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Dynamic mechanical behavior of supramolecular C60-containing polymeric materials
26 October 2001
Chemical Physics Letters 347 (2001) 344±348 www.elsevier.com/locate/cplett
Dynamic mechanical behavior of supramolecular C60-containing polymeric materials Jianying Ouyang a, Suat Hong Goh a,*, Yi Li b b
a Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore Department of Materials Science, National University of Singapore, 10 Science Drive 4, Singapore 117543, Singapore
Received 16 July 2001
Abstract The dynamic mechanical behavior of materials based on 1,2-dihydro-1,2-methanofullerene[60]-61-carboxylic acid (F-CA), poly(styrene-co-4-vinylpyridine) and poly(styrene-co-butadiene) was studied. The interaction between the carboxylic acid group of F-CA and the pyridine group as evidenced by X-ray photoelectron spectroscopy (XPS) ensures a good adhesion between F-CA and the polymer matrix. The storage modulus of the polymer matrix is signi®cantly increased by the incorporation of F-CA, and F-CA is a more eective reinforcing ®ller than unfunctionalized C60 . Ó 2001 Elsevier Science B.V. All rights reserved.
1. Introduction Since the discovery of [60]fullerene (C60 ) in 1985 [1] and its large-scale synthesis in 1990 [2], much eort has been made to explore its unusual properties [3±8]. There are many potential applications of C60 -containing polymers which combine the characteristic properties of C60 and those of polymers such as elasticity, ®lm formation and processability [9±12]. However, it can be dicult to link C60 covalently onto polymers. Direct mixing of C60 with polymers leads to the formation of big C60 particles dispersed in the polymer matrix [13]. Lu et al. [13] recently reported that a multifunc-
*
Corresponding author. Fax: +65-779-1691. E-mail address: [email protected] (S. Hong Goh).
tional C60 derivative can be dispersed more evenly in polyethylene than C60 does. We have recently prepared several supramolecular C60 -containing polymers [14±16]. C60 is functionalized to contain functional groups which are capable of interacting with complementary functional groups of a polymer. The speci®c interactions between the complementary functional groups enable the C60 derivative to be physically linked to the polymer. The interactions are so strong that when the solutions of the C60 derivative and the polymer are mixed, the supramolecular materials precipitate out from the solvent in which both components are initially soluble. For cases involving two polymers, the precipitates are commonly called interpolymer complexes [17]. Some of the supramolecular C60 -containing polymers possess unusual thermal properties such that they are thermally more stable than their parent polymers
0009-2614/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 9 - 2 6 1 4 ( 0 1 ) 0 1 0 7 3 - 9
J. Ouyang et al. / Chemical Physics Letters 347 (2001) 344±348
and the C60 derivatives. The strong interactions between the functional groups might have delayed the onset of degradation. However, the strong interactions also make these materials behave like highly crosslinked materials, compromising their processability. It is therefore necessary to control the number and intensity of interactions in order to make these materials processable by conventional means such as solution casting and melt blending. We now report the dynamic mechanical behavior of supramolecular C60 -containing polymeric materials based on 1,2-dihydro-1,2-methanofullerene[60]-61-carboxylic acid (F-CA), a monofunctional C60 derivative, and poly(styreneco-4-vinylpyridine) (PSVPy). The use of monofunctional F-CA and copolymer of vinylpyridine eectively reduces the number of interactions, and the resulting materials are processable by solution casting and melt blending. 