Infrared characterization of MgCl2 supported Ziegler-Natta catalysts with monoester and diester as a modifier

An i.r. study of MgCl 2 supported TiCl 4 Ziegler-Natta catalysts for propylene polymerization using Lewis base modifiers has been carried out. Two series of catalysts were prepared, differing mainly by the method used to prepare the MgCl 2 support. One was prepared by precipitation and the other by ball-milling. Four different Lewis bases, of which two are diesters (di-2-ethyl phthalate and diisobutyl phthalate) and two are monoesters (ethyl benzoate and 2-ethyl hexyl benzoate), were employed. The i.r. investigation of the catalyst was focused on the identification of complexes formed. It was found that the diester-containing catalysts contain significant amounts of TiCl 4 · diester complexes and phthaloyl mono- and di-chlorides complexed to MgCl 2 , whereas the monoester-containing catalysts are virtually free of these compounds. The chlorides are believed to be formed from the reaction of TiCl 4 and diester weakly bonded to MgCl 2 . The TiCl 4 · monoester complex is relatively weak so that the coordination of monoester with MgCl 2 is much more favorable. The effects of the complexes, particularly their relative amounts, on the catalyst activity was investigated by carrying out propylene polymerizations with catalysts prepared by precipitation and by ball-milling method at three different activation temperatures.