Stereospecific Polymerization of 1,3-Butadiene Catalyzed by [NNO] Cobalt Complexes

A series of cobalt dicholoride complexes (1 similar to 4) bearing [2-(4, 5-diphenylimidazolyl) phenylimino phenol ligands ([N<^>N<^>O] tridentate ligands) have been synthesized and characterized by FTIR spectra and elemental analysis. These cobalt complexes were applied in the stereospecific polymerization of 1, 3-butadiene under various reaction parameters. The type of cocatalyst, AI/Co molar ratio, reaction temperature and ligand structure of cobalt complexes were investigated in order to verify their influences on the catalytic activity and the properties of resulting polymers. Among the Al-based cocatalysts, ethylaluminum sesquichloride (EASC) was proven to be the best cocatalyst, yielding higher conversion of butadiene and cis-1,4 content of polybutadienes. The increase of Al/Co molar ratio enhanced the conversion of butadiene and slightly affected the molecular weight and microstructure of polymers. The catalytic systems displayed good thermal stability in the temperature range of 25 similar to 90 degrees C; however, the higher temperature led to the lower molecular weight and broader molecular weight distribution, and the decrease in the cis-1,4 content and the increase in the trans-1, 4 and 1,2 content. Upon activation with EASC, all the cobalt complexes displayed high catalytic activity for the polymerization of 1,3-butadiene, and high cis-1,4 contents in the resulting polymers were obtained.