Dear @Giacomo Del Bianco, first MFI (melt viscosity) and brookfield (solution viscosity) both have indications on MW. Also note that MFI is meaningfull only for polyolefins (PE and PP). There are many studies going with this topic. Please have a look at the following similar RG thread and the references therin and the other documents. My Regards
Brookfield viscosity is usually measured for liquid systems (paints, oligomers, solutions) while MFI is usually measured on melts. The two methods are widely different. Complex shear viscosity (rheometry) can be performed for both kinds of systems.