A post-reaction modification of polypropylene by which to obtain increased melt strength is by reactive extrusion of randomly functionalized PP with polyfunctional monomers. In this study, reactive melt processing of maleated polypropylene (PP-g-MA) with poly[methylene (phenylene isocyanate)] (PMPI), hexamethylene diamine (HMDA), and poly(propylene glycol)-bis-(2-propylamine) (Jeffamine D-400) was carried out. The resulting chain-extended PP-g-MA was confirmed by FTR analysis. Its thermal and theological properties were also measured. HMDA and D-400 react with both the carboxylic acid and anhydride form of MA. Though PMPI only reacts with the carboxylic acid of MA, PP-g-MA reacted with PMPI has higher gel content and storage modulus compared to PP-g-MA reacted with the amine. This is because of the higher functionality of PMPI and localized reaction between the isocyanate in PMPI and the carboxylic acid in PP-g-MA.