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On the polymerization mechanism of the Chromium(III) and Chromium(II)‐B Silica Gel Catalysts
Author(s) -
Rebenstorf B.
Publication year - 1989
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.19895710116
Subject(s) - chromium , silanol , polymerization , catalysis , chemistry , polymer , methylene , polymer chemistry , adsorption , ethylene , inorganic chemistry , organic chemistry
FTIR spectra of the chromium(III)/silica gel catalyst after short polymerization with ethylene show weak bands at 2 685 and 1 447 cm −1 from the stretching and the deformation vibration of the methylene group, which binds the growing polymer to the active chromium(III) site. The band at 2 685 cm −1 is reversibly removed by CO adsorption at low temperatures (−145°C). This adsorbed CO shows a broad band at 2 184 cm −1 . From the intensity of CO IR bands on unchanged chromium(III) before and after polymerization it was calculated that 12% of the chromium(III) is catalytically active, which is in good agreement with previous measurements by an entirely different determination method (11%). The chromium(II)‐B catalyst showed also a weak band at 2 685 cm −1 and it is therefore concluded that in this case the chromium(II) is oxidised by the ligating surface silanol group (in cooperation with an ethylene molecule). The band at 2 685 cm −1 is discussed in relation to that from normal methylene groups at 2 925 and 2 855 cm −1 and to that from the chromium(II)‐A catalyst at 2 750 cm −1 . Evidence for the existence of a mononuclear chromium(II)‐A species is found. This one is, in contrast to the dinuclear chromium(II)‐A species, not polymerization active.