Self-Organized Honeycomb-Patterned Microporous Polystyrene Thin

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Self-Organized Honeycomb-Patterned Microporous Polystyrene Thin Films Fabricated by Calix[4]arene Derivatives Eisaku Nomura,*,† Asao Hosoda,‡ Masafumi Takagaki,‡ Hajime Mori,‡ Yasuhito Miyake,‡ Motonari Shibakami,§ and Hisaji Taniguchi‡ † Department of Material Science, Wakayama National College of Technology, 77 Noshima, Nada, Gobo, Wakayama 644-0023, Japan, ‡Industrial Technology Center of Wakayama Prefecture, 60 Ogura, Wakayama 649-6261, Japan, and §Institute of Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), Central fifth, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan

Received January 29, 2010. Revised Manuscript Received March 10, 2010 Calix[4]arene derivatives bearing carboxyl groups at the upper rim and alkyl groups at the lower rim were synthesized. Micrometer-size porous honeycomb-patterned thin films were prepared by evaporating chloroform solution of polystyrene containing the calixarene derivatives under high humidity. These films were coated on gold electrodes of QCM, and the high-frequency changes were observed to detect volatile organic compounds such as dichlorobenzene.

Inroduction Considerable attention has been paid to patterned microporous polymer thin films prepared by casting polymer solution in high humidity, which is known as the “breath figure” method.1-6 This technique is quite simple as follows. Micrometer-size porous honeycomb-patterned thin films were prepared by evaporating polymer solution under high humidity. Micrometer-size water droplets as templates were condensed on the surface of the cooled polymer solution and resulted in the highly ordered porous thin film after evaporation of both solvent and water. While this phenomenon was not completely understood, the hexagonal arrangement seemed to be driven by capillary attractive forces3 and convection currents.5 Architecture of polymer was also an important factor to condense water microdroplets without coalescence. A variety of polymers such as star polymers,1,7 *Corresponding author. E-mail: [email protected]. (1) Widawski, G.; Rawiso, M.; Francois, B. Nature 1994, 369, 387–389. (2) Maruyama, N.; Karthaus, O.; Ijiro, K.; Shimomura, M.; Koito, T.; Nishimura, S.; Sawadaishi, T.; Nishi, N.; Tokura, S. Supramol. Sci. 1998, 5, 331–336. (3) Pitois, O.; Franc-ois, B. Eur. Phys. J. B 1999, 8, 225–231. (4) Karthaus, O.; Maruyama, N.; Cieren, X.; Shimomura, M.; Hasegawa, H.; Hashimoto, T. Langmuir 2000, 16, 6071–6076. (5) Srinivasarao, M.; Collings, D.; Philips, A.; Patel, S. Science 2001, 292, 79–83. (6) Stenzel, M. H. Aust. J. Chem. 2002, 55, 239–243. (7) (a) Connal, L. A.; Vestberg, R.; Gurr, P. A.; Hawker, C. J.; Qiao, G. G. Langmuir 2008, 24, 556–562. (b) Karikari, A. S.; Williams, S. R.; Heisey, C. L.; Rawlett, A. M.; Long, T. E. Langmuir 2006, 22, 9687–9693. (8) (a) Jenkhe, S. A.; Chen, X. L. Science 1999, 283, 372–375. De Boer, B.; Stalmach, U.; Nijland, H.; Hadziioannou, G. Adv. Mater. 2000, 12, 1581–1583. (b) Lin, C.-L.; Tung, P.-H.; Chang, F.-C. Polymer 2005, 46, 9304–9313. (9) (a) Tung, P.-H.; Huang, C.-F.; Chen, S.-C.; Hsu, C.-H.; Chang, F.-C. Desalination 2006, 200, 55–57. (b) Tian, Y.; Liu, S.; Wang, L.; Liu, B.; Shi, Y. Polymer 2007, 48, 2338–2334. (c) Bolognesi, A.; Galeotti, F.; Giovanella, U.; Bertini, F.; Yunus, S. Langmuir 2009, 25, 5333–5338. (10) (a) Nemoto, J.; Uraki, Y.; Kishimoto, T.; Sano, Y.; Funada, R.; Obata, N.; Yabu, H.; Tanaka, M.; Shimomura, M. Bioresour. Technol. 2005, 96, 1955–1958. (b) Fukuhira, Y.; Kitazono, E.; Hayashi, T.; Kanako, H.; Tanaka, M.; Shimomura, M.; Sumi, Y. Biomaterials 2006, 27, 1797–1802. (c) Kadla, J. F.; Asfour, F. H.; Bar-Nir, B. Biomacromolecules 2007, 8, 161–165. (d) Sun, H.; Li, W.; Wu, L. Langmuir 2009, 25, 10466–10472. (11) (a) Karthaus, O.; Cieren, X.; Maruyama, N.; Shimomura, M. Mater. Sci. Eng., C 1999, 10, 103–106. (b) Yabu, H.; Tanaka, M.; Ijiro, K.; Shimomira, M. Langmuir 2003, 19, 6297–6300. (c) Xu, Y.; Zhu, B.; Xu, Y. Polymer 2005, 46, 713– 717. (d) Bolognesi, A.; Mercogliano, C.; Yunus, S.; Civardi, M.; Comoretto, D.; Turturro, A. Langmuir 2005, 21, 3480–3485. (e) Deepak, V. D.; Asha, S. K. J. Phys. Chem. B 2006, 110, 21450–21459. (f) Vivek, A. V.; Babu, K.; Dhamodharan, R. Macromolecules 2009, 42, 2300–2303.

