Synthesis and styrene polymerization properties of dinuclear half-titanocene complexes with xylene linkage

Preparation of new dinuclear half-titanocene complexes with ortho- and meta-xylene linkages and investigation of styrene polymerization

“…This indicates that the stereoregular configuration is induced by a repulsing interaction between the phenyl ring of the last unit of the growing chain and the phenyl ring of the incoming monomer and accounts for the finding that in the case of syndiospecific styrene polymerization, variation of the catalyst ligand sphere has only a minor effect on polymer structure. Many homogenous metallocene catalysts were able to produce SPS with a decrease in syndiotacticity and melting temperature as polymerization temperature increased [7,8,14]. This general trend has also been demonstrated in this experiment.…”

“…To the contrary, Do and coworkers reported that the activity of dinuclear half-titanocene with two phenyl spacers was, in actuality, similar to the mononuclear half-titanocene, demonstrating that the nature of the bridging unit in dinuclear metallocenes exerted a significant influence on determining the characteristics of the catalysts [22]. We have also reported that para-xylene bridged dinuclear half-titanocene exhibited greater activity than the polymethylene bridged, demonstrating the effect of the bridge rigidity on the catalyst [14,15].…”

“…The preparative route to obtain new compounds was different from the synthetic procedure to make the corresponding catalyst with a para-xylene bridge [14]. It was found that biscyclopentadienyls connected through ortho-or meta-xylene 1o and 1m gave rise to the formation of polymeric structure which was difficult to be separated as a stable compound.…”

“…It is not surprising that the presence of a xylene bridge can deliver more electrons to the metal center than the linear pentamethylene bridge [14,15]. Electron density increase to the active site should lead to an increase in activity.…”

“…In fact, the dinuclear metallocene systems display not only the defining characteristics of well-defined mononuclear metallocenes, but also a strong dependence upon the nature of the bridging ligand [12][13][14][15][16][17][18]. The initial attempts to exploit dinuclear half-titanocenes were performed by Royo et al and Flores et al [19][20][21].…”