Polymer Blending through Host–Guest Interactions - American

Article pubs.acs.org/Macromolecules

Polymer Blending through Host−Guest Interactions Marco Dionisio,† Lucia Ricci,‡ Giulia Pecchini,† Daniele Masseroni,† Giacomo Ruggeri,‡ Luigi Cristofolini,§ Enrico Rampazzo,⊥ and Enrico Dalcanale*,† †

Dipartimento di Chimica and INSTM, UdR Parma, Università di Parma,Viale delle Scienze 17/A, 43124 Parma, Italy Dipartimento di Chimica e Chimica Industriale and INSTM, UdR Pisa, Università di Pisa, Via Risorgimento 35, 56126 Pisa Italy § Dipartimento di Fisica, Università di Parma, Viale delle Scienze 7/A, 43124 Parma, Italy ⊥ Dipartimento di Chimica “G. Ciamician” and INSTM, UdR Bologna, Università di Bologna, Via Selmi 2, 40126 Bologna, Italy ‡

S Supporting Information *

ABSTRACT: In this work, a supramolecular approach, based on molecular recognition, was used to direct the blending of immiscible polymers toward compatibility and even molecular miscibility. A slight modification of the two immiscible polymers polystyrene (PS) and poly(butyl methacrylate) (PBMA), with the introduction of the two recognition groups tetraphosphonate cavitand (HOST) and methylpyridinium (GUEST), respectively, led to the formation of compatible mixtures between them, characterized by a single Tg and by an homogeneous texture at the surface level, as evidenced by AFM measurements. The energetically favorable host−guest interactions among polymeric chains overcome their repulsive interfacial energy, leading to the suppression of phase segregation at the level of material. The complexation between PS−HOST and PBMA−GUEST copolymers has been demonstrated to be reversible by the action of a specific external stimulus in the form of guest exchange with the competitive N-methylbutyl ammonium chloride.

T

one polymer. The microscopic segregation observed in most polymer blends, even for structurally related polymers, jeopardizes their use. The covalent introduction of compatibilizers or reactive functional groups in the side chain of the polymers are usually employed to minimize the interfacial energy and, in turn, the phase segregation. Recently, Zimmerman proposed the use of hydrogen bonding to overcome the miscibility problems in polymer chemistry.11 Introduction of guanosine urea (UG) and 2,7-diamido-1,8-naphthyridine (DAN) in the side chain of poly(butyl methacrylate) and polystyrene, respectively, led to the formation of a polymer blend. This is due to the formation of an heterocomplex between the two recognition units even at low molar content. Interestingly, this approach was further improved by introducing redox sensible molecular recognition units for the control of supramolecular polymer network.12 More recently Hawker and Kramer introduced 2-ureido-4[1H]-pyrimidinone (UPy) and 2,7-diamido-1,8-naphthyridine (Napy) as chain end groups in

he merging of polymer science with supramolecular chemistry has generated a new, thriving research field, broadly defined as supramolecular polymer chemistry.1 The positive results of this merging is demonstrated by the appearance of supramolecular polymers presenting unique mechanical,2 electronic,3 biological4 and self-healing properties.5 The supramolecular approach6 is very attractive for the design of adaptive materials7 featuring reversibility and responsiveness to external stimuli. Molecular recognition is the most sophisticated form of weak interaction in terms of precise responsiveness, since it requires a well-defined arrangement of complementary noncovalent interactions to operate at its best. For polymer science, the macroscopic expression of molecular recognition is the next step necessary to harness its full potential.8 In this regard, the recent work of Harada and coworkers9 on the selective gel formation through molecular recognition is groundbreaking. They nicely showed that molecular recognition events at the molecular level produce specific and controlled macroscopic responses. Polymer blending is a long-standing issue in polymer science,10 with relevant practical implications. The blending of polymers is an economically attractive route to develop new materials that combine the desirable properties of more than © 2014 American Chemical Society

Received: July 17, 2013 Revised: November 25, 2013 Published: January 8, 2014 632

