C60–Polymer Nanocomposite Networks Enabled by Guest–Host

Article pubs.acs.org/Macromolecules

C60−Polymer Nanocomposite Networks Enabled by Guest−Host Properties Gaumani Gyanwali, Rangika S. Hikkaduwa Koralege, Mathis Hodge, Kevin D. Ausman, and Jeffery L. White* Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078, United States S Supporting Information *

ABSTRACT: A modular approach for the synthesis of polymer networks with well-defined node and cross-linking dimensions is described. Each node or tie point in the network is a cyclodextrin molecule, which imparts discrete molecular guest−host capabilities to the network. C60 fullerenes homogeneously intercalate in the network, presumably via van der Waals guest−host interactions with the hydrophobic γ-cyclodextrin cavity, resulting in stable C60-filled polymer networks with improved mechanical properties. Networks prepared with α-cyclodextrin, whose inner cavity is smaller than γ-cyclodextrin, and smaller than the C60 diameter, do not yield materials with stable C60 intercalation. Characterization of the final composites reveals that the cross-linked γ-cyclodextrin-based composites maintain stable C60 concentrations, even after multiple extractions with toluene, which itself is a good solvent for C60. Membranes prepared from the cyclodextrin polymer network, prior to C60 intercalation, should also be useful for C60 extraction from C60−solvent mixtures. The synthetic route we describe here is not limited to C60 and should be generally applicable to a wide variety of guests.

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INTRODUCTION Creating new hybrid materials able to satisfy multiple performance constraints in energy, biomedical, and consumer product applications requires novel synthetic strategies. Polymer composites and nanocomposites made from organic macromolecules and inorganic fillers comprise a rapidly growing segment in the materials science area, as many recent reviews highlight.1−4 The most common polymer nanocomposites for materials science applications utilize inorganic components such as layered clays, silsesquioxanes, or, in some cases, mesoporous silicates. Alternatively, mechanical property improvements through the use of fullerene C60 as a structurally uniform nanoscopic filler in polymers are now appearing in the literature.5−9 C60−polymer composites have potential energytransfer advantages for light-harvesting and photovoltaic polymer applications.10−12 Several literature reports have focused on the best methods for homogeneously dispersing C60 in the polymer matrix, and blend properties that require homogeneous dispersion of C60 depend critically on the method of preparation.13−16 Polymer network composites are topologically unique, since the reinforcing filler is distributed throughout the matrix of cross-linked polymer chains. Composite networks are not new, and carbon black- or silica-filled synthetic elastomers like reinforced polybutadienes, polyisobutylenes, and polyisoprenes, among many others, have been commonly used in industrial applications for decades. These systems are often characterized by heterogeneous filler dispersions and particle sizes and distributions in the molecular weight of the polymer chains between cross-linking sites.17−19 Our long-standing interest in elastomer networks20−22 and in polymer blends23−25 has © 2013 American Chemical Society

motivated us to create well-defined polymer networks that are synthetically tailored to accept monodisperse nanoscopic fillers like C60. In this contribution, we describe C60−polymer network composites in which the polymer network is formed by cross-linking γ-cyclodextrin (γ-CD) molecules together with dodecyl chains, thereby creating a matrix of covalently bonded and essentially equally spaced CD cavities that are dimensionally suited for the intercalation of C60. Previous literature reports have established that C60 coordinates to the hydrophobic γ-CD cavity, which has the largest cavity dimension relative to α- and β-CD, when free CD and free C60 are mixed in solution.26−28 However, exploiting this specific guest−host interaction has not been described as an enabling route for polymer composite network formation, and indeed, relatively few contributions discuss C60-based polymer composites in which the C60 is not derivatized or chemically altered in some way. The C60−CD polymer nanocomposite networks, which have (1) monodisperse filler sizes from the C60, (2) monodisperse 12-carbon tie chain lengths, and (3) guest− host capabilities from the CD nodes, are represented graphically in Scheme 1. The synthesis, characterization, and properties of the materials are discussed below.

