Copolymerization of norbornene with 1-hexene catalyzed by sulfur-containing Schiff base titanium complex and density functional theory analysis

Sulfur-containing salicylaldimine ligand and corresponding titanium complex were synthesized and characterized this work, indicating structural conformity with the design. By using diethylaluminum chloride (EADC) as a cocatalyst, the titanium complex exhibited high activity (∼106 g·mol−1·h−1) in the copolymerization of norbornene (NB) and 1-hexene (1-C6), producing oligomer with a molecular weight of approximately 500. The catalytic copolymerization results were interpreted by combining experimental analysis and density functional theory (DFT). The results indicated that the insertion of norbornene and 1-hexene into Ti catalysts was thermodynamically feasible. Although the reaction barrier for norbornene monomer insertion into the metal active center was lower than that of 1-hexene, the strong steric hindrance between NBE monomer and NBE units in the oligomer chain hindered continuous NBE insertion. By comparing the reaction rates in equimolar systems, the initial insertion step of 1-hexene monomer into the Ti-Et structure was found to be much easier than norbornene insertion, resulting in a lower quantity of norbornene groups in the copolymerization product than 1-hexene groups.