A continuous process for incorporating a thermally sensitive additive into a polymer melt of virgin polymer at a temperature at least 10.degree. C. below a temperature at which the virgin polymer is typically processed. The virgin polymer is first processed in an apparatus which extensively shear-thins the polymer until its normally entangled molecules are substantially disentangled. This is preferably done in a TekFlow.RTM. processor. The additive is then added to the resulting modified melt which is then processed in a high-shear apparatus, e.g. a co-rotating, twin-screw extruder, but more preferably in a second TekFlow.RTM. processor. This novel process allows making concentrates having a level of additive which could not be made to date and yet have the additive substantially uniformly dispersed. In particular a concentrate of polypropylene having a 30% by wt concentration of an organoclay in which the platelets are substantially uniformly dispersed, at least 10% more strongly intercalated than prior to treatment, and substantially fully exfoliated, is made with this process.