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EXPERIMENTAL SECTION

Synthesis of Dodecyl/γ-Cyclodextrin Networks. The initial dodecyl/γ-cyclodextrin networks, prior to incorporation of C60, were typically prepared by dissolving 0.3−0.4 g of γ-CD in 4 mL of Received: June 14, 2013 Revised: July 17, 2013 Published: July 25, 2013 6118

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The as-prepared C60/dodecyl/γ-cyclodextrin nanocomposite networks were dark brown to black. Additional control experiments were carried out in which the DMF in the individual dissolution/swelling/ combination steps was replaced with toluene. No significant amount of C60 uptake into the dodecyl/γ-CD networks was observed, and the polymer itself did not undergo the characteristic white to black color change indicative of homogeneous fullerene incorporation. Solid-State NMR Analyses of Insoluble Networks. 1Hdecoupled (75 kHz decoupling field strength) solid-state 13C MAS (magic-angle spinning) NMR spectra of the dried network products were obtained using a Bruker DSX-300 spectrometer operating at 7.05 T field strength (300 MHz 1H Larmor frequency). 13C single-pulse (π/2 pulse width) data were obtained for all samples prepared, and unless otherwise stated, 5 kHz MAS speeds were used. A 120 s recycle delay yielded quantitative spectra for the dodecyl/γ-CD networks in 512−1024 scans, as the measured carbon T1 was 25 s for the longest CD carbon relaxation time, while 160 s was used for the C60/dodecyl/ γ-cyclodextrin nanocomposite networks. No change in the C60 peak intensity was observed at 160 s versus 120 s delay, consistent with literature reports showing C60 T1’s of 40 s or less in mixed polymer/ C60 systems.40,41 Cross-polarization (CP/MAS) spectra were acquired with 1 ms contact time and 75 kHz 1H decoupling. Characterization. In addition to solid-state NMR, thermal gravimetric analysis (TGA) and UV−vis spectroscopy were used to interrogate the thermal stability of the composite networks and the nature of C60 in solution, respectively. TGA data were acquired on a TA 2950 instrument, using a ramp rate of 10 °C/min, in air, up to a final temperature of 400 °C. UV−vis data were acquired on solution extracts using a Cary 100 spectrometer.

Scheme 1. Representation of C60/γ-Cyclodextrin/Dodecyl Polymer Networka

a

Each γ-CD ring is functionalized with an average of five C12 chains.

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deionized water, and 0.080 g of NaOH was added. The mixture was heated at 70 °C for half an hour under stirring. Separately, 0.65−0.75 g of dibromododecane (DBDD), a bifunctional reagent, was added into a vial with 4 mL of DMSO. The mixture was heated at 50 °C to dissolve the solid completely. After increasing the temperature to 80− 100 °C, the DBDD solution was added into the CD solution dropwise. After mixing the two solutions together, the mixture was stirred for 18 h. The final ratio of the reagents was CD:NaOH:DBDD = 1:8:8. Acetone was added to the cooled reaction flask until further precipitation was observed. The precipitate was filtered, and residue was washed again with acetone, then washed with ethanol, and finally with water to ensure removal of all unreacted reagents, including DBDD, from the product. The resulting solid was dried under vacuum. The remaining solution was reacted with AgNO3, and the characteristic AgBr precipitated out of solution, indicating that free bromide existed following reaction of the DBDD and CD. Based on quantitative solid-state NMR data for the dried network, there exists on average a ratio of five C12 chains per γ-CD molecule in the network. The final dodecyl/γ-CD product is not soluble in any common solvents but does swell in DMF, DMSO, and toluene, indicative of network properties as expected from the bifunctional DBDD reagent and similar to those we have previously reported using α- and β-CD networks prepared with shorter bifunctional hexyl tie chains.29 Formation of C60/Dodecyl/γ-Cyclodextrin Nanocomposite Networks. In a typical synthesis, 20 mg (10.1 mmol) of the purified and dried dodecyl/γ-CD product was placed in 5 mL of DMF (dimethylformamide), and the network was observed to swell in the solvent. In a separate container, 2 mg (2.7 mmol) of C60 was dissolved in 5 mL of DMF. These reagent amounts correspond to a C60:CD ratio of 1:3.6, but additional experiments with 1:1 and 2:1 C60:CD ratios were also completed. Each reaction vessel was stirred separately at room temperature overnight and then heated at 60 °C for 30 min, at which time the C60 mixture was added to the dodecyl/γ-CD network mixture. The combined solution was then heated for an additional 3 h, after which time the heat was removed but stirring continued for 15 h. The mixture was then filtered via vacuum filtration, and the resulting film was air-dried overnight at room temperature. Following a wash with toluene to remove any free C60, and subsequent drying, the film was removed from the filter paper using forceps. Henceforth, we refer to this as the “as-prepared” C60/polymer composite network. Additional toluene washes were done to determine the stability of C60 in the network and are specifically described as such in the text.

