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Fullerene Derivatives in Poly(methyl methacrylate): An EPR and Zero-Field ODMR Study of Their Photoexcited Triplet States

1996; American Chemical Society; Volume: 100; Issue: 32 Linguagem: Inglês

10.1021/jp960528j

1541-5740

Giancarlo Agostini, Carlo Corvaja, Michele Maggini, Luigi Pasimeni, Maurizio Prato,

Carbon Nanotubes in Composites

Samples of two fullerene derivatives, namely, C60C2H4N(CH3) and C60C2H4N(Ph2C6H4-4-OCH3) in poly(methyl methacrylate) (PMMA), were prepared either by solvent evaporation from CHCl3 solutions or by thermal polymerization of methyl methacrylate monomers containing the fulleropyrrolidines.In the first case PMMA behaves as a neutral polymeric matrix, while in the second the material swells by absorption of the solvent and its glass transition temperature is shifted up by 8 °C with respect to undoped material.Both pieces of evidence are typical of cross-linking between the polymer chains that involves fulleropyrrolidines.EPR and ODMR spectroscopies are applied to the study of the cross-linked species.It is found that its excited triplet state is characterized by unusually large electron dipolar splitting (| D| = 248 × 10-4 cm-1).Calculations of D have been carried out using a model that considers 3C60 and the fullerene derivatives as a collection of fully localized double bonds.The experimental negative sign of D has been reproduced for 3C60, and a positive sign of D is expected for cross-linked fulleropyrrolidine affected by cross-links in the equatorial region.Such a sign reversal can explain the different spin polarization patterns exhibited by their EPR spectra.