Quasi‐living copolymerization of ethylene with 1‐hexene by heteroligated (salicylaldiminato β‐enaminoketonato) titanium complexes

A series of heteroligated (salicylaldiminato)(β-enaminoketonato)titanium complexes [3-But-2-OC6H3CH = N(C6F5)] [PhN = C(R1)CHC(R2)O]TiCl2 [3a: R1 = CF3, R2 = tBu; 3b: R1 = Me, R2 = CF3; 3c: R1 = CF3, R2 = Ph; 3d: R1 = CF3, R2 = C6H4Ph(p); 3e: R1 = CF3, R2 = C6H4Ph(o); 3f: R = CF3, R2 = C6H4Cl(p); 3g: R1 = CF3; R2 = C6H3Cl2(2,5); 3h: R1 = CF3, R2 = C6H4Me(p)] were investigated as catalysts for ethylene (co)polymerization. In the presence of modified methylaluminoxane as a cocatalyst, these complexes showed activities about 50%–1000% and 10%–100% higher than their corresponding bis(β-enaminoketonato) titanium complexes for ethylene homo- and ethylene/1-hexene copolymerization, respectively. They produced high or moderate molecular weight copolymers with 1-hexene incorporations about 10%–200% higher than their homoligated counterpart pentafluorinated FI-Ti complex. Among them, complex 3b displayed the highest activity [2.06 × 106 g/molTi•h], affording copolymers with the highest 1-hexene incorporations of 34.8 mol% under mild conditions. Moreover, catalyst 3h with electron-donating group not only exhibited much higher 1-hexene incorporations (9.0 mol% vs. 3.2 mol%) than pentafluorinated FI-Ti complex but also generated copolymers with similar narrow molecular weight distributions (Mw/Mn = 1.20–1.26). When the 1-hexene concentration in the feed was about 2.0 mol/L and the hexene incorporation of resultant polymer was about 9.0 mol%, a quasi-living copolymerization behavior could be achieved. 1H and 13C NMR spectroscopic analysis of their resulting copolymers demonstrated the possible copolymerization mechanism, which was related with the chain initiation, monomer insertion style, chain transfer and termination during the polymerization process. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2787–2797