A Giant Surfactant of Polystyrene-(Carboxylic Acid-Functionalized. Polyhedral Oligomeric Silsesquioxane) Amphiphile with Highly Stretched

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1 A Giant Surfactant of Polystyrene-(Carboxylic Acid-Functionalized Polyhedral Oligomeric Silsesquioxane) Amphiphile with Highly Stretched Polystyrene Tails in Micellar Assemblies Xinfei Yu, Sheng Zhong, Xiaopeng Li, Yingfeng Tu, Shuguang Yang, Ryan M. Van Horn, Chaoying Ni, Darrin J. Pochan, Roderic P. Quirk, Chrys Wesdemiotis, Wen-Bin Zhang *, and Stephen Z. D. Cheng * Department of Polymer Science and Department of Chemistry, The University of Akron, Akron, Ohio 44325, USA; Department of Materials Science and Engineering, University of Delaware, Newark, Delaware 19716, USA. Experimental Section Chemicals and Solvents. Styrene (99%, Aldrich) and benzene (EM Science, ACS grade) were purified as described previously. 1 Benzene was distilled as needed from poly(styryl)lithium directly into the polymerization reactor. Sec-Butyllithium (Chemetall Foote Corp., 12 wt % in cyclohexane) was used as received after double titration with allyl bromide. 2 Chlorodimethylsilane (98%, Aldrich) was purified by stirring over calcium hydride with periodic degassing for 12 h followed by distillation and collection of the middle fraction into flame-sealed ampoules. Toluene (Aldrich, 99.5%) was purified by stirring over calcium hydride for 24 h followed by distillation. OctaVinyl POSS (OVPOSS, Hybrid Plastics), mercaptoacetic acid (Aldrich, 98%), methanol (MeOH, Fisher Scientific, reagent grade), tetrahydrofuran (THF, Aldrich, 99%), CDCl 3 (Aldrich, 99.8 atom % D), DMSO-d 6 (Aldrich, 99.9 atom % D), 2,2-dimethoxy-2-phenylacetophenone (DMPA, Aldrich, 99%), and the Karstedt s catalyst, 1,3- divinyltetramethyldisiloxane-platinum complex (Gelest, wt % Pt in xylene) were used as received. S1

2 Characterization. Size-exclusion chromatography analyses (SEC) were performed using a Waters 150-C Plus instrument equipped with three HR-Styragel columns [100 Å, mixed bed (50/500/103/104 Å), mixed bed (103/104/106 Å)] and a double detector system. The detector system consisted of a differential refractometer (Waters 410) and a laser light scattering detector (Wyatt Technology, DAWN EOS, λ= 670 nm). THF was used as eluent with a flow rate of 1.0 ml/min at 30 C. Regular SEC calibrations were conducted with polystyrene standards (Polymer Laboratories). All 1 H NMR, 13 C NMR spectra were acquired using a Varian Mercury 300 spectrometer. NMR samples were prepared in CDCl 3 or DMSO-d 6 with concentration of 10 mg/ml for 1 H NMR and 40 mg/ml for 13 C NMR. Infrared spectra were recorded on an Excalibur Series FT-IR spectrometer (DIGILAB, Randolph, MA). FT-IR samples were prepared by casting polymer films on KBr plates from polymer solutions with concentration of 5 mg/ml in THF. The polymer films were subsequently dried at C to remove the solvent. For the measurements of the degree of ionization of carboxylic acids, micellar solutions were freeze-dried under vacuum to obtain solvent-free samples. The freeze-dried sample was then ground with KBr powder. The mixtures were pressed into the solid disks for FT-IR characterization. The data were processed using Win-IR software. Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectra were obtained on a Bruker Ultraflex III TOF/TOF mass spectrometer (Bruker Daltonics, Billerica, MA), equipped with a Nd:YAG laser emitting at a wavelength of 355 nm. All spectra were measured in positive reflector mode. The instrument was calibrated externally with a polystyrene standard, prior to each measurement. Dithranol served as matrix and was prepared in CHCl 3 at concentration of 20 mg/ml. Silver trifluoroacetate served as cationizing agent and was prepared in MeOH/CHCl 3 (1:3, v/v) at concentrations of 5 mg/ml. The sample was dissolved in CHCl 3 at 5 mg/ml. The matrix and AgTFA were mixed with the ratio of 10:1 (v/v). The sample preparation involved depositing 0.5 μl of matrix and salt mixture on the wells of a 384-well ground-steel plate, allowing the spots to dry, S2

