This paper describes the first examples of ABA- and AB-type block copolymerizations of a nonpolar monomer, in this case ethylene, with polar monomers, such as methyl methacrylate (MMA), epsilon -caprolactone (CL), and 2,2-dimethyltrimethylene carbonate (DTC), initiated by the unique catalytic function of rare earth metal complexes [Sm(II) and Ln(III) (Ln = Y, Sm)] as initiators. The Sm(II) species conducts the ABA-type triblock copolymerization, leading to poly(MMA-co-ethylene-co-MMA), poly(CL-co-ethylene-co-CL), or poly(DTC-co-ethylene-co-DTC) by the efficient catalysis ofracemic Me2Si(C5H2-2-Me3Si-4-tBu)(2)Sm(THF)(2) (1) or meso Me2Si(Me2SiOSiMe2)(C5H2-3-tBu)Sm(THF) (2b). The resulting block copolymers are completely insoluble in THF and CHCl3, but the homopolymers of MMA, CL, and DTC are freely soluble in these solvents. TEM profiles provide direct evidence for the block copolymerizations, where the spheric morphology of homogeneously dispersed polar polymers was observed. Ln(III) species, such as racemic Me2Si(C5H2-2Me(3)Si-4-tBuMe(2)Si)YH (5) and Me2Si(C5H2-2-Me3Si-4-tBu)SmH (6), afford AB-type block copolymers between ethylene and MMA or CL, whose TEM images reveal the homogeneous dispersion of poly(MMA) or poly(CL) units in the polyethylene region. The ABA- and AB-type block copolymers demonstrate high break stress and high tensile modulus as compared with their corresponding blended polymers.