Gas Permeability of Hexaphenylbenzene Based Polymers of

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Gas Permeability of Hexaphenylbenzene Based Polymers of Intrinsic Microporosity Mariolino Carta,† Paola Bernardo,‡ Gabriele Clarizia,‡ Johannes C. Jansen,‡ and Neil B. McKeown*,† †

School of Chemistry, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, Edinburgh, U.K. Institute on Membrane Technology, ITM-CNR, Via P. Bucci 17/C, 87036 Rende (CS), Italy

‡

S Supporting Information *

ABSTRACT: The synthesis and characterization of a series of novel hexaphenylbenzene (HPB) based polymers of intrinsic microporosity (PIM-HPBs) containing methyl, bromine, and nitrile substituents are reported. The successful formation of thin films from these polymers allowed the evaluation of the influence of the substituents on intrinsic microporosity and gas permeability. Analysis by the time-lag method also yielded information about gas diffusion coefficients and, indirectly, the gas solubility. The gas permeability varies as a function of the polarity of the substituents and shows a significant increase after treatment of the samples with methanol, especially for films cast from THF as the solvent. This enhancement, which is mostly due to an increase in the diffusion coefficient, is only partially lost upon aging of the membranes for 5 months. Measurements at different feed pressures confirm the typical dual mode sorption behavior, with increasing diffusivity and decreasing permeability and solubility as a function of the feed pressure.

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INTRODUCTION Microporous organic polymers1 (i.e., with pore diameters H2 > He > O2 > N2 > CH4, reproducing the behavior observed for most PIMs reported to date.9a,10 Moreover the permeation data show reduced permeation rates in the substituted HPB polymers. Generally, permeability and diffusion coefficients follow the trend PIM-HPB > PIM-CH3-HPB > PIM-Br-HPB > PIM-CN-HPB. It is known that polymer gas transport properties are influenced by the type of solvent used for film preparation, both by changing D

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Figure 5. Robeson plots for the CO2/CH4, CO2/N2, and O2/N2 separations. Red = PIM-HPB, green = PIM-CH3-HPB, gray = PIM-Br-HPB, and purple = PIM-CN-HPB. Circles: as-cast membranes. Triangles: MeOH-treated membranes. Thick line: 2008 upper bound. Thin line: 1991 upper bound.

between selectivity and permeability was quantified by Robeson in his famous plots for different gas pairs of interest,26 identifying also the so-called upper boundthe existence of which was supported by theoretical considerations.27 The permeability and selectivity of the PIM-HPBs polymers are plotted as Robeson diagrams in Figure 5 for some relevant gas pairs (CO2/N2, CO2/CH4, and O2/N2; for other gas pairs see the Supporting Information). The removal of residual solvent from the membrane by alcohol treatment causes an increase in permeability for all gases and a slight decrease in selectivity, without any modification of the gas permeation order. The PIM-Br-HPB and PIM-CN-HPB containing more polar substituents are more affected by this treatment. However, the relative differences in permeability between the PIM-HPBs become less marked due to the removal of tightly held residual solvent, particularly THF. In the Robeson diagrams, the alcohol-treated samples follow the usual trade-off between permeability and

Figure 6. Diffusion selectivity vs diffusivity for the CO2/N2, and O2/N2 separations. Red = PIM-HPB, green = PIM-CH3-HPB, gray = PIM-Br-HPB, and purple = PIM-CN-HPB. Circles: as-cast membranes. Triangles: MeOH-treated membranes.

Selectivity of the cast films follows the trade-off between permeability and selectivity, which is typical for polymeric materials applied in membrane gas separation; i.e., the more the polymer is permeable, the less it is selective. This trade-off

Figure 7. CO2 permeation data in the PIM-HPB membranes in different states: as cast, immediately after MeOH treatment, and aged for 5 months. (a) CO2 permeability. (b) CO2/N2 ideal selectivity. (c) CO2 diffusivity. (d) CO2 solubility. E

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Figure 8. CO2 permeation in the PIM-HPB series at different feed pressures: (a) permeability, (b) diffusivity, (c) solubility, and (d) concentration. Lines in (a−c) are provided as a guide to the eye; lines in (d) represent a least-squares fit of the data with eq 1 and are indicated for qualitative evaluation only (note: 1 mg CO2 = 0.51 cm3 (STP)).