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Chart 1

ation in solution, molecular mixing in the solid state and reversibility of the blending, induced by an external stimulus. Synthesis and characterization of PS−HOST and PBMA−GUEST Copolymers. The styrene-footed tetraphosphonate cavitand monomer Tiiii[styrene,CH3,Ph] (1)20 and its (6-methacryloyloxy)hexyl isonicotinate (2) counterpart (Chart 1) were prepared to be incorporated in the corresponding polymers. Cavitand 1 was synthesized in three steps starting from a monohydroxy-footed silylcavitand, already reported in the literature21 (Scheme S1, Supporting Information). The key step is the introduction of the styrene moiety at the lower rim of the resorcinarene skeleton. The direct coupling between the monohydroxy-footed silylcavitand and the 4-vinyl benzoic acid, under Steglich conditions22 led to the styrenefooted intermediate. After removal of the silyl protecting groups, the resulting resorcinarene was ready to be bridged with dichlorophenylphosphine. This latter reaction gave rise to a tetraphosphonite intermediate which was oxidized in situ with hydrogen peroxide to give the tetraphosphonate cavitand 1 in 10% overall yield. Only the diastereomer with all the four PO groups inward was formed, due to the stereoselectivity of the bridging reaction.14a,23 The pyridine methacrylate monomer 2 was prepared in two steps (Scheme S2). A first, monoesterification of 1,6-hexanediol with methacryloyl chloride allowed the introduction of a single methacrylate group for incorporation in PBMA. Then, the monoester derivative was reacted with isonicotinoyl chloride leading to monomer 2. The free radical copolymerization of 1 with styrene introduced the Tiiii host in the polystyrene backbone. The

low molecular weight polybenzyl methacrylate and polybutyl acrylate, showing that their heterodimerization suppresses segregation.13 These noteworthy results inspired us to explore the potential of host−guest interactions to induce polymer blending. In recent years, we reported how the interactions between tetraphosphonate cavitands and cationic species, such as Nmethylpyridinium and N-methylbutyl ammonium salts, can lead to supramolecular host−guest polymers14 and hybrid inorganic−organic materials.15 In particular, the complex formed between tetraphosphonate cavitand and the N-methylpyridinium moiety is highly stable (Ka = 5.8 × 106 in chlorinated solvents)16 and reversible, both chemically17 and electrochemically.18 These results prompted us to select this host−guest system to address the polymer blending issue. To this purpose, four copolymers were prepared (Chart 1): two polystyrene hosts, featuring tetraphosphonate cavitand units as side chains (PS−HOST 2.5% and 4%) and two poly(butyl methacrylate) guests, equipped with N-methylpyridinium motifs (PBMA− GUEST 2.5% and 4%)). The corresponding parent homopolymers are immiscible, leading to phase segregation at the microscopic level.19 Energetically very favored host−guest complexes are required to overcome the strong repulsive interactions between the two polymers with a minimal incorporation of recognition units. The tetraphosphonate cavitand-methypyridinium system fits the bill nicely, since their association is not only strong, but also both enthalpy and entropy driven.16 The present work describes preparation of PS−HOST and PBMA−GUEST copolymers, their complex633

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Table 1. GPC/SLS Characterization of the Polymers and Average Number of Host/Guest Units F polymer PS−HOST-4% PBMA−GUEST-4% PS−HOST-2.5% PBMA−GUEST-2.5% PS PBMA

Mna 20 800 27 300 22 300 25 600 22 500 21 500

Mwa

Mw SLS

27 100 40 000 30 600 36 700 23 000 31 800

28000 ± 2000 30000 ± 6000

PDIa 1.30 1.47 1.37 1.43 1.02 1.48

mol % F units b

3.9 3.8b 2.3b 2.4c 0 0

average no. of F units per chaind 5.3 6.8 3.9 4.1 0 0

a

Relative molecular weights against PS standards obtained from GPC in CHCl3. bDetermined by elemental analyses. cDetermined by 1H NMR integration. dCalculated from the number-average molecular weights (Mn) and mol % recognition unit of the polymers.

