Abstract A series of novel compatibilizers with different length of oligocaprolactone branch chains, which are capped with one, two or three carboxyl groups at one of these branch chains’ extremities, were synthesized by a three-step approach involving: (1) the oligomerization of ϵ-caprolactone initiated by various of hydroxy acids (glycollic acid, dl-malic acid, or citric acid); (2) the reaction of acryloyl chloride with α-hydroxyl-ω-carboxyl (1,2,3)-oligocaprolactone (HCPCL); and (3) the graft copolymerization of α-acryloyl-ω-carboxyl (1,2,3)-oligocaprolactone (ACPCL) with polypropylene. Effects of various parameters such as monomer ACPCL and initiator benzoyl peroxide concentration, reaction time, and ACPCL kinds on the grafting percentage of ACPCL onto polypropylene (PP) in xylene solution were studied. The grafting of ACPCL onto PP in a laboratorial single screw extruder was also investigated. The maximum extents of grafting achieved in solution and melt were about 10.2 and 12.3%, respectively. The intermediate products, HCPCL and ACPCL were characterized by acid–base titration, hydroxyl value titration, Fourier transform infrared spectroscopy (FTIR), 1H- and 13C-nuclear magnetic resonance analyses, respectively. The grafting copolymers were also characterized by electrometric titration, FTIR analysis, and differential scanning calorimetric, respectively.