2. Experimental C60 (99.9% purity) was supplied by Peking University, China. F-CA was synthesized and characterized following the method reported by Issacs et al. [18,19]. Two PSVPy samples containing 20 and 32 mol% of pyridine, denoted as PSVPy20 and PSVPy32, respectively, were prepared by free radical polymerization [20]. Poly(styrene-co-butadiene) with a melt index of 2.8/10 min at 200 °C/5 kg was obtained from Aldrich. F-CA was dissolved in 1,2-dichlorobenzene (0.41 mg/ml) into which an appropriate amount of PSVPy was added. After continued stirring overnight, the solution mixture was added dropwise to petroleum ether. The precipitates were isolated by centrifugation and washed repeatedly with petroleum ether, followed by drying in vacuo at 60 °C for one week. The F-CA content of supramolecular material as determined by thermogravimetric analysis (TGA) agrees well with the feed composition. F-CA has a very limited solubility in common organic solvents and is only slightly soluble in 1,2-dichlorobenzene. However, the supramolecular materials dissolve readily in tetrahydrofuran and chloroform, good solvents for PSVPy. This shows that the attraction between the acid group
345
of F-CA and the pyridine group helps the solubilization of F-CA. Melt blending of materials was made using a Laboratory Mixing Molder (ATLAS, USA) at 210 °C for 30 min at a speed of 120 rpm. The glass transition temperatures (Tg ) of materials were determined with a TA Instruments 2920 dierential scannining calorimeter in nitrogen using a heating rate of 20 °C/min. TGA measurements were made using a TA Instruments SDT2920 simultaneous DTA±TGA in nitrogen using a heating rate of 20 °C/min. Dynamic mechanical analysis was performed using a TA Instruments 2980 dynamic mechanical analyzer in air using a frequency of 1 Hz and a heating rate of 3 °C/min. X-ray photoelectron spectroscopy (XPS) measurements were made on a VG Scienti®c ESCALAB spectrometer using a MgKa X-ray source (1253.6 eV). The X-ray source was run at 12 kV and 10 mA. A pass energy of 20 eV and a rate of 0.05 eV/step were used for all acquisition with a binding energy (BE) width of 12 eV. All spectra were obtained at a take-o angle of 75° and they were curve-®tted with XPSPEAK3.1. All BE values were referenced to the saturated hydrocarbon C1s peak at 285.0 eV. TEM micrographs were obtained with a JEOL CX100 operating at an accelerating voltage of 100 kV. 3. Results and discussion All the F-CA/PSVPy materials show well-de®ned glass transition temperatures (Tg ). Fig. 1 shows the DSC curves of several F-CA/PSVPy20 materials. In contrast, we could not detect the glass transition temperatures of all the supramolecular materials based on multi-functional C60 derivatives [14±16]. The highly `crosslinked' nature of those materials reduces the free volumes signi®cantly and moves the glass transitions beyond the degradation temperatures. The TGA curves (not shown) of the F-CA/PSVPy materials are intermediate to those of F-CA and PSVPy. The behavior is also dierent from that previously observed for materials based on multi-functional C60 derivatives as mentioned earlier.
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J. Ouyang et al. / Chemical Physics Letters 347 (2001) 344±348
Fig. 1. DSC curves of F-CA/PSVPy20 containing (a) 40, (b) 29, (c) 21 and (d) 0 wt% of F-CA.
The TEM micrograph of a C60 /PSVPy32 mixture obtained from its suspension in tetrahydrofuran shows the presence of large agglomerates of C60 (Fig. 2). In contrast, the TEM micrograph of F-CA/PSVPy32 shows a better dispersion of F-CA in the polymer matrix. The presence of interactions in various F-CA/ PSVPy materials is evident from XPS studies. Fig. 3 compares the N1s spectra of PSVPy32 and one F-CA/PSVPy32 material. The N1s spectrum of PSVPy32 features a symmetrical peak centered at 399.3 eV. For the F-CA/PSVPy32 material, a shoulder at the high-BE region is perceptible even though the signals are rather noisy. The high-BE peak is located at 401.4 eV. Our previous studies have shown that when the pyridine nitrogen is protonated by acidic polymers, the BE value of N1s is increased by 2.0 eV or more whereas hydrogen-bonding interaction will increase the BE value by about 1.0 eV [20±22]. Thus XPS shows that F-CA protonates some of the pyridine nitrogen in PSVPy, leading to ionic interaction. The brittleness of PSVPy made it dicult to prepare F-CA/PVSPy samples for DMA measurements. Instead, a mixture of 22 parts of PSVPy20 and 78 parts of poly(styrene-co-butadiene) was used as the matrix. PSVPy20, poly(styrene-co-butadiene) and various amounts of F-CA or C60 were melt blended. The materials were then compressed into ®lms at 135 °C by a hydraulic press. The dynamic mechanical behavior of vari-
Fig. 2. TEM micrographs of (a) C60 /PSVPy32 and (b) F-CA/ PSVPy32.
