kaddish after Pirkei Avos

Kaddish Derabonon came from the Sephardic Nusach. Therefore when later it was accepted in Ashkenaz - Nusach Hateffiloh was not changed, and it was accepted to be used only outside of the Teffiloh, and not after Pirkei Ovos and Bameh Madlikin which are said in the middle of the Teffiloh.

Michael FRBSH