Photochemical Generation of Polymeric Alkyl-C60 Radicals: ESR Detection and Identification

Abstract

Electron spin resonance (ESR) spectroscopy has been used to study various alkylfullerene radical adducts generated by UV-photoinitiated reactions between low-density polyethylene (LDPE) and C60 in the presence or absence of benzophenone (BP) as a photoinitiator under different conditions. Photolysis of LDPE/BP/C60 mixture in toluene at 323 K produced benzylfullerene (RC60) radical adducts, showing a strong ESR signal of g = 2.002 70 with several well-resolved pairs of 13C satellites. On the other hand, a well-resolved ESR spectrum characteristic of polymeric alkylfullerene (PC60) radical adducts was observed during UV irradiation of the LDPE/BP/C60 in benzene or in the molten state (413 K). Detailed analyses of hyperfine structures (hfs) revealed that the ESR spectrum for PC60 radical adducts consisted of three components: (1) a broad singlet at g = 2.002 50 arising from C60 radical anions; (2) an innermost pair of 13C satellites; and (3) a 12-line spectrum superimposed on the broad singlet. Spectroscopi...