Polymeric Modification of Graphene through Esterification of Graphite Oxide and Poly(vinylahcohol). Experimental procedure Methods.

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1 Polymeric Modification of Graphene through Esterification of Graphite Oxide and Poly(vinylahcohol). Horacio J. Salavagione*, Marián A. Gómez, Gerardo Martínez Experimental procedure Graphite powder, PVA (99+% hydrolyzed, Mw ~ ), N-Ndicyclohexylcarbo-diimide (DCC), 4-dimethylaminopyridine (DMAP, 99%) and thionyl chloride (SOCl 2 ) were purchased from Aldrich. Potassium permanganate (KMnO 4 ), sulphuric acid (H 2 SO 4 ), hydrogen peroxide (H 2 O 2 ), sodium nitrate (NaNO 3 ), methanol (OHCH 3 ), tetrahydrofuran (THF), and hydrazine (N 2 H 4 ) were purchased from Panreac, Spain. Methods. Graphite oxide (GO) was obtained using the Hummer s method. 1 Briefly, 2 g of graphite were mixed with 1 g of NaNO 3 and 50 ml of H 2 SO 4, and the mix cooled down to 0ºC. Then, 6 g KMnO 4 were added slowly maintaining the temperature below 5ºC. The cooling bath was removed and the suspension was maintained by half-an-hour. After that, 100 ml of water was added and the temperature increased to 90 ºC. The mixture was further diluted with 300 ml of water, treated with 50 ml of 5% H 2 O 2, filtered and washed with hot water. The graphite oxide was dried by vacuum obtaining a final mass of 3.2 g. The GO powder was examined by X-ray diffraction (XRD) and FTIR (Figure S1). The graphite oxide obtained by the Hummer s method was partially oxidized in our case (Fig S1a). The XRD pattern shows that the (002) diffraction line of graphite (d-space 0.34 nm at º) diminishes and a new band due to graphite oxide appears (d-space 0.75 nm at º). Although some original graphite remain, GO is highly soluble in water, after ultrasound treatment during 15 min., giving brownish solutions stable for days. The presence of oxygenated groups has been also proved by FTIR. 2 1

2 (A) Intensity / a.u graphite graphite oxide θ 0.8 (B) Intensity / a.u wavenumber / cm -1 graphite oxide graphite Fig S 1: X-ray diffraction patterns (a) and FTIR spectra (b) of graphite and graphite oxide. PVA-functionalization of GO (method 1). The esterification procedure for GO was the following: 40 mg of GO and 0.4 g of PVA (9 mmol equivalent to OH group) were suspended in DMSO (20 ml). The suspension was gently stirred and maintained at 70ºC under nitrogen for 3 days. Then, a solution of N-N-dicyclohexylcarbodiimide (DCC) (1.85 g, 9 mmol) and 4-dimethylaminopyridine (DMAP) (0.135 g, 1.1 mmol) in DMSO (20 ml) were added, and the resulting mixture was stirred at room temperature for 3 days. The coagulation of the polymer nanocomposite was accomplished by adding the suspension into 100 ml of methanol under vigorous stirring. The solid nanocomposite (named as GO-es-PVA) was filtered, washed with methanol and dried at 50ºC under vacuum. In order to eliminate rest of non-reacted GO, the nanocomposites were redissolved in hot water, centrifuged at a high speed (12,000 rpm) and the supernatant dark-colored solution coagulated with methanol. The procedure was repeated twice. 2