ous samples was then studied from room temperature to 160 °C. The storage moduli of various materials are shown in Fig. 4. Both C60 and F-CA increase the storage modulus of the matrix, of which F-CA is more eective. For instance, the addition of 4.2 wt% F-CA has nearly the same eect as that of 10.2 wt% of C60 . The increase in storage modulus brought by 10.0 wt% F-CA is twice of that by 10.2 wt% C60 . The properties of polymer composites depend on a number of factors, of which the interfacial adhesion between matrix and ®ller is important. We have already demonstrated the presence of interactions between F-CA and PSVPy. Thus a good dispersion as well
J. Ouyang et al. / Chemical Physics Letters 347 (2001) 344±348
347
Fig. 5. Tan d plot of various materials.
Fig. 3. N1s spectra of (a) PSVPy32 and (b) F-CA/PSVPy32.
Fig. 4. Storage moduli of various materials. From top to bottom: 10.0% F-CA; 6.6% F-CA; 10.2% C60 ; 4.2% F-CA; 5.7% C60 ; 3.4% C60 ; un®lled.
as a strong adhesion with the matrix makes F-CA a better reinforcing ®ller than unfunctionalized C60 . It is also noted that the reinforcing eects of F-CA and C60 diminish at higher temperatures and all materials have nearly the same moduli beyond 120 °C. The inability of F-CA and C60 to sustain the reinforcing eect at temperature higher than
the Tg of the matrix is noteworthy. In comparison, carbon nanotubes show a better ability to impart stiness to polymer matrices at high temperatures as exempli®ed by carbon nanotube/poly(vinyl alcohol) (PVA) [23] and carbon nanotube/poly(methyl methacrylate) (PMMA) composites [24]. Fig. 5 shows the tan d peaks of various materials. Except for a slight change in the high temperature region, the presence of F-CA or C60 has no signi®cant eect on the tan d peak. In contrast, the tan d peaks of nanotube/PMMA composites show some broadening and move to slightly higher temperatures with increasing nanotube content [24]. For nanotube/PVA composites, the tan d peaks broaden signi®cantly upon the addition of carbon nanotubes [23]. In conclusion, we have demonstrated that supramolecular materials based on F-CA and PSVPy can be fabricated by solution casting and melt blending. The interaction between F-CA and PSVPy makes F-CA a more eective reinforcing ®ller than unfunctionalized C60 . This approach can be used to fabricate a variety of supramolecular C60 -containing polymeric materials by varying the nature of the functional groups of C60 derivatives and polymers. Acknowledgements We thank the National University of Singapore for ®nancial support of this work. Assistance by
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J. Ouyang et al. / Chemical Physics Letters 347 (2001) 344±348
Mr. K.H. Wong on XPS and Ms. G.L. Loy on TEM is gratefully acknowledged. References [1] H.W. Kroto, J.R. Heath, S.C. O'Brien, R.F. Curl, R.E. Smalley, Nature 318 (1985) 162. [2] W. Kratschmer, L.D. Lamb, K. Fostiropoulos, D.R. Human, Nature 347 (1990) 354. [3] A. Hirsh, The Chemistry of the Fullerenes, Thieme, Stuttgart, 1994. [4] S. Eguchi, M. Ohno, S. Kojima, N. Koide, A. Yashiro, Y. Shirakawa, H. Ishida, Fullerene Sci. Technol. 4 (1996) 303. [5] S. Eguchi, Fullerene Sci. Technol. 5 (1997) 977. [6] A. Hirsh, J. Phys. Chem. Solids 11 (1997) 1729. [7] D.V. Konarev, R.N. Lyubovskaya, Russ. Chem. Rev. 68 (1999) 19. [8] E.N. Karaulova, E.I. Bagrii, Russ. Chem. Rev. 68 (1999) 889. [9] Y. Chen, Z.E. Huang, R.F. Cai, B.C. Yu, Eur. Polym. J. 34 (1998) 137. [10] L. Dai, J. Macromol. Sci.-Rev. Macromol. Chem. Phys. C 39 (1999) 273. [11] K.E. Geckeler, S. Samal, Polym. Int. 48 (1999) 743.
