Prospects for the Use of Al/Mg Cocatalysts (AlknAlCl3–n + Alk2Mg) in the Polymerization of Olefins. Studies of the Interactions between the Activator Components

Abstract

Based on previously accumulated experimental material on the use of {nEt₂AlCl + Bu₂Mg} mixtures for the activation of Ti postmetallocene precatalysts for ethylene polymerization, an attempt is made to find the reason for the universal activating ability of such cocatalysts by analyzing the chemical processes occurring during the interaction of alkylaluminum chlorides and dibutylmagnesium. ¹H and ²⁷Al NMR spectroscopy data indicate that in nonsolvating media the formation of ionic products (with which earlier the unique activating ability of Al/Mg activators was associated) does not occur. The “true” Al/Mg cocatalysts are uncharged adducts of MgCl₂ with alkylaluminum chlorides and/or trialkylaluminum. It was shown that all used Al/Mg cocatalyst compositions are capable of activating a model titanium dichloride complex with a saligenin ligand with varying efficiencies. The product of the ethylene polymerization is an ultrahigh molecular weight polymer (M_v from 1.1 to 5.1 × 10⁶ Da); the latter is evidenced by the possibility of solid-phase processing of nascent polymer powders into high-strength, high-modulus tapes (breaking strength up to 2.4 GPa and elastic modulus up to 112 GPa).