reaction was conducted in toluene at 70 °C using AIBN as initiator. The initial molar ratio between styrene and 1 was 96:4, which is reflected in the final PS−HOST-4% 3 compositions (see below). Therefore, the reactivity of the styrene moiety in 1 is not affected by the presence of the bulky cavitand substituent in para position. The installation of 2 in PBMA to give PBMA−GUEST-4% 4 (Chart 1) was carried out in two steps: first radical copolymerization between BMA and 2 in toluene with AIBN at 70 °C, followed by the N-methylation of the pyridine residues in polymer 5 with methyl iodide. Also in this case the 96:4 initial molar compositions is substantially retained in the final polymers. Given the large molecular weight of Tiiii[styrene,CH3,Ph] monomer compared to that of styrene, the Tiiii units make up 35% w/w of PS−HOST 3 at 4% molar incorporation. To lower this ratio and to test the effectiveness of this host−guest complex at blending incompatible polymers, “lighter” versions of both PS−HOST 3 and PBMA−GUEST 4 were prepared, incorporating 2.5% of host and guest units, respectively. The two PS−HOST copolymers 3 were fully characterized by several complementary techniques. FT-IR and 1H NMR analyses confirmed the formation of the desired products (Figures S1−S4). From the comparison of integrals of the signals at 8.1 and 6.8−6.0 ppm of 1H NMR spectrum of PS−HOST-4%, the amount of HOST in the copolymer has been estimated in 4.3 mol %. This value is in line with the 3.9 mol % obtained via phosphorus elemental analysis (Table S1). The same analysis for PS−HOST-2.5% led to a value of 2.3% molar incorporation both by NMR integration and elemental analysis (Table S2). The incorporation of monomer 2 in the PBMA chain of 5 was confirmed by 1H NMR (Figures S5−S6). The progression of the N-methylation of the pyridine groups was monitored with UV−vis spectroscopy, following the decreasing of the band at 273 nm (Figure S7).24 The 1H NMR analysis (in particular the signal at 4.8 ppm of the methyl groups bound to nitrogen) confirms the results obtained by UV−vis analysis. In 1 H NMR spectrum, all aromatic signals of pyridine protons are shifted at lower field with respect to nonmethylated PBMA− GUEST 5 (Figure S8), indicating that almost all pyridine groups are N-methylated. The amount of GUEST in 4 is 3.8 mol % by nitrogen elemental analysis (Table S3) and 3.5 mol % by 1H NMR integration. The same procedure was followed to characterize PS−HOST-2.5% and PBMA−GUEST-2.5% (Supporting Information). In this case the guest incorporation was estimated in 2.4% by NMR signals integration. The weight-average molecular weight (Mw), the numberaverage molecular weight (Mn) and the polydispersity index (PDI) of 3 and 4 were determined via gel permeation chromatography (GPC) in chloroform with standard polystyrene calibration. The results are summarized in Table 1 and

the refractive index chromatographic traces are reported in Figures S10−S11. The average number of host/guest units (F)11 per chain was calculated from the experimentally determined monomer molar ratios and Mn of the polymers, obtained respectively by elemental analysis and GPC. Since PS−HOST polymers present bulky cavitand side groups, which could jeopardize GPC analyses, their Mw was independently confirmed using static light scattering (SLS). The values obtained are in line with the ones determined by GPC (Table 1 and Figures S12−S13). The average molecular weight (20−27 KDa range for Mn) and the comonomer composition are important parameters for the successive molecular level mixing between PS−HOST and PBMA−GUEST. The relatively low molecular weight of the copolymers allows the minimization of physical entanglement of polymer coils in semidilute solutions. The 2.5/4 mol % content of both host and guest counterparts assures a strong interaction, without altering the main features of the pristine polymers. Complexation Properties of the Copolymers in Solution. Intermolecular association between PS−HOST-4% 3 and PBMA−GUEST-4% 4 was readily observed by 31P NMR spectroscopy (Figure 1). The free PS−HOST showed a singlet at 6.5 ppm. After addition of 0.5 equiv of PBMA−GUEST-4%, calculated according to the F values reported in Table 1, a peak at 9.6 ppm was recorded. This was assigned to the complex formed between the tetraphosphonate cavitand residue and the N-methylpyridinium moiety, in agreement with previous observations.15b Moreover, the presence of both peaks (6.5

Figure 1. 31P NMR in CDCl3 monitoring of host−guest driven association between PS−HOST-4% 3 and PBMA−GUEST-4% 4 (0.45 mM solution each). 634

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Figure 2. 2D (left) and 3D-view of a detail (right) AFM topographic images of PS/PBMA (a), PS−HOST-4%/PBMA−GUEST-4% (3·4) (b), and PS−HOST-4% 3/nonmethylated PBMA−GUEST-4% 5 (c).

temperature (10−15 °C), by employing a Peltier cell and a dry chamber (needed to prevent condensation phenomena). We prepared a film from a 0.45 mM solution of a 1:1 molar mixture of PS and PBMA in DCM, which was spin-coated on a flat silicon surface covered by its native oxide layer. The resulting film had typical thickness 200−300 nm, well above the threshold for the onset of confinement induced effects.26 The AFM topography (Figure 2a) shows a pitted surface and evident surface segregation. The morphology obtained was also highly dependent on the solvent chosen for the spin-coating: typically chloroform yielded rougher surfaces than DCM.