polymers such as polyimides (15−30 m2 g−1),28 but lower than the value typically reported for other PIMs (e.g., PIM-1 = 700−800 m2 g−1).10 The apparent BET surface areas and total pore volumes accessible during nitrogen adsorption are known to correlate roughly with permeability,10 and this correlation is also observed for PIM-HPBs. Hence, the lower values for gas permeabilities and diffusivities, coupled with an increase in gas selectivities, observed for the PIM-HPBs with more polar substituents (Br and CN) appear to be related to less microporosity, presumably caused by enhanced polymer cohesion interactions. Similarly, a reduced porosity was observed in modified PIM-1, by replacing its nitrile groups with other more polar or bulkier functionalities which can induce a rigidification of the polymeric matrix and a finer ultramicroporosity of the porous texture, by an extensive network of intermolecular H-bonding.29,30 The permeability data for PIM-HPB measured after the methanol treatment are much higher than the values reported previously for a film subjected to vacuum and heating21a procedure that is known to cause accelerated physical aging.

selectivity. For the CO2/N2 and CO2/CH4 gas pairs the performance of each of the PIM-HPB polymers is close to the 2008 upper bounds.26a The data points for the O2/N2 separation lie close to the 1991 upper bound. Overall, the gas permeability performance of the PIM-HPBs is similar to that reported for many other PIMs, especially those based on spirobisindan as site of contorsion.10 The differences in gas permeability among the PIM-HPBs can be better understood by analyzing the contribution of diffusivity and solubility coefficients, according to the solutiondiffusion transport model. For molecules with comparable sizes (e.g., CO2 and N2) the absolute value of the diffusion coefficient depends on the polymer structure, but their selectivity is ∼1 and is independent of the molecular structure (Figure 6a). For gas pairs with different sizes such as O2/N2 (Figure 6b), H2/N2, and H2/CH4, the diffusion selectivity follows a Robeson-like trade-off. Table 1 reports the apparent BET surface area of the PIMHPB polymers, which lie in the range 410−500 m2 g−1. These values are larger than a typical value for common glassy F

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Five months after the MeOH treatment, the PIM-HPB films all show a notable decrease in permeability due to physical aging (Figure 7). However, the permeability remains significantly above the original value of the as cast films, especially for PIMCN-HPB and PIM-Br-HPB, once again demonstrating that the relatively low permeability of the as-cast films is due to solvent retention. Aging is somewhat more evident for the slower gases (N2 and CH4), thus leading to a slight increase in selectivity (Figure 7a). Because of aging in PIM-CN-HPB, the values of P and D for CO2 decrease, but the CO2 solubility remains significantly higher than in the other HPBs. For other gases like methane and oxygen, values for S are relatively lower for PIMCN-HPB. Therefore, this enhanced solubility may be due to specific interactions of CO2 with the additional nitrile groups in the polymer. It is likely that the aged membranes correspond more closely to the samples subjected to nitrogen adsorption analysis because the pretreatment (i.e., thermal degassing under reduced pressure) carried out before analysis causes accelerated aging.31 Indeed, the results obtained after 5 months of aging on the unsubstituted PIM-HPB are much closer to the data reported by Short et al. for the same polymer in which the heat treatment after MeOH soaking induced accelerated aging.21 For example, the CO2 permeability in the aged HPB polymer is 2400 barrer, while Short et al. reported a value of 1750 barrer. Methanol treatment is known to swell the PIMs (e.g., 10% increase in film thickness) and thus helps to remove tightly bound solvent but also introduces additional free volume which is lost with aging. The interaction of CO2 with the different PIM-HPB polymers was further investigated by means of CO2 permeability measurements at variable feed pressures (Figure 8a). For each polymer CO2 permeability decreases with the feed pressure, particularly for the unsubstituted PIM-HPB, while the effect is smallest for PIM-CH3-HPB. The decrease of the permeability as a function of the CO2 feed pressure is the result of the decrease in gas solubility (Figure 8b,c), consistent with the dual mode sorption model. This analysis confirms that the CO2 sorption is highest in PIM-CN-HPB and decreases in the order PIM-BrHPM > PIM-CH3-HPB > PIM-HPB (Figure 8c). The relatively narrow pressure interval considered in the measurements did not allow an accurate quantitative evaluation of the model parameters. Although the indirect calculation of the solubility from the relation P = D × S should be done with care in the case of pressure-dependent transport parameters,32 qualitatively the sorption data fit well with the dual mode model: c = kDp +

C Hbp 1 + bp

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CONCLUSIONS A series of novel hexaphenylbenzene based polymers of intrinsic microporosity (PIM-HPBs) was prepared with sufficiently high molecular mass to enable the fabrication of cast films suitable for gas permeation studies. The chosen synthetic pathway for the preparation of the bis(catechol) monomers facilitates the introduction of methyl, bromine, and nitrile substituents to allow quantification of their effect on microporosity and gas permeabilities. The introduction of polar groups modulated intrinsic microporosity and decreased permeability albeit with increased selectivity for some important gas pairs. This approach could be useful for tuning the performance of membranes for gas separation, particularly those involving CO2.

