Polymerization of olefins through heterogeneous catalysis. XIII. The influence of comonomer in the solution copolymerization of ethylene

Abstract

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...

Condensed Mode Cooling for Ethylene Polymerization: Part II. The Effect of Different Condensable Comonomers and Hydrogen on Polymerization Rate

“…The comonomer effect has been shown to be a function of the type, quantity, and chain length of the α‐olefin in question. Studies have shown that at low comonomer concentrations, the rate increases with respect to homopolymerizations for monomers like 1‐hexene or 1‐octene, but then decreases after some optimum concentration added . When polymerization takes place on a supported catalyst, similar trends have been observed, where the rate can become significantly higher than the rate of ethylene homopolymerization for small quantities of α‐olefin, but after an optimal amount, the rate once again decreases and can become even lower than the reference value during homopolymerization .…”

Kinetic elucidation of comonomer‐induced chemical and physical activation in heterogeneous ziegler‐natta propylene polymerization

“…In Ziegler‐Natta olefin polymerization, the enhancement of polymerization rate ( R p ) by the addition of comonomer is well known as the comonomer effect 1. The effect has been widely observed in copolymerization of ethylene with α‐olefins and of propylene with ethylene or the other α‐olefins 7, 11, 24–33. A great deal of effort has been devoted to providing several mechanistic explanations of the comonomer effect.…”

Polymerization of olefins through heterogeneous catalysis. XVIII. A kinetic explanation for unusual effects

“…While maintaining consistency with the hoethylene and 1-hexene over a TiCl 4 /MgCl 2 catamopolymerization results, the parameters of the lyst. The data provided in the work of Jaber and expanded model were then used to match the obRay 31 has been used as the basis for this example, served rate, yield, degree of polymerization, and since it provides the most detail in terms of the comonomer incorporation for the 1-hexene copolyreaction system and conditions used. Furthermerization.…”