Stimulating question. Although it's not quite in my field....... Following

Rheological properties depend on the molecular mass, mass distribution and architecture of your polymer. The initiation kinetics is different for the two initiators you mention. Since the initiation conditions will affect the molar mass and mass distribution of the polymer you get, this will likewise affect the rheological properties. So determine which molar mass you need for certain rheological properties (from the literature), and then choose the reaction conditions needed to get that polymer (also from literature).

Thanks Dr.Lamia and Dr.Karen