Tandem Action of SNS-Cr and CGC-Ti in Preparation of Ethylene-1-Hexene Copolymers from Ethylene Feedstock

摘要

Ethylene-1-hexene copolymer materials, ranging from semicrystalline linear low-density poly ethylene (LLDPE) to completely amorphous polyethylenes (PEs), are prepared from ethylene alone in a single reactor by the tandem polymerization of bis(2-dodecylsulfanylethyl) amine-CrCl_3 (SNS-Cr) and (N- tert -butylamido) (tetramethylcyclopentadienyl)-titanium dichloride (CGC-Ti) at 75 °C and under atmospheric pressure. The polymerization activities are on the order of 10 ~5 -10 ~6 g (mol Ti)~(-1) h~(-1). 1-Hexene incorporation in the resulting copolymers can be adjusted by varying the Cr-Ti molar ratio and/or applying a short period of pre-trimerization. Copolymers with high 1-hexene incorporation up to 15 mol% are obtained. Few vinyl and vinylene chain ends are detected by ~(13)C NMR, suggesting that 1-hexene does not act as a chain-transfer agent. Narrow molecular-weight distributions with polydispersities from 1.9 to 2.6 are obtained, characteristic of a single-active-site nature of the catalyst system.