Giulio Natta and the Development of Stereoselective Propene Polymerization

Abstract

This chapter looks back at the fascinating history of isotactic polypropylene, the first man-made stereoregular polymer, from the largely serendipitous discovery to the modern technologies for the industrial production of reactor blends with high-yield Ziegler–Natta catalysts featuring highly controlled morphology. This is also the story of a great man, Giulio Natta, winner of the 1963 Nobel Prize in Chemistry, and his team of incredibly talented young coworkers at the Milan Polytechnic, who in just a few years at the end of the 1950s elucidated the structure of the new polymer and that of the novel TiCl₃-based catalysts leading to its formation. The pioneering studies that followed on chain microstructure and the origin of the stereocontrol, and the first educated guesses on the nature of the active species, are critically reviewed, and re-visited with the aid of modern experimental and computational tools and methods, to highlight the current picture of what still represents a most important and lively area of polymer science and organometallic catalysis.

Appendix: Some Biographic Notes on Giulio Natta

Whoever goes through the numerous biographies (see for example [52]) of Giulio Natta (Fig. 14) cannot but realize that the discovery of iPP and stereoselective olefin polymerization was diligently prepared by Fate. Born in 1903 in a family of judges and lawyers, Natta developed a passion for chemistry that made him build, during his studies in chemical engineering at the Milan Polytechnic, a small laboratory in his apartment to carry out “private” experiments in his spare time. The Milan Poly was in the 1920s a world-leading center in X-ray diffraction, which set the stage for Natta’s interest in the still-young chemical crystallography (key to interpretation of the events of March 1954). Subsequently, he worked on electron diffraction in Freiburg; that Hermann Staudinger was a professor there was certainly more than influential on Natta’s formation. Back in Italy, he went through a rapid academic career that saw him Professor of General Chemistry in Pavia, of Physical Chemistry in Rome, and of Industrial Chemistry, at Turin Polytechnic first and at Milan Polytechnic from 1938 until his retirement in 1973. As for many academic chemists in Europe at that time, the forthcoming war prompted Natta to move the focus of his research to the synthesis of strategic materials. In particular, he expanded his studies in catalysis, which were pre-existing and had already led him to important achievements in oxosynthesis in the early 1930s, to the production of synthetic rubber. The interest in polymers with elastomeric properties never faded, and is another key part of the puzzle. After the war, Italy entered the most vital and productive period of its recent history, and the Italian chemical industry began an impressive growth. At that point Fate played a wild card and made the young Natta meet Piero Giustiniani, on the way to becoming CEO of Montecatini, one of the largest and most advanced Italian chemical companies. The two began a collaboration that in 1947 led them to travel to the USA, where they discovered the modern organization of the American chemical companies, employing hundreds of researchers and well ahead in the transition from coal to oil chemistry. That journey imprinted both of them and resulted in a strategic alliance that made Montecatini associate Natta as a consultant and establish at the Milan Polytechnic an “Advanced School in Aliphatic Chemistry,” where brilliant chemistry and chemical engineering graduates from all over Italy received hands-on research training in chemical syntheses and characterizations. They joined the academic staff on fundamental and applied projects under Natta’s leadership, in most cases in preparation to a career in Montecatini. The modernity of this organization, with a strong multi-disciplinary character and a simple albeit efficient structure, amazes me when I compare it with the present painful situation of Italian chemical research. When in 1952 Natta attended the Achema Conference in Frankfurt, where Karl Ziegler gave an account of his work on the “Aufbau-Reaktion,” all parts of the puzzle could perfectly fit together. Natta had no difficulty in convincing Giustiniani and Montecatini to contract Ziegler as a consultant and to take a license on the developments of Al-mediated ethene oligomerization, even though the real industrial interest of that process was not yet clearly established. What came afterwards is told in the previous sections of this chapter.

Fig. 14

Giulio Natta (1903–1979)

A precocious Parkinson disease forced Natta to a rather early retirement, which makes me feel sad for him, and in a way for me too, because I dare to look at him as a grandfather that I never met. When I read that he was a reserved, almost shy man I have no difficulties in believing that. In my 20 years of collaboration with Paolo Corradini and, for a much shorter but highly fascinating period, with Adolfo Zambelli, I seldom heard them mention “Il Professore” or tell anecdotes about him. They had been working under Natta for many years, and shared with him the most heart-shaking experience a scientist could dream about, and yet “Il Professore” seemed to me, through them, to be a silent presence in the background. Some of his comments, of course, surfaced to their memories, and these were all modest, humble even: “we have been lucky” was a recurrent one. On the other hand, Natta was of course well-aware of the importance of his discoveries. I have been especially impressed by a recollection of Lido Porri, another well-known Natta coworker, in a recent article for a special issue of the Italian Chemical Society journal celebrating the 50th anniversary of Natta’s Nobel Prize [53]. Porri recalls that Natta used to say: “I believe that research in this field will continue until the next century.” Well, “Professore,” here we are indeed!