Activation of iPr(CpFluo)ZrCl_2 by methylaluminoxane, 3 Kinetic investigation of the syndiospecific hex-1-ene polymerization in hydrocarbon and chlorinated media

摘要

The homopolymerization of hex-1-ene in presence of the iPr(CpFluo)ZrCl_2/MAO system has been investigated in solvents of various polarity and coordinating power (toluene, methylene dichloride and o-dichlorobenzene). Polymerization kinetics were monitored by dilatometry. A strong enhancement of the activity is observed in polar solvents compared to toluene. Besides, the use of polar media enables to reduce drastically the amount of methylaluminoxane (MAO) to reach the plateau of maximum activity. However, unlike the rac-Et(Ind)_2ZrCl_2/MAO system, a rapid deactivation of the active species is observed in the different solvents examined in the case of the iPr(Cpfluo)ZrCl_2/MAO catalyst. Moreover, in CH_2Cl_2, an important loss of the catalyst syndiospecificity, proportional to the monomer concentration, is observed. The possible mechanisms involved are discussed.