Polymerization ofN‐vinylcarbazole with ziegler‐type catalyst systems

The polymerization ofN‐vinylcarbazole with the TiCl4–Al(i‐Bu)3, TiCl4–AlEt3, TiCl3–Al(i‐Bu)3, and the TiCl4–n‐BuLi systems was studied. It was found thatN‐vinylcarbazole undergoes a very facile cationic polymerization with TiCl4, or TiCl3, and that catalyst complexes which contain a low metal alkyl/transition metal halide ratio promote a very rapid cationic polymerization. When the catalyst components are mixed in the presence of monomer, considerable cationic polymerization due to the transition metal halide alone takes place before the reaction between the titanium halide and metal alkyl is complete. Experiments with catalyst components mixed in the absence of monomer have shown that the rate of the reaction is markedly dependent on the ratio of the catalyst components and that each system studied had a characteristic ratio at which the catalytic activity suffered a marked drop. With TiCl3–Al(i‐Bu)3this drop occurred at an Al/Ti ratio of 0.8, with TiCl4–Al(i‐Bu)3at an Al/Ti ratio of 3, and with TiCl4–n‐BuLi at a Li/Ti ratio of 1.5. This was interpreted as indicating that at these ratios the surface of the titanium halide becomes completely modified by the metal alkyl so that noN‐vinylcarbazole–titanium halide interaction could take place. The per cent reduction of TiCl4to lower valence states was studied with then‐BuLi–TiCl4system as a function of the Li/Ti ratio and it was found that the maximum per cent reduction takes place at a Li/Ti ratio of 2. The per cent reduction rapidly decreased to zero at higher Li/Ti ratios. The polymers ofN‐vinylcarbazole formed with Ziegler‐type catalyst systems were examined by x‐ray diffraction, by their appearance under a polarizing microscope, by infrared spectroscopy, and by nuclear magnetic resonance. These measurements indicated that only amorphous, atactic polymers were formed.