RESULTS AND DISCUSSION The choice of γ-CD as a functional node and that of dodecyl chains as cross-linkers was motivated by the desire to create well-defined networks that can homogeneously incorporate discrete molecular components like C60. We have previously shown that the NaOH-based reactions involving CD and difunctional cross-linkers leads to networks in the case of α-CD and dibromohexane,29 but as we will discuss below, those networks do not yield stable C60 incorporation. Solution NMR characterization of the swollen product networks in that former case were of limited utility due to poor resolution, and 13C solid-state MAS NMR methods were used to quantify the degree of CD ring derivatization. The latter method provides good resolution and dynamic discrimination between network moieties and is consistent with our desire to characterize the final solid networks. The solid-state 13C MAS NMR spectrum of pure DBDD and the dodecyl/γ-CD network product is shown in Figure 1, and peak assignments are shown in the structure inset. The characteristic spectrum from pure CD is given as a reference in Figure 1a, in which one observes the signature crystallographically inequivalent carbon signals for each chemical moiety that disappear following reaction.30 As a control, the dried network was washed several times with hot water, which removes any free CD/DBDD inclusion complexes that were not incorporated in the network.30 Comparing the chemical shifts and the line widths for the DBDD peaks in the 20−40 ppm region of the product to that of the pure DBDD clearly shows that no residual, unreacted crystalline DBDD exists in the final dodecyl/γ-CD network, as pure DBDD is crystalline. While not shown here, the CP/MAS spectrum for the same sample shown in Figure 1a looks nearly identical to the quantitative single-pulse spectrum in Figure 1c in terms of peak widths and peak intensities. Since CP preferentially emphasizes rigid components, this equivalent result suggests all of the dodecyl chains covalently bonded to the CD rings and thus incorporated in the network. From integrations of the 6119

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Figure 3. Images of (a) the C60/dodecyl/γ-CD network membranes immediately after removal from DMF and placed in a dry container and (b) the same films after reimmersion in toluene. These membranes were obtained after six separate 24 h washings in toluene; note that the membrane is still intact and homogeneous with respect to C60 distribution. Note that the field of view here is ca. 2.5−3 times larger than in Figure 2.

toughness to be extracted with tweezers as a single film from solution and transferred multiple times to other environments (Figure 3b). The stability of the C60 incorporation was verified by soaking the as-prepared composites multiple times with excess toluene for 24 h. Each of the membranes in Figure 3 was soaked in toluene six times, for 24 h each soaking; note the film is still intact with homogeneous dispersion of C60, which indicates stable C60 intercalation. Toluene is an excellent solvent for C60 and is known to actually solvate aggregated clusters of C60, breaking the clusters apart into individual fullerene molecules.31,32 These results suggest C60 binds competitively with the dodecyl/γ-CD network. When dry network membranes are placed in water, or water droplets are placed on the dry film surfaces, no apparent wetting occurs. In order to quantify the nature of C60 binding in the C60/ dodecyl/γ-CD networks, solid-state 13C MAS NMR data were collected for the as-prepared network composites and after multiple 24 h toluene washings. In addition, UV−vis experiments on the toluene extracts were also examined to determine the nature and quantity of C60. Figure 4 shows the NMR results for pure C60, pure dodecyl/γ-CD network, and the composites as a function of number of toluene extractions. The sample shown in Figure 4 was prepared with an initial composition corresponding to 1:3.6 C60:CD ratio. Based on quantitative analysis of the peak areas in Figure 4b−d, the amount of C60 in the membrane relative to that included in the reaction mixture is 91, 73, and 66% for one, three, and six toluene washings, respectively. Note that the as-prepared membranes are subjected to one toluene wash, as described in the Experimental Section, and that 91% of the total possible C60 is incorporated into the network, resulting in a composite network with 14 wt % C60. Even after 144 h of soaking in toluene, an excellent C60 solvent, two-thirds of the C60 remains (9 wt %) in the thin (ca. 500 μm) film composite. TGA data (see Supporting Information) indicated that the onset of detectable mass loss from the dried, multiply washed C60/dodecyl/γ-CD network membranes occurs at 190 °C, which is 100 deg higher than in the pure dodecyl/γ-CD networks. UV−vis spectra were recorded for the toluene extracts following removal of the composites as a function of the number of washes. Shown in Figure 5 are the data following two, three, and six washes. We note that the toluene solutions were slightly purple after removal of the membrane, indicating that the C60 that is extracted back into toluene exists as isolated molecules and not aggregated clusters.33 Figure 5 indicates that

