The radical-mediated addition of alkanethiols to the terminal unsaturation of polypropylene (PP) is used to prepare functional polyolefin derivatives without altering the molecular weight of the parent material. The sulfide product of thiol−ene addition, as well as the internal olefin resulting from a remarkable thiyl radical-mediated olefin migration, is characterized using a model hydrocarbon, 2,4-dimethylhept-1-ene. The yield of 3-mercaptopropyltrimethoxysilane (MPTMS) addition to atactic-PP is examined in detail, and the functionalization of high molecular weight isotactic-PP is used to produce moisture-curing resins that bind to siliceous fillers. The limited unsaturation content of PP, along with the high temperatures needed to modify the resin in its melt state, is shown to impact negatively on the reaction conversion due to the reversibility of thiyl radical attack on olefin.