Study of Silica‐Supported Chromocene Catalysts for Ethylene Polymerization

Abstract

Ultrahigh molecular weight polyethylene (UHMWPE) has drawn great interest from researchers because it possesses many excellent properties such as superb strength and impact resistance, which other polyolefin cannot achieve. A silica‐supported chromocene catalyst, for the production of UHMWPE, is successfully developed. The polyethylene (PE) produced by the chromocene catalyst can achieve a molecular weight (MW) of over 3 × 106 g mol−1 with narrow molecular weight distribution (MWD) a value of approximately three. The activity calculated by Cr per unit reaches the maximum when the loading of Cr is 1.7 wt%. With the increasing loading of chromocene, the MW shows a small increase and the MWD becomes narrower. The chromocene catalyst for ethylene polymerization also shows a significant hydrogen response. With 0.01 MPa hydrogen added into the ethylene polymerization, the MW of the PE decreases immensely to only 0.7 × 106 g mol−1 and the MWD is broadened from <3 to ≈12. If the amount of hydrogen increases, the MW continues to decrease and the MWD becomes wider. The MW of the PE produced by the chromocene catalyst can be regulated easily by adjusting the amount of hydrogen.

Novel Imido‐Cr/Silica Ethylene Polymerization Catalysts Modified from the Phillips Catalyst

“…It is consistent with the results of other works, that is organic‐chromium catalysts often exhibit an excellent sensitivity to H 2 . [ 28,29 ]…”

“…It is consistent with the results of other works, that is organic-chromium catalysts often exhibit an excellent sensitivity to H 2 . [28,29] The copolymerization behaviors of the three catalysts for C 2 H 4 /1-hexene were investigated as well. It is evident that the activities decrease more when more 1-hexene is added.…”

Evaluation and Control of the Molar Mass Bimodality and Properties of Polyethylene from Novel Chromocene‐Based Dual Sites Catalysts

“…Two novel SiO 2 ‐supported dual sites catalysts, chromocene/chromium oxide dual sites catalyst, and chromocene/vanadium dual sites catalyst, were prepared in previous work. [ 36–38 ] The detail information about the catalysts’ name was listed in Tables 1 [ 36 ] and 2 . [ 37 ] The Cr loading by impregnated in chromium acetate aqueous solution was named Cr (1).…”

“…In our published researches, the characteristics of SiO 2 ‐supported chromocene catalysts had been disclosed that this active center could produce UHMWPE with MW more than 3 × 10 6 g mol −1 , was sensitive to hydrogen, and presented limited ability for ethylene/1‐hexene copolymerization. [ 38 ] In that case, two novel SiO 2 ‐supported chromocene‐based dual sites catalysts were further designed and synthesized: chromocene (S‐9)/chromium oxide (CrO X ) and chromocene (S‐9)/vanadium (V) dual sites catalysts. [ 36,37 ] These catalysts showed high polymerization activity and produced PE with bimodal MWD, including UHMW fraction.…”

Shish‐kebab structure evolution of HDPE/UHMWPE during hot drawing

“…Further stretching results in the reduction of micropores and the rupture of the original lamellae, with the reorganization process of broken lamellae contributing to the growth of highly developed shish‐kebab structures in fiber morphology crystals. Wang 42 studied blends of UHMWPE and HDPE with different melt flow indices (MFI). It was found that during hot drawing, a certain degree of friction occurs between the relatively short molecular chains of HDPE with a higher MFI and the extremely long molecular chains of UHMWPE.…”