Bis(polyethylenyl)magnesium prepared by Nd/Mg mediated polyethylene chain growth catalysis has been successfully used as cocatalyst in combination with Nd-(BH4)(3)(THF)(3) to afford unprecedented sequenced (polyethylene)-b-(trans-polyisoprene) copolymers. Size exclusion chromatography, differential scanning calorimetry, and NMR, as well as gas chromatography and MALDI-TOF spectrometry of oligomers, are utilized to establish the grafting of the stereoregular polydiene sequence to the polyethylene fragment.