A strategy for high ethylene polymerization performance using titanium single-site catalysts

Abstract

The synthesis of heterogeneous Ti(IV)-based catalysts for ethylene polymerization following surface organometallic chemistry concepts is described. The unique feature of this catalyst arises from the silica support, KCC-1₇₀₀. It has (i) a 3D fibrous morphology that is essential to improve the diffusion of the reactants, and (ii) an aluminum-bound hydroxyl group, [(Si–O–Si)(Si–O–)₂Al–OH] 2, used as an anchoring site. The [(Si–O–Si)(Si–O–)(Al–O–)TiNp₃] 3 catalyst was obtained by reacting 2 with a tetrakis-(neopentyl) titanium TiNp₄. The structure of 3 was fully characterized by FT-IR, advanced solid-state NMR spectroscopy [¹H, ¹³C], elemental and gas-phase analysis (ICP-OES and CHNS analysis), and XPS. The benefits of combining these morphological (3D structure) and electronic properties of the support (aluminum plus titanium) were evidenced in ethylene polymerization. The results show a remarkable enhancement in the catalytic performance with the formation of HDPE. Notably, the resulting HDPE displays a molecular weight of 3 200 000 g mol⁻¹ associated with a polydispersity index (PD) of 2.3. Moreover, the effect of the mesostructure (2D vs. 3D) was demonstrated in the catalytic activity for ethylene polymerization.