Linked cyclopentadienyl-amido titanium catalysts supported on pyridylethylsilane-modified silica for heterogeneous ethylene homo- and copolymerization

Abstract

Linked cyclopentadienyl-amido titanium dimethyl and dichloro complexes, Ti(η 5:η 1-C 5Me 4SiMe 2N t Bu)X 2 (X=Me, Cl), were reacted with trityl tetrakis(pentafluorophenyl)borate (TB), Ph 3C +[B(C 6F 5) 4] −, and methylaluminoxane (MAO), followed by treatment with toluene suspension of pyridylethylsilane-modified silica, to give two new supported-type titanium catalysts, PySTiTB and PySTiMAO. PySTiTB polymerized ethylene in the presence of triisobutylaluminum (TIBA) in hexane at 60 °C and 5 bar with slightly higher activity than the corresponding homogeneous system under the same conditions. PySTiMAO showed relatively high activity even without any use of alkylaluminum compound. The activity could be improved to reach the value comparable with that of the corresponding homogeneous system, when TIBA and modified MAO (MMAO) were employed as external aluminum compounds. Polyethylenes obtained with PySTiTB were found to have molecular weights ( M w) slightly above 10 6 and narrow molecular weight distributions (MWDs), M w/ M n=1.8–3.0. Polyethylenes obtained with PySTiMAO have M w ranging from 1.5×10 5 to 1.2×10 6 and narrow MWDs when combined with TIBA, but very broad MWDs ( M w/ M n=5.0–13.4), when MMAO was used instead of TIBA. Both new supported titanium catalysts also showed modest activities in random copolymerization of ethylene with 1-octene. The present supported catalysts produced copolymers with lower 1-octene contents compared to the corresponding homogeneous systems. PySTiMAO, when combined with MMAO, gave copolymers with highest 1-octene contents, and the MWDs of the resulting copolymers were found to be in a wide range varying from 3.0 up to as broad as 25.