Communication pubs.acs.org/cm
Perylene Based Porous Polyimides: Tunable, High Surface Area with Tetrahedral and Pyramidal Monomers K. Venkata Rao,† Ritesh Haldar,† Chidambar Kulkarni,†,‡ Tapas Kumar Maji,†,‡,* and Subi J. George†,* †
Supramolecular Chemistry Laboratory, New Chemistry Unit, and ‡Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Jakkur P.O., Bangalore 560064, India S Supporting Information *
KEYWORDS: polyimides, perylene diimide, micro- and mesoporous materials, surface area
D
uptake at high pressure.31 Herein we report for the first time the synthesis and properties of perylene derived porous polyimides (Scheme 1). The surface area and pore size of
esign of low-density microporous materials, such as metal−organic frameworks (MOFs), has been of immense research interest in the past decade, because of their vital importance in gas storage1−4 and catalysis.5 Recently, microporous organic materials, obtained via linking of various organic building blocks, with large surface area are shown to be an attractive alternative to MOF.6,7 These porous organic systems are designed with strong covalent bonds instead of the coordination bonds employed in MOFs and hence benefit from better thermal and hydrothermal stabilities. In particular, covalent organic framework (COF) materials have emerged as perfect organic analogues of MOFs, in terms of porous framework structure, crystalline nature, and excellent surface areas.8−10 However, with the realization that the crystalline order is not a prerequisite for controlling the pore distribution and surface area of organic frameworks, microporous organic polymers with an amorphous two or three-dimensional network have recently emerged as a new class of porous organic materials.11−19 These porous macromolecules can be synthesized with relatively easy polymerization reactions and, more importantly, their pore dimensions can be controlled by the appropriate choice of structure directing monomers.6,7 Hence various common organic reactions have been utilized to exploit the synthesis of microporous polymers such as hypercross-linked polymers (HCPs),20−22 polymers with intrinsic microporosity (PIM),23,24 and conjugated microporous polymers (CMPs).11−19 Aromatic porous polyimides, which can be easily synthesized from amine linkers and polyaromatic anhydrides, are attractive for energy storage applications because of their high mechanical strength, excellent redox behavior, and superior chemical and thermal stability compared to the other porous macromolecules.25−27 In this respect, selective CO2 adsorption over methane and good hydrogen uptake has been reported recently for this class of organic porous materials.28−31 Interestingly, very high surface areas are predicted for diamondoid polyimides having polyaromatic linkers such as perylene.32 However, the synthesis of polymides has been restricted to the naphthalene (NDA)29,30 and pyromellitic (PMDA)31,33 aromatic cores to date, and there are no reports pertaining to their core extended π-conjugated analogues. The highest reported surface area for a porous polyimide is 1407 m2/g containing a tetrahedral pyromellitic derivative, which also showed 3 wt % of H2 © 2012 American Chemical Society
Scheme 1. Synthesis of Tr-PPI and Td-PPI Polyimides
these highly stable perylene diimide (PDI) polymers have been controlled by the use of trigonal pyramidal and tetrahedral shaped structure directing monomers. Furthermore, the tetrahedrally organized perylene polyimide showed a BET surface area of ∼2213 m2/g, which is the highest value reported in aromatic porous polyimides. The perylene based polyimides, Tr-PPI and Td-PPI, have been synthesized by the condensation reaction of perylene dianhydride (PDA) with tris(4-aminophenyl)amine (TAPA), having a trigonal pyramidal geometry, and tetra(4aminophenyl)methane (TAPM) with a tetrahedral geometry, respectively (Scheme 1).34 The trigonal and tetrahedral structure directing amine monomers were synthesized according to the literature procedures and would ensure geometrically a three-dimensional chain growth as already shown in CMPs.12 The resulting polymers were purified and structurally Received: December 1, 2011 Revised: February 28, 2012 Published: March 9, 2012 969
dx.doi.org/10.1021/cm203599q | Chem. Mater. 2012, 24, 969−971
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Communication
pores in the network. The apparent BET surface area of TdPPI was 2213 m2/g, which is higher than any of the analogous polyimide networks reported in the literature (see Table 1 for a