[12] P.C. Eklund, A.M. Rao (Eds.), Fullerene Polymers and Fullerene Polymer Composites, Springer, Berlin, 2000. [13] Z. Lu, C. He, T.S. Chung, Polymer 42 (2001) 5233. [14] Z.H. Lu, S.H. Goh, S.Y. Lee, Macromol. Chem. Phys. 200 (1999) 1515. [15] S.H. Goh, S.Y. Lee, Z.H. Lu, C.H.A. Huan, Macromol. Chem. Phys. 201 (2000) 1037. [16] X.D. Huang, S.H. Goh, S.Y. Lee, C.H.A. Huan, Macromol. Chem. Phys. 201 (2000) 281. [17] M. Jiang, M. Xiang, H. Zhou, Adv. Polym. Sci. 146 (1999) 121. [18] L. Issacs, A. Wehrsig, F. Diederich, Helv. Chim. Acta 76 (1993) 1231. [19] L. Issacs, F. Diederich, Helv. Chim. Acta 76 (1993) 2454. [20] S.H. Goh, S.Y. Lee, J. Dai, K.L. Tan, Polymer 37 (1996) 5305. [21] X. Zhou, S.H. Goh, S.Y. Lee, K.L. Tan, Appl. Surf. Sci. 126 (1998) 141. [22] X. Zhou, S.H. Goh, S.Y. Lee, K.L. Tan, Polymer 39 (1998) 3631. [23] M.S.P. Shaer, A.H. Windle, Adv. Mater. 11 (1999) 937. [24] Z.X. Jin, K.P. Pramoda, G.Q. Xu, S.H. Goh, Chem. Phys. Lett. 337 (2001) 43.
Chemical Physics Letters 347 (2001) 344±348 www.elsevier.com/locate/cplett
Dynamic mechanical behavior of supramolecular C60-containing polymeric materials Jianying Ouyang a, Suat Hong Goh a,*, Yi Li b b
a Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore Department of Materials Science, National University of Singapore, 10 Science Drive 4, Singapore 117543, Singapore
Received 16 July 2001
Abstract The dynamic mechanical behavior of materials based on 1,2-dihydro-1,2-methanofullerene[60]-61-carboxylic acid (F-CA), poly(styrene-co-4-vinylpyridine) and poly(styrene-co-butadiene) was studied. The interaction between the carboxylic acid group of F-CA and the pyridine group as evidenced by X-ray photoelectron spectroscopy (XPS) ensures a good adhesion between F-CA and the polymer matrix. The storage modulus of the polymer matrix is signi®cantly increased by the incorporation of F-CA, and F-CA is a more eective reinforcing ®ller than unfunctionalized C60 . Ó 2001 Elsevier Science B.V. All rights reserved.
1. Introduction Since the discovery of [60]fullerene (C60 ) in 1985 [1] and its large-scale synthesis in 1990 [2], much eort has been made to explore its unusual properties [3±8]. There are many potential applications of C60 -containing polymers which combine the characteristic properties of C60 and those of polymers such as elasticity, ®lm formation and processability [9±12]. However, it can be dicult to link C60 covalently onto polymers. Direct mixing of C60 with polymers leads to the formation of big C60 particles dispersed in the polymer matrix [13]. Lu et al. [13] recently reported that a multifunc-
*
Corresponding author. Fax: +65-779-1691. E-mail address: [email protected] (S. Hong Goh).