10266 DOI: 10.1021/la100434b

rod-coil block copolymer,8 amphiphilic copoymers,2,9 bioresource polymers,10 and other polymers11 were used for the fabricating films. Among those, the presence of hydrophilic groups in the polymeric structure or additives seems to be an important role to condense the water droplets and form highly ordered holes on the film surface. Various applications of these films were reported as follows: tissue engineering,12 optoelectronics,13 superhydrophobic film,14 and so on. We considered that the similar honeycomb films would be fabricated by calixarene derivatives having both hydrophobic and hydrophilic groups or their composites. Calixarenes have been paid considerable attention because of their potential utility as molecular receptors and ionophores.15 We thought that the promising utilization of the calixarene-based honeycomb-patterned films for quartz crystal microbalance (QCM) gas sensor would be attractive because of an excellent molecular recognition ability of calixarenes. The QCM technique is based on oscillation frequency shift caused by transient absorption of analytes onto quartz surface.16 The gas sensor responses of QCM based on calixarene films have been studied, for example, self-assembled monolayers of calixresorcinarene derivative,17 Langmuir-Blodgett (LB) (12) (a) Nishikawa, T.; Nishida, J.; Ookura, R.; Nishimura, S.-I.; Wada, S.; Karino, T.; Shimomura, M. Mater. Sci. Eng., C 1999, 8-9, 495–500. (b) Beattie, D.; Wong, K. H.; Williams, C.; Poole-Warren, L. A.; Davis, T. P.; Barner-Kowollik, C.; Stenzel, M. H. Biomacromolecules 2006, 7, 1072–1082. (c) Tanaka, M.; Nishikawa, K.; Okubo, H.; Kamachi, H.; Kawai, T.; Matsushita, M.; Todo, S.; Shimomura, M. Colloids Surf., A 2006, 284-285, 464–469. (d) Suuami, H.; Ito, E.; Tanaka, M.; Yamamoto, S.; Shimomura, M. Colloids Surf., A 2006, 284-285, 548–551. (e) Yamamoto, S.; Tanaka, M.; Sunami, H.; Ito, E.; Yamashita, S.; Morita, Y.; Shimomura, M. Langmuir 2007, 23, 8114–8120. (13) (a) de Boer, B.; Stalmach, U.; van Hutten, P. F.; Melzer, C.; Krasnikov, V. V.; Hadziioannou, G. Polymer 2001, 42, 9097–9109. (b) Yabu, H.; Shimomira, M. Langmuir 2005, 21, 1709–1711. (14) Yabu, H.; Takebayashi, M.; Tanaka, M.; Shimomura, M. Langmuir 2005, 21, 3235–3237. (15) (a) Gutsche, C. D. In Calixarenes, Monographs in Supramolecular Chemistry; Stoddart, J. F., Ed.; The Royal Society of Chemistry: Cambridge, 1989. (b) Gutsche, C. D. In Calixarenes Revisited, Monographs in Supramolecular Chemistry; Stoddat, J. F., Ed.; The Royal Society of Chemistry: Cambridge, 1998. (c) Calixarenes in the Nanoworld; Vicens, J., Harrowfield, J., Eds.; Springer: Dordrecht, 2007. (16) Nakamoto, T.; Moriizumi, T. In Artificial Olfactory System Using Neural Network, Handbook of Sendors and Actuators; Yamasaki, H., Ed.; Elsevier Science: Amsterdam, 1996; Vol. 3. (17) Schierbaum, K. D.; Weiss, T.; Thoden van Velzen, E. U.; Engbersen, J. F. J.; Reinhoudt, D. N.; G€opel, W. Science 1994, 265, 1413–1415.

