Polymer alloys composed polylaurolactam (polyamide 12) and segmented polyalurolactam with different content of soft segments are interesting engineering thermoplastic materials having a broad spectrum of properties. The reason for this broad spectrum are the phase structure and the special interactions between the components at the phase boundaries: From scanning electron microscopy and torsion vibration analysis it is to be concluded, that the components are thermodynamically incompatible with one another. High resultion electron microscopy, however, shows that there is a strong interaction between the components at the phase boundaries. The bond between the components is formed by crystalline lamellae which seem to originate from both components: from the hard segments of the segmented polylaurolactam and from the polyamide 12 molecules.