Although polypropylene (PP) grafted by maleic anhydride (MAH) has been successfully commercialized, the grafting mechanism under the existence of a second monomer is not very clear. To simulate the grafting process of MAH onto PP with 1-decene as the second monomer, the MAH/1-decene copolymer and Alder ene reaction product were prepared and grafted onto PP with dicumyl peroxide as the initiator. We found that the grafting of the copolymer and the reactive product greatly improved the grafting degree of MAH. Particularly, the grafting degree with a 3% content of the Alder ene reactive product was 1.89%, which was 178% higher than that of pure MAH-g-PP, the maximum value of which was 0.68%. The molecular weight of the synthesized product affected the grafting efficiency and crystallization behavior of the grafted system. The system grafted with the Alder ene reaction product showed a higher crystallization temperature and crystalline degree. When the molecular weight of the copolymer was higher than 1700, the improvement of the grafting degree could be neglected. For MAH-g-PP with 1-decene as the second monomer, the possible grafting mechanisms were as follows: first, the formation of MAH/1-decene copolymer or the Alder ene reaction product, and second, the grafting of the previously formed product onto PP, in which, the effect of the Alder ene reaction product was more pronounced. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 3724-3732, 2011