tional C60 derivative can be dispersed more evenly in polyethylene than C60 does. We have recently prepared several supramolecular C60 -containing polymers [14±16]. C60 is functionalized to contain functional groups which are capable of interacting with complementary functional groups of a polymer. The speci®c interactions between the complementary functional groups enable the C60 derivative to be physically linked to the polymer. The interactions are so strong that when the solutions of the C60 derivative and the polymer are mixed, the supramolecular materials precipitate out from the solvent in which both components are initially soluble. For cases involving two polymers, the precipitates are commonly called interpolymer complexes [17]. Some of the supramolecular C60 -containing polymers possess unusual thermal properties such that they are thermally more stable than their parent polymers
0009-2614/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 9 - 2 6 1 4 ( 0 1 ) 0 1 0 7 3 - 9
J. Ouyang et al. / Chemical Physics Letters 347 (2001) 344±348
and the C60 derivatives. The strong interactions between the functional groups might have delayed the onset of degradation. However, the strong interactions also make these materials behave like highly crosslinked materials, compromising their processability. It is therefore necessary to control the number and intensity of interactions in order to make these materials processable by conventional means such as solution casting and melt blending. We now report the dynamic mechanical behavior of supramolecular C60 -containing polymeric materials based on 1,2-dihydro-1,2-methanofullerene[60]-61-carboxylic acid (F-CA), a monofunctional C60 derivative, and poly(styreneco-4-vinylpyridine) (PSVPy). The use of monofunctional F-CA and copolymer of vinylpyridine eectively reduces the number of interactions, and the resulting materials are processable by solution casting and melt blending. 2. Experimental C60 (99.9% purity) was supplied by Peking University, China. F-CA was synthesized and characterized following the method reported by Issacs et al. [18,19]. Two PSVPy samples containing 20 and 32 mol% of pyridine, denoted as PSVPy20 and PSVPy32, respectively, were prepared by free radical polymerization [20]. Poly(styrene-co-butadiene) with a melt index of 2.8/10 min at 200 °C/5 kg was obtained from Aldrich. F-CA was dissolved in 1,2-dichlorobenzene (0.41 mg/ml) into which an appropriate amount of PSVPy was added. After continued stirring overnight, the solution mixture was added dropwise to petroleum ether. The precipitates were isolated by centrifugation and washed repeatedly with petroleum ether, followed by drying in vacuo at 60 °C for one week. The F-CA content of supramolecular material as determined by thermogravimetric analysis (TGA) agrees well with the feed composition. F-CA has a very limited solubility in common organic solvents and is only slightly soluble in 1,2-dichlorobenzene. However, the supramolecular materials dissolve readily in tetrahydrofuran and chloroform, good solvents for PSVPy. This shows that the attraction between the acid group
345
of F-CA and the pyridine group helps the solubilization of F-CA. Melt blending of materials was made using a Laboratory Mixing Molder (ATLAS, USA) at 210 °C for 30 min at a speed of 120 rpm. The glass transition temperatures (Tg ) of materials were determined with a TA Instruments 2920 dierential scannining calorimeter in nitrogen using a heating rate of 20 °C/min. TGA measurements were made using a TA Instruments SDT2920 simultaneous DTA±TGA in nitrogen using a heating rate of 20 °C/min. Dynamic mechanical analysis was performed using a TA Instruments 2980 dynamic mechanical analyzer in air using a frequency of 1 Hz and a heating rate of 3 °C/min. X-ray photoelectron spectroscopy (XPS) measurements were made on a VG Scienti®c ESCALAB spectrometer using a MgKa X-ray source (1253.6 eV). The X-ray source was run at 12 kV and 10 mA. A pass energy of 20 eV and a rate of 0.05 eV/step were used for all acquisition with a binding energy (BE) width of 12 eV. All spectra were obtained at a take-o angle of 75° and they were curve-®tted with XPSPEAK3.1. All BE values were referenced to the saturated hydrocarbon C1s peak at 285.0 eV. TEM micrographs were obtained with a JEOL CX100 operating at an accelerating voltage of 100 kV. 3. Results and discussion All the F-CA/PSVPy materials show well-de®ned glass transition temperatures (Tg ). Fig. 1 shows the DSC curves of several F-CA/PSVPy20 materials. In contrast, we could not detect the glass transition temperatures of all the supramolecular materials based on multi-functional C60 derivatives [14±16]. The highly `crosslinked' nature of those materials reduces the free volumes signi®cantly and moves the glass transitions beyond the degradation temperatures. The TGA curves (not shown) of the F-CA/PSVPy materials are intermediate to those of F-CA and PSVPy. The behavior is also dierent from that previously observed for materials based on multi-functional C60 derivatives as mentioned earlier.
