13−6.95 (m, 8H, Ar). FT-IR (ATR, cm−1): 3375, 3189, 1651, 1635, 1497, 1270, 1253, 1099, 992. HR-MS (ESI) calcd for C20H12N2NaO6 399.0588; found: 399.0577 (M + Na)+. Synthesis of the Bis(ester) Intermediate Compound. Under a N2 atmosphere, anhydrous DMF (3 mL) was added to 1,2-dihydroxybenzene (0.092 g, 0.84 mmol) and dimethyl 2,3,5,6-tetrafluoroterephthalate (0.106 g, 0.40 mmol). After complete dissolution of the two reactants, anhydrous K2CO3 (0.348 g, 2.52 mmol) was added, and the reaction was heated to 65 °C. After 24 h, the reaction was allowed to cool down and stirred in water (50 mL) for 2 h. The solid was then collected by vacuum filtration and purified via column chromatography eluting with diethyl ether/hexane (1/4 v/v ratio). The bis(ester) intermediate compound was obtained as a white solid (0.070 g, 43% yield). 1H NMR (400 MHz, DMSO-d6) δ ppm: 7.13− 6.90 (m, 8H), 3.96 (s, 6H). FT-IR (ATR, cm−1): 2923, 1732, 1497, 1448, 1251, 1037, 988. HR-MS (ESI) calcd for C22H14NaO8 429.0581; found: 429.0569 (M + Na)+. Synthesis of the Bis(acid) Model (3). A solution of KOH (0.030 g, 0.42 mmol) in water (2 mL) was added to a suspension of the bis(ester) intermediate (0.020 g, 0.05 mmol) in DMSO (3 mL). The mixture was heated to 100 °C and stirred for 24 h. The reaction was allowed to cool down and diluted with water (20 mL). The unreacted starting material was then filtered out. The filtrate was acidified with HCl (2 mL, 1 M), and the yellow precipitate was collected and allowed to dry under vacuum overnight. The bis(acid) model compound (3) was obtained as a yellow solid (0.014 g, 76% yield). 1H NMR (400 MHz, DMSO-d6) δ ppm: 14.02 (s, COOH), 7.07−6.77 (m, 8H). FT-IR (ATR, cm−1): 2805, 2569, 1714, 1448, 1277, 1253, 1034, 997. HR-MS (ESI) calcd for C20H9O8 377.0303; found: 377.0298 (M − H)−. Attempted Synthesis of C-PIMs via Base Hydrolysis. Note: the functional group conversion of nitrile to carboxylic acid was B

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Figure 1. Stacked 1H NMR spectra of the model compounds 1−3 all in DMSO-d6. undertaken using one consistent batch of PIM-1. The base-hydrolyzed product was labeled as “C-PIM-B-reaction time”. The base hydrolysis followed the same procedure taken from the previous literature, except that PIM-1 powder was used instead of the film.11 PIM-1 finely crushed powder (0.153 g) was stirred in 20% NaOH solution in 1:1 H2O/EtOH (16.0 mL) at 120 °C in an oil bath. Samples were taken out for analysis at 5, 24, 48, and 72 h (3 days). The solids were individually isolated, washed with water (100 mL), and then refluxed in water (12.50 mL) with 4 drops of 1 M HCl solution for 2 h. After the reflux, the products were collected, further washed with water (150 mL) and MeOH (50 mL), and dried in a vacuum oven overnight. The final product appeared as a milky white, free-flowing powder. NMR results of C-PIM-B-72h were reported as follows: 1H NMR (400 MHz, DMSO-d6) δ ppm: 13.3−14.2 (br), 7.4−8.1 (br), 6.7−7.0 (br, 2H), 6.0−6.4 (br, 2H), 1.8−2.5 (br, 4H), 0.7−1.8 (br, 12H). 13C NMR (101 MHz, DMSO-d6) δ ppm: 162.5, 161.9, 148.4, 145.7, 139.8, 133.6, 113.4 111.3, 110.1, 58.4, 56.7, 43.1, 31.0, 29.6.

