The recent observation that the rate of methylation of t-BuCl by Me3Al is several orders faster than that of t-bubr, Which in turn is much faster than that of t-BuI, Provides the basis of a new synthetic method for the preparation of block and bigraft copolymers. This presentation concerns the synthesis and characterization of the first well-defined block and bigraft copolymers produced by the carbenium ion mechanisum i. e., poly(styrene-b-isobutylene), poly[(ethylene-co-propylence)-gStyrence-g-α-methylstyrence)]. The synthesis of the block copolymers involved three key steps: 1)the synthesis of a chlorobrominated alkane initiator, 2) the selective initiation of styrence polymerization by the chlorobrominated alkane in conjunction with alkylayuminum halide under conditions of no chain transfer, and 3)selective initiation of isobutylence polymerization by the polystyrence-Br in conjuction with alkylaluminum halide. Selective solubility, DSC, and GPC data indicate pure block copolymer. The effect of temperatute on the intrinsic viscosity of poly(styrence-b-isobutylence) exhibited peculiarities characterstic of block copolymers. The bigraft was synthesized by chlorobrominating an ethylene-propylene copolymer and selectively initiating first the polymerization os styrence and subsequently that of α-methylstyrence of isobutylene by the chlorobrominated copolymer plus an alkylaluminum compound.