Synthesis of ultra-high molecular weight poly(ethylene)-co-(1-hexene) copolymers through high-throughput catalyst screening

Abstract

A family of permethylindenyl titanium constrained geometry complexes, Me₂SB(^R′N,^3-RI*)TiX₂ ((3-R-η⁵-C₉Me₅)Me₂Si(^R′TiX₂)), supported on solid polymethylaluminoxane (sMAO) are investigated as slurry-phase catalysts for ethylene/H₂ homopolymerisation and ethylene/1-hexene copolymerisation by high-throughput catalyst screening. Me₂SB(^tBuN,I*)TiCl₂ supported on sMAO [sMAO-Me₂SB(^tBuN,I*)TiCl₂] is responsive to small quantities of H₂ (<1.6%), maintaining high polymerisation activities (up to 4900 kg_PE mol_Ti⁻¹ h⁻¹ bar⁻¹) and yielding polyethylenes with significantly decreased molecular weight (M_w) (from 2700 to 41 kDa with 1.6% H₂). In slurry-phase ethylene/1-hexene copolymerisation studies, a decrease in polymerisation activity and polymer molecular weights compared to ethylene homopolymerisation is observed. Compared to many solid supported system, these complexes all display high 1-hexene incorporation levels up to a maximum incorporation of 14.2 mol% for sMAO-Me₂SB(^iPrN,I*)TiCl₂). We observe a proportionate increase in 1-hexene incorporation with concentration, highlighting the ability of these catalysts to controllably tune the amount of 1-hexene incorporated into the polymer chain to produce linear low-density polyethylene (LLDPE) materials.