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 C-60 in the presence or absence of benzophenone (BP) as a photoinitiator under different conditions. Photolysis of LDPE/BP/C-60 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 C-13 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/C-60 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 C-60 radical anions; (2) an innermost pair of C-13 satellites; and (3) a 12-line spectrum superimposed on the broad singlet. Spectroscopic simulation allowed the 12-line spectrum to be attributed to the coexistence of two polymeric radical adducts of C-60 (i.e., the tertiary carbon radical adduct, -(CH2)(3)C-C-60., designated as PAC60., and the secondary carbon radical adduct, -(CH2)(2)CH-C-60., designated as PBC60.), which have slightly different g values (g(A) - 2.002 48 and g(B) 3 2.002 44) and integral intensities IA/IB (48.4/51.6). These results clearly indicated the generation of C-60-bonded LDPE materials simply by photoirradiation of LDPE/C-60 with BP as a photoinitiator.