A chain-straightened poly(cc-olefin) series was prepared via the use of a Ni(II) alpha-diimine catalyst. The resulting polymers are structurally nearly equivalent to ethylene-propylene copolymers with the exception that methyl groups can be evenly spaced along the polymer main chain. The monomers used ranged from ethylene to 1-decene (excluding 1-heptene and 1-nonene). With the exception of 1-decene, the polyolefins prepared have similar plateau moduli, similar to 1.5 MPa at 323 K. This is comparable with values determined over the last 40+ years for copolymers formed using conventional Ziegler-Natta catalysis. Thus, the chain-straightening polymerization systems yield amorphous ethylene-propylene like polymers from single, or mixed, a-olefin monomer feeds. Using this unique type of polymerization allows for the avoidance of ambient temperature gaseous ethylene and propylene while permitting the use of higher molecular weight alpha-olefins that are both abundant and inexpensive.