a process for making a thermoplastic molding composition comprising forming a vertically falling stream of molten polymer , and bringing at least one additive in solid or liquid states , in solution , in the form of a dispersion or in suspension into contact with at least a part of the surface of said stream and to introduce the additive in said stream to produce combined stream , and introducing the combined stream into a pump to form a pre - mix and introducing the premix into a mixer to form a homogeneous polymer melt . the entraining stream is then introduced to a pump to form a pre - mix which is then introduced to a mixer to form a homogeneous polymer melt . the process results in a compositions having advantageous material properties .