Activating agents for hafnium-based metallocene components

A metallocene catalyst system comprising:

• (a) a hafnium-based metallocene catalyst component described by formula I
• R″(CpR4)(FluR′8)Hf Q2 (I)
• wherein Cp is a cyclopentadienyl ring;
• Flu is a fluorenyl ring;
• each R is the same or different and is hydrogen or a hydrocarbyl radical containing from 1 to 20 carbon atoms;
• each R′ is the same or different and is hydrogen or a hydrocarbyl radical containing from 1 to 20 carbon atoms;
• R″ is a structural bridge between two Cp rings;
• Q is a hydrocarbyl radical having from 1 to 20 carbon atoms, a hydrocarboxy radical having from 1 to 20 carbon atoms or a halogen and can be the same or different from each other;
• and
• (b) an activating agent having a low or no co-ordinating capability comprising an aluminoxane and a Lewis base, wherein the activating agent comprises a ratio of Lewis base to total aluminum of from 0.5:1 to 0.9:1.