Gaseous Ethylene Polymerization over Ziegler-Natta Catalyst in the Absence of Solvent

Abstract

Using catalyst systems, TiC13-A1Et3 and TiC13-AIEt2Cl, polymerizations of ethylene were carried out in gas phase. The effects of hydrogen on the polymerization rate and on the average molecular weight of produced polymers have been investigated in connection with the kinetic behaviors of polymerization. The kinetic behaviors of polymerization are similar to those of the propylene polymerizations with the same catalyst systems. The effects of hydrogen on the rate of polymerization with these catalysts were different; a small but clear enhancement of the rate in the region of small amounts of hydrogen added was observed in the case with TiCl3-AIEt2Cl, while a monotonic depression of the rate with increasing amount of hydrogen added was observed with TiC13-AIEt3. The stationary polymerization rate in the latter case is expressed by,
R0
RH=------
1+ PnH2
and the average molecular weight is expressed by
MOV
MHV=------
1+ PmH2
with a=a6exp(-11 kca1/RT), b=b0exp(-5kcal/RT), n=O.6 and m=0.6. In these equations, superscripts H and O designate the values in the presence and absence of hydrogen, respectively. The latter expression can be also applied to the polymerization with TiCl3-AIEt2Cl, providing that m=O.5.
The above results have been understood on the basis of supposition that dissociative hydrogen atoms on the catalyst surface are participating in the transfer of growing chains.