Heterogeneous Ziegler-Natta, metallocene, and post-metallocene catalysis: Successes and challenges in industrial applica
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troduction—The polyolefin success story With a global production volume of nearly 150 million tons per year, polyolefins are undoubtedly a success story that was essentially enabled by the original discoveries of Karl Ziegler and Giulio Natta in the 1950s (see the Introductory article in this issue of MRS Bulletin). For polyethylene (PE), the gradual expansion of the density range toward very low crystallinities and the controlled variation of the molecular weight distribution (MWD) required constant modifications of polymerization technologies and catalyst performance. For isotactic polypropylene (iPP), the discovery that electron donors in the catalyst system can control the stereoselectivity and increase productivity, combined with carrier technology developments that enabled controlling the polymer particle morphology as well, led to the amazing growth of iPP from the first kilogramscale production in 1957, to the close to 60 million tons today. Together with multistage polymerization technologies, modern iPP catalysts allow the production of “reactor-based thermoplastic elastomers” with high impact toughness in a temperature range from +80 to –30°C. While the market penetration of
metallocene (MC) and other “single-site” catalysts has been significantly slower than anticipated, due in part to the continuous improvement of the traditional—and cheaper—Ziegler-Natta (ZN) systems, the former have enabled an unprecedented finetuning of chain microstructure by ligand design. Polymers have been going through a hard time recently: for the first time since the oil crisis of the early 1970s, global production of polymers in general decreased in 2008 as a result of the unexpected economic crisis overlapping with the expected downturn of the cyclic polyolefin market. At the same time, public perception of “plastics” deteriorated, with critical views on issues such as endocrine disruption, littering, and waste. Despite all the “green” concerns, polyolefins still excel in performance and energy efficiency over other materials. Largescale food distribution and preservation would be unthinkable without polyolefi ns. Bimodal high and medium density PE grades have revolutionized water and gas distribution systems, being light, corrosion-resistant, and the safest choice in case of earthquakes. Efficient individual mobility requires cars combining low weight and high passenger safety with
Markus Gahleitner, Borealis Polyolefine GmbH, Linz, Austria; [email protected] Luigi Resconi, Borealis Polyolefine GmbH, Linz, Austria; [email protected] Petar Doshev, Borealis Polyolefine GmbH, Linz, Austria; [email protected] DOI: 10.1557/mrs.2013.47
© 2013 Materials Research Society
MRS BULLETIN • VOLUME 38 • MARCH 2013 • www.mrs.org/bulletin
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HETEROGENEOUS ZIEGLER-NATTA, METALLOCENE, AND POST-METALLOCENE CATALYSIS
high-impact polypropylene (PP) copolymers at the frontline of this development. In addition to reviewing the development of catalysts and resulting products, this article also presents some future pers
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