H2O2 to afford the bis(amide) model compound (2). Evidently, the NH2 protons of amide appeared as two nicely resolved peaks at 7.77 and 8.07 ppm, in addition to the aromatic multiplets between 6.95−7.13 ppm. Indeed, the two amide −NH protons are possibly nonequivalent due to the restricted rotation around the C−N bond in the primary amide (−C( O)NH2). Hence, the two hydrogen nuclei are expected to

3. RESULTS AND DISCUSSION Model Compound Studies. To assist with the structural and spectroscopic investigation of the product obtained from the base hydrolysis of PIM-1, three model compounds including the bis(nitrile) (1), bis(amide) (2), and bis(acid) (3) were synthesized, as shown in Scheme 2. For characterization, we are mainly interested in FT-IR, UV−vis, and NMR as these techniques can also be employed on the corresponding polymer. First, the bis(nitrile) model compound (1) was synthesized by the coupling of catechol with TFTPN in high yield, as reported by Mason et al.14 The 1H NMR spectrum (Figure 1) only shows a multiplet in the region of 7.00−7.25 ppm, assigned to the eight aromatic protons. The bis(nitrile) model compound (1) was then completely hydrolyzed using

Figure 2. 1H−15N HSQC spectrum of the model compound 2 in DMSO-d6 at 300 K. C

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Figure 3. FT-IR spectra of all the model compounds 1−3 between 1400 and 2300 cm−1.

Figure 6. FT-IR spectra comparison between (a) C-PIM-B-72h and (b) after soaking in 2 M NaOH.

display different chemical shifts. Figure 2 illustrates the 1 H {15N} HSQC (heteronuclear single quantum coherence) NMR result for bis(amide) model compound (2). This crucial experiment provides additional insight into spectroscopic correlations that are very useful in determining the amide nature of the two resonances at 7.77 and 8.07 ppm in 1H NMR. The experiment, which measured one-bond H−N correlations, clearly showed that there are two cross-peaks at 7.77 ppm 1H and 124 ppm 15N as well as 8.07 ppm 1H and 124 ppm 15N, respectively. This indicated that these two proton resonances were attached to one single nitrogen atom. The nitrogen has

Figure 4. UV−vis spectra of the model compounds 1−3 in DMSO.

Figure 5. Progressive FT-IR spectra of the base hydrolysis of PIM-1 (up to 72 h). D

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Figure 7. 1H NMR spectra comparison of PIM-1, C-PIM-B-5h, C-PIM-B-24h, C-PIM-B-48h, and C-PIM-B-72h.

a 15N chemical shift of 124 ppm is indicative of an amide nitrogen environment. Finally, the bis(acid) model compound (3) was synthesized by base hydrolysis of the bis(ester) intermediate, which was obtained from condensation between the dimethyl tetrafluoroterephthalate and catechol. Critically, the 1H NMR (Figure 1) of the product displays the carboxylic acid signal at 14.02 ppm. It is logical that the carboxylic acid signal are generally more downfield shifted (deshielded) than amide proton since the carboxylic acid possesses stronger hydrogen bonding in the form of dimer formation. The FT-IR spectra of all the model compounds are shown in Figure 3. The region between 1400 and 2300 cm−1 is expanded to show the different −CO and −CN stretches. The bis(nitrile) compound (1) shows a strong peak at 2240 cm−1 corresponding to the −CN stretching. The bis(amide) model compound (2) displays an amide CO stretch at 1651 cm−1, but no peak is present at 2240 cm−1; this indicates complete conversion by hydrogen peroxide. The bis(ester) intermediate shows a CO stretch at 1732 cm−1. After hydrolysis, the carbonyl stretching of the bis(acid) model compound (3) was shifted to 1714 cm−1. Hence, different carbonyl stretch vibrations are distinguishable in the order of ester > acid > amide in terms of frequency. The UV−vis absorption spectra of the model compounds 1−3 in DMSO are given in Figure 4. Initially, the bis(nitrile) model compound (1) showed a major absorption peak at 428 nm from the nitrile group. After hydrolysis, the spectra of bis(amide) (2) and bis(acid) (3) model compounds conveyed great similarities, both exhibiting bimodal peaks near 295 and 330 nm. Therefore, UV−vis offers little value for differentiating between the amide and acid functionalities.

