Search

To understand how the silyl-bridged metallocene catalysts rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2 behave against dienes under the same reaction condition because of its importance as a commercial polymerization catalyst and ethylene propylene diene monomers (EPDM). Adding diene depressed the catalytic activity, especially 5-ethylidene-2-norbornene (ENB) exerted the most substantial deactivation effect. Firstly, we examine the (ENB, vinyl norbornene (VNB) and 4-vinylcyclohexene (VCH)) non-conjugated and conjugated (isoprene (IP), butadiene (BD)) diene and address how polymerization catalysts behave against these dienes. For example, the catalytic activity was enhanced with IP and BD (3–3.3106 gm/mmolMt·h) compared to ENB, VNB and VCH. The VNB incorporation rate was prolonged (5.4 mol%), but with IP and BD, it was relatively moderate. E/P/IP and E/P/BD with higher incorporation of E produced a higher MW, which means that the chain transfer reaction with ethylene is slower than P. Secondly, we address how the dienes exocyclic and exocyclicπ bonds of non-conjugated and conjugated properties of IP and BD affect the kinetic measurements such as active centers [Zr]/[C*] fraction, EPDM chain propagation, termination, and isomerization. Finally, we compare [Zr]/[C*] and kpPE, kpP and kpDienes for different EPDM. After collecting these kinetic parameters, we can describe the mechanism's intricacy and the existence of considerable catalyst dormancy with dienes under identical reaction conditions. [ABSTRACT FROM AUTHOR]

Kinetics of propylene polymerization with two TiCl4/MgCl2 model catalysts of different Ti load (Cat‐1: Ti 0.1 wt%; Cat‐2: Ti 1.0 wt%) was investigated in this work. Time‐dependent variations of active centers fraction ([C*]/[Ti]) and active center distribution of the two catalysts were compared. In propylene polymerization with Cat‐1, [C*]/[Ti] was only 7.8 % in the initial stage, but increased for more than three times in reaction period of 600 s. Propylene polymerization with Cat‐2 had much lower [C*]/[Ti]. Active center distributions of the two catalysts were markedly different. Cat‐1 has evidently higher proportion of aspecific active centers and less isospecific ones than that of Cat‐2. These catalysts also showed different time‐dependent variations of active center distribution. The chain propagation rate constant of isospecific centers in Cat‐2 was evidently higher than that in Cat‐1, but propagation rate constants of either aspecific and medium‐isospecific centers were only slightly changed by enhancing Ti content of the catalyst. The results suggest that isospecific centers are mainly originated from clustered Ti species, but non‐clustered Ti species are the main source of active centers with lower stereoselectivity. By considering factors like dispersion states of Ti species and release of shielded active species through disintegration of catalyst particles, active center models have been proposed to explain the different kinetic behaviors of the two model catalysts. [ABSTRACT FROM AUTHOR]