Polyfullerenes, which are polymers of covalently cross-linked fullerene molecules, are a new class of all-carbon polymeric materials in addition to graphite and diamond. The facile preparation of these materials can be accomplished by taking advantage of a unique property of the fullerenes C-60 and C-70, namely that they form clusters in solvent mixtures consisting of fullerene-soluble and fullerene-insoluble components. The formation and properties of C-60 and C-70 clusters in toluene-acetonitrile mixtures are investigated. High molecular weight polyfullerenes are prepared from photochemical reactions of the fullerene clusters in carefully deoxygenated toluene-acetonitrile solutions at room temperature. The polymers are characterized by photon correlation spectroscopy of quasi-elastic light scattering, matrix-assisted laser desorption ionization time-of-flight mass spectroscopy, NMR, FT-IR, and optical spectroscopic methods.