and 9.6 ppm) accounted for a slow exchange on the NMR time scale. Addition of further 0.5 equiv of PBMA−GUEST led to complete disappearance of PS−HOST signal at 6.5 ppm. The NMR titration indicated that the F values reported in Table 1 are correct for the determination of the 1:1 host−guest molar ratio between the two polymers. AFM Morphology Study. A series of AFM studies were engaged to visualize the polymer blending in the solid state. To minimize artifacts due to tip−surface interactions, given the low Tg of one of the two polymers (PBMA, ∼26 °C),25 we chose to operate either in noncontact mode, or in contact mode at low 635

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Careful analysis of the morphology of the film showed the presence of islands and depressions, with a mean-square roughness of 45−50 nm. The islands present a lateral dimension ranging from ca. 800 to 500 nm, while the depth of the depressions were estimated 100 nm, in agreement with previous observation.27 Because of the higher mobility of PBMA molecules, they tend to “flow” around and to migrate to the silicon surface because of its lower surface tension. The phase segregation results from the combination of the low chemical affinity between the two polymers, and the great difference in terms of their surface energy.19 By contrast, the topographic image of 1:1 molar mixture of PS−HOST-4% 3 and PBMA−GUEST-4% 4 was quite flat, with few surface features, mean-square roughness of just 1−2 nm and without apparent phase separation (Figure 2b). The vertical scale of Figure 2b has been expanded by a factor of 10 to show the residual roughness. Moreover the topographical data supported a level land. These evidence, combined with the DSC data below, demonstrate the mixing of the two copolymers at molecular level, hence their compatibilization. The AFM visualization was replicated on the 1:1 molar mixture of PS−HOST-2.5% 3 and PBMA−GUEST-2.5% 4 to verify if a lower number of host−guest complexes per chain could be sufficient for polymer blending. The AFM image reported in Figure S18 shows that the mixing is effective even at 2.5% molar incorporation, a clear indication of the strong impact on polymer compatibilization of these specific host− guest interactions. DSC analyses. The miscibility of a polymer blend is often assessed by the measurement of a single glass transition temperature (Tg) as a function of composition, through differential scanning calorimetry (DSC).28 We, thus, performed a systematic DSC analysis on a series of samples, including the functionalized polymers, as well as different blends compositions (Table S4). To erase any thermal history, the Tg was measured at the second heating run, after 3 min of isothermal stage at the lowest cooling temperature. For the PBMA− GUEST, no differences were noted in comparison with the parent polymer before methylation. After salt formation, a small increase in Tg was observed both at 2.5% and 4% guest incorporation. In the case of PS−HOST a slightly increase of Tg from 95 to 97 °C was observed both for 2.5% and 4% host incorporation. This might be due to the bulky cavitand side chains that stiffen somehow the polymer. When a 1:1 molar mixture of 3 and 4 at 4% was submitted to a DSC analysis, only one Tg is observed at about 40 °C, consistent with the formation of an homogeneous blend (Figure 3). Interestingly, when one of the two components exceeds the other, only one Tg is still observed. In particular when 2:1 PS−HOST and PBMA−GUEST molar mixture was prepared, the Tg raises to ca. 50 °C; on the other hand, for 1:2 PS−HOST and PBMA− GUEST mixture the Tg falls to about 32 °C, without discernible changes in the AFM topography. The successful blending at imbalanced host−guest stoichiometric ratio indicated that a lower complex incorporation could be sufficient. Actually, this hypothesis turned out to be the true: the DSC analysis of the 1:1 mixture of of 3 and 4 at 2.5% showed a single Tg at 56 °C (Table S4 and Figure S15). Instead, a 1:1 molar mixture of PS and PBMA showed two different Tg: one at 26 °C and the other at 95 °C, corresponding to those of the pristine polymers. This is in accordance with the immiscibility of the two homopolymers (Figure 2a).29

Figure 3. DSC thermograms (2nd heating run) of PBMA−GUEST4% 4 (black line), PS−HOST-4% 3 (orange line), and 3/4 1:2 (red line), 1:1 (blue line), 2:1 (magenta line) blends.

