120th Birthday: Giulio Natta

Giulio Natta was born on February 26, 1903, in Imperia, Italy. He was an Italian chemical engineer and is well-known for his work on Ziegler–Natta catalysts for the synthesis of polymers from terminal alkenes. The Nobel Prize in Chemistry 1963 was awarded jointly to Giulio Natta and Karl Ziegler “for their discoveries in the field of the chemistry and technology of high polymers.”

Life and Career

Natta studied chemical engineering at the Polytechnic University of Milan, Milan, Italy, and received his doctoral degree there in 1924. He passed his “‘Libero Docente” (examination for a university teaching qualification) in 1927. After serving as an Assistant Lecturer in chemistry in Milan, he moved to the University of Pavia, Italy, as Professor of General Chemistry in 1933. In 1935, Natta became Director of the Institute of Physical Chemistry in Rome, Italy, and in 1937, he moved to Turin to serve as Professor of Industrial Chemistry. From 1938 until his retirement in 1973, Natta served as Professor at the Polytechnic University of Milan.

Natta was diagnosed with Parkinson’s disease in 1956. When he received the Nobel Prize in 1963, his condition had progressed to the point that he required assistance and his Nobel Lecture was read by a colleague. Giulio Natta died on May 2, 1979, in Bergamo, Italy.

Research

Early in his career, Natta investigated the structure of low-molecular-weight inorganic substances using X-ray analysis and electron diffraction, but after meeting Hermann Staudinger, the “father of polymer chemistry”, in 1932, he became interested in the study of the structure of polymers.

Natta was involved in several areas of research with important industrial applications. He worked, for example, on the structure of heterogeneous catalysts employed in industry using X-ray analysis. He was part of an Italian research program focused on the production of synthetic rubber that led to the industrial production of butadiene-styrene copolymer rubbers. Natta also developed a commercial process for the separation of butadiene from 1-butene.

Ziegler–Natta Catalysts

In 1953, Karl Ziegler discovered that polyethylene could be produced at low pressures via a catalytic route using a mixture of TiCl₄ and triethyl aluminum [1]. Natta was convinced that this catalyst was key for the regular polymerization of other unsaturated compounds and developed the work further with financial aid from the Italian chemical company Montecatini.

Natta extended Ziegler’s research to achieve stereospecific polymerizations of propene. He discovered new classes of polymers with a sterically ordered structure (stereoregularity), such as isotactic and syndiotactic polymers [2]. In isotactic polypropylene, for example, the methyl groups are arranged to one side of the backbone, while in syndiotactic polypropylene, the arrangement alternates between the two sides (pictured below). The stereoregularity of the polymer is determined by the catalyst used to prepare it. Natta determined the arrangement of chains in the lattice of the discovered crystalline polymers using X-ray analysis.

Today, there are two classes of Ziegler–Natta catalysts: Heterogeneous, supported catalysts based on titanium compounds in combination with organoaluminum compounds such as triethylaluminium, as well as homogeneous catalysts based on complexes of titanium, zirconium, or hafnium with, e.g., methylaluminoxane (MAO) as an organoaluminum co-catalyst. An example mechanism for a zirconium complex is shown below.

(Image Credit: Smokefoot, wikimedia commons, CC BY-SA 4.0)

A zirconium precatalyst is first methylated by a reaction with MAO and then coordinates an alkene monomer. Successive insertion reactions into the Zr–C bond then form the polymer.

Giulio Natta is the answer to Guess the Chemist (134).