Poly(2-vinylthiophene) (PVT) can be cross linked with FeCl3 either in dichloromethane solution or when immobilized on silica particles. Extend of cross linking is strongly dependent on the FeCI3/PVT ratio used for the reaction as shown by GPC plots and gravimetric analyses of the formed insoluble polymer fraction. A stoichiometric FeCl3/PVT ratio of about four is necessary to achieve complete conversion, because consecutive formations of thiophene H+FeCl4- and bisthiophene H+FeCl4-sigma complexes take place. PVT can be also cross linked when adsorbed on silica using the same procedure. The cross-linking is proved by IR and C-13 CPiMAS NMR spectroscopy.