Control Experiment. The evidence gathered so far allows to assert that molecular recognition between the host−guest counterparts drives polymer blending. The following control experiment was conducted to validate this statement: a 1:1 molar solution of PS−HOST-4% 3 and nonmethylated PBMA−GUEST-4% 5 was spin coated on a silicon slice to study its morphology by AFM. The images recorded showed a non homogeneous and pitted topography (Figure 2c), similar to that formed by the mixture of the parent homopolymers, with a typical value for the mean square roughness of 11−13 nm, an order of magnitude larger than that of the compatibilized form (Figure 2b). It can be noted, however, that the morphology of the segregation domains is different from that of the film formed by mixing the pristine polymers (Figure 2a). This can be explained considering that the domain morphology is the result of the long-range molecular migration, which takes place during the spin coating process in the final steps of the solvent evaporation. This effect is known to be solvent-dependent, and it is reasonable to assume that is also affected by the presence of the large cavitand and pyridine side groups attached to the polymeric main chains, reducing their mobility and hence limiting the extension of the segregation domains. A part of the same material was analyzed via DSC: two distinct Tg were recorded, respectively at 20 and 68 °C (Figure 4). These data confirm that the two copolymers are not miscible, because of the suppression of host−guest interactions determined by the absence of the charged N-methyl group, even if a partial interaction between polar groups at the interface of the segregated polymer domains determines a decrease in the Tg of the component PS−HOST. Reversibility of Polymer Blending via Guest Exchange. This experiment was conceived to test the reversibility of the polymer blending upon exposure to an external stimulus, in the form of a competitive guest. N-Methylammonium salts form stronger complexes with tetraphosphonate cavitands than N-methylpyridinium salts because of the presence of two additional hydrogen bonds between two adjacent PO bridges and the two nitrogen protons.17 Hence, we treated a 1:1 molar solution of PS−HOST-4% 3 and PBMA−GUEST-4% 4 with a progressive amount of N-methyl butyl ammonium chloride (6) solution. 6 replaced the N-methylpyridinium in the tetra636

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CONCLUSIONS In this article, we have described the polymer blending at the molecular level of two immiscible polymers, namely PS and PBMA, driven by host−guest interactions. Complementary tetraphosphonate cavitand hosts and N-methylpyridinium guests were introduced in low molar percent in PS and PBMA respectively via radical copolymerization of the corresponding monomers. The resulting copolymers PS− HOST 3 and PBMA−GUEST 4 are fully miscible in the solid state in a wide molar ratio, as demonstrated by the presence of a single Tg in the DSC thermograms of the mixtures and by AFM topography of the corresponding films. Reducing the content of host/guest units from 4% to 2.5% does not affect polymer blending, indicating the effectiveness of the cavitand−methylpyridinium interactions to induce molecular level mixing. The exhaustive formation of the host−guest complexes among the polymeric chains was proven in solution via 31P NMR and in the solid state through a control experiment with nonmethylated PBMA−GUEST 5. The absence of the N-methyl group, necessary for the complexation with the tetraphosphonate unit, suppresses polymer blending. From the thermodynamic point of view, this work demonstrates that a limited number of strong host−guest interactions is sufficient to reverse the free energy of mixing of two polymers from positive to negative.30 Finally, the reversibility of host−guest polymer blending was successfully tested via guest exchange with competitive N-methyl butyl ammonium chloride 6. The monotopic guest replaced PBMA−GUEST in the interaction with PS−HOST, restoring the original polymer immiscibility. In conclusion, this work demonstrated that specific host− guest interactions among polymeric chains are expressed at the material level in polymer blending. The proposed approach is of general value for the reversible compatibilization of a wide variety of polymeric materials, to control phase separation in copolymers 31 and to promote interface affinity 32 and adhesion.33

Figure 4. DSC thermograms (2nd heating run) of nonmethylated PBMA−GUEST-4% 5 (black line), PS−HOST-4% 3 (blue line), and 1:1 3/5 blend (magenta line).

phosphonate cavity, thus disconnecting the polymeric chains. The exchange was followed by 31P NMR: the peak at 9.6 ppm relative to the 3·4 complex was progressively replaced by the peak at 10.4 ppm, attributed to the complex formed between the tetraphosphonate cavitand residue of PS−HOST-4% host and 6 (Figure 5a). After addition of 1 equiv of 6, the 9.6 ppm signal disappeared, indicating that all N-methylpyridinium moieties of PBMA−GUEST-4% were displaced by 6. The AFM topography of the film, obtained via spin coating of an aliquot of the NMR final solution, mapped an heterogeneous surface (Figure 5b), which bears a striking resemblance to that of the PS−PBMA film (Figure 2a). The depressions reached about 100 nm of depth, and the islands were clearly visible. Therefore, a chemical stimulus in the form of a competitive guest triggers off polymer segregation by suppressing the polymeric host−guest interactions responsible of the original blending