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ASSOCIATED CONTENT

* Supporting Information S

Full experimental details for the synthesis of precursors and polymers; nitrogen adsorption isotherms and gel permeation chromatograhy; measurements of the gas permeabilities. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail [email protected] (N.B.M.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The work leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement no. NMP3-SL2009-228631, project DoubleNanoMem, and from the Italian National Program, Programma Operativo Nazionale Ricerca e Competitività 2007-2013, project PON01_01840 “MicroPERLA”.

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REFERENCES

(1) (a) Rose, M. ChemCatChem 2014, 6, 1166−1182. (b) Wu, D.; Xu, F.; Sun, B.; Fu, R.; He, H.; Matyjaszewski, K. Chem. Rev. 2012, 112, 3959−4015. (c) Dawson, R.; Cooper, A. I.; Adams, D. J. Prog. Polym. Sci. 2012, 37, 530−563. (d) Cooper, A. I. Adv. Mater. 2009, 21, 1291−1295. (e) McKeown, N. B.; Budd, P. M. Macromolecules 2010, 43, 5163−5176. (f) McKeown, N. B.; Budd, P. M. Chem. Soc. Rev. 2006, 35, 675−683. (2) (a) Rabbani, M. G.; El-Kaderi, H. M. Chem. Mater. 2011, 23, 1650−1653. (b) Ghanem, B. S.; Hashem, M.; Harris, K. D. M.; Msayib, K. J.; Xu, M. C.; Budd, P. M.; Chaukura, N.; Book, D.; Tedds, S.; Walton, A.; McKeown, N. B. Macromolecules 2010, 43, 5287−5294. (c) McKeown, N. B.; Budd, P. M.; Book, D. Macromol. Rapid Commun. 2007, 28, 995−1002. (d) 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, 1804−1807. (e) Shen, C.; Bao, Y.; Wang, Z. Chem. Commun. 2013, 49, 3321−3323. (f) Chang, Z.; Zhang, D.-S.; Chen, Q.; Bu, X.-H. Phys. Chem. Chem. Phys. 2013, 15, 5430−5442. (3) (a) Wang, Y.; McKeown, N. B.; Msayib, K. J.; Turnbull, G. A.; Samuel, I. D. W. Sensors 2011, 11, 2478−2487. (b) Thomas, J. C.; Trend, J. E.; Rakow, N. A.; Wendland, M. S.; Poirier, R. J.; Paolucci, D. M. Sensors 2011, 11, 3267−3280. (c) Rakow, N. A.; Wendland, M. S.; Trend, J. E.; Poirier, R. J.; Paolucci, D. M.; Maki, S. P.; Lyons, C. S.; Swierczek, M. J. Langmuir 2010, 26, 3767−3770.

(1)

where c is sorbate concentration, p is sorbate pressure, kD is the Henry’s law constant, CH is the Langmuir (monolayer) sorption capacity constant, and b is the Langmuir affinity constant. For PIM-CH3-HPB the CO2 concentration c has an almost linear pressure dependence, indicating that Langmuir sorption is relatively small compared to the Henry sorption. This may be due to the methyl groups reducing the interchain interactions so that the polymer is more prone to dilation especially when compared with PIM-Br-HPB and PIM-CN-HPB containing more polar substituents. Because of a very high affinity for CO2, a significant portion of the Langmuir sorption sites is already saturated below 1.3 bar, as is commonly observed in PIMs.11a,13b,32 G