Published on Web 03/24/2010

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Scheme 1. Synthesis of Tetracaboxylcalixarene Derivatives

Figure 1. Optical micrograph of the film cast from the chloroform solution of 4c and PS (CA% = 50). Scale bar is 1 μm long.

film of p-tert-butylcalix[6]arene,18 and nonporous casting films of calixarenes19,20 and calixresorcinarene derivatives.19 In their reports, the sensor responses depended on molecular structures of calixarenes. To our best knowledge, the honeycomb-patterned films consisted of calixarene derivatives or their composites were not investigated. Therefore, their property of the molecular recognition is very interesting to be applied to sensor films. In this paper, we prepared calixarene derivatives bearing carboxyl groups at the upper rim and alkyl groups at the lower rim and fabricated honeycomb-patterned thin films by evaporating chloroform solution containing the calixarene derivatives and polystyrene (PS) in a given ratio under high humidity. The surface morphology was characterized by optical and scanning electron microscopy (SEM), and the molecular recognition property of their films was investigated by oscillation frequency shifts of QCM coated on the gold electrodes toward various volatile organic compounds.

Results and Discussion The calixarene derivatives were prepared as shown in Scheme 1. Alkyl groups as lipophilic groups and carboxyl groups as hydrophilic groups were introduced into the lower rim and the upper rim of the p-tert-butylcalix[4]arene (1), respectively. The calixarene tetraalkyl ethers 2a-c were prepared by the reaction of 1 with alkyl bromide in DMF in the presence of NaH in high yield. Formyl groups were introduced to the para positions by using hexamethylenetetramine (HMT) and trifluoroacetic acid (Duff reaction) to give the derivatives 3a-c in moderate yields.21 The formyl groups were oxidized to afford tetracarboxylated calixarene 4a-c.22 These derivatives had cone structures, in which all phenol units have same direction, determined by means of NMR spectral data which showed double doublet signals based on methylene bridges of the calixarene ring. The 1 mg/mL chloroform solution containing equal weights of calixarene 4c and PS (CA% = 50) was prepared and fabricated on a glass surface by evaporating the solution under highhumidity air flow. The surface of the resulting films reflected (18) (a) Mu~noz, S.; Nakamoto, T.; Moriizumi, T. The Transactions of The Institute of Electrical Engineers of Japan; 1999, 119-E, 430–435. (b) Mu~noz, S.; Nakamoto, T.; Moriizum, T. Sens. Mater. 1999, 11, 427–435. (19) (a) Koshets, I. A.; Kazantseva, Z. I.; Shirshov, Yu. M.; Cherenok, S. A.; Kalchenko, V. I. Sens. Actuators, B 2005, 106, 177–181. (b) Dickert, F. L.; B€aumler, U. P. A.; Stathopulos, H. Anal. Chem. 1997, 69, 1000–1005. (20) Dickert, F. L.; Schuster, O. Microchim. Acta 1995, 119, 55–62. (21) Komori, T.; Shinkai, S. Chem. Lett. 1992, 901–904. (22) Sansone, F.; Barboso, S.; Casnati, A.; Fabbi, M.; Pochini, A.; Ugozzoli, F.; Ungaro, R. Eur. J. Org. Chem. 1998, 897–905.

Langmuir 2010, 26(12), 10266–10270

iridescent color, as shown in Figure 1. The optical micrographs of the films that were fabricated by carixarene 4c and PS in a given ratio under high humidity are shown in Figure 2. Whatever weight ratio of 4c to PS was varied from 0.1 to 0.9 in the chloroform solution, honeycomb-patterned films having ca. 1-2 μm pores were obtained (Figure 2a-e). However, when the chloroform solutions of the low percentage of 4c (CA% 50. However, there are no significant difference in the honeycomb-patterned films obtained from the given CA% solutions, as shown in Figures 2 and 3. As mentioned above, no spectral differences between their nonporous and porous films for the measurements of FT-IR and XPS Langmuir 2010, 26(12), 10266–10270

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the water droplets. By this process, the content of the calixarene could be got the same concentration on the surface of the films containing the calixarene (CA% = 30-90). In the case of low percent of the calixarene (CA%=10), it was assumed that suitable molecular array of the calixarene and/or PS on the surface was established at this composition.

