The core-shell grafting copolymer of alpha-methyl styrene-methyl acrylate on poly(butyl acrylate) was synthesized. The particle morphology of latex and core-shell grafting polymerization was investigated as a function of : (a) reaction temperature; (b) initiator concentration used in the secondary polymerization; (c) monomer to polymer ratio; (d) emulsifier concentration. The compatibility of this copolymer with poly(vinyl chloride) (PVC) was determined by the method of solubility parameter and scanning electron microscopy. The theological behavior of the blend of this copolymer with PVC was investigated. The mechanical properties of the blend were determined. The results show that this copolymer can be used as processing aid for PVC.