Figure 1. 13C MAS single-pulse spectra for (a) pure γ-CD, (b) pure DBDD, and (c) the dodecyl/γ-CD network formed from the reaction of dibromododecane (DBDD) and γ-CD. The inset shows the carbon labeled by their respective chemical shifts for the CD region (60−110 ppm) of the spectrum. The DBDD and dodecyl signals are in the 20− 40 ppm region of (b) and (c), respectively.

signals in Figure 1, the degree of chain functionalization on the CD rings corresponds to an average of five C12 chains per CD ring. Images for dry and solvent-swollen films prepared from the dodecyl/γ-CD networks are shown in Figure 2. Solvent-swollen

Figure 2. Images of (a) the swollen dodecyl/γ-CD network film in DMF and (b) the same film after casting and drying. The dry film in (b) is brittle and lacks sufficient toughness to be lifted from the Petri dish without breaking into several pieces.

networks are translucent (Figure 2a) and maintain clarity after drying (Figure 2b). The networks swell in DMF, DMSO, and toluene but are insoluble in other common laboratory solvents. The physical behavior of these networks, whether as swollen or dried films, is fragile. As shown in Figure 2, they are delicate and lack sufficient toughness to be lifted from their respective containers as a single film. Any attempts to extract the swollen film from the container in Figure 2a resulted in collapsed strands of material, independent of the amount of network that was swollen or the overall network:solvent ratio. In contrast, the as-prepared and dried C60/dodecyl/γ-CD composite networks exhibited completely different physical properties relative to those without C60. Figure 3 shows images for C60/dodecyl/γ-CD films in solution and after drying, and it is clear that intact membranes persist in the swollen state (Figure 3a), and they have sufficient structural integrity and 6120

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CD networks, as depicted in Scheme 1, or nonselectively adsorb within the swelled network free-volume between dodecyl cross-linking chains. The toluene extraction results described above suggest a strong association, as might be expected for C60/CD noncovalent binding, but are not definitive. In order to determine if the successful synthesis of the C60/dodecyl/γ-CD composite networks was facilitated by guest−host interactions, identical networks were made using dibromododecane and α-CD, whose 0.57 nm inner cavity diameter (van der Waals dimension of large toroid end) is significantly smaller than C60’s 1.0 nm van der Waals diameter and also smaller than C60’s 0.68 nm atom-center to atom-center diameter. For γ-CD, the inner diameter of the large opening in the toroidal cavity is 0.83 nm by comparison. Figure 6

Figure 4. 13C solid-state MAS NMR spectra of (a) pure C60, compared with the membranes after (b) one, i.e., as-prepared, (c) three, and (d) six 24 h toluene washings. The dodecyl/γ-CD network is shown in (e) for reference.

