Twin-screw extruders have been used as a continuous reactor for reactions, such as polymerization and compatibilization, to take place. In order to achieve a uniform dispersion of the phases, and therefore improved properties in blends, high levels of dispersive and distributive mixing are required. However, the effect of process conditions along the extruder barrel can significantly change the dispersion and distributive state of the melt during its processing especially when it comes to reactive extrusion. Herein a method of evaluation of the kinetic of reactive extrusion along the extruder length is proposed and validated. A device was designed to couple an ATR/MIR probe placed along the extruder and divert a small but representative amount of the melt from the extruder to a cavity where the IR analysis is performed. The device can be attached in different location along the barrel leading to the possibility of following the development of the reaction, as well as the effect of the process condition variation on the reaction kinetic such as temperature, screw speed, profile and feed rate. In a validation exercise, PA6/PP-g-MAH blends were studied; in particular, the variation of the peak area ratio of carbonyl stretching in amide in PA6 at 1640 cm-1 standardized to the area of the peak at 1170 cm-1 relative to PP is used to evaluate the dispersion of the blend. The decrease of the standard deviation (s.d.) of the peak of carbonyl stretching in was used to correlate to the dispersion condition of PA6 in the PP matrix. According to the results, the dispersion of PA6 phase in PP matrix is increased by increasing the temperature, the feed rate and the screw speed. A remarkable trend of decrease of the s.d. was seen right after all the studied mixing zones and it was more pronounced when extensional flow imposed mixing zones were used. These results validate the use of this technique as a means of tracing in real time the kinetics during extrusion of complex systems.