Magnesium chloride supported high mileage catalysts for olefin polymerization. XII. Polymerization of ethylene

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Abstract
Polymerizations of ethylene by the MgCl2/ethylbenzoate/p‐cresol/AlEt3 TiCl4‐AlEt3/methyl‐p‐toluate (CW‐catalyst) have been studied. The initially formed active site concentration, [Ti] has a maximum value of 50% of total titanium at 50°C and lower values at other temperatures. The Ti decays rapidly to Ti sites with conc. ca. 10 mol %/mol Ti. The rate constants for four chain transfer processes have been obtained at 50°C: for transfer with AlEt3, k = 2.1 × 10−4 s−1 and k = 4.8 × 10−4 s−1; for transfer with monomer, k = 3.6 × 10−3 (M s)−1 and K = 8.3 × 10−3 (M s)−1; for β‐hydride transfer, k = 7.2 × 10−4 s−1 and k = 4.9 × 10−4 s−1; and transfer with hydrogen, k = 4.0 × 10−3 torr1/2 s− and k = 5.1 × 10−3 torr1/2 s−1. The rate constants for the termination assisted by hydrogen is k = 1.7 (M1/2 torr1/2 S)−1. If monomer is assisting termination as was observed for propylene polymerization, then k = 7.8 (M3/2 s)−1. Values of all the rate constants can be higher or lower at other temperatures. Detailed comparisons were made with the results of propylene polymerizations. There are more than four times as many Ti active sites for ethylene polymerization than there are for stereospecific polymerization of propylene; the difference is more than a factor of two for the Ti sites. Certain rate constants are nearly the same for both monomers while others are markedly different. Some of the differences can be explained by stereoelectronic effects.

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