Conclusions

Figure 4. Frequency shifts (-ΔHz) of the QCM coat by porous or

nonporous films (2 μg, CA% = 10) in the presence of mixed gases: A (CH2Cl2, CHCl3, CCl4, ClCH2CH2Cl, Cl2CdCCl2, 100 ppm), B (benzene, ethylbenzene, toluene, xylene, styrene, 100 ppm), C (chlorobenzene, o-, m-, and p-dichlorobenzene, 100 ppm), D (MeOH, cyclohexanol, 2-propanol, 1-butanol, 100 ppm).

Figure 5. Frequency shifts (-ΔHz) of the QCM coat by porous and nonporous films (2 μg, CA%=10) in the presence of 10 ppm haloganated aromatic hydrocarbons. CB=chlorobenzene; o-DCB, m-DCB, and p-DCB=o-, m-, and p-dichlorobenzene, respectively.

Figure 6. Frequency shifts (-ΔHz) of the QCM coat by porous and nonporous films (4 μg) containing various CA% in the presence of 10 ppm p-DCB.

spectra were detected. It was assumed that these results reflected the molecular arrangement of the calixarene molecule and PS on the surface of the films. It was speculated that the calixarene molecules were concentrated in the surface layer of the porous film. In the course of the fabricating process of the film, the amphiphilic calixarene molecules migrate to the interface contacting micrometer-size water droplets as a template, and as a result the calixarene molecules were concentrated in the surface. This presumption could be explained by the formation of the calixarene-based honeycomb-patterned films by stabilization of Langmuir 2010, 26(12), 10266–10270

Preparation and properties of the honeycomb-patterned PS films fabricated by the calixarene derivatives having carboxyl groups and alkyl groups were investigated. The films with regular pores were obtained in a given ratio of the calixarenes to PS. The molecular recognition property of their films was investigated by coating on QCM, and the large oscillation frequency shifts were observed toward dichlorobenzene. It was also suggested that the fine surface structure of the calixarene composite films was estimated by means of the frequency shifts of the QCM.

