The polymerization of C60 by covalent bonding has been studied as a function of pressure and temperature using a new method, in which a rod-shaped sample is heated at one end. After quenching a reaction record is obtained, documenting the results of different reaction conditions along the rod. The results are analyzed using Raman spectroscopy. It is shown that dimers dominate the reaction results over a narrow temperature rane from 0.8 to 1.8 GPa, and that pure polymeric phases are not obtained at any reaction coordinate below 2 GPa and 500 K.