In the present thesis, the effect of interphase modification at nanocomposites of polyamide-imide and complete exfoliated montmorillonite on thermal, mechanical and dielectric properties was investigated. First, the focus was set on how nanocomposites of polyamide-imide and montmorillonite with completely exfoliated states of particles can be achieved. With in situ polymerization, a novel approach towards exfoliated PAI-MMT-nanocomposites was developed and compared to the solvent casting method. The second part of this study focused on the modification of MMT-surfaces with aminosilane in order to provide an amino group which is able to graft MMT covalently to the polymer matrix to enable the grafting reaction via imide ring opening reaction under formation of an amide link. The third part dealt with the question, how this affects the performance of PAI in terms of mechanical, thermomechanical and dielectrical properties via covalently bonded exfoliated PAI-MMT-nanocomposites. In summary it can be said that the interface-modified nanocomposite showed significantly changes with a higher modulus, heat resistance, glass transition temperature and dielectric breakdown strength. Morphological investigations via FIB/SEM-analyses revealed that these effects originate from changes in the internal structure of the nanocomposite. Concluding, a model of the resulting composite-morphology was suggested where single polymer chains are able to crosslink several montmorillonite particles.