A series of poiyolefins with different ethene/propene ratios was grafted with maleic anhydride (MA) both in the melt and in solution. The MA graft content and the degree of branching/crosslinking or degradation were determined by FT-IR and rheometry, respectively. The MA graft content is low for polyolefins with high propene content, increases as the propene content decreases and reaches a plateau at propene levels below 50 wt.%. Branching/crosslinking occurs for polyolefins with low propene content, while degradation is the main side reaction for polyolefins with a high propene content. A detailed chemical mechanism is proposed to explain these results. (C) 2001 Elsevier Science Ltd. All rights reserved.