Middle-range n-alkyl chlorides are the most suitable components among a variety of tested alkyl halides in the preparation process of the highly active Ti-Mg catalyst MTK,. A material balance of the initial components RCI, THF and CCI, revealed the formation of oligomers, chloro-containing telomers and poly-THF apart from low-molecular side products. The former are important modifiers of the suspension catalyst and exert a positive influence on catalyst activity and polymer properties, as was shown in the polymerization of ethylene. Schlenk equilibrium and extent of Wurtz type coupling in the Grignard synthesis step, which have been evaluated by titration of R-Mg bonds and C1 analysis of both the liquid and solid phase of the catalyst, predetermine the quality of the catalyst being formed. a) Part 2: cf. ref. 42). 0 1994, Huthig & Wepf Verlag, Basel CCC 1022-1352/94/$08.00 230 H. Fuhrmann, B. StriibingThe purpose of this paper is to give an insight into the processes proceeding during the preparation of the aforementioned catalyst by means of a mass balance and to elucidate the role of modifiers and side products in the activation and stabilization of the catalytic system.
Experimental partThe preparation of the standard catalytic system (MTK,), inclusive of the purification of the starting material, has been described elsewhere lo* I). Variations of the standard system were achieved by using different alkyl halides in the Grignard reaction as the first step of the catalyst synthesis. The used alkyl halides were pre-dried with CaC1, and then fractionated over P4Ol0. In some cases the Grignard synthesis was prolonged for some hours and started with an excess of the halide in a more concentrated THF solution which became progressively diluted with hexane as the reaction proceeded. At the end of the reaction the mole ratio of the components Mg, alkyl halide and THF was the same as for the standard system. The reaction of the Grignard suspension with the TiCI4/CCI4 mixture as the second step of the catalyst preparation was identical with the standard procedure described in ref. lo).The ethylene polymerization was performed in a suspension process at a constant pressure of 6 bar. Hydrogen was used to control the molecular weight. For more details cf. ref. ' I ) .The determination of R-Mg bonds in the Grignard suspension before the complexation with the titanium halide was accomplished by titration with sec-butyl alcohol/xylene and o-phenanthroline as indicator in an argon atmosphere ").Characterization of reaction products generated during the catalyst preparation was achieved by GC (HP 5880 A, computer-aided evaluation, 50 m OV-1 fused silica capillary column, programmed from 30 to 200 "C at 5 "C/min; C, analysis: GCHF chromatron, packed column, 6 m Octoil on Chromosorb W, 5 m A1,0,, temperature 9OoC), computerized gas chromatography/mass spectroscopy (GC/MS) (HP 589012, 50 m SE 54 fused silica capillary column, combined with AMD 402/3 mass spectrometer, Intectra), NMR(Bruker AC 250 MHz), FT-IR (Nicolet 550) and vap...