Base Hydrolysis of PIM-1 with Extended Reaction Time. Normally the nitrile hydrolysis reaction is clean and high yield. Typically, the hydrolysis of nitriles may occur via two different pathways (i.e., basic and acidic conditions). For example, the 4-nitrophthalonitrile is common starting material to afford bisanhydride monomer for polyimide synthesis.26 However, chemical transformation on polymers-analogous reaction is tougher than small molecules since they generally show lower solubility and reactivity. For example, alkaline polyacrylonitrile (PAN) hydrolysis is dependent on its molecular weight, the choice of the base and its concentration, reaction temperature, and reaction medium.27−30 In the case of PAN, the side reaction involved the nearest-neighbor group participation, which yielded undesirable cyclized amidine structures.30 With respect to the well-studied PAN, the hydrolysis of PIM-1 has never been studied in depth despite its increasing interests in membrane separation field.11,12,24 The exact structure of the hydrolyzed products remains controversial. In this work, the base hydrolysis of PIM-1 was carried out under the same condition as originally reported work,11 except the hydrolysis time was pushed up to 72 h. All polymer samples were obtained from a single hydrolysis reaction, with samples taken out from the reaction vessel via a syringe and worked up after 5, 24, 48, and 72 h. The resulting products were labeled as “C-PIM-B-reaction time”. All polymers were soluble in DMSO, DMF, and NMP but insoluble in THF, chloroform, and DCM. The hydrolyzed products were analyzed mainly using FT-IR and NMR techniques and compared to the model compounds prepared in the previous section. To show the progression of nitrile hydrolysis, Figure 5 displays the consecutive spectra of the base-hydrolyzed products obtained with increasing modification time. After undergoing E

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Figure 8. 13C NMR spectra comparison of PIM-1, C-PIM-B-5h, and C-PIM-B-72h.

Table 1. Spectral Findings and Comparison between the Amide and Carboxylic Acid Functional Groups in the Hydrolyzed PIM-1 Products distinctive spectral features of the hydrolyzed product from PIM-1 characterization techniques

amide functional group

carboxylic acid functional group

FT-IR

the amide carbonyl stretching vibration shows the absorption at 1666 cm−1

the carboxylic acid group shows carbonyl stretching vibration peak at 1720 cm−1, which is higher than that of amide carbonyl group; after NaOH treatment, the CO stretching band of the carboxylic acid around 1720 cm−1 disappears, and the characteristic metal carboxylates stretching band at 1594 cm−1 appears

1

the amide proton exhibits the bimodal shape signals in the range of δ 7.0−8.5 ppm in DMSO-d6

the carboxylic acid exhibits the broad active proton signals at the downfield in the range of δ 13.0−14.0 ppm in DMSO-d6

the carbon chemical shift for amide carbonyl is around δ = 161.9 ppm in DMSO-d6

the carbon chemical shift for carboxylic acid situates at δ = 162.5 ppm in DMSO-d6, which is slightly downfield shifted compare to the amide carbonyl

H NMR

13

C NMR

observed for the amide peak at 1666 cm−1. At 72 h (C-PIM-B72h), the acid peak at 1720 cm−1 was almost 80% of the amide peak height at 1666 cm−1. In other words, the acid carbonyl stretch was unambiguously distiguishable to the amide carbonyl. Moreover, when sample C-PIM-B-72h was treated with 2 M NaOH(Figure 6), the carbonyl (−CO) stretching shoulder peak at 1720 cm−1 disappeared. Concomitantly, the corresponding carboxylate salt (−COO−) stretching at 1594 cm−1 appeared strongly owning to the antisymmetric carboxylate stretch mode while the amide peak at 1666 cm−1 remained

the base hydrolysis for 5 h (C-PIM-B-5h), the original −CN stretch at 2240 cm−1 mostly disappeared. The spectrum showed a CO stretch at 1666 cm−1 and broad multimode stretches between 3000 and 3500 cm−1. Model compounds studies suggested that this CO stretch belonged to the primary amide. As the hydrolysis continued to 24 h (C-PIM-B-24h), a second CO stretch at 1720 cm−1 started to emerge. Based on data for the model compounds, the location of this peak is consistent with the acid carbonyl stretch. After 48 h (C-PIM-B-48h), the acid signal continued to increase while no change was F

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two main absorbance peaks at 289 and 410 nm. After 5 h of reaction time, the absorbance peak at 410 nm totally disappeared, suggesting a total hydrolysis of the nitrile groups. However, all base-hydrolyzed products showed two major peaks at 307 and 326 nm. No significant difference was found on the UV−vis spectra with increased hydrolysis time. As mentioned previously in the Model Compound Studies section, UV−vis may not be a useful tool to distinguish between amide and acid structures. Lastly, the hydrolyzed products from PIM-1 in basic treatment were also verified by elemental analysis. In theory, the fully “carboxylated” PIM-1 contains no nitrogen atom. However, even for the C-PIM-B-72h sample, the nitrogen content was 1.88%. Thus, the only sound explanation for this is the incomplete hydrolysis.

