High-mileage initiator

Literature values of the active-site concentrations range from tenths or hundredths of a percent to tens of percents of the transition metal concentration [Lieberman and Barbe, 1988 Tait and Watkins, 1989]. Much of this is indicative of the range of activity of different initiators, especially when comparing older initiators to the recent high-mileage initiators. However, some of the variation is due to the problems inherent in measurement of [C ]. Literature values of kp and other rate constants also show a considerable range. 

The high-mileage supported initiators previously mentioned involve a species similar to XX as part of a mixed titanium-magnesium-chloride lattice, usually involving Mg—Cl—Ti bonds. Ti and Mg are interchangeable within the metal lattice. 

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