Figure 6. Comparison of as-prepared dry membranes with those obtained after washing in excess toluene for 1 h: (a) γ-CD/dodecyl network after C60 incorporation and before wash; (b) same membrane as in (a) after toluene wash; (c) α-CD/dodecyl network membrane after C60 incorporation and before wash; (d) same membrane as in (c) after toluene wash. The insets in the lower left of (a) and (c) are 10× zoomed images.

compares results for C60/dodecyl/γ-CD versus C60/dodecyl/αCD composites, each of which has an average of five dodecyl chains per CD node in the network. Each membrane was made using the same synthesis steps described in the Experimental Section, with the only difference arising from the presence of αCD at each network node instead of γ-CD. After initial preparation, the color and surface texture of the γ-CD and αCD are different, as can be seen by comparing Figures 6a and 6c, respectively. The C60/dodecyl/γ-CD membrane has a smooth surface, and the dark color is homogeneous throughout the membrane (Figure 6a). In contrast, the C60/dodecyl/α-CD membrane has a rough texture (see inset), more similar to that of the pure membranes shown above prepared without any C60, and the color is not uniform throughout (Figure 6c). After a 1 h toluene extraction, essentially all of the C60 is removed from the C60/dodecyl/α-CD sample, as shown by the almost white image in Figure 6d, while a similar treatment results in only minimal loss of C60 from the γ-CD network (Figure 6b). As described above, the C60/dodecyl/γ-CD sample in Figure 6a

Figure 5. UV−vis spectroscopy results for toluene extracts from the C60/dodecyl/γ-CD networks as a function of the number of extractions.

after six washes no additional C60 is removed from the composite, and from the NMR data in Figure 4, this corresponds to 66% of the original C60 content still remaining in the composite network. The 336 nm absorption for the extracted C60 is identical to that expected for pure, underivatized C60, indicating that the bulk of the C60 is not transformed to any other derivative during the preparation of the composite, which is consistent with the purple color of the solution extracts. Mechanism of C60 Incorporation in the Network. C60 can either selectively bind to the CD cavities in the dodecyl/γ6121

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can be washed in toluene five more times, and two-thirds of the C60 remains, while essentially the entire fullerene amount is removed after a single wash for the smaller cavity α-CD membrane. From the data presented above, the following conclusions may be drawn. First, the dodecyl/γ-CD networks incorporate strongly bound C60, but the smaller cavity dodecyl/α-CD membranes do not. Continuous membranes are formed from the dodecyl/γ-CD networks when C60 is added, but not in the absence of C60. While some C60 is removed from dodecyl/γ-CD networks by washing/soaking with toluene, the majority is not. In total, these results strongly suggest the picture in Scheme 1, particularly for networks that have been through several toluene washes to remove any C60 which is not associated with CD cavities. In addition, the results of Figure 2 and Figure 6c,d, in which discontinuous and fragile networks occur when C60 and CD are not proximate, suggest that C60 itself acts as a crosslinker to mechanically toughen the dodecyl/γ-CD networks through interactions with CD. Previous reports involving pure CD and pure C60 coordination in solution indicate a propensity for a bicoordinate or bicapped complex in both γ-CD and the slightly smaller pore β-CD, in which one C60 molecule simultaneously coordinates to the large end cavity of two different CD’s.26,29,34,35 For the covalently networked CD’s within our materials, it is not clear whether single-coordinate (e.g., like that shown in Scheme 1) or bicoordinate C60/CD complexes form. Calculated bicoordinate CD/C60 complexes are shown in Scheme 2, with both the space-filling and hybrid

CONCLUSIONS AND FUTURE WORK In this contribution, we have described an approach for making networks whose cyclodextrin-enabled guest−host properties facilitate stable and homogeneous incorporation of C60. While the network tie chains used here are nonpolar dodecyl linkers, the type of chain and the length of the chain can be easily varied through known cyclodextrin functionalization routes. Also, the type of cyclodextrin and therefore the inner cavity dimension is an accessible variable, and the cyclodextrins do not have to be incorporated as network nodes; they could simply be grafted into existing polymer chain structures as recently described in the literature.37 Other routes for preparing nanoporous cyclodextrin polymers or “nanosponges” have been described in the literature, and in theory such materials should also provide a basic platform for guest−host nanocomposite network formation.38,39 As described here, the technique should be generally applicable for preparation of reinforced and networked composites involving monodisperse fillers. We plan to pursue the synthesis of different network compositions and characterize their associated physical properties, assess how effective the cyclodextrin/network membranes are at sequestering fullerene impurities from mixed solutions, and explore electrical conductivity in higher loading fullerene/network membranes.

