Poly(α-methylstyrene-b-isobutyl vinyl ether-b-α-methylstyrene) triblock polymers have been prepared by blocking α-methyl-styrene (αMeSt) from biheaded quasiliving poly(isobuty1 vinyl ether) (PIBVE) cations generated with the bifunctional p-dicumyl chloride/AgSbF6initiating system in methylene chloride solvent at -90°C. The products were fractionated with 2-propanol, a good solvent for PIBVE and a nonsolvent for PaMeSt. The 2-propanol-insoluble fractions had much higher molecular weights (Mn= 30,500–69,100) than the starting PIBVE (Mn=6,600–10,600) and contained 13–29 wt% IBVE together with 87–71 wt% αMeSt units. The 2-propanol-soluble fractions (Mn= 7,300–11,600) contained ∼90 wt% IBVE and ∼10 wt% αMeSt units.