A study of the ziegler‐type combinations TiCl4‐n‐C5H11Na and TiCl4‐(C2H5)2AlBr

Abstract

The reaction between catalyst components has been studied and polymerization experiments carried out on ethylene using the systems pentyl‐sodium – TiCl₄ (I) and diethylaluminium bromide – TiCl₄ (II). Results of reduction of TiCl₄ can be interpreted on the basis of the following equations: AmNa + TiCl₄ → TiCl₃ + NaCl + Am^•, in the case of I, Et₂AlBr + TiCl₄ → TiX₃ + EtAlX₃ + Et^• and EtAlX₂ + TiCl₄ → TiX₃ + + AlX₃ + Et^• (X = Cl, Br), in the case of II. The occurrence of the second reaction in II was confirmed by analyses of the precipitates formed in the reaction and by reacting TiCl₄ with EtAlBr₂. The reducing power of the organometallic compounds examined decreases in the range: AmNa > Et₂AlBr > EtAlBr₂.Polymerization results with system I showed that active catalysts are obtained only with AmNa/TiCl₄ mole ratios > unity. The polymer yield appeared to increase with increasing catalyst ratio. This may reasonably be explained by postulating the existence of an AmNa‐TiCl₃ complex as the actual catalytic species. In this range of catalyst ratios, the intrinsic viscosities of the polyethylenes remain approximately constant.In the case of system II, polymerization results could also be interpreted by assuming the existence of one complex or a mixture of a number of complexes as the catalyst. With Et₂AlBr/TiCl₄ mole ratios > ∼ 2, a complex between Et₂AlBr and TiCl₃ (Et₂AlX‐TiX₃) is postulated. With catalyst ratios in the vicinity of unity and lower, ambiguous results were obtained due to the occurrence of reactions between the catalyst components during polymerization.