Comments on the Analysis of Copolymers of C 60 with Vinyl Monomers Obtained by Free Radical Polymerization Padma L. Nayak, † Shridhara Alva, ‡ Ke Yang, ‡ Pradeep K. Dhal, † Jayant Kumar, † and Sukant K. Tripathy* ,† Departments of Chemistry and Physics, Center for Advanced Materials, University of Massachusetts at Lowell, Lowell, Massachusetts 01854 Received March 7, 1997 Revised Manuscript Received September 18, 1997 Design and synthesis of fullerene-containing polymers have been receiving increasing interest. This approach would potentially enable better processing of fullerene- based materials, which is important from the standpoint of certain practical applications. 1 Direct copolymeriza- tion of fullerene with vinyl monomers is an attractive approach to synthesize polymeric fullerene derivatives. Recently, three research groups have reported the copolymerization of C 60 with vinyl monomers such as styrene and methyl methacrylate. 2-4 It was reported that C 60 acts like a vinyl comonomer and gets incorpo- rated into the polymer backbone through free radical initiated chain reaction involving C-C bond formation. Different spectroscopic and molecular mass determina- tion techniques were utilized to characterize these copolymers and establish incorporation of C 60 moieties in the polymer chain. Particularly, Sun et al. 2 and Cao and Webber 3 have pursued a detailed study of the copolymers of C 60 with styrene using, among other techniques, UV-vis and fluorescence spectroscopy. Synthesis of novel organic materials exhibiting in- teresting optical and electronic properties is an ongoing research activity in our laboratory. 5 Unique electronic and optical properties exhibited by fullerene derivatives has prompted us to synthesize fullerene-containing functional vinyl polymers. For example, we have copo- lymerized C 60 with 4-vinylbenzoic acid (VBA) and 2- and 4-vinylpyridine to prepare C 60 -based polyelectrolytes that can be processed from an aqueous medium. Spec- troscopic techniques have been employed to characterize and investigate optical properties of these functional copolymers, and their interesting polyelectrolyte behav- iors have been investigated. 6 Syntheses of these copolymers were carried out by free radical polymerization by following the reported literature procedures. 2-4 In a typical polymerization experiment, appropriate amounts of VBA, C 60 , and 2,2′- azobis(isobutyronitrile) (AIBN) were dissolved in o- dichlorobenzene, and the solutions were bubbled with argon for 30 min. Subsequently, the polymerization mixtures were heated to 70 °C and stirred at this temperature for 24 h under a positive pressure of argon. Formation of polymer was evident from its precipitation from the reaction medium. After 24 h, the reaction mixture was cooled to room temperature. After the solvent was decanted, the residue was dissolved in methanol, and the solution was filtered and precipitated into excess diethyl ether. The process was repeated three times. Finally, the polymer was dissolved in 0.1 M aqueous NaOH solution, and the solution was filtered through a filter paper and acidified with dilute HCl to pH 2.0 to precipitate the polymer. It was filtered off, washed with distilled water, and dried in a vacuum oven at 50 °C to constant weight. Compositions of the polymerization recipe to prepare different copolymers of varying compositions are summarized in Table 1. Synthesis and workup of styrene-C 60 copolymers was carried out in an analogous manner by following the literature procedure. 2b The UV-vis “spectra” of one of these copolymers (10 wt % C 60 , Table 1, entry 4) as well as one of the earlier reported styrene-C 60 copolymers (5 wt % C 60 ) are presented in Figure 1. These spectra, in general, appear to be anomalous. The solution UV spectrum of pure C 60 is well resolved, exhibiting three absorption peaks at 340, 250, and 210 nm. 3a On the other hand, the spectra of the copolymers under discussion are featureless. The structureless curves tailing beyond 500 nm appear to have an inverse high-power type (∼1/λ 4 ) wavelength dependence. The UV-vis spectra were recorded on a Perkin-Elmer Lambda-9 instrument in our laboratory from visually clear solutions. The UV-vis spectra of C 60 -VBA copolymers synthesized in our laboratory and those of C 60 -styrene copolymers reported by these researchers are very similar. The published reports have ascribed the disappearance of the characteristic peaks of C 60 upon copolymerization to incorporation of substituents onto C 60 molecules as a result of polymer- † Department of Chemistry. ‡ Department of Physics. Table 1. Syntheses of Copolymers of C60 with 4-Vinylbenzoic Acid (VBA) of Varying Compositions a various components in polymerization mixture entry VBA (g) C60 (mg) AIBN (mg) polymer yield (wt %) b 1 5 50 75 2 2.45 24.5 50 60 3 2.50 125 50 70 4 2.55 255 50 75 5 2.45 25 143 65 6 2.50 125 285 70 a Polymerization reactions were carried out at 70 °C as a 10% solution of the monomers in o-dichlorobenzene. b Based on the weights of the purified polymers. Figure 1. UV-vis absorption spectra of (a) 10 wt % C60- VBA copolymer in methanol and (b) 5 wt % C60-styrene copolymer in chloroform. The solution concentration for both polymers is 0.05 mg/mL. 7351 Macromolecules 1997, 30, 7351-7354 S0024-9297(97)00318-5 CCC: $14.00 © 1997 American Chemical Society