Polypropylene (PP) functionalization with vinyltriethoxysilane (VTES) was accomplished via a free radical process in a melt-mixer chamber, using dicumyl peroxide as the initiator. Fourier-Transform Infrared Spectroscopy (FTIR), Rutherford Back scattering Spectrometry (RBS), and gel permeation chromatography (GPC) were used to follow silane incorporation and product molecular weights. The influence of silane (0-10.0 wt %) and peroxide (0-1.0 wt %) concentrations on the functionalization degree and molecular weight of products was investigated. Chain-breaking reactions were present in all experiments, evidenced by smaller product molecular weights. This decrease was more pronounced for higher peroxide concentrations. Silane incorporation occurred even in peroxide absence, and it was seen to increase with increasing silane concentration.