Experimental Section General. p-tert-Butylcalix[4]arene was prepared by the literature method. Other solvents and reagents were purchased from Wako Pure Chemical Industries, Ltd., and used without further purification. Melting points were determined by a Yanaco micro melting point apparatus and are uncorrected. 1H and 13C NMR spectra were recorded on a Varian Unity-plus 300 spectrometer and a Burker Avance-400 using a residual solvent as an internal standard. FT-IR spectra were obtained on a Shimadzu IRPrestige-21 FT-IR 8400S spectrometer using a single reflection horizontal ATR MiRacle (ZnSe). ESI-TOF MS spectra were measured on a positive mode using a PE Biosystems Mariner spectrometer. Scanning electron microscopy (SEM) was conducted on a JEOL JSM-6480LV. QCM measurements were performed by a Kazu Technica quartz oscillator sensor system KZQCM1D. Calix[4]arene Tetradodecyl Ether (2a). To a solution of 0.5 g (1.18 mmol) of calix[4]arene in anhydrous DMF (10 mL) was added 0.22 g (5.6 mmol) of NaH (62% in oil). After the mixture was stirred for 10 min at room temperature 1.41 g (5.6 mmol) of dodecyl bromide was added. The mixture was stirred for 15 h at 80 °C. Ice-water was added to the reaction mixture and stirred for 1 h. The resulting precipitate was filtrated and washed with water and methanol. The precipitate was purified by recrystallization form chloroform/methanol twice and dried under reduced pressure to afford 1.12 g (86%) of white crystals; mp = 59-64 °C. IR (ATR): ν 2914, 2847, 1454 cm-1. 1H NMR (400 MHz, CDCl3, 22 °C): δ 0.90 (t, J=7.14, 12H), 1.2-1.5 (m, 72H), 1.85-2.00 (m, 8H), 3.15 (d, J=13.55, 4H), 3.88 (t, J=7.42, 8H), 4.45 (d, J =13.37, 4H), 6.55-6.65 (m, 12H). 13C NMR (100 MHz, CDCl3 22 °C): δ 14.12, 22.71, 26.38, 29.44, 29.76, 29.83, 29.87, 29.99, 30.02 30.35, 30.98, 31.97 75.14, 121.83, 128.06 135.15, 156.60. MS (ESI-TOF) m/z calcd for (MþNa)þ C76H120O4Na 1119.91; found 1119.89. p-Tetraformylcalix[4]arene Tetradodecyl Ether (3a). A solution of 0.4 g (0.36 mmol) of calixarene 2a and 2.0 g (14.6 mmol) of hexamethylenetetramine in 15 mL of trifluoloacetic acid was refluxed for 1 day. After the reaction the mixture was poured into ice-water. The organic portion was extracted with ethyl acetate. The organic layer was washed with water, saturated NaHCO3, water, and brain, followed by dried over MgSO4. After evaporation of the solvent, the product was purified through SiO2 column (hexane/ethyl acetate = 5/1) to afford 0.23 g (53%) of white crystals; mp = 112-115 °C. IR (ATR): ν 2916, 2851, 1694, 1678, 1593 1462 cm-1. 1H NMR (400 MHz, CDCl3, 22 °C): δ 0.86 (t, J = 7.07, 12H), 1.16-1.43 (m, 72H), 1.80-1.92 (m, 8H), 3.32 (d, J = 13.89, 4H), 3.94 (t, J = 7.45, 8H), 4.47 (d, J = 13.64, 4H), 7.13 (s, 8H), 9.56 (s, 4H). 13C NMR (100 MHz, CDCl3 22 °C): δ 14.09, 22.68, 26.18, 29.40, 29.71, 29.77, 29.82, 29.89, 30.31, 30.90, 31,92, 75.70, 130.19, 131,34, 135.58, 161.87, 191.27. MS (ESITOF) m/z calcd for (M þ H)þ C80H121O8 1209.91; found 1209.90. DOI: 10.1021/la100434b