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ASSOCIATED CONTENT

S Supporting Information *

Experimental procedures and analytical data for synthesized Tiiii[Styrene,CH3,Ph] (1) and 6-methacryloxy)isonicotinate (2), NMR spectra, elemental analysis, FT-IR spectra, GPC,

Figure 5. (a) 31P NMR titration of PS−HOST-4% 3·PBMA−GUEST-4% 4 complex with competitive guest 6. (b) 3D AFM image of the surface topography of 3·4 after treatment with 1 equiv of N-methylbutyl ammonium chloride 6. 637

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(18) Gadenne, B.; Semeraro, M.; Yebeutchou, R. M.; Tancini, F.; Pirondini, L.; Dalcanale, E.; Credi, A. Chem.Eur. J. 2008, 14, 8964− 8971. (19) Chen, C.; Wang, J.; Woodcock, S. E.; Chen, Z. Langmuir 2002, 18, 1302−1309. (20) For the nomenclature adopted for phosphonate cavitands, see: Pinalli, R.; Suman, M.; Dalcanale, E. Eur. J. Org. Chem. 2004, 451−462. (21) Hauke, F.; Myles, A. J.; Rebek, J., Jr. Chem. Commun. 2005, 4164−4166. (22) Neises, B.; Steglich, W. Angew. Chem., Int. Ed. Engl. 1978, 17, 522−524. (23) Nifantyev, E. E.; Maslennikova, V. I.; Merkulov, R. V. Acc. Chem. Res. 2005, 38, 108−116. (24) Cetina, M.; Tranfic, M.; Sviben, I.; Jukic, M. J. Mol. Struct. 2010, 969, 25−32. (25) Fox, R. B. Glass Transition Temperature for Selected Polymers. In CRC Handbook of Chemistry and Physics, 87th ed.; Lide, D. R., Ed.; CRC Press: Boca Raton, FL, 2006−2007, . (26) (a) Keddie, J. L.; Jones, R. A. L.; Cory, R. A. Europhys. Lett. 1994, 27, 59−64. (b) Cristofolini, L.; Arisi, S.; Fontana, M. Phys. Rev. Lett. 2000, 85, 4912−4915. (27) Affrossman, S.; Jerome, R.; O’Neil, S. A.; Schmitt, T.; Stamm, M. Colloid Polym. Sci. 2000, 278, 993−999. (28) Aubon, M.; Prud’homme, R. E. Macromolecules 1988, 21, 2945− 2949. (29) (a) Chuai, C.; Almdal, K.; Lyngaae-Jørgensen, J. J. Appl. Polym. Sci. 2004, 91, 609−620. (b) Ton-That, C.; Shard, A. G.; Daley, R.; Bradley, R. H. Macromolecules 2000, 33, 8453−8459. (30) (a) Flory, P. J. J. Chem. Phys. 1941, 9, 660−661. (b) Huggins, M. L. ibid 1941, 9, 440. (31) Tang, C.; Lennon, E. M.; Fredrickson, G. H.; Kramer, E. J.; Hawker, C. J. Science 2008, 322, 429−432. (32) Ahn, Y.; Jang, Y.; Selvapalam, N.; Yun, G.; Kim, K. Angew. Chem., Int. Ed. 2013, 52, 3140−3144. (33) Anderson, C. A.; Jones, A. R.; Briggs, E. M.; Novitsky, E. J.; Kuykendall, D. W.; Sottos, N. R.; Zimmerman, S. C. J. Am. Chem. Soc. 2013, 135, 7288−7295.

and SLS analyses of PS−HOST (3), NMR spectra, elemental analysis, UV−vis spectra, FT-IR spectra, and GPC analysis of PBMA−GUEST (4) and nonmethylated PBMA−GUEST (5), polymer blends preparation and films deposition, differential scanning calorimetry (DSC) of PS, PBMA, 3, 4, 5 and their blends, and AFM topographical images of PS, PS−HOST (3), PBMA, and PBMA−GUEST (4). 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: (E.D.) [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The project described was supported by the EC through Project BION (ICT-2007-213219) and by MIUR through FIRB “RINAME” (RBAP114AMK).

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REFERENCES

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