Isoprene polymerizations catalyzed by TiCl4/MgCl2 type Ziegler-Natta catalysts with different titanium contents

The isoprene polymerization kinetics by using TiCl 4 /MgCl 2 type Ziegler-Natta catalysts (TMC) with different titanium contents were studied for better understanding the possible active-specie structures of heterogeneous Ziegler-Natta (Z-N) catalysts for conjugated diene polymerizations. The catalytic features including the catalytic activity (CA), number of active centers ([C*]/[Ti]), rate constant for polymerization (k p ), stereoregularity of these TMC catalysts were studied. The low titanium content catalyst TMC-1 (Ti = 0.09 wt.%) with more isolated mononuclear titanium species showed higher CA and yielded cis-1,4-/trans-1,4- mixed microstructure polyisoprene with low molecular weight ( M w ) in the initial polymerization stage. The medium high titanium content catalyst TMC-2 (Ti = 2.38 wt.%) with more clustered mononuclear titanium species showed lower CA and yielded cis-1,4-/trans-1,4- mixed microstructure polyisoprene with high M w in the early stage of polymerization. The high titanium content catalyst TMC-3 (Ti = 3.76 wt.%) presented lowest CA and yielded high trans-1,4- polyisoprene with higher M w .