Scheme 2. CPK (left) and Partial Ball-and-Stick (right) Structures of C60 and γ-Cyclodextrin Complexes in Solution, Calculated via Geometry Optimization Using the MM+ Molecular Mechanics Potential in HyperChem 7.52

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ASSOCIATED CONTENT

S Supporting Information *

The reaction scheme and TGA results. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION

Corresponding Author

*E-mail jeff[email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS J.L.W. acknowledges support by the National Science Foundation through grants DMR-0756291 and DMR1203848. K.A. acknowledges support by the National Science Foundation under CHE-1254898. R.H.K. acknowledges support by the Gilberty and Nancy Williams Chemistry Graduate Fund.

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REFERENCES

(1) Bitinis, N.; Hernandez, M.; Verdejo, R.; Kenny, J. M.; LopezManchado, M. A. Recent Advances in Clay/Polymer Nanocomposites. Adv. Mater. 2011, 23, 5229−5236. (2) Xu, L.; Hiroyoshi, N.; Evangelos, M.; Ramanan, K. Tailored Nanocomposites of Polypropylene with Layered Silicates. Macromolecules 2009, 42, 3795−3803. (3) Kumar, S.; Jouault, N.; Benicewicz, B.; Neely, T. Nanocomposites with Polymer Grafted Nanoparticles. Macromolecules 2013, 46, 3199− 3214. (4) Krishnamoorti, R.; Vaia, R. A. Polymer Nanocomposites. J. Polym. Sci., Part B: Polym. Phys. 2007, 45, 3252−3256. (5) Prato, M. [60]Fullerene Chemistry for Materials Science Applications. J. Mater. Chem. 1997, 7, 1097. (6) Sariciftci, N. S.; Smilowitz, L.; Heeger, A. J.; Wudl, F. Photoinduced Electron Transfer from a Conducting Polymer to Buckminsterfullerene. Science 1992, 258, 1474−1476. (7) Sanz, A.; Ruppel1, M.; Douglas, J. F.; Cabral1, J. T. Plasticization Effect of C60 on the Fast Dynamics of Polystyrene and Related

ball-and-stick structures shown for clarity. The MM+ molecular mechanics calculations followed that described by Seridi for the interactions of C60 and β-CD,36 but modified for the γ-CD structure. These calculated energy-minimized structures, along with literature data for the association of CD and C60 in solution, suggest that C60 can stabilize network formation and integrity through bicoordinate or bicapping associations with CD’s. We do not expect that all C60’s in the network coordinate to two CD rings, as the CD themselves are connected by the dodecyl tie chains. However, such coordination can occur between regions of the network where the overall tie chain density is too low to impart the physical toughness required to form stable membranes in the absence of C60. This would explain the results of Figures 3 and 6a,b versus the pure CD networks in Figure 2. 6122