4. CONCLUSIONS We undertook a detailed investigation on the exact chemical components of alkaline hydrolyzed PIM-1. More specifically, it is concluded that: (1) The peaks between 7.5 and 8.5 ppm in 1H NMR are assigned to the primary amide protons in hydrolyzed products. (2) The assumed “carboxylated” PIM-1 via a rapid 5 h base hydrolysis protocol is actually the amidefunctionalized PIM-1 with negligible carboxylic acid content. (3) Based on our spectroscopic data obtained from FT-IR, 1H NMR,13C NMR, and 1H {15N} HSQC, the amide and carboxylic acid groups are unambiguously distinguishable. We have summarized it in Table 1. In view of these findings, we felt the investigation for an alternative and more efficient route, such as acid hydrolysis pathway,12 to obtain fully carboxylated PIM-1 is necessary.

Figure 9. UV−vis spectra of PIM-1 in THF and progression of C-PIM-B series in DMF at different reaction times.

intact. Hence, the peak around 1720 cm−1 can be attributed to the carboxylic acid in hydrolyzed PIM-1 product. 1 H NMR spectra of four base-hydrolyzed products are displayed alongside that of PIM-1 to allow direct comparison in Figure 7. Here, we would like to focus our attention solely on the active protons in amide and carboxylic acid. For the C-PIMB-5h sample, the emergence of the active protons occurred between 7.5 and 8.5 ppm; this region was assigned to the carboxylic acid in the original paper.11 We believe that the carboxylic acid proton cannot apprear as broad bimodal peaks. The signals between 7.5 and 8.5 ppm should belong to the primary amide based on our bis(amide) model compound studies, especially from the strong evidence of 1H{15N} HSQC NMR data. Indeed, the original discussion on the temperaturedependent NMR investigation could be better interpreted if the signals were assigned to the primary amide. At low temperature (50 °C), the amide peaks displayed a bimodal shape due to the unequivalence of two amide protons. As the temperature increased, the amide signals not only shifted upfield but also merged into a broad single peak. This could be due to the faster bond rotation at elevated temperature. Thus, the signals from the two amide protons were homogenized on the NMR time scale. More importantly, the broad proton signals at the downfield in the range of 13.0−14.0 ppm were first noticed for all the extensively hydrolyzed samples (C-PIM-B-24h, C-PIMB-48h, and C-PIM-B-72h). It was suspected this region was where the actual carboxylic acid signal was supposed to be located, and it displayed good agreement with our bis(acid) model compound study in the earlier section. Figure 7 clearly demonstrated both the amide and carboxylic acid signals were detectable by proton NMR at the same time. 13 C NMR spectra in Figure 8 also provide additional information regarding the structures of the base hydrolyzed PIM-1. For the C-PIM-B-5h sample, the nitrile carbon (C12) of PIM-1 at 112.3 ppm disappeared, and the new amide carbonyl peak at 161.9 ppm was observed. As the hydrolysis progressed, the carbonyl carbon region of C-PIM-B-72h sample split into two peaks at 161.9 ppm (amide carbonyl) and 162.5 ppm (acid carbonyl). Overall, as summarized in Table 1, the characteristics of amide and carboxylic acid functionalities were conclusively distinguishable by FT-IR, 1H NMR, and 13C NMR. The UV−vis spectra of four different C-PIM-B samples are shown in Figure 9. The starting polymer PIM-1 in THF shows

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.7b00344. FT-IR and 1H spectra of model compounds 1−3; FT-IR, 1 H NMR, and 13C NMR spectra of C-PIM-B-5h, C-PIMB-24h, C-PIM-B-48h, and C-PIM-B-72h (PDF)

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AUTHOR INFORMATION

Corresponding Author

*Tel +64 9 9236624, e-mail [email protected] (J.J.). ORCID

Jianyong Jin: 0000-0002-5521-6277 Author Contributions

B.S. and P.Y. contributed equally to this work. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Dr. Jianyong Jin thanks The Science for Technological Innovation (SfTI) seed fund, New Zealand National Science Challenges (NSC), and Product Accelerator programme from the Ministry of Business, Innovation and Employment (MBIE) for their financial assistance. Paam Yanaranop also thanks his parents for funding his studies at the University of Auckland.

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REFERENCES

(1) Budd, P. M.; Msayib, K. J.; Tattershall, C. E.; Ghanem, B. S.; Reynolds, K. J.; McKeown, N. B.; Fritsch, D. Gas separation

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DOI: 10.1021/acs.macromol.7b00344 Macromolecules XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.macromol.7b00344 Macromolecules XXXX, XXX, XXX−XXX