3 depositing 0.5 μl of each sample on a spot of dry matrix, and adding another 0.5 μl of dithranol and salt mixture on top of the dry sample (sandwich method). Data analyses were conducted with Bruker s flexanalysis software. The dynamic light scattering experiments were conducted using a Brookhaven Instrument coupled with a Bi-200SM goniometer, BI-9000AT correlator, and an EMI-9863 photomultiplier tube for photo counting. A Meller Griot 35 mw He-Ne laser was used as light source (632.8 nm). A cylindrical glass scattering cell with diameter of 12 mm was placed at the center of a thermostated bath (±0.01 C) with decahydronaphthalene used for refractive index matching. Correlation functions at 90 o and other angles were recorded at 25 C. The intensity-intensity time-correlation function G (2) (t) of the distributed object in self-beating mode was measured. 3 It is related to the normalized first-order electric field time correlation function g (1) (t). A Laplace inversion program, CONTIN, was applied to analyze g (1) (t) to obtain the hydrodynamic radius, R h,app, as well as its distribution. Bright field images of TEM were recorded in a JEOL-1230 microscope with an accelerating voltage of 120 kv. 3 μl of the micelle solutions were deposited onto copper grids. After ca. 3 min, the excess solution was wicked away by a piece of filter paper. The sample was then allowed to dry under ambient conditions. When needed, negative staining was performed using ca. 1 wt % phosphotungstic acid solution. TEM images were recorded on a digital CCD camera and processed with the accessory digital imaging system. Images of cryo-tem were recorded on a Tecnai 12 microscope operated at 120 kv. A small droplet of the solution (5 10 μl) was placed on a holey carbon film supported on a TEM copper grid within a Vitrobot vitrification system (FEI Inc.). The specimen was blotted and plunged into a liquid ethane reservoir cooled by liquid nitrogen. The vitrified samples were transferred to a Gatan 626 cryoholder and cryo-transfer stage cooled by liquid nitrogen. During the observation of the vitrified samples, the cryoholder temperature was maintained below -170 ºC to prevent sublimation of vitreous water. The images were recorded digitally with a Gatan CCD camera. S3