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J. Ouyang et al. / Chemical Physics Letters 347 (2001) 344±348
Fig. 1. DSC curves of F-CA/PSVPy20 containing (a) 40, (b) 29, (c) 21 and (d) 0 wt% of F-CA.
The TEM micrograph of a C60 /PSVPy32 mixture obtained from its suspension in tetrahydrofuran shows the presence of large agglomerates of C60 (Fig. 2). In contrast, the TEM micrograph of F-CA/PSVPy32 shows a better dispersion of F-CA in the polymer matrix. The presence of interactions in various F-CA/ PSVPy materials is evident from XPS studies. Fig. 3 compares the N1s spectra of PSVPy32 and one F-CA/PSVPy32 material. The N1s spectrum of PSVPy32 features a symmetrical peak centered at 399.3 eV. For the F-CA/PSVPy32 material, a shoulder at the high-BE region is perceptible even though the signals are rather noisy. The high-BE peak is located at 401.4 eV. Our previous studies have shown that when the pyridine nitrogen is protonated by acidic polymers, the BE value of N1s is increased by 2.0 eV or more whereas hydrogen-bonding interaction will increase the BE value by about 1.0 eV [20±22]. Thus XPS shows that F-CA protonates some of the pyridine nitrogen in PSVPy, leading to ionic interaction. The brittleness of PSVPy made it dicult to prepare F-CA/PVSPy samples for DMA measurements. Instead, a mixture of 22 parts of PSVPy20 and 78 parts of poly(styrene-co-butadiene) was used as the matrix. PSVPy20, poly(styrene-co-butadiene) and various amounts of F-CA or C60 were melt blended. The materials were then compressed into ®lms at 135 °C by a hydraulic press. The dynamic mechanical behavior of vari-
Fig. 2. TEM micrographs of (a) C60 /PSVPy32 and (b) F-CA/ PSVPy32.
ous samples was then studied from room temperature to 160 °C. The storage moduli of various materials are shown in Fig. 4. Both C60 and F-CA increase the storage modulus of the matrix, of which F-CA is more eective. For instance, the addition of 4.2 wt% F-CA has nearly the same eect as that of 10.2 wt% of C60 . The increase in storage modulus brought by 10.0 wt% F-CA is twice of that by 10.2 wt% C60 . The properties of polymer composites depend on a number of factors, of which the interfacial adhesion between matrix and ®ller is important. We have already demonstrated the presence of interactions between F-CA and PSVPy. Thus a good dispersion as well
J. Ouyang et al. / Chemical Physics Letters 347 (2001) 344±348
347
Fig. 5. Tan d plot of various materials.
Fig. 3. N1s spectra of (a) PSVPy32 and (b) F-CA/PSVPy32.
Fig. 4. Storage moduli of various materials. From top to bottom: 10.0% F-CA; 6.6% F-CA; 10.2% C60 ; 4.2% F-CA; 5.7% C60 ; 3.4% C60 ; un®lled.
