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A critical examination of polyethylene molecular weight distribution control through the combination of soluble metallocene/methylalumoxane catalysts
Author(s) -
D’Agnillo Luigi,
Soares João B. P.,
Penlidis Alexander
Publication year - 1998
Publication title -
polymer international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.592
H-Index - 105
eISSN - 1097-0126
pISSN - 0959-8103
DOI - 10.1002/(sici)1097-0126(199811)47:3<351::aid-pi68>3.0.co;2-d
Subject(s) - metallocene , polymerization , polyethylene , molar mass distribution , polymer , catalysis , materials science , post metallocene catalyst , polymer chemistry , zirconium , chemical engineering , chemistry , organic chemistry , composite material , engineering
The concept of molecular weight distribution (MWD) tailoring using metallocene catalysts is visualized as follows: catalysts which individually produce polymer of narrow MWD but of different average molecular weights can be selectively combined in varying amounts in order to achieve a high degree of control over the final polymer MWD. Although widely lauded, this concept is seldom put to the test in the open literature. We have observed that soluble metallocene/methylalumoxane catalysts individually produce polymer of a very consistent and reproducible MWD, although the rate at which they produce polymer is subject to high variability. In semi‐batch polymerizations, this causes difficulty in controlling both the reaction rate and the MWD of the final product. In this study we present the results of several polymerization experiments combining rac ‐ethylenebis(indenyl)zirconium dichloride with both biscyclopentadienylzirconium dichloride and bisdicyclopentadienyltitanium dichloride. We also present a model in an attempt to predict the final MWD of a polymerization combining two catalysts. By considering the variances of catalyst activity, it is possible to generate a confidence interval around the prediction for a future polymerization. These predictions are compared with the results of actual experiments. It is observed that precise control is hindered by an inability to predict the activity of the catalysts combined in a polymerization. Some means of improving the predictions of MWD are given. © 1998 Society of Chemical Industry