4 Synthesis of PS-SiH. Chain-end silyl hydride-functionalized polystyrene (PS-SiH) was prepared as previously reported by Quirk et al. 4 Poly(styryl)lithium was prepared under high vacuum conditions in sealed, all-glass reactors using sec-butyllithium as the initiator in benzene (10-15 vol.% monomer) at 30 C. After 12 h, poly(styryl)lithium was terminated with chlorodimethylsilane in benzene at room temperature followed by precipitation into cold methanol and freeze-drying in benzene (yield: 95%). 1 H NMR (CDCl 3, 300 MHz, ppm, ): (br, m, 140H), (br, m, 1H), (br, m, 81H), (m, 6H), -0.2 (m, 6H). Calcd: M n = 3020 Da. 13 C NMR (CDCl 3, 75 MHz, ppm, ): 145.5, 128.0, 126.0, 124.5, 46.0, 45.5, 44.0, 41.0, 32.0, 31.0,30.5, 29.0, 28.0, 26.5, 19.0, 19.5, 11.5, SEC results: M n = 3300 Da, M w /M n = FT-IR (KBr) v (cm -1 ) (given in Figure S3a): 2111 (Si-H). Synthesis of PS-VPOSS. PS-SiH, (2.00 g, 0.71 mmol, M n = 2800 Da), octavinyl POSS (OVPOSS, 2.00 g, 3.16 mmol), and dry toluene (60 ml) were added into a 250 ml flask in dry box. Then, the flask was fitted with a septum and removed from the dry box. To the mixture was added Karstedt s catalyst (0.1 ml). The solution was stirred at 60 C under positive argon pressure for 36 h. The reaction mixture was concentrated and excess OVPOSS was removed by silica gel chromatography using hexane/toluene mixed solvent (v/v = 4/1) as eluent. Further elution with toluene gave the desired product. The product was purified by fractional precipitation from toluene with methanol five times to yield monofunctionalized PS-VPOSS (0.8 g, 34%). 1 H NMR (CDCl 3, 300 MHz, ppm, ): (br, m, 146H), 6.0 (m, 21H), (br, m, 87H), 0.7 (m, 6H), (m, 4H), -0.2 (m, 6H). Calcd: M n = 3760 Da. 13 C NMR (CDCl 3, 75 MHz, ppm, ) 145.3, , 127.6, 125.6, 46.0, 43.8, 40.5, 31.5, 30.0, 29.0, 18.7, 11.06, 4.4, 4.2, SEC results: M n = 3900 Da, M w /M n = FT-IR (KBr) v (cm -1 ) (given in Figure S3b): 1120 (Si-O-Si). Synthesis of PS-APOSS. PS-VPOSS (0.30 g, mmol, M n = 3400 Da), 2,2-dimethoxy-2- phenylacetophenone (DMPA, 1 mg), and mercaptoacetic acid (0.2 ml, 2.9 mmol) were dissolved in 2 ml of THF and exposed to UV (365 nm) irradiation for 0.5 h. The mixture was then precipitated into water three times to remove excess mercaptoacetic acid. The product was collected as a white solid and S4

5 further purified by column chromatography using toluene as the eluent. The desired product was eluted with THF. The fractions were concentrated under reduced pressure and then freeze-dried from a benzene solution (0.16 g, 52%). 1 H NMR (DMSO-d 6, 300 MHz, ppm, ): 12.5 (s, 7H), (br, m, 152H), 3.4 (d, 14H), 2.7 (m, 14H), (br, m, 86H), 1.0 (br, 14H), 0.8 (br, m, 6H), (br, m, 4H),-0.2 (m, 6H). Calcd: M n = 4600 Da. 13 C NMR (DMSO-d 6, 75 MHz, ppm, ): 172 (C=O), 145.5, 128.4, 127.5, 44.4, 43.1, 33.4, 31.5, 31.0, 27.5, 26.3, 19.7, 18.9, 12.4, 11.4, 4.4, SEC results: M n = 5100 Da, M w /M n = FT-IR (KBr) v (cm -1 ) (given in Figure S3c): 1714 (C=O), 1120 (Si-O-Si). Micelle Preparation. The PS-APOSS was first dissolved in a common solvent (1,4-dioxane or DMF) and stirred at room temperature overnight to ensure complete dissolution of the polymer to prepare a stock solution. The solution was then filtered through a filter of 0.22 μm pore size to remove any dust. Deionized water was filtered through a filter of 0.22 μm pore size and added dropwise at a rate of 10 μl/min using a syringe pump into a vial containing 5.00 g of the stock solution. Water addition was continued until a final water content of 50 wt% was reached. Then the micelle solution was dialyzed against deionized water for three days to remove the common solvent and fixed the micellar morphology. Results and Discussion SEC Characterization. SEC result of the crude PS-VPOSS (Figure S1, red line) shows a shoulder with a high molecular weight peak, which indicates that more than one PS chains reacted with POSS cage during the hydrosilylation reaction. Pure mono-functionalized PS-VPOSS was obtained after fractional precipitation from toluene with methanol for five times, as shown in Figure S1 (dark line). The size exclusion chromatography (SEC) overlay of PS-SiH, PS-VPOSS and PS-APOSS clearly shows the sequential progression of the reactions, as illustrated in Figure S2. S5

