Block copolymers of methyl methacrylate (MMA) and poly(diethylene glycol Phthatic Anhydride) (PPAG) was synthesized using a novel redox system-potassium diperiodatonickelate(IV) [DPN]/PPAG system in an alkaline medium. Block copolymers with high percentage of blocking were obtained, which indicated that DPN/ PPAG redox system was an efficient initiator for this blocking. Effects of different factors on the blocking parameters were examined. The overall activation energy of this blocking was calculated to be 55.12 kJ/mol. The structure of the block copolymer was determined by infrared, X-ray diffraction, and scanning electron microscope (SEM). A mechanism is proposed to explain the generation of radicals and the initiation of block copolymerization. The block copolymer was used as the compatibilizer in blends of PMMA and Nylon6. The SEM photographs show that the block copolymer greatly improved the compatibility of the blend.