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p-Tetracarboxylcalix[4]arene Tetradodecyl Ether (4a). A solution of 0.13 g (0.107 mmol) of calixarene 3a and in 10 mL of CHCl3 and 10 mL of acetone was cooled in an ice bath. A solution of 132 mg (1.36 mmol) of sulfamic acid, and 102 mg (1.13 mmol) of sodium chlorite in 0.5 mL of water was added once every hour to the above solution until after the reaction was completed, checking by TLC. After the reaction the solvent was evaporated and 10 mL of 6 M HCl was added to produce precipitate. The precipitate was filtrated and washed with water and methanol to afford 129 mg (94%) of white powder; mp > 250 °C. IR (ATR): ν 2916, 2851, 1697, 1686 cm-1. 1H NMR (400 MHz, THF-d8, 22 °C): δ 0.89 (t, J = 7.07, 12H), 1.17-1.52 (m, 72H), 1.882.04 (m, 8H), 3.30 (d, J = 13.64, 4H), 3.99 (t, J = 7.33, 8H), 4.49 (d, J = 13.39, 4H), 7.38 (s, 8H), 10.91 (bs, 4H). 13C NMR (75 MHz, THF-d8 40 °C): δ 14.51, 23.67, 27.45, 30.48, 30.74, 30.81, 30.90, 30.97, 31.02, 31.42, 32.02, 33.03, 76.34, 126.07, 131,36, 135.70, 161.43, 168.45. MS (ESI-TOF) m/z calcd for (M þ Na)þ C80H120O12Na 1295.87; found 1295.82. Calix[4]arene Tetraoctyl Ether (2b). To a solution of 0.5 g (1.18 mmol) of calix[4]arene in anhydrous DMF (10 mL) was added 0.22 g (5.6 mmol) of NaH (62% in oil). After the mixture was stirred for 10 min at room temperature, 1.41 g (5.6 mmol) of dodecyl bromide was added. The mixture was stirred for 15 h at 80 °C. Ice-water was added to the reaction mixture and stirred for 1 h. The organic potion was extracted with chloroform (50 mL  2), washed with water (30 mL  3), and dried over MgSO4. After evaporating the solvent, the product was purified through SiO2 column (hexane/CHCl3=10/1) to afford 0.76 g (74%) of white crystals; mp = 76-79 °C. IR (ATR): ν 2920, 2851, 1454, 1377 cm-1. 1H NMR (400 MHz, CDCl3, 22 °C): δ 0.87 (t, J =7.33, 12H), 1.2-1.4 (m, 40H), 1.80-1.95 (m, 8H), 3.12 (d, J =13.14, 4H), 3.85 (t, J = 7.33, 8H), 4.42 (d, J=13.14, 4H), 6.50-6.65 (m, 12H). 13C NMR (100 MHz, CDCl3 22 °C): δ 14.11, 22.72, 26.37, 29.65, 29.94, 30.37, 30.98, 31.99, 75.15, 121.83, 128.06 135.16, 156.59. MS (ESITOF) m/z calcd for (M þ Na)þ C60H88O8Na 895.66; found 895.61. p-Tetraformylcalix[4]arene Tetraoctyl Ether (3b). The reaction was carried out in a manner similar to that for 3a. This reaction afforded white crystals (39% yield); mp = 123-125 °C. IR (ATR): ν 2920, 2851, 1682, 1593 cm-1. 1H NMR (400 MHz, CDCl3, 22 °C): δ 0.87 (t, J = 7.07, 12H), 1.20-1.43 (m, 40H), 1.80-1.93 (m, 8H), 3.32 (d, J = 13.89, 4H), 3.94 (t, J = 7.33, 8H), 4.47 (d, J = 13.89, 4H), 7.13 (s, 8H), 9.56 (s, 4H). 13C NMR (100 MHz, CDCl3 22 °C): δ 14.07, 22.67, 26.18, 29.52, 29.77, 30.34, 30.91, 31,90, 75.72, 130.20, 131,37, 135.59, 161.89, 191.30. MS (ESI-TOF) m/z calcd for (M þ H)þ C64H89O8 985.66; found 985.61. p-Tetracarboxylcalix[4]arene Tetraoctyl Ether (4b). The reaction was carried out in a manner similar to that for 4a. This reaction afforded white powder (93% yield); mp > 280 °C. IR (ATR): ν 2920, 2851, 1697, 1597 cm-1. 1H NMR (400 MHz, THF-d8, 22 °C): δ 0.91 (t, J=7.07, 12H), 1.26-1.51 (m, 40H), 1.89-2.01 (m, 8H), 3.31 (d, J = 13.39, 4H), 4.00 (t, J = 7.33, 8H), 4.49 (d, J = 13.39, 4H), 7.38 (s, 8H), 11.08 (bs, 4H). 13C NMR (75 MHz, THF-d8, 40 °C): δ 14.53, 23.69, 27.44, 30.62, 30.91, 31.42, 32.01, 33.05, 76.34, 125.95, 131,40, 135.78, 161.52, 168.67. MS (ESI-TOF) m/z calcd for (M þ Na)þ C64H88O12Na 1071.62; found 1071.61. Calix[4]arene Tetrabutyl Ether (2c). The reaction was carried out in a manner similar to that for 2b. This reaction afforded white crystals (75% yield); mp = 118-122 °C. IR (ATR): ν 2955, 2928, 2862, 1454 cm-1. 1H NMR (300 MHz, CDCl3, 22 °C): δ 0.98 (t, J = 7.42, 12H), 1.37-1.51 (m, 8H), 1.83-1.93 (m, 8H), 3.13 (d, J = 13.46, 4H), 3.87 (t, J = 7.35, 8H), 4.43 (d, J = 13.32, 4H), 6.52-6.61 (m, 12H). 13C NMR (75 MHz, CDCl3 22 °C): δ 14.08, 19.36, 30.97, 32.30, 74.80, 121.84, 128.08 135.14, 156.57. MS (ESI-TOF) m/z calcd for (M þ Na)þ C44H56O4Na 671.41; found 671.38. 10270 DOI: 10.1021/la100434b

Nomura et al.

