Half-Titanocenes Bearing Unsymmetric Imidazolin-2-iminato Ligand that Exhibits Efficient Cyclic Olefin Incorporation in Ethylene Copolymerization

Cyclic olefin copolymers (COCs) are promising amorphous materials with high transparency and thermal resistance, and the design of efficient catalysts, which enable the preparation of copolymers with high cyclic olefin contents remains highly desirable. A half-titanocene catalyst containing an unsymmetric imidazolin-2-iminato ligand (L), CpTiCl2(L) [L = 1-N-adamantyl-3-N-mesityl-(CHN)2C=N] (ImAd,MesN), demonstrates superior catalytic activity and more efficient cyclic olefin incorporation than related titanium complex catalysts, such as TiCl3(L), L2TiCl2, and previously reported half-titanocene catalysts bearing symmetric imidazolin-2-iminato ligands in the ethylene (E) copolymerization with norbornene (NBE) and tetracyclododecene (TCD) in the presence of a methylaluminoxane (MAO) cocatalyst. In particular, the catalytic activity of CpTiCl2(L) increases at elevated temperatures (80 °C), affording high molar mass COCs with high glass transition temperatures (Tg = 230–290 °C, TCD content = 45–54 mol %) with uniform compositions, which cannot be achieved by the reported catalysts in the copolymerization.