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Long chain branching in ethylene polymerization using constrained geometry metallocene catalyst
Author(s) -
Wang Wenjun,
Yan Dajing,
Charpentier Paul A.,
Zhu Shiping,
Hamielec Archie E.,
Sayer Brian G.
Publication year - 1998
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/(sici)1521-3935(19981101)199:11<2409::aid-macp2409>3.0.co;2-a
Subject(s) - branching (polymer chemistry) , catalysis , ethylene , polymer chemistry , polymerization , chemistry , metallocene , melt flow index , polymer , chain transfer , polyethylene , molar mass distribution , polypropylene , continuous stirred tank reactor , shear thinning , analytical chemistry (journal) , materials science , radical polymerization , organic chemistry , composite material , rheology , copolymer
We report an experimental investigation on long chain branching (LCB) in ethylene polymerization with the Dow Chemical's constrained geometry catalyst system, CGC‐Ti/TPFPB/MMAO, using a continuous stirred‐tank reactor (CSTR) at 140°C, 3.45 × 10 3 kPa, and a mean residence time (τ) of 4 min. The effects of the catalyst (CGC‐Ti) and co‐catalyst (TPFPB and MMAO) concentrations on the catalyst activity, polymer molecular weight, and shear thinning were systematically examined. The boron cocatalyst had a great influence on the CGC activity. Increasing the ratio TPFPB/CGC‐Ti from 0.66 to 5 gave ethylene propagation rates from 1.65 × 10 3 to 1.36 × 10 4 L · mol −1 · s −1 . The addition of MMAO appeared to be essential, most likely acting as an impurity scavenger. The LCB polyethylenes showed enhanced shear thinning properties. The melt flow index ratios I 10 / I 2 were in the range of 6.96 to 23.4, with the I 2 of 0.172 to 0.681 g/10 min. The weight‐average molecular weight M w was correlated to I 2 using a power equation within narrow I 10 / I 2 ranges. The exponential factors were in the range of 4.24 to 6.31. The experimental and calculated M w 's were in a good agreement.