The high reactivity of 1-phthalimido-1,3-butadiene for either homopolymerization or copolymerization was applied to prepare a graft copolymer with isotactic polypropylene using a roll mill. Five reaction systems containing the monomer 0, 1, 3, 5 and 10% in polypropylene were allowed to react at 175°C. under atmospheric pressure for 10 min. to give the graft copolymers. The resulting resin, tough and rigid, was melt-spun to give a single filament. This filament was extracted with 1,2-dichloroethane to remove the remaining monomer and homopolymer. The percentage of the grafted monomer against the feed was determined by ultraviolet spectroscopy. This modified method did not result in gel formation or decreased viscosity. Accordingly, spinning could be easily carried out. After fivefold stretching of the filament in hot water of 95°C., the tensile strength was almost identical to that of a sample obtained from the original polypropylene. However, a considerable decrease in elongation was observed. The filament can be dyed uniformly with some basic dyes at a rate proportional to the imidobutadiene contents. After hydrazinolysis, the filament acts as an anion-exchange fiber and imbibes acid dyes homogeneously throughout.