Synthesis of ultra-high molecular weight poly(ethylene)-co-(1-hexene) copolymers through high-throughput catalyst screening†
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 kgPE molTi−1 h−1 bar−1) and yielding polyethylenes with significantly decreased molecular weight (Mw) (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.