as a strong adhesion with the matrix makes F-CA a better reinforcing ®ller than unfunctionalized C60 . It is also noted that the reinforcing eects of F-CA and C60 diminish at higher temperatures and all materials have nearly the same moduli beyond 120 °C. The inability of F-CA and C60 to sustain the reinforcing eect at temperature higher than
the Tg of the matrix is noteworthy. In comparison, carbon nanotubes show a better ability to impart stiness to polymer matrices at high temperatures as exempli®ed by carbon nanotube/poly(vinyl alcohol) (PVA) [23] and carbon nanotube/poly(methyl methacrylate) (PMMA) composites [24]. Fig. 5 shows the tan d peaks of various materials. Except for a slight change in the high temperature region, the presence of F-CA or C60 has no signi®cant eect on the tan d peak. In contrast, the tan d peaks of nanotube/PMMA composites show some broadening and move to slightly higher temperatures with increasing nanotube content [24]. For nanotube/PVA composites, the tan d peaks broaden signi®cantly upon the addition of carbon nanotubes [23]. In conclusion, we have demonstrated that supramolecular materials based on F-CA and PSVPy can be fabricated by solution casting and melt blending. The interaction between F-CA and PSVPy makes F-CA a more eective reinforcing ®ller than unfunctionalized C60 . This approach can be used to fabricate a variety of supramolecular C60 -containing polymeric materials by varying the nature of the functional groups of C60 derivatives and polymers. Acknowledgements We thank the National University of Singapore for ®nancial support of this work. Assistance by
348
J. Ouyang et al. / Chemical Physics Letters 347 (2001) 344±348
Mr. K.H. Wong on XPS and Ms. G.L. Loy on TEM is gratefully acknowledged. References [1] H.W. Kroto, J.R. Heath, S.C. O'Brien, R.F. Curl, R.E. Smalley, Nature 318 (1985) 162. [2] W. Kratschmer, L.D. Lamb, K. Fostiropoulos, D.R. Human, Nature 347 (1990) 354. [3] A. Hirsh, The Chemistry of the Fullerenes, Thieme, Stuttgart, 1994. [4] S. Eguchi, M. Ohno, S. Kojima, N. Koide, A. Yashiro, Y. Shirakawa, H. Ishida, Fullerene Sci. Technol. 4 (1996) 303. [5] S. Eguchi, Fullerene Sci. Technol. 5 (1997) 977. [6] A. Hirsh, J. Phys. Chem. Solids 11 (1997) 1729. [7] D.V. Konarev, R.N. Lyubovskaya, Russ. Chem. Rev. 68 (1999) 19. [8] E.N. Karaulova, E.I. Bagrii, Russ. Chem. Rev. 68 (1999) 889. [9] Y. Chen, Z.E. Huang, R.F. Cai, B.C. Yu, Eur. Polym. J. 34 (1998) 137. [10] L. Dai, J. Macromol. Sci.-Rev. Macromol. Chem. Phys. C 39 (1999) 273. [11] K.E. Geckeler, S. Samal, Polym. Int. 48 (1999) 743.
[12] P.C. Eklund, A.M. Rao (Eds.), Fullerene Polymers and Fullerene Polymer Composites, Springer, Berlin, 2000. [13] Z. Lu, C. He, T.S. Chung, Polymer 42 (2001) 5233. [14] Z.H. Lu, S.H. Goh, S.Y. Lee, Macromol. Chem. Phys. 200 (1999) 1515. [15] S.H. Goh, S.Y. Lee, Z.H. Lu, C.H.A. Huan, Macromol. Chem. Phys. 201 (2000) 1037. [16] X.D. Huang, S.H. Goh, S.Y. Lee, C.H.A. Huan, Macromol. Chem. Phys. 201 (2000) 281. [17] M. Jiang, M. Xiang, H. Zhou, Adv. Polym. Sci. 146 (1999) 121. [18] L. Issacs, A. Wehrsig, F. Diederich, Helv. Chim. Acta 76 (1993) 1231. [19] L. Issacs, F. Diederich, Helv. Chim. Acta 76 (1993) 2454. [20] S.H. Goh, S.Y. Lee, J. Dai, K.L. Tan, Polymer 37 (1996) 5305. [21] X. Zhou, S.H. Goh, S.Y. Lee, K.L. Tan, Appl. Surf. Sci. 126 (1998) 141. [22] X. Zhou, S.H. Goh, S.Y. Lee, K.L. Tan, Polymer 39 (1998) 3631. [23] M.S.P. Shaer, A.H. Windle, Adv. Mater. 11 (1999) 937. [24] Z.X. Jin, K.P. Pramoda, G.Q. Xu, S.H. Goh, Chem. Phys. Lett. 337 (2001) 43.