Multiple materials on same object

hi all,

I edited my mesh in C4D and applied 6 Textures to it. They are duplicates with the same content, but different alphamasks. The idea is to change colors of different parts of the texture by script. I exported the model as FBX with materials with embeded textures and materials.

When I do this with different face selections for each texture it works. Unity also imports just one material, but I duplicate it, change it and drag it onto the desired part of the model.

But now I have 6 textures congruent to each other. Dragging won't work. How can I select the different textures of my model? Like I mentioned before, Unity just imports one material.

Thanks :)