C2-Symmetric Ni(II) α-Diimines Featuring Cumyl-Derived Ligands: Synthesis of Improved Elastomeric Regioblock Polypropylenes

A series of chiral, nickel alpha-diimine complexes featuring ligands based on bulky cumyl-substituted aniline moieties was synthesized. Each complex was capable of polymerizing propylene upon activation with methylaluminoxane (MAO). The catalysts were shown to be highly regioregular and isoselective for propylene polymerization at low temperature (e.g., -60 degrees C), whereas at higher reaction temperatures (e.g., 0 degrees C) the catalysts furnished regioirregular polypropylene (rirPP) composed of 1,2- and 3,1-enchainments. Many of the catalysts exhibited living behavior for propylene polymerization from -78 to 0 degrees C. From the screening results, the best catalyst was selected and used to produce regioblock polypropylenes featuring three or five blocks. Mechanical testing revealed that the materials exhibited good elastomeric behavior and improved performance at elevated temperatures (e.g., 65 degrees C) over block copolymers synthesized using a previously prepared chiral, nickel a-diimine catalyst.