characterized by solid-state NMR, FT-IR, powder XRD, UV− vis spectroscopy, and elemental analysis.34 The thermal stability and porous nature of these polyimides were further analyzed by thermogravimetric analysis (TGA) and N2 adsorption measurements, respectively.34 A qualitative insight into the different molecular organization of PDI chromophores in the Tr-PPI and Td-PPI polymer network is evident from the different colors of these polymer samples.34 UV−vis reflectance spectra of Tr-PPI showed broad peaks from 250 to 800 nm with a maxima at 460 nm, whereas two separated bands with maxima at 470 and 525 nm were observed for Td-PPI and both the polymers were nonfluorescent.34 TGA analysis from 30 to 700 °C showed high thermal stability for both the polyimides with no decomposition up to 500 °C.34 Small weight loss ( 0.8, suggesting the presence of meso
Table 1. Surface Areas of Various Polyimides polyimide PMDA31,33 NDA29,30 PDA (this paper)
SBET (m2 g−1) Trigonal
SBET (m2 g−1) tetrahedral
ratio (tetrahedral/ trigonal)
818 232 400 (Tr-PPI)
1407 732 2213 (Td-PPI)
1.72 3.155 5.53
comparison). In contrast, the surface area of Tr-PPI was only 400 m2 g−1, although this is higher than the similar triphenyl amine based imide networks with naphthalene core (Table 1). Figure 1b shows the differential pore volume distributions for both the polymers, as a function of pore width calculated using the nonlocal DFT (NLDFT) method. Both Tr-PPI and TdPPI have narrow pore-size distribution in the micropore region, and their pore sizes are centered at 10.8 Å and 5.4 Å, respectively (Figure 1b). Although micropores are dominant for both the polymers, there is a significant proportion of mesoproes centered at 44.5 Å in the Td-PPI network. The calculated pore volumes of Tr-PPI and Td-PPI are 4.33 cm3/g and 0.63 cm3/g, respectively. In addition, hysteresis with desorption lying above the adsorption was observed for both the samples which could be either due to the swelling of the network during gas uptake or due to the presence of mesopores.12 Although powder XRD measurements of the polyimides showed broad peaks, as commonly observed for organic microporous polymers, the presence of several peak maxima in the diffractogram indicated the ordered nature of these networks.34 Interestingly, Tr-PPI and Td-PPI showed low angle peaks corresponding to the d-spacing of 1.62 and 0.72 nm, which reflects the same trend as that of calculated pore widths. In addition, both polyimides showed wide-angle peaks characteristic of π−π interactions of the aromatic moiety. Further insights into the molecular structural features, which resulted in the differences in surface area of the polyimide polymers, have been provided by the atomistic simulation for the small fragments of these networks. Figure 2 shows the energy minimized conformations of the first generation oligomers for both polyimides and the schematic of their
Figure 1. (a) N2 sorption isotherms of Tr-PPI and Td-PPI at 77 K; inset is shown for Tr-PPI isotherm for clarity (filled circles show adsorption, empty circles show desorption, P0 is the saturated vapor pressure of the gas at 77 K). (b) Pore size distributions of Tr-PPI and Td-PPI calculated by the NLDFT method.
Figure 2. Energy minimized geometries of the first generation oligomers of (a) Tr-PPI and (b)Td-PPI and a model of their expected final polymer structure. 970
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(5) Wang, Z.; Chen, G.; Ding, K. Chem. Rev. 2009, 109, 322. (6) Cooper, A. I. Adv. Mater. 2009, 21, 1291. (7) Thomas, A. Angew. Chem., Int. Ed. 2010, 49, 8328. (8) Côté, A. P.; Benin, A. I.; Ockwig, N. W.; O’Keeffe, M.; Matzger, A. J.; Yaghi, O. M. Science 2005, 310, 1166. (9) Wan, S.; Guo, J.; Kim, J.; Ihee, H.; Jiang, D. Angew. Chem., Int. Ed. 2008, 47, 8826. (10) Kuhn, P.; Antonietti, M.; Thomas, A. Angew. Chem., Int. Ed. 2008, 47, 3450. (11) Jiang, J.-X.; Su, F.; Wood, C. D.; Campbell, N. L.; Niu, H.; Dickinson, C.; Ganin, A. Y.; Rosseinsky, M. J.; Khimyak, Y. Z.; Cooper, A. I.; Trewin, A. Angew. Chem., Int. Ed. 2007, 46, 8574. (12) Weber, J.; Thomas, A. J. Am. Chem. Soc. 2008, 130, 6334. (13) Pandey, P.; Katsoulidis, A. P.; Eryazici, I.; Wu, Y.; Kanatzidis, M. G.; Nguyen, S. T. Chem. Mater. 2010, 22, 4974. (14) Ben, T.; Ren, H.; Ma, S.; Cao, D.; Lan, J.; Jing, X.; Wang, W.; Xu, J.; Deng, F.; Simmons, J. M.; Qiu, S.; Zhu, G. Angew. Chem., Int. Ed. 2009, 48, 9457. (15) Stöckel, E.; Wu, X.; Trewin, A.; Wood, C. D.; Clowes, R.; Campbell, N. L.; Jones, J. T. A.; Khimyak, Y. Z.; Adams, D. J.; Cooper, A. I. Chem. Commun. 2009, 212. (16) Ren, H.; Ben, T.; Wang, E.; Jing, X.; Xue, M.; Liu, B.; Cui, Y.; Qiua, S.; Zhu, G. Chem. Commun. 