p-Tetraformylcalix[4]arene Tetrabutyl Ether (3c). A solution of 3.0 g (4.62 mmol) of calixarene 2c and 23.3 g (166.32 mmol) of hexamethylenetetramine in 90 mL of trifluoloacetic acid was refluxed for 15 h. After the reaction the mixture was poured into a 100 mL of ice-water. The organic portion was extracted with dichloromethane. The organic layer was washed with water, followed by dried over MgSO4. After evaporation of the solvent, the product was recrystallized from chloroform-methanol to afford 2.8 g (80%) of crystals; mp = 237-240 °C. IR (ATR): ν 2959, 2932, 2866, 2789, 2720, 1686, 1694,1593 cm-1. 1H NMR (400 MHz, CDCl3, 22 °C): δ 1.01 (t, J = 7.32, 12H), 1.42-1.51 (m, 8H), 1.82-1.92 (m, 8H), 3.35 (d, J = 13.92, 4H), 3.98 (t, J = 7.32, 8H), 4.50 (d, J = 13.92, 4H), 7.16 (s, 8H), 9.55 (s, 4H). 13C NMR (100 MHz, CDCl3 22 °C): δ 13.95, 19.21, 30.89, 32.24, 75.41, 130.21, 131,37, 135.59, 161.88, 191.29. MS (ESI-TOF) m/z calcd for (M þ Na)þ C48H56O8Na 783.39; found 783.34. p-Tetracarboxylcalix[4]arene Tetrabutyl Ether (4c). The reaction was carried out in a manner similar to that for 4a. This reaction afforded white powder (89% yield); mp > 280 °C. IR (ATR): ν 2959, 2932, 2866, 2835, 1694, 1686, 1601 cm-1. 1H NMR (300 MHz, DMSO-d6, 22 °C): δ 0.97 (t, J = 7.31, 12H), 1.35-1.55 (m, 8H), 1.80-1.88 (m, 8H), 3.39 (d, J = 13.38, 4H), 3.92 (t, J = 7.16, 8H), 4.35 (d, J = 13.07, 4H), 7.32 (s, 8H), 12.36 (bs, 4H). 13C NMR (75 MHz, DMSO-d6, 40 °C): δ 13.51, 18.55, 29.92, 31.52, 74.47, 124.50, 129.44, 134.04, 159.60, 166.47. MS (ESI-TOF) m/z calcd for (M þ Na)þ C48H56O12Na 847.37; found 847.35. Preparation of Honeycomb Films. The 1 mg/mL chloroform solutions containing various weight ratios of 4 and/or PS were prepared. PS having Mw = 1.09  106 (TOSOH TSK standard PS F-128, Mw/Mn = 1.08) was used. In the case of remaining insoluble material of 4, 1% of tetrahydrofuran may be used to dissolve it before preparation of the solution or ultrasonic irradiation may be also used. The honeycomb films were fabricated on a glass surface or gold electrode on QCM at room temperature by evaporating 2-5 μL of the solution under flow of high-humidity air (relative humidity > 90%, flow rate = 5-10 L/ min). The moist air was generated by blowing air into water, and humidity was checked by a digital hygrometer. QCM Measurement. The porous and nonporous films (2 or 4 μg) were deposited on the gold electrode of QCM (9 MHz, ATcut, gold electrode of 4.6 mm in diameter) by a 2 or 4 μL of the chloroform solution prepared above method with using a microsyringe. The nonporous films were prepared under flow of dry air at room temperature. Gas samples used were four ether solutions containing organic compounds as follows. A: haloganated compounds (CH2Cl2, CHCl3, CCl4, ClCH2CH2Cl, Cl2CdCCl2); B: aromatic compounds (benzene, ethylbenzene, toluene, xylene, styrene); C: halogenated aromatic compounds (chlorobenzene, o-, m-, p-dichlorobenzene); D: alcohols MeOH, cyclohexanol, 2-propanol, 1-butanol). After introduction of dry nitrogen gas until oscillation frequency of QCM was stable, 1 μL of the mixed solution, which evaporated to reach the concentration at 100 ppm of each VOC in a gaseous state in a glass flask, was injected into the flask which was kept at 22 °C by a water jacket. Reduction of oscillation frequency of the QCM was measured in 10 min after the injection. Acknowledgment. The authors gratefully acknowledge financial support by the Cooperation for Innovative Technology and Advanced Research in Evolutional Area (CITY AREA) program from the Ministry of Education, Culture, Sports, Science and Technology Japan. We thank Mr. S. Niiyama and Ms. H. Nakao (Industrial Technology Center of Wakayama Prefecture) for the operation of SEM and optical microscopes. We are also grateful to Mr. K. Goto (Kazu Technica Co., Ltd.) for his assistance in an instrumental improvement of the QCM sensor system. Supporting Information Available: NMR spectral data for compounds 2-4. This material is available free of charge via the Internet at http://pubs.acs.org. Langmuir 2010, 26(12), 10266–10270