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Polymers: an Incoherent Neutron Scattering Study. J. Phys.: Condens. Matter 2008, 20, 104209. (8) Mirau, P. A.; Lyons, M. Intermolecular Interactions and Dynamics in Polymer/C60 Blends. Macromolecules 2010, 43, 625−629. (9) Weng, D.; Lee, H. K.; Levon, K.; Mao, J.; Scrivens, W. A.; Stephens, E. B.; Tour, J. M. The Influence of Buckminsterfullerenes and their Derivatives on Polymer Properties. Eur. Polym. J. 1999, 35, 867−878. (10) Liu, W. L.; Liu, R. G.; Wang, W.; Li, W. W.; Liu, W. Y.; Zheng, K.; Ma, L.; Tian, Y.; Bo, Z. S.; Huang, Y. Tailoring Nanowire Network Morphology and Charge Carrier Mobility of Poly(3 hexylthiophene)/ C60 Films. J. Phys. Chem. C 2009, 113, 11385−11389. (11) Liu, Y.; Chen, G.-S.; Chen, Y.; Zhang, N.; Chen, J.; Zhao, Y.-L. Bundle-Shaped Cyclodextrin−Tb Nano-Supramolecular Assembly Mediated by C60: Intramolecular Energy Transfer. Nano Lett. 2006, 6, 2196−2200. (12) Biryulin, Y. F.; Zgonnik, V. N.; Melenevskaya, E. Y.; Mikov, S. N.; Moliver, S. S.; Orlov, S. E.; Novoselova, A. V.; Petrikov, V. D.; Rozanov, V. V.; Sykmanov, D. A.; Yagovkina, M. A. Structure and Optical Properties of C60 Films on Polymer Substrates. Semiconductors 2003, 37, 347−353. (13) Kropka, J. M.; Garcia Sakai, V.; Green, P. F. Local Polymer Dynamics in Polymer−C60 Mixtures. Nano Lett. 2008, 8, 1061−1065. (14) Bandyopadhyay, D.; Douglas, J. F.; Karim, A. Influence of C60 Nanoparticles on the Stability and Morphology of Miscible Polymer Blend Films. Macromolecules 2011, 44, 8136−8142. (15) Kropka, J. M.; Putz, K. W.; Pyramitsyn, V.; Ganesan, V.; Green, P. F. Origin of Dynamical Properties in PMMA−C60 Nanocomposites. Macromolecules 2007, 40, 5424−5432. (16) Ravi, P.; Dai, S.; Wang, C.; Tam, K. C. Fullerene-Containing Polymers: A Review on Their Synthesis and Supramolecular Behavior. J. Nanosci. Nanotechnol. 2007, 7, 1176−1196. (17) Kwang-Jea, K.; White, J. L. Dispersion of Agglomerated Nanoparticles in Rubber Processing. Polym. Nanocompos. Handb. 2010, 123−149. (18) Datta, S.; Paul, D. R.; Bucknall, C. B. Polym. Blends 2000, 2, 477. (19) Klueppel, M. The Role of Disorder in Filler Reinforcement of Elastomers on Various Length Scales. Adv. Polym. Sci. 2003, 164, 1− 86. (20) White, J. L.; Schaffer, T.; Ruff, C. J. Incorporation of Isoprene in Isobutylene/Isoprene Copolymers: NMR Identification of Branching in Butyl Rubber. Macromolecules 1995, 28, 3290−3300. (21) Adriaensens, P.; Pollaris, A.; Vanderzande, D.; Gelan, J.; White, J. L.; Dias, A. J.; Kelchtermans, M. Critical Analysis of Network Heterogeneity in Isobutylene-Based Elastomers by NMR Imaging. Macromolecules 1999, 32, 4692−4699. (22) Adriaensens, P.; Pollaris, A.; Vanderzande, D.; Gelan, J.; White, J. L.; Kelchtermans, M. Relationships Between Microvoid Heterogeneity and Physical Properties in Cross-linked Elastomers: An NMR Imaging Study. Macromolecules 2000, 33, 7116. (23) Wolak, J.; Jia, X.; Gracz, H.; Stejskal, E. O.; Wachowicz, M.; Jurga, S. J.; White, J. L. Polyolefin Miscibility: Solid-State NMR Investigation of Phase Behavior in Saturated Hydrocarbon Blends. Macromolecules 2003, 36, 4844−4850. (24) Wachowicz, M.; Gill, L.; Wolak, J. E.; White, J. L. Polypropylene and Polyethylene-Copolymer Blend Miscibility: Slow Chain Dynamics in Individual Blend Components Near the Glass Transition. Macromolecules 2008, 41, 2832. (25) Gill, L.; Damron, J.; Wachowicz, M.; White, J. L. Glass Transitions, Segmental Dynamics, and Friction Coefficients for Individual Polymers in Multicomponent Polymer Systems by Chain Level Experiments. Macromolecules 2010, 43, 3903. (26) Buvari-Barcza, A.; Rohonczy, J.; Rozlosnik, N.; Gilanyi, T.; Szabo, B.; Lovas, G.; Braun, T.; Samu, J.; Barcza, L. Aqueous Solubilization of [60]Fullerene via Inclusion Complex Formation and Hydration of C60. J. Chem. Soc., Perkins Trans. 2001, 2, 191−196. (27) Ikeda, A.; Aono, R.; Maekubo, N.; Katao, S.; Kikuchi, J.; Akiyama, M. Pseudorotaxane Structure of Fullerene DerivativeCyclodextrin 1:2 Complex. Chem. Commun. 2011, 47, 12795−12797.