6 Figure S1. SEC curves of crude PS-VPOSS (red line) and mono functionalized PS-VPOSS (dark line) after fractional precipitation from toluene with methanol for five times. Figure S2. SEC overlay of PS-SiH (dark line), PS-VPOSS (red line), and PS-APOSS (blue line). FT-IR Spectra Analyses. FT-IR spectroscopy is very useful in analyzing the presence of various functional groups. The successful chemical transformations in the synthesis are evident from the FT-IR spectra (Figure S3). Figure S3a shows a strong absorption band at 2111 cm -1, assignable to the Si H stretching vibration mode for PS-SiH. 4 After the hydrosilylation reaction, the FT-IR spectrum of PS- S6

7 VPOSS shows complete disappearance of the Si H stretching band and the appearance of the strong Si O Si vibration band at 1120 cm -1, which is characteristic of the POSS cage (Figure S3b). Figure S3c shows the FT-IR spectrum of PS-APOSS, from which the C=O vibration band at 1714 cm -1 and the -OH vibration band around cm -1 can be clearly observed. Figure S3. FT-IR spectra of (a) PS-SiH, (b) PS-VPOSS, and (c) PS-APOSS. 1 H NMR Analysis. After hydrosilylation reaction, the 1 H NMR spectrum for PS-VPOSS (Figure S4a) exhibits characteristic resonances from vinyl protons (-CH=CH 2 ) bonded to POSS cage at = ppm and from methylene protons (-CH 2 -CH 2 -) bonded between the POSS cage and the PS block at = ppm. The absence of a peak at chemical shift = 3.7 ppm (Si-H) is consistent with the complete functionalization of the chain-end as observed from FT-IR spectrum (Figure S3b). 4 After thiol-ene click reaction, distinct resonances from the sulfur-bonded methylene protons (-CH 2 -S-CH 2 - COOH) can be clearly seen at = 2.7 and 3.4 ppm, respectively. The carboxylic acid proton was also observed at = 12.5 ppm (-COOH). The complete disappearance of the peaks around = ppm attributable to the vinyl protons unambiguously indicates the completeness of the reaction. The peak at 3.30 ppm is due to the hydrogen in residual water. 5 S7

8 Figure S4. 1 H NMR spectra of (a) PS-VPOSS (CDCl 3 ) and (b) PS-APOSS (DMSO-d 6 ). 13 C NMR Analysis. Figure S5a shows the 13 C NMR spectrum of PS-VPOSS, which shows the characteristic peaks for the vinyl carbons attached on the POSS cage are showed at = 136 ppm. After the thiol-ene click reaction, these vinyl carbon peaks disappeared and carbonyl carbon appeared at = ppm (Figure S5b). S8

9 Figure S5. 13 C NMR characterizations of (a) PS-VPOSS (CDCl 3 ) and (b) PS-APOSS (DMSO-d 6 ). Dynamic Light Scattering Analysis for the Micellar Assemblies of PS-APOSS. Please refer to main text for discussions. Figure S6. Angular dependence of the diffusion coefficient D eff plotted against the square of the scattering q for vesicles of PS-APOSS. S9

10 Figure S7. The CONTIN analysis of dynamic light scattering results at scattering angle 90 o for vesicles of PS-APOSS. S10

11 Figure S8. (a) Angular dependence of the diffusion coefficient D eff plotted against the square of the scattering q for spherical micelles of PS-APOSS. (b) The CONTIN analysis of dynamic light scattering results at scattering angle 90 o for spherical micelles of PS-APOSS. References: (1) Quirk, R. P.; Chen, W. C. Makromol. Chem. 1982, 183, (2) Gilman, H.; Cartledge, F. K. J. Organomet. Chem. 1964, 2, (3) Chu, B. Light Scattering; 2 nd ed.; Academic Press: New York, (4) Quirk, R. P.; Kim, H.; Polce, M. J.; Wesdemiotis, C. Macromolecules 2005, 38, (5) Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. J. Org. Chem. 1997, 62, S11