The invention concerns a metallocene catalyst composition for preparing linear
isotactic polymers, wherein said catalyst composition contains a metal complex
and an activator. The invention also concerns a process for preparing linear, isotactic
polymers which have a structure of which the tacticity varies within the range
of between 25 and 60 % of [mmmm] pentad concentration, an arbitrary or rather regular
sequence of isotactic and atactic blocks being excluded, in which process a C2
to C20 olefin is reacted with the catalyst composition.
