SYNOPSISThe copolymerization of ethylene with highly active TiC14/ MgC12-supported catalysts in solution reactors at 185°C and 400 Psig pressure is presented. The performance of these highly active supported catalysts at high reaction temperature is characterized by a high initial rate that decays rapidly within the 10 min polymerization time period. In the presence of hydrogen and a comonomer, catalyst yields up to about 300 kg/g ( T i ) are achieved. Kinetic data obtained on the influence of a comonomer, e.g., 1-octene or 1-hexene, indicate rate enhancement when used in moderate concentrations. Higher concentrations of comonomer result in a decreasing rate of ethylene consumption. Comonomer/ethylene molar ratios in the range 0-0.827 resulted in comonomer incorporation up to about 2.6 mol % and a small reduction in the polymer molecular weight. 0 1993 John Wiley & Sons, Inc.
I NTRO DUCT10 NIn the first paper of this series,' the essential features of solution ethylene copolymerization processes were reviewed and extensive experimental results presented showing the effect of hydrogen concentration on the rate profile and polymer properties. In this paper, we report the results of a study using the same experimental system in which we vary the amount and type of comonomer for the case of two different solvents.Copolymers of ethylene with higher linear a-olefins continue to be of increasing importance to industry. Thus, it is important to develop a fundamental understanding of this copolymerization process. In Ziegler-Natta polymerizations, it is normally observed that the addition of a small amount of a comonomer, e.g., 1-octene, to an ethylene polymerization system results in enhancing the rate of ethylene consumption relative to homopolymerization. The magnitude of this enhancement effect is dependent on the catalytic system and to a large extent on the length of the carbon chain of the a-olefin comonomer. The comonomer not only affects the polymerization kinetics but also induces some fundamental changes to the polymer structure. In copolymerization, the chain microstructure of the polymer depends on the type of the comonomer used, the distribution of the comonomer units along the molecules, and the molecular weight of the polymer. These properties ultimately influence the physical properties of the polymer, i.e., viscolastic, mechanical, and melting behavior.2 The comonomer effect on the kinetics of olefin polymerization has been investigated by many authors in this field. The majority of these investigations were conducted in slurry polymerizations, 3-6 and much fewer in or solution-phase polymerizations.'Orll Tait et al.3 investigated ethylene copolymerization in the slurry phase with a number of a-olefins. An enhancement effect was observed upon introduction of a small amount of the comonomer. The authors3 attributed such enhancement effects to different chemical and physical factors and suggested that no single explanation may be adequate to describe the behavior of a variety of different catalytic systems...
SYNOPSISThe influence of temperature variation on the kinetics and the polymer properties in the homo-and copolymerization of ethylene in a solution reactor is discussed. The polymerization is conducted in a semibatch mode at 320 Psig total reactor pressure for 10 min polymerization time. Temperature variations in the range 145-200°C in both homo-and copolymerization of ethylene with 1-octene shows that the highest catalyst yield was obtained at temperature of 165-175°C. At the optimal temperature, a high initial maximum in the rate of ethylene consumption is attained in a few seconds followed by a relatively slow decay when compared with polymerization conducted at higher temperatures. Polymerization at temperatures 2 185°C resulted in a lower peak in the consumption rate of ethylene accompanied by a rapid decay with time. In the case of ethylene/l-octene copolymerization, a rather low comonomer incorporation level is obtained at the conditions employed; the 1-
SYNOPSISThe copolymerization of ethylene with highly active TiCl,/MgCl,-supported catalysts in solution reactors at 185°C and 400 Psig pressure is presented. The performanbe of these supported catalysts at these conditions is characterized by a high initial rate that decays rapidly within the 10 min polymerization period. In the presence of hydrogen and a comonomer, catalyst yields up to about 300 kg/g ( T i ) are achieved. The kinetic data indicate rate enhancement when hydrogen is added in moderate concentrations. However, a high concentration of hydrogen results in a decreasing rate of ethylene consumption. Increasing the H2/C2 molar ratio in the range 0-10.66 -leads to a reduction in the M , values from 31,600 to 17,400.
The effect of varying 14C0 contact time upon the concentration of active centres C* in ethylene homopolymerization using the TiCI, /MgH, . Al(C2H5), catalytic system shows that the polymer radioactivity, and hence C*, increase sharply in the first sixty minutes of I4CO contact with the polymerization centres. For contact times longer than one hour, the polymer radioactivity continues to increase, but very slowly. Studies on the effect of the mole ratio AI(C,H,),/Ti on ethylene homopolymerization show that both the catalytic activity and C* increase sharply when increasing the mole ratio Al(C,H,),/Ti in the range from 5 to 20. When increasing the mole ratio A1(C2H5),/Ti above 50, C* tends to decrease very slightly. In ethylene/l-hexene copolymerization a similar effect of the mole ratio AI(C2H,), /Ti on the polymerization is observed. However, even though the catalytic activity in copolymerization is observed to be higher than in homopolymerization, at the same mole ratio AI(C2H5), /Ti, yet C* in both cases is found to be more or less the same.
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