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Propylene polymerization using MgCl 2 /ethylbenzoate/TiCl 4 catalyst: Determination of titanium oxidation states
Author(s) -
AlArifi A. S. N.
Publication year - 2004
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.20378
Subject(s) - polymerization , titanium , catalysis , tacticity , polymer , polymer chemistry , polypropylene , materials science , molar mass distribution , hydrogen , ziegler–natta catalyst , inorganic chemistry , chemistry , organic chemistry , composite material
The chemical interaction of the catalyst MgCl 2 /ethylbenzoate/TiCl 4 with the cocatalysts triethylaluminum and trisobutylaluminum was investigated to establish a relationship between the titanium oxidation states and the catalytic activity, polymer isotacticity, and polymer molecular weight in propylene polymerizations. This interaction was studied using different Al : Ti molar ratios by measuring the changes of the titanium oxidation states at different polymerization times. Both hydrogen and alkyl aluminum caused a reduction of Ti 4+ species to lower oxidation states species Ti 3+ and Ti 2+ . However, the Ti 4+ species reduction appeared to be incomplete. It was found that the Ti 4+ species undergoes a severe reduction as the Al : Ti molar ratio increases from 50 to 230 as overreduction takes place. This change of the Ti 3+ species percentage with time was found to correlate with the rate–time profiles of propylene polymerization. From this observation, it would be fair to conclude that the trivalent titanium species is more likely to be the active titanium species for propylene polymerization than the aforementioned catalyst system. On the other hand, hydrogen addition was found to cause an increase in Ti 3+ species. The increases in both hydrogen amount and/or Al : Ti molar ratio were found to cause a decrease in both molecular weight and polypropylene isotactic index. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 56–62, 2004