Comonomer enhancement effect of 1‐hexene in ethylene copolymerization catalyzed over MgCl₂/THF/TiCl₄ catalysts

Abstract

SYNOPSISHomo-and copolymerization of ethylene were performed by using a catalyst system composedof TiC1,/THF/MgC12 complex activated with A1Et3 at 70°C and 3 atm. T o investigate the effect of the compositional difference of the catalyst on the rates of homo-and copolymerization and on the reactivity in ethylene-hexene copolymerization, a series of six catalysts with different compositions ( Mg/Ti = 0.4-16.5) were prepared by coprecipitation. The catalytic activity in ethylene polymerization increased sharply with the Mg/Ti ratio from 21 (Mg/Ti = 0.4) to 1477 kg PE/g-Ti h (Mg/Ti = 16.5). The activity in copolymerization with 1-hexene also increased with Mg/Ti ratio. The values of rl were 120, regardless of Mg/Ti ratios within the experimental error range. Enhancement of the polymerization rate by the addition of l-hexene in the reaction medium was observed only for the catalysts of low Mg/Ti ratio. This unusual effect of 1-hexene on the polymerization rate was explained by chemical and physical processes that occurred during polymerization.

Effects of molecular dispersion state of surface Ti species on ethylene-propylene copolymerization with TiCl3-based Ziegler-Natta model catalyst

“…These phenomena are well known as the activation effect in copolymerization, where two kinds of monomers synergistically enhance the activity, and have widely observed for copolymerization both of ethylene with α-olefins and of propylene with higher α-olefins, being irrespective of employed catalysts (ZN or metallocene catalysts). [12][13][14][15][16][17][18][19][20][21][22] Though it has not been completely clarified yet, various mechanisms for the activation effect have been proposed; i) decrease of crystallinity of formed copolymers due to the incorporation of comonomer to accelerate the diffusion of monomers or alkylaluminum, 12,13 ii) reactivation of dormant sites by comonomer, [14][15][16] iii) increase of the active site concentration in copolymerization with the assumption that active sites for ethylene and propylene polymerization might not be identical and that both the active sites work for copolymerization, [17][18][19] iv) acceleration of catalyst particles disintegration during copolymerization, 18 and so on. Considering that Cat-A gave poorly crystalline polypropylene (X c~8 wt%), the mechanism i) was not likely relevant to the observed activation.…”

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.…”

Titanium(III, IV)-Containing Catalytic Systems for Production of Ultrahigh Molecular Weight Polyethylene Nascent Reactor Powders, Suitable for Solventless Processing—Impact of Oxidation States of Transition Metal

“…For correct comparison of the mechanical properties of UHMWPE films obtained from different catalytic systems, we selected samples with the same drawing rate equal to 20 (entries 3, [16][17][18][19]21). As seen from the Table 2 (entries 6 and 16), the samples obtained from catalytic system II and from a mixture of TiCl4 2THF + ZrCl4 2THF did not show good mechanical properties, probably due to a long polymerization time.…”

“…Reaction of MgCl 2 with a Lewis base, typically alcohols or ethers such as THF, is a generally known method of its activation [17][18][19][20]. Alternatively, THF can serve as a ligand interacting with TiCl 4 .…”