3 PVA-functionalization of GO(method 2) 50 mg of these GO were reacted in 20 ml of SOCl 2 (containing 1 ml of DMF) at 70ºC for 24 hours to convert the carboxylic acids into acyl chlorides (acyl chloride-derivative graphite, GOCl). After centrifugation, the supernatant was decanted and the remaining solid was washed with anhydrous THF. After centrifugation, the remaining solid was dried at room temperature under vacuum. A mixture of the resulting GOCl and 1 g of PVA was dispersed in 20 ml of DMSO and stirred vigorously at 50ºC for 65 h. To eliminate the nonreactive GO, we have followed the same protocol that in method 1. Reduction of GO in PVA-functionalized GO 50 mg of GO-es-PVA were dissolved in 20 ml of hot water. The temperature of the solution was left to cool to room temperature and 2 ml of hydrazine were added. The mixture was maintained under magnetic stirring at room temperature during 72 h. Then, the polymer was coagulated in 100 ml of methanol, filtered and washed with abundant methanol. Equipments. The 1 HNMR spectra were recorded at 400 MHz on a Varian Inova 400 spectrometer at room temperature with dimethyl sulfoxide-d 6 (10 wt % solutions) as a solvent. Fourier transform infrared spectra (FTIR) of the nanocomposites in the transmission mode were obtained in KBr pellets using a Perkin-Elmer System 200 spectrometer with a 4 cm -1 resolution. Raman spectra were obtained with a Renishaw invia Raman microscope. The excitation line was provided by a 320 mw diode array laser at 785nm. The laser beam was focused through a 50 x long-working objective (0.75 NA). The diameter of the laser beam spot on the sample surface was 2 µm. The thermogravimetric analysis was done in a TGA Q500 equipment from TA instruments. Samples were dried under dynamic vacuum before the experiments and then placed in a platinum pan. The loss of weight was monitored from room temperature to 950 C using a heating rate of 10 C.min -1 in a nitrogen atmosphere. The crystallization and melting behavior were investigated by DSC using a Mettler TA4000/DSC30. The experiments were carried out in nitrogen atmosphere using ~ 5 mg of sample sealed in aluminium pans. The samples were heated from room temperature to 240 ºC, maintained at this temperature during 5 minutes, then cooled to room temperature and heated again to 240 ºC. The heating and cooling rates were 10 ºC.min -1 in all cases. The transition temperatures were taken as the peak maximum in the calorimetric curves. 3

4 Results Upon the attachment to GO the PVA proton signals become a little wider but maintain similar chemical shifts (Figure S2) GO-es-PVA GOCl-es-PVA PVA δ / ppm Fig S 2: HNMR spectra, in room temperature DMSO-d 6 of PVA, GO-es-PVA and GOCles-PVA. The Raman spectrum for GOCl-es-PVA shows the most of the bands of PVA and D and G bands of GO (Figure S3a). The GO-es-PVA Raman spectrum shows the same bands of GO on top of a broad fluorescent band 3 while the bands of PVA becomes imperceptibles (Figure S3b). It has recently demonstrated that solid GO emits photoluminescence (PL). The formation of GO from graphite generates an electronic band gap for single graphene sheets caused by the disruption of the π network. 3 However, the PL of GO is altered (diminishes) by chemical reduction with hydrazine, which restore π network eliminating of the electronic band gap. 3 Therefore, the the Raman spectrum of RGO-es-PVA is better defined than those obtained for GO-es-PVA. The elimination of the PL could be indicative of effective reduction of PVA-modified GO to PVA-modified graphene. 4

5 A intensity / a.u GOCl-es-PVA PVA λ / cm B Intensity / a.u GO-es-PVA RGO-es-PVA λ / cm Fig S 3: Raman spectra of (A) PVA (black line) and GOCl-es-PVA (green) and (B) GOes-PVA (blue) and RGO-es-PVA (red) at 785 nm exitation The crystalline behavior of PVA is remarkably affected after modification. The table 1 shows the Tg values, where it is clear the remarkable changes on the dynamics of the polymer after esterification. 5

6 Table 1. Tg / ºC PVA 84 GOCl-es-PVA 96 Go-es-PVA 119 The derivative of the TGA curves shows the increase in the rate of maximum degradation for the esterified products. DTGA curves PVA GO-es-PVA GOcl-es-PVA T / ºC Fig S 4. Derivatives of TGA curves for PVA (black line), GO-es-PVA (red) and GOCles-PVA (blue) GO-es-PVA has been reduced as described above. The obtained product (named RGO-es-PVA) had a blackish color, different from the original slightly brown for GOes-PVA (Figure S5). RGO-es-PVA is also water-soluble, giving transparent films as well (Figure S5). 6

7 Fig S 5. Photographies of GO-es-PVA (top left) and GOR-es-PVA (top, right) powders The bottom photography shows transparent films of GO-es-PVA, GOCl-es-PVA and RGO-es-PVA (from left to right). 1 W. S. Hummers, Jr., Offeman, R.E. J. Am. Chem. Soc. 1958, 80, Szabo, T.; Berkesi, O.; Dekany, I. Carbon, 2005, 43, Luo, Z.; Vora, P. M. ; Mele, E.J. ; Johnson, A. T. C. ; Kikkawa, J. M. Appl. Phys. Lett. 2009, 94,