(28) Yoshida, Z. I.; Takekuma, H.; Takekuma, S. I.; Matsubara, Y. Molecular Recognition of C60 with γ-Cyclodextrin. Angew. Chem., Int. Ed. Engl. 1994, 33, 1597−1599. (29) Gyanwali, G.; Hodge, M.; White, J. L. Cyclodextrin Functionaliztion: Simple Routes to Tailored Solubilities and Nanoscopic Networks. J. Polym. Sci., Part A: Polym. Chem. 2012, 50, 3269. (30) Rusa, C. C.; Wei, M.; Bullions, T. A.; Rusa, M.; Gomez, M. A.; Porbeni, F. E.; Wang, X. G.; Shin, I. D.; Tonelli, A. E. Cryst. Growth Des. 2004, 4, 1431. (31) Murdianti, B. S.; Damron, J. T.; Hilburn, M. E.; Maples, R. D.; Hikkaduwa Koralege, R. S.; Kuriyavar, S. I.; Ausman, K. D. C60 Oxide as a Key Component of Aqueous C60 Colloidal Suspensions. Environ. Sci. Technol. 2012, 46, 7446−7453. (32) Ruoff; Tse; Malhotra; Lorents. Solubility of C60 in a Variety of Solvents. J. Phys. Chem. 1993, 97, 3379−3383. (33) Creegan, K. M.; Robbins, J. L.; Robbins, W. K.; Millar, J. M.; Sherwood, R. D.; Tindall, P. J.; Cox, D. M.; McCauley, J. P.; Jones, D. R. Synthesis and Characterization of C60O, the First Fullerene Epoxide. J. Am. Chem. Soc. 1992, 114, 1103−1105. (34) Andersson, T.; Westman, G.; Wennerstrom, O.; Sundahl, M. NMR and UV-VIS Investigation of Water-soluble Fullerene-60-γCyclodextrin Complex. J. Chem. Soc., Perkin Trans. 2 1994, 1097− 1101. (35) Nishibayashi, Y.; Saito, M.; Uemura, S.; Takekuma, S.; Takekuma, H.; Yoshida, Z. A Non-Metal System for Nitrogen Fixation. Nature 2004, 428, 279−280. (36) Seridi, L.; Boufelfel, A. Simulations of Docking C60 in BetaCyclodextrin. J. Mol. Liq. 2011, 162, 69−77. (37) Busche, B. J.; Tonelli, A. E.; Balik, C. M. Morphology of Polystyrene/Poly(dimethyl siloxane) blends Compatibilized with Polymers Containing a Cyclodextrin Core and Polystyrene Arms. Polymer 2010, 51, 1465−1471. (38) Ma, M.; Li, D. New Organic Nanoporous Polymers and Their Inclusion Complexes. Chem. Mater. 1999, 11, 872−874. (39) Cavalli, R.; Trotta, F.; Tumiatti, V. Cyclodextrin-based Nanosponges for Drug Delivery. J. Inclusion Phenom. Macrocyclic Chem. 2006, 56, 209−213. (40) Piersimoni, F.; Chambon, S.; Vandewal, K.; Mens, R.; Boonen, T.; Gadisa, A.; Izquierdo, M.; Filippone, S.; Ruttens, B.; D’Haen, J.; Martin, N.; Lutsen, L.; Vanderzande, D.; Adriaensens, P.; Manca, J. Influence of Fullerene Ordering on the Energy of the Charge-Transfer State and Open-Circuit Voltage in Polymer:Fullerene Solar Cells. J. Phys. Chem. C 2011, 115, 10873−10880. (41) Yang, C.; Hu, J.; Heeger, A. J. Molecular Structure and Dynamics at the Interfaces within Bulk Heterojunction Materials for Solar Cells. J. Am. Chem. Soc. 2006, 128, 12007−12013.

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dx.doi.org/10.1021/ma401231c | Macromolecules 2013, 46, 6118−6123