dx.doi.org/10.1021/ma501925j | Macromolecules XXXX, XXX, XXX−XXX

Macromolecules

Article

B. S.; Swaidan, R.; Litwiller, E.; Pinnau, I. Adv. Mater. 2014, 26, 3688− 3692. (g) Ghanem, B. S.; Swaidan, R.; Ma, X. H.; Litwiller, E.; Pinnau, I. Adv. Mater. 2014, DOI: 10.1002/adma.201401328. (h) Swaidan, R.; Al-Saeedi, M.; Ghanem, B.; Litwiller, E.; Pinnau, I. Macromolecules 2014, 17, 5104−5114. (12) Xiao, Y.; Low, B. T.; Hosseini, S. S.; Chung, T. S.; Paul, D. R. Prog. Polym. Sci. 2009, 34, 561−580. (13) (a) Du, N. Y.; Robertson, G. P.; Song, J. S.; Pinnau, I.; Guiver, M. D. Macromolecules 2009, 42, 6038−6043. (b) Mason, C. R.; Maynard-Atem, L.; Al-Harbi, N. M.; Budd, P. M.; Bernardo, P.; Bazzarelli, F.; Clarizia, G.; Jansen, J. C. Macromolecules 2011, 44, 6471−6479. (c) Du, N.; Park, H. B.; Robertson, G. P.; Dal-Cin, M. M.; Visser, T.; Scoles, L.; Guiver, M. D. Nat. Mater. 2011, 10, 372−375. (d) Mason, C. R.; Maynard-Atem, L.; Heard, K. W. J.; Satilmis, B.; Budd, P. M.; Friess, K.; Lanc, M.; Bernardo, P.; Clarizia, G.; Jansen, J. C. Macromolecules 2014, 47, 1021−1029. (e) Du, N.; Robertson, G. P.; Dal-Cin, M. M.; Scoles, L.; Guiver, M. D. Polymer 2012, 53, 4367− 4372. (14) (a) Dilthey, W.; Hurtig, G. Ber. Dtsch. Chem. Ges. 1934, 67B, 495−496. (b) Fieser, L. F. Org. Synth. 1966, 46, 44−48. (c) Gibson, J.; Holohan, M.; Riley, H. L. J. Chem. Soc. 1946, 456−461. (15) (a) Almenningen, A.; Bastiansen, O.; Skancke, P. N. Acta Chem. Scand. 1958, 12, 1215−1220. (b) Bart, J. C. J. Acta Crystallogr., Sect. B: Struct. Sci., Cryst. Eng. Mater. 1968, 24, 1277−1287. (16) (a) Liu, Y.; Hu, C.; Comotti, A.; Ward, M. D. Science 2011, 333, 436−440. (b) Maly Kenneth, E.; Gagnon, E.; Maris, T.; Wuest James, D. J. Am. Chem. Soc. 2007, 129, 4306−4322. (17) Jimenez-Garcia, L.; Kaltbeitzel, A.; Pisula, W.; Gutmann, J. S.; Klapper, M.; Muellen, K. Ang. Chem., Int. Ed. 2009, 48, 9951−9953. (18) Pisula, W.; Feng, X.; Muellen, K. Chem. Mater. 2011, 23, 554− 567. (19) (a) Rathore, R.; Burns, C. L.; Abdelwahed, S. A. Org. Lett. 2004, 6, 1689−1692. (b) Sun, D.; Rosokha, S. V.; Kochi, J. K. Ang. Chem., Int. Ed. 2005, 44, 5133−5136. (20) Chen, Q.; Luo, M.; Wang, T.; Wang, J.-X.; Zhou, D.; Han, Y.; Zhang, C.-S.; Yan, C.-G.; Han, B.-H. Macromolecules 2011, 44, 5573− 5577. (21) Short, R.; Carta, M.; Bezzu, C. G.; Fritsch, D.; Kariuki, B. M.; McKeown, N. B. Chem. Commun. 2011, 47, 6822−6824. (22) Bhandari, S.; Ray, S. Synth. Commun. 1998, 28, 765−771. (23) Dakin, H. D.; West, R. J. Biol. Chem. 1928, 78, 757−764. (24) Park, K.; Bae, G.; Moon, J.; Choe, J.; Song, K. H.; Lee, S. J. Org. Chem. 2010, 75, 6244−6251. (25) (a) Zhang, L.; Fang, W.; Jiang, J. J. Phys. Chem. C 2011, 115, 11233−11239. (b) Yampolskii, Y.; Alentiev, A.; Bondarenko, G.; Kostina, Y.; Heuchel, M. Ind. Eng. Chem. Res. 2010, 49, 12031−12037. (26) (a) Robeson, L. M. J. Membr. Sci. 2008, 320, 390−400. (b) Robeson, L. M. J. Membr. Sci. 1991, 62, 165−186. (27) Freeman, B. D. Macromolecules 1999, 32, 375−380. (28) Park, H. B.; Jung, C. H.; Lee, Y. M.; Hill, A. J.; Pas, S. J.; Mudie, S. T.; Van Wagner, E.; Freeman, B. D.; Cookson, D. J. Science 2007, 318, 254−258. (29) Mason, C. R.; Maynard-Atem, L.; Al-Harbi, N. M.; Budd, P. M.; Bernardo, P.; Bazzarelli, F.; Clarizia, G.; Jansen, J. C. Macromolecules 2011, 44, 6471−6479. (30) (a) Weber, J.; Du, N.; Guiver, M. D. Macromolecules 2011, 44, 1763−1767. (b) Swaidan, R.; Ghanem, B. S.; Litwiller, E.; Pinnau, I. J. Membr. Sci. 2014, 457, 95−102. (31) Bernardo, P.; Bazzarelli, F.; Jansen, J. C.; Clarizia, G.; Tasselli, F.; Mason, C. R. Proc. Eng. 2012, 44, 874−876. (32) Tocci, E.; De Lorenzo, L.; Bernardo, P.; Clarizia, G.; Bazzarelli, F.; McKeown, N. B.; Carta, C.; Malpass-Evans, R.; Friess, K.; Pilnácě k, K.; Lanč, M.; Yampolskii, Y. P.; Strarannikova, L.; Shantarovich, V.; Mauri, M.; Jansen, J. C. Macromolecules 2014, DOI: 10.1021/ ma501469m.

