A novel self-condensable macromonomer that has a polymerizable group at one terminal and an initiator at the other was synthesized by the combination of the conventional macromonomer technique and the SmI2-induced transformation. Namely, living poly(tetrahydrofuran) [poly(THF)] carrying alpha-methacryloyl group was prepared by using methacryloyl chloride and silver trifluoromethanesulfonate. The living chain end was capped with sodium 2-bromoisobutyrate, and the sequential reduction of the terminal C-Br bond with SmI2 gave a terminating samarium enolate. The resulting samarium enolate copolymerized the alpha-methacryloyl group with methyl methacrylate, giving a hyperbranched block copolymer whose dendritic part consists of two kinds of polymer segments.