Effects of Alterations to Ziegler–Natta Catalysts on Kinetics and Comonomer (1‐Butene) Incorporation

Abstract

system. Ziegler-Natta (ZN) catalysts generally dominate in PE and PP production, but they have their limitations when higher α-olefins are used for copolymerization. The disadvantages of ZN systems in this case are uneven and limited comonomer incorporation. The comonomer is incorporated randomly along the polymer chain, with a tendency to higher comonomer concentrations in the low-molecular weight fractions and less in the high molecular weight part. Further, ZN catalysts lead to broad molecular weight distributions (MWDs), which may be problematic with respect to the amount of extractable material.Higher-branched low molecular weight parts lead to a faster degradation which reduces the durability of the polymer material. Therefore, polyolefines with a homogeneous comonomer incorporation show beneficial properties concerning tensile strength, film transparency, and environmental stress cracking, which results in advantages for many applications, such as films and pipes. Metallocenes can tackle these requirements, as they can polymerize longer α-olefins (up to C26), yield narrow and homogeneous MWDs, and support comonomer incorporation of up to 20%. The demand for metallocene-based polyolefins, especially PE, is increasing significantly. The Various MgCl 2 -supported Ziegler-Natta (ZN) catalysts are synthesized with the intention to influence polymerization performance and 1-butene incorporation in an ethylene copolymer. Modifications are introduced during different steps in the synthesis process, namely support preparation, titanation, and catalyst workup. While multiple different effects are observed upon modification, heat treatment during titanation shows the greatest impact. Increasing the heat-treatment temperature increases polymerization activity. More importantly, the 1-butene distribution can be shifted toward a more homogeneous profile. The amount of 1-butene incorporated is similar to both for short-and for very long-chain molecules. This behavior has so far been known only from metallocene-based polyethylene and suggests that active sites are distributed more homogeneously in the ZN catalyst.

Impact of Polymerization Process Parameters on Improved Comonomer Incorporation Behavior in Ziegler‐Natta Catalysis

“…It is commonly known that for ZN catalysts polymerization activity increases with rising temperature. [12,14] At higher concentrations and with increasing comonomer chain length, incorporation efficiency of the catalyst decreases. Poorer incorporation efficiency of the comonomer results in a significantly higher amount of unused comonomer, which interferes with the polymerization conditions (e.g., solubility equilibrium of C 2 H 4 in propane and the corresponding comonomer).…”

“…Thus, a polymer is produced which varies in its properties, since the comonomer content alters across the entire molar-mass distribution. [11][12][13][14] In a study by Aigner, [14] the synthesis of a ZN catalyst was modified to achieve more uniform comonomer incorporation. For this purpose, the temperature of the titanation step was varied during catalyst synthesis.…”

Engineering Poly(ethylene-co-1-butene) through Modulating the Active Species by Alkylaluminum

“…[82][83][84][85] The chlorine atoms might play less important roles in the complexation between Ti and Al in this case, but they are critical for obtaining reasonable activity in olefin polymerization possibly due to electronic effects. [86][87][88] On the other hand, in the cases involving chlorinated derivatives of alkylaluminum, 32,[34][35][36][37] the Ti-Cl-Al bonding may need to be considered regarding the coordinative capability of them [24][25][89][90] .…”

“…What is known as the fact is that employing different alkylaluminums could impact the copolymer composition not only in soluble molecular catalyst systems [28][29][30][31] , but also in supported Ziegler-Natta-type ones [32][33][34][35][36][37] . Noteworthily, the US patent 8546499 B2 of Borealis AG taught that employing Et 2 AlCl instead of Et 3 Al during polymerization could produce flat comonomer distribution at the price of slightly decreased overall comonomer incorporation.…”

“…36 And employing EtAlCl 2 during catalyst preparation could result in similar effects. 37 It is superior to the usual circumstance where ZNCs produce copolymer with decreasing comonomer incorporation over molecular weight (MW), [38][39][40] because a relatively high degree of comonomer incorporation in the high molecular weight fraction of polyethylene is desired for obtaining high impact toughness and high environmental stress cracking resistance (ESCR). [41][42][43][44][45][46] Thus it would be as well of industrial interest as of the academic one to better understand the likely involvement of aluminum species into the chain formation, particularly on the comonomer enchainment.…”