(4) (a) Kraft, S. J.; Sanchez, R. H.; Hock, A. S. ACS Catal. 2013, 3, 826−830. (b) Zhang, Y.; Riduan, S. N. Chem. Soc. Rev. 2012, 41, 2083−2094. (c) Kaur, P.; Hupp, J. T.; Nguyen, S. T. ACS Catal. 2011, 1, 819−835. (d) Mackintosh, H. J.; Budd, P. M.; McKeown, N. B. J. Mater. Chem. 2008, 18, 573−578. (e) Xia, F.; Pan, M.; Mu, S.; Malpass-Evans, R.; Carta, M.; McKeown, N. B.; Attard, G. A.; Brew, A.; Morgan, D. J.; Marken, F. Electrochim. Acta 2014, 128, 3−9. (f) Carta, M.; Croad, M.; Bugler, K.; Msayib, K. J.; McKeown, N. B. Polym. Chem. 2014, 5, 5262−5266. (5) (a) Byun, J.; Je, S.-H.; Patel, H. A.; Coskun, A.; Yavuz, C. T. J. Mater. Chem. A 2014, 2, 12507−12512. (b) Dawson, R.; Adams, D. J.; Cooper, A. I. Chem. Sci. 2011, 2, 1173−1177. (c) Del Regno, A.; Gonciaruk, A.; Leay, L.; Carta, M.; Croad, M.; Malpass-Evans, R.; McKeown, N. B.; Siperstein, F. R. Ind. Eng. Chem. Res. 2013, 52, 16939−16950. (d) Du, N. Y.; Park, H. B.; Dal-Cin, M. M.; Guiver, M. D. Energy Environ. Sci. 2012, 5, 7306−7322. (e) Woodward, R. T.; Stevens, L. A.; Dawson, R.; Vijayaraghavan, M.; Hasell, T.; Silverwood, I. P.; Ewing, A. V.; Ratvijitvech, T.; Exley, J. D.; Chong, S. Y.; Blanc, F.; Adams, D. J.; Kazarian, S. G.; Snape, C. E.; Drage, T. C.; Cooper, A. I. J. Am. Chem. Soc. 2014, 136, 9028−9035. (6) Budd, P. M.; McKeown, N. B. Polym. Chem. 2010, 1, 63−68. (7) (a) Sanders, D. E.; Smith, Z. P.; Guo, R.; Robeson, L. M.; McGrath, J. E.; Paul, D. R.; Freeman, B. D. Polymer 2013, 54, 4729− 4761. (b) Yampolskii, Y. Macromolecules 2012, 45, 3298−3311. (8) Budd, P. M.; Ghanem, B. S.; Makhseed, S.; McKeown, N. B.; Msayib, K. J.; Tattershall, C. E. Chem. Commun. 2004, 230−231. (9) (a) Budd, P. M.; McKeown, N. B.; Ghanem, B. S.; Msayib, K. J.; Fritsch, D.; Starannikova, L.; Belov, N.; Sanfirova, O.; Yampol’skii, Y. P.; Shantarovich, V. J. Membr. Sci. 2008, 325, 851−860. (b) Budd, P. M.; Msayib, K. J.; Tattershall, C. E.; Ghanem, B. S.; Reynolds, K. J.; McKeown, N. B.; Fritsch, D. J. Membr. Sci. 2005, 251, 263−269. (10) (a) McKeown, N. B. ISRN Mater. Sci. 2012, Article ID 513986. (b) Fritsch, D.; Bengtson, G.; Carta, M.; McKeown, N. B. Macromol. Chem. Phys. 2011, 212, 1137−1146. (c) Emmler, T.; Heinrich, K.; Fritsch, D.; Budd, P. M.; Chaukura, N.; Ehlers, D.; Ratzke, K.; Faupel, F. Macromolecules 