Herein, we report a simple strategy to synthesize quasi-block graft copolymers using the binary phase structure of semicrystalline polymers as the template. An unsaturated ionic liquid, 1-vinyl-3-butylimidazolium bis (trifluoromethylsulfonyl) imide ([VBIm] [TFSI]), is thermodynamically miscible with poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-co-HFP)) in solution. The solidification of P(VDF-co-HFP)/[VBIm] [TFSI] blend leads to the expelling of ILs from the crystalline region and the ILs are only located in the amorphous region. The electron-beam irradiation (EBI) at the solid state of the blends results in the locally grafting of the ILs onto the polymer blocks in the amorphous region, while the EBI does not affect the chemical structure of the crystalline region. Therefore, the quasi-block graft copolymers were achieved with IL-grafted blocks segregated by the unmodified blocks. The achieved block copolymers can be microphase separated into the various nanostructures, as the block copolymers with well-defined structure, upon varying the grafting ratios. The microphase separated quasi-block grafted copolymers exhibit excellent mechanical properties and good electrical properties. The elongation at break is 480% and the stress at break is as high as 30 MPa for the sample with the lamellar-like structure having the grafting ratio of 45.4 wt%.