By nanoblends, it is meant that the scale of dispersion of one polymer phase in the other is below 100 nm. A novel method was developed to prepare nanostructured blends (nanoblends) of polypropylene (PP) and polyamide-6 (PA-6) directly in a screw extruder. It consisted of polymerizing a monomer of PA-6, E-caprolactam (is an element of-CL), in the matrix of PP. A fraction of the latter bore 3-isopropenyl-,alpha,alpha-dimethylbenzene isocyanate (TMI) which acted as growing centers to initiate PA-6 chain growth. As such, formation of PA-6 and a graft copolymer of PP and PA-6 took place simultaneously in the matrix of the PP, leading to compatibilized PP/PA-6 blends. The size of the particles of the dispersed phase (PA-6) was between 10 and 100 nm, which could not be achieved otherwise by melt blending premade PP and PA-6.