Giulio Natta a Pioneer in Polypropylene

Abstract

Giulio Natta, who shared the Nobel Prize in chemistry with Karl Ziegler, was an Italian crystallographer who used the “Ziegler catalyst” to produce polypropylene. His wife, Rosita, coined the tacticity terms after Giulio had shown that stereoregular polymers could be produced by the polymerization of alpha substituted ethylenes.

Young polymer chemists who aspire to become millionaires, like Karl Ziegler and Giulio Natta, should be forewarned that neither of these inventors was educated as a polymer scientist. Ziegler was essentially a physical organic chemist who learned some polymer chemistry from Hermann Staudinger and Natta was a crystallographer who read Flory’s “Principles of Polymer Chemistry.” Both learned enough about macromolecules to conduct their experiments and obtain patents on polyethylene and polypropylene.

Polyethylene had been produced by von Peckmann in the 19th century by the decomposition of diazomethane. Polypropylidene (-CH-)(C₂H₅) isomeric with polypropylene had also been obtained by the decomposition of diazopropane. Later, low melting, amorphous polypropylene was produced by the ionic polymerization of propylene but the softening point of this product was too low to consider its use as a plastic.

However, a solid polypropylene which was useful both as a plastic and a fiber was produced by Giulio Natta and several other scientists in the mid 1950’s. Based on verifiable dates of conception of the invention, the U.S. Patent Office finally agreed, after an extremely long and expensive patent suit, that P. Hogan and R. Banks of Phillips Petroleum Company were the inventors of crystalline polypropylene but chemists at DuPont, Standard Oil of Indiana, Standard Oil of New Jersey, Shell, Hercules and the Max Planck Institut were all contemporary inventors.

Karl Ziegler of the Max Planck Institut patented the polymerization of ethylene at ordinary pressures and temperatures in the presence of titanium chloridetriethylaluminum (Ziegler catalyst) but he did not include propylene in his patent application. Hogan and Banks at Phillips and Zletz at Standard Oil of Indiana polymerized propylene in the presence of metal oxides. Ed Vandenburg at Hercules, S.B. Lippincott of Standard Oil of New Jersey, and B. Wright of Petrochemicals LTD (Shell), like Natta, received licenses to use the Ziegler catalyst.

Bernard Wright of Petrochemicals LTD in England made solid polypropylene on a large commercial scale one day when the HDPE plant ran out of ethylene. Wright and his supervisor T. Barrows did not inform Ziegler of this production since it was assumed that the production of polypropylene was covered by the Ziegler patent. This was untrue, Actually, H. Breil had produced polypropylene at the Max Planck Institut before the Wright production but did not recognize the product as polypropylene.

Breil became impatient when the drop in pressure, during the polymerization of the less volatile propylene was not as great as that with the more volatile ethylene and hence, he added ethylene and observed the anticipated drop in pressure. Later, Ziegler claimed that the product was a copolymer but some polypropylene must have been produced initially before the addition of ethylene.

The polymerization of propylene was repeated successfully by H. Martin some months later in May of 1954. Ziegler then filed a patent application and after sending a sample to Dr. Natta, learned that Natta had filed a patent application on the polymerization of propylene several days earlier.

Dr. Paoli Chini used Ziegler’s catalyst to produce polypropylene in Natta’s laboratory on March 11, 1954. After seeing the solid product, Dr. Natta wrote in his notebook, “today we made polypropylene.”

Dr. Natta attempted to publish an account of this successful experiment in a communication to the editor of The Journal of the American Chemical Society but the paper was rejected by the editor because of lack of experimental data. however, Dr. Paul Flory, who was a member of the editorial board, asked that this decision be reversed and the communication was published in the spring of 1955.

When Ziegle’s patent attorney suggested that he include propylene as well as ethylene in his low pressure polymerization patent application, his reply was “Es Geht Nicht.” Breil supported this negative attitude when he noted very little decrease in pressure during the formation of polypropylene. When asked why he did not inform Dr. Ziegler that he had produced solid polypropylene, Dr. Natta replied,“ I did not tell him because I had to take out patents first. I asked him whether he had polymerized propylene in order to know whether my process was new.”

Because of familiarity with x-ray crystallography and IR spectroscopy, Natta was able to show that solid polypropylene was a crystalline stereoregular polymer with a three fold helical conformation. As stated in Flory’s book, which was read by Natta, C. Schildknecht had previously shown that polyvinyl alkyl ethers produced at low temperature, were stereospecific polymers. Of course, solid polypropylene had not been reported at the time that Schildknecht conducted his investigations.

Natta used the optically active isomeric terminology DD, DL, etc. when he first described his stereoregular polypropylene. However, his wife Rosita Beati Natta had a better idea and coined the term isotactic “DD”, syndiotactic (DL) and atactic (DLLDLDD) to designate these stereospecific polymers. Later, one pundit called her the real creator of isotactic polypropylene.

Natta’s group extended the use of the Ziegler catalyst to produce stereoregular polymers from 1-butene, 4-methyl-1-pentene and styrene. Fred Forster of Firestone and Sam Home of Goodrich used the lithium and Ziegler catalyst respectively, to polymerize isoprene to produce cis-1, 4-polyisoprene which was identical to natural rubber. Later (in 1973), the editors of Chemical and Engineering News, who had a “blimp complex,” credited this discovery to Goodyear. Later, another commercial elastomer was produced by the copolymerization of ethylene and propylene in the presence of a diene (EPDM).

Giulio Natta was born at Imperia near Genoa, Italy on February 26, 1903. His father was a judge and it was expected that he, like other members of his family, would study law. However as the result of reading a chemistry book, at the age of 12, he decided to study science.

After graduating from Christopher Columbus High School he majored in mathematics at the University of Genoa and later enrolled in Milan Polytechnic where he was awarded a doctoral degree in chemical engineering in 1924. He received a Libero Docente degree from Milan in 1927 where he served as an assistant professor until 1933.

He spent the next two years as a full professor at the University of Pavia and left to accept a position as professor of physical chemistry at the University of Rome. In 1938, after a year as head of the Institut of Industrial Chemistry at Turin, he returned to Milan and spent the rest of his professional life as a consultant for Montecatini Chemical Company and much of his success in the discovery of isotactic polypropylene may be attributed to continued financial support from that large chemical firm.

Both Giulio and Rosita Natta were fond of the outdoors. She was an avid fisherwoman and he was a collector of fossils and mushrooms. His trips, however, were limited. His mother was killed in an automobile accident and he, not only did not drive, but was even reluctant to ride in an automobile. Nevertheless, he continued as an active director of the Institut but in later life was stricken with Parkinson’s Disease and was seriously handicapped in his speech and walk. He was supported by his son Giuseppe when he received the Nobel Prize in 1963. His speech was read by a colleague. He received the Lomonosov Gold Medal of the USSR Academy of Science in 1909 and was awarded honor degrees from many universities.

After his wife’s death in 1968 he lived with his daughter Frances and retired in 1973. He died in Bergamo, Italy on May 2, 1979.

In 1948, Dr. Natta concluded that “a revolution will be marked by the development of processes that lead to the formation of macromolecules having a predetermined structure. They will make some branches of industry independent of agriculture and increase the area of land used for the production of food.” His contributions to polypropylene plastics, film and fibers as well as ethylene-propylene copolymers and polyisoprene elastomers have helped make his 36 year old prediction come true, Over 6 million pounds of these polymers of propylene were produced in the US in 1987. The largest producer of polypropylene is Himont which is owned jointly by Montedison (successor to Natta’s Montecatini) and Hercules where Ed Vandenburg produced polypropylene in the mid 1950’s.