Titanium complexes: A possible catalyst for controlled radical polymerization

Pentamethylcyclopentadienyltitanium trichloride, bis(cyclopentadienyl)titanium dichloride (Cp2TiC12), and bis(pentamethylcyclopentadienyl)titanium dichloride were used in the polymerization of styrene without the aid of Group I-111 cocatalysts. The properties of the resulting polymer indicated that polymerization was more controlled than in thermal polymerization. The kinetic studies indicated that a lower level of termination is present and that the polymer chain can be extended by adding an additional monomer. To elucidate the mechanism of polymerization, a series of experiments was performed. All results supported the involvement of a radical mechanism in the polymerization using Cp2TiC12. The possibility of atom transfer radical polymerization (ATRP) mechanism was investigated by isolating the intermediate species. We could confirm the activation step from the reaction of 1-PECI with Cp2TiCl by detecting the coupling product of the generated active radicals. However, the reversible deactivation reaction competes with other side reactions, and it detection was difficult with our model system.