Free radical grafting of vinyltrimethoxysilane (VTMS) onto isotatic polypropylene (PP) in vapour phase was studied. The effects of VTMS monomer and initiator concentration on the grafting degree, molecular weight and gel content of the silane modified samples were investigated. The influence of the second monomer, i.e. styrene (St) and maleic anhydride (MAH), and interfacial agent (toluene) was also investigated. Moreover, the silane grafting reaction was characterized by FTIR, and the thermal stability of the silane crosslinked samples was studied by a thermogravimetric (TG) method. (c) 2005 Elsevier B.V. All rights reserved.