2010, 46, 291. (17) Chen, L.; Honsho, Y.; Seki, S.; Jiang, D. J. Am. Chem. Soc. 2010, 132, 6742. (18) Katsoulidis, A. P.; Kanatzidis, M. G. Chem. Mater. 2011, 23, 1818. (19) Rao, K. V.; Mohapatra, S.; Kulkarni, C.; Maji, T. K.; George, S. J. J. Mater. Chem. 2011, 21, 12958. (20) Lee, J.-Y.; Wood, C. D.; Bradshaw, D.; Rosseinsky, M. J.; Cooper, A. I. Chem. Commun. 2006, 2670. (21) Germain, J.; Fréchet, J. M. J.; Svec, F. J. Mater. Chem. 2007, 17, 4989. (22) Wood, C. D.; Tan, B.; Trewin, A.; Niu, H.; Bradshaw, D.; Rosseinsky, M. J.; Khimyak, Y. Z.; Campbell, N. L.; Kirk, R.; Stöckel, E.; Cooper, A. I. Chem. Mater. 2007, 19, 2034. (23) McKeown, N. B.; Gahnem, B.; Msayib, K. J.; Budd, P. M.; Tattershall, C. E.; Mahmood, K.; Tan, S.; Book, D.; Langmi, H. W.; Walton, A. Angew. Chem., Int. Ed. 2006, 45, 1804. (24) Budd, P. M.; Ghanem, B. S.; Makhseed, S.; McKeown, N. B.; Msayib, K. J.; Tattershall, C. E. Chem. Commun. 2004, 230. (25) Song, Z.; Zhan, H.; Zhou, Y. Angew. Chem., Int. Ed. 2010, 49, 8444. (26) Weber, J.; Antonietti, M.; Thomas, A. Macromolecules 2008, 41, 2880. (27) Song, Z.; Zhan, H.; Zhou, Y. Angew. Chem., Int. Ed. 2010, 49, 8444. (28) Fang, J.; Kita, H.; Okamoto, K.-i. Macromolecules 2000, 33, 4639. (29) Farha, O. K.; Spokoyny, A. M.; Hauser, B. G.; Bae, Y. S.; Brown, S. E.; Snurr, R. Q.; Mirkin, C. A.; Hupp, J. T. Chem. Mater. 2009, 21, 3033. (30) Farha, O. K.; Bae, Y. S.; Hauser, B. G.; Spokoyny, A. M.; Snurr, R. Q.; Mirkin, C. A.; Hupp, J. T. Chem. Commun. 2010, 46, 1056. (31) Wang, Z.; Zhang, B.; Yu, H.; Sun, L.; Jiao, C.; Liu, W. Chem. Commun. 2010, 46, 7730. (32) Trewin, A.; Cooper, A. I. CrystEngComm 2009, 11, 1819. (33) Wang, Z.; Zhang, B.; Yu, H.; Li, G.; Bao, Y. Soft Matter 2011, 7, 5723. (34) See Supporting Information.
extended network constructed from the basic unit. The less surface area of Tr-PPI compared to Td-PPI could be due to the differences in the geometry of corresponding structure directing monomers. The trigonal pyramidal geometry of TrPPI allows the network to grow in three directions, and due to the possibility of pyramidal inversion around the N-center, formation of hyperbranched structures is preferred compared to close ring structures, as recently reported.33 This kind of conformational flexibility of the building blocks is known to hamper the surface area.33 On the other hand, the conformationally more rigid tetrahedral geometry of tetraphenyl methane in Td-PPI allows the network to grow along the four vertices of tetrahedron to result in a closely packed threedimensional network, with more surface area as predicted by Trewin and Cooper.32 Moreover, this observed trend in surface area is in agreement with the similar NDA and PMDA based polyimides reported by Hupp et al.29,30 and Wang et al.,31,33 respectively (see Table 1), and hence can be generalized. The actual size of micropores in Td-PPI (5.4 Å) is smaller than that of the calculated 38.13 Å based on the ordered network model,32 which suggests the presence of an interpenetrated network. The larger pore size of Tr-PPI compared to Td-PPI, despite having a hyperbranched structure, could be attributed to a smaller degree of interpenetrated networks. Furthermore, CO2 gas adsorption measurements for both the polyimides performed at 195 K showed excellent uptake of ∼45 wt % and ∼31 wt % for Tr-PPI and Td-PPI, respectively.34 These values are remarkable, as the highest CO2 uptake reported for porous polyimides is ∼35 wt % at high pressures.29,30 In conclusion, we have synthesized two perylene based porous polyimides for the first time, from trigonal and tetrahedral structure directing monomers. The BET surface area of the tetrahradal polyimide derivative was as high as 2213 m2/g, which is the highest value reported so far for an imide based porous macromolecule. The extension of this design strategy to other extended π-conjugated systems and their gas storage characteristics are currently in progress.
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ASSOCIATED CONTENT
S Supporting Information *
Supporting figures and synthetic procedures (PDF). This material is available free of charge via the Internet at http:// pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*
[email protected],
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We thank JNCASR and DST for financial support. We thank Prof. S. Balasubramanian for the computational facilities. K.V.R. and R.H. thank CSIR for a research fellowship.
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REFERENCES
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