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Kinetics and Mechanism Comparison between Cr/Ti‐Based Bimetallic and Ti‐Based Monometallic Catalysts for Ethylene Polymerization
Author(s) -
Zhou Yi,
He Xuelian,
Liu Boping
Publication year - 2021
Publication title -
macromolecular reaction engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.37
H-Index - 32
eISSN - 1862-8338
pISSN - 1862-832X
DOI - 10.1002/mren.202000041
Subject(s) - bimetallic strip , crystallinity , differential scanning calorimetry , polymerization , materials science , kinetics , alkyl , catalysis , polymer chemistry , polymer , polyethylene , nuclear chemistry , adduct , chemistry , organic chemistry , composite material , physics , quantum mechanics , thermodynamics
Two (SiO 2 /MgR 2 /MgCl 2 )·TiCl x model catalysts are made by refluxing TiCl 4 with 0.35 wt% Cr modified silica gel/alkyl Mg adducts or silica gel/alkyl Mg adducts, which are named as Cr/Ti‐based bimetallic Cat‐1 and Ti‐based monometallic Cat‐2, respectively. The kinetics, active center counting, morphology, and polymer characterizations are studied to disclose the effect of low loading Cr active sites on the Cr/Ti‐based bimetallic Cat‐1 polymerization under mild conditions. The activity of Cat‐1 is 120.4% higher than that of Cat‐2, with a 114.1% higher [ C *]/[ M ] value. Morphology results show the Cat‐1 fragmentation in the first 3 min is highly accelerated, which helps to release buried clustered Ti sites. Differential scanning calorimetry results show that low‐temperature heat absorbing shoulder of polyethylene (PE) from Cat‐2 demonstrates the signal of low crystallinity polymer made by Cat‐2 during the first 60 s, verifying the fluffy polymer in morphology results. GPC results show PE from Cat‐1 has a higher M w in the first 3 min while a lower M w in the end. The Cat‐1, which release active sites faster, has a high M w in the early time. Lower M w in the 900 s attributes to the effect of relative lower M w polymer made by Cr sites, compared with Cat‐2.