ISSN:
0360-6376
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Electron paramagnetic resonance (EPR) was used to study a MgCl2-supported, high-mileage olefin polymerization catalyst. Anhydrous Toho MgCl2 was the starting material. Treatment with HCl at an elevated temperature, ethyl benzoate by ball-milling, p-cresol, AlEt3, and TiCl4produced a catalyst that contained a single EPR observable Ti+3 species A, which was strongly attached to the catalyst surface, had a D3h symmetry, and no other Ti+3 ion in an immediately adjacent site. Species A constitutes only 20% of all the trivalent titaniums; the remainder is EPR-silent and may be attributed to those Ti+3 ions that have adjacent sites occupied by one or more Ti+3 ions. Activation with preformed AlEt3/methyl-p-toluate complexes produced a single Ti+3 species (C) with rhombic symmetry and displaying 27Al superhyperfin splitting which has attributes for a stereospecific active site. This species is unstable under polymerization conditions and is transformed to another species with axial symmetry and solubilization. Both processes could lead to catalyst deactivation and loss of stereospecificity. Catalysts activated by AlEt3 and methyl-p-toluate separately in various sequential orders produced a multitude of EPR-observable Ti+3 species with varying degrees of motional freedom deemed detrimental to stereospecific polymerization of α-olefins.
Additional Material:
10 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1982.170200909
