Different approaches for free-radical initiated grafting of functional monomers to polypropylene (PP) have been investigated with a view to enabling crosslinking of the polymer upon subsequent exposure to moisture, resulting in gel contents as high as 50-60 wt%. The first approach involved grafting a co-agent such as triallyl trimellitate (TATM) to the polymer using peroxide initiator to add carbon-carbon double bond functionality to the polymer, followed by peroxide-initiated grafting of mercaptopropyltrimethoxysilane (MPTMS) to the PP-TATM adduct. The second approach was the more traditional peroxide-mediated grafting of vinyltrimethoxysilane (VTMS) to polypropylene, and was most effective at increasing melt state dynamic storage modulus. In the third approach, peroxide-mediated grafting of VTMS was followed by peroxide-initiated grafting of MPTMS. This process took advantage of the unsaturation created via chain scission in the first step to provide graft sites for the MPTMS in the second step. POLYM. ENG. SCI., 51:237-246, 2011. (C) 2010 Society of Plastics Engineers