The melt grafting of unsaturated silanes onto powdered polypropylene (PP) in a Haake Rheocord RC90 batch mixer and curing in hot water were studied. The influences of grafting formulations and processing conditions on the equilibrium torque during processing and the gel percentage of crosslinked PP were investigated. The gel percentages of methacryloylpropyltrimethoxysilane (VMMS) grafted PP were markedly higher than those of vinyltriethoxysilane (VTES) grafted PP, while significantly less degradation of PP during grafting was observed for VMMS grafted PP. When benzoyl peroxide (BPO) was used as initiator, only a minor degradation of PP during grafting was observed; whereas the use of dicumyl peroxide (DCP) as initiator resulted in severe degradation of PP, especially at high DCP concentrations. Introduction of styrene into the grafting system greatly improved the gel percentage of crosslinked PP and reduced the degradation of PP during grafting. Processing temperature and initial particle size of PP also had influences on both gel percentages and degradation of PP. (C) 2000 Elsevier Science Ltd. All rights reserved.