Small-angle neutron scattering (SANS) has been shown to be an appropriate technique for the structural characterization of fullerenes in solvents with strong SANS contrast (e.g., CS2) [Affholter, K. A.; Henderson, S. J.; Wignall, G. D.; Bunick, G. J.; Haufler, R. E.; Compton, R. N. J. Chem. Phys. 1993, 99, 9224]. Since deuterated solvents (e.g., toluene-d(8)) have a high scattering length density (SLD) which is close to that of C-60 and C-70 fullerenes, there is virtually no SANS contrast with the solvent, and these particles are practically "invisible" in such media. On the other hand, the negative scattering length of hydrogen means that the SLD of H-1-containing materials is much lower, so they have a strong contrast with toluene-d(8). Thus, SANS makes it possible to study the sizes and shapes of polymer-substituted fullerenes (flagellenes) [Samulski, E. T.; DeSimone, J. IM.; Hung, M. O., Jr.; Menceloglu, Y. Z.; Jarnagin, R. C.; York, G. A.; Labat, K. B.; Wang, H. Chem. Mater. 1992, 4, 1153]. Mono- and dipolystyrene-substituted C-60 were synthesized via termination of living anionic polymerization of styrene in an optimization of our previous work [Samulski et al.]. These materials were characterized by gel permeation chromatography (GPC) and small-angle neutron scattering(SANS). The extrapolated cross section at zero angle of scatter [d Sigma/d Omega(0)] is a function of the number of pendant chains, so SANS can be used to assess the number of "arms" which are covalently attached to the fullerene "core". Close agreement (+/- 4%) between the measured and calculated values of d Sigma/d Omega(0) and with independent estimates of the radius of gyration (R(g)) and second virial coefficient (A(2)) for a linear polystyrene calibration sample serves as a cross check on the validity of this methodology.