This paper concerns the rate of the activated anionic polymerisation of epsilon-caprolactam (CL) onto 3-isopropenyl-alpha,alpha-dimethylbenzyl isocyanate bearing PP (PP-g-TMI) in the melt to form a graft copolymer with PP as backbone and PA6 as grafts. The polymerisation was catalysed by sodium F-caprolactam, (NaCL). The PP-g-TMI/NaCL/CL polymerisation system being heterogeneous, the polymerisation was carried out in a batch mixer. Emphasis was placed on the effects of temperature and the concentrations of NaCL and the isocyanate group in the form of PP-g-TMI on the polymerisation rate. Results suggested that if the polymerisation is to be carried out by a reactive extrusion process whose mean residence time is less than a few minutes, it is recommended that the polymerisation temperature be higher than 220 degrees C. Moreover, the molar ratio between NaCL and CL should be higher than 0.5 and at the same time that between the isocyanate group in the form of PP-g-TMI and NaCL, should be smaller than 4. (c) 2005 Elsevier Ltd. All rights reserved.