2010, 43, 6075−6084. (d) Du, N. Y.; Robertson, G. P.; Pinnau, I.; Guiver, M. D. Macromolecules 2010, 43, 8580−8587. (e) Ritter, N.; Antonietti, M.; Thomas, A.; Senkovska, I.; Kaskel, S.; Weber, J. Macromolecules 2009, 42, 8017−8020. (f) Ghanem, B. S.; McKeown, N. B.; Budd, P. M.; Al-Harbi, N. M.; Fritsch, D.; Heinrich, K.; Starannikova, L.; Tokarev, A.; Yampolskii, Y. Macromolecules 2009, 42, 7881−7888. (g) Du, N. Y.; Robertson, G. P.; Pinnau, I.; Guiver, M. D. Macromolecules 2009, 42, 6023−6030. (h) Du, N.; Robertson, G. P.; Pinnau, I.; Thomas, S.; Guiver, M. D. Macromol. Rapid Commun. 2009, 30, 584−588. (i) Carta, M.; Msayib, K. J.; McKeown, N. B. Tetrahedron Lett. 2009, 50, 5954−5957. (j) Song, J.; Du, N.; Dai, Y.; Robertson, G. P.; Guiver, M. D.; Thomas, S.; Pinnau, I. Macromolecules 2008, 41, 7411−7417. (k) Ghanem, B. S.; McKeown, N. B.; Budd, P. M.; Fritsch, D. Macromolecules 2008, 41, 1640−1646. (l) Ghanem, B. S.; McKeown, N. B.; Budd, P. M.; Fritsch, D. Adv. Mater. 2008, 20, 2766−2771. (m) Du, N. Y.; Robertson, G. P.; Song, J. S.; Pinnau, I.; Thomas, S.; Guiver, M. D. Macromolecules 2008, 41, 9656−9662. (n) Carta, M.; Msayib, K. J.; Budd, P. M.; McKeown, N. B. Org. Lett. 2008, 10, 2641−2643. (o) Ma, X.; Salinas, O.; Litwiller, E.; Pinnau, I. Macromolecules 2013, 46, 9618−9624. (p) Carta, M.; Malpass-Evans, R.; Croad, M.; Rogan, Y.; lee, M.; Rose, I.; McKeown, N. B. Polym. Chem. 2014, 5, 5267−5272. (q) Carta, M.; Croad, M.; Jansen, J. C.; Bernardo, P.; Clarizia, G.; McKeown, N. B. Polym. Chem. 2014, 5, 5255−5261. (11) (a) Carta, M.; Croad, M.; Malpass-Evans, R.; Jansen, J. C.; Bernardo, P.; Clarizia, G.; Friess, K.; Lanc, M.; McKeown, N. B. Adv. Mater. 2014, 26, 3526−3531. (b) Rogan, Y.; Malpass-Evans, R.; Carta, M.; Lee, M.; Jansen, J. C.; Bernardo, P.; Clarizia, G.; Tocci, E.; Friess, K.; Lanc, M.; McKeown, N. B. J. Mater. Chem. A 2014, 2, 4874−4877. (c) Carta, M.; Malpass-Evans, R.; Croad, M.; Jansen, J. C.; Bernardo, P.; Bazzarelli, F.; McKeown, N. B. Science 2013, 339, 303−306. (d) Bezzu, C. G.; Carta, M.; Tonkins, A.; Jansen, J. C.; Bernardo, P.; Bazzarelli, F.; McKeown, N. B. Adv. Mater. 2012, 24, 5930−5933. (e) Guiver, M. D.; Lee, Y. M. Science 2013, 339, 284−285. (f) Ghanem, H

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