Attualità

The Scientific Activity of Giulio Natta from 1949 to 1973 by Piero Pino

his most significant period of the sci- T entific activity of Prof. Natta started with his first contacts with the U.S.A. chemical industry, where a very rapid development of petrochemistry was pro- ducing substantial and unexpected changes. The profound emotions that Professor Natta felt during his first trip to the U.S.A. are well described in a paper published in La Chimica e l’Industria [1]. Since Natta had received his education in chemistry and chemical engineering in the twenties, i.e. when industrial organic chemistry was mainly based on coal and fermentation products, he was fascinat- ed by the new possibilities offered to the chemical industry by the practically un- limited availability of unsaturated hydro- carbons like ethylene, propylene, butenes and butadiene easily obtainable from petroleum and he immediately rec- ognized the industrial potential of the Figure 1 - Summary of Natta’s research in the field of carbon monoxide chemistry chemistry of aliphatic compounds. P. Giustiniani - at that time GeneraI Man- sent number of U.S.A. researchers, graduates in chemistry and industrial ager of Terni SpA, and later Managing these figures seem insignificant” [1]. In chemistry should be engaged every year Director of Montecatini SpA - with whom the same article he also writes: “In my to be trained in industrial aliphatic organ- Natta visited the U.S.A. for the first time, life as a modest researcher there were ic chemistry at the Industrial Chemistry shared his enthusiasm. Thus, by the end ten at the most chemists under my direc- Institute of the Politecnico, before they of the forties, the Industrial Chemistry In- tion, and to follow them all seemed to be would start to work in the Montecatini stitute of the Politecnico of Milan and a very hard work to me. I wonder how a laboratories. After the didactic experi- Montecatini Company (later Montedison) single man can direct 500 to 600 re- ence made in the more developed coun- established that fruitful collaboration searchers“. Being highly interested in re- tries in Europe and in the U.S., the which was to produce extremely impor- search organization, he often urged me trainee would have to carry out a re- tant industrial achievements, among to describe how research was carried search project independently and attend which the commercial production of iso- out at the Organic Chemistry Laboratory courses on industrial organic chemistry, tactic polypropylene. On his trip to the of the Polytechnic Institute of Zurich, as well as on advanced topics of organic U.S.A., Professor Natta was impressed where I had gone in 1950 to specialize in chemistry, physical chemistry, and in- by the number of scientists who worked organic chemistry under the direction of strumental analysis. It is to Mr. Giustini- at the research laboratories and by the Professor Ruzicka, a scientist whom ani’s credit that he acceded to Natta’s re- way in which research was organized. Natta admired for his achievements in quest without faltering. Actually, Natta’s In 1948 he wrote: “It often happens that the field of organic syntheses. plans would never have been realized the number of chemists working in those Thinking that the academic world - without the support of the industry. huge Iaboratories is 400 to 600. A few scarcely ready for substantial innova- Thanks to the careful selection of the years ago it amazed us that the number tions - could hardly have provided young trainees and to the high quality of the of chemists working at the I.G. laboratory graduates with the up-to-date prepara- teachers (in addition to Prof. Natta him- of Reppe was about 100, and that the re- tion required for the large-scale introduc- self, I wish to mention Prof. A. Quilico, search on nylon was carried out by 30 tion of petrochemistry in Italy, and, at the Prof. G.B. Bonino, the late Prof. R. Pio- scientists. Now, compared with the pre- same time, wishing to avail himself of a ntelli, as well as notable industrial man- research team capable of competing agers, such as G. Greco and the late F. P. Pino, Eidgenössische Technische Hoch- with the U.S.A. teams, Natta proposed, Tredici), and to the climate in which the schule - Zürich. and Mr. Giustiniani agreed, that 10-20 trainees were able to develop their sci-

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entific work, the chemists educated at catalytic activity of the cobalt-based cat- ly to a minor part of his scientific activity. the Milan Politecnico in the early fifties alysts discovered by Rohlen was higher Indeed Natta obtained his most impor- still constitute the supporting structure of than that of the nickel catalysts discov- tant achievements in the field of high the major laboratories of the Italian ered by Reppe, Natta reinvestigated the polymers. His first research in this field chemical industry. Some of their names carbonylation of acetylene. started in 1932 during his stay in and present positions are mentioned in The research he carried out in this field Freiburg im Breisgau where he met Pro- parentheses in Figures 1 and 6, after the from 1947 to 1954 resulted finally in a fessor H. Staudinger [18]. Later, he con- description of the research works they new one step synthesis of succinic acid tributed to the first production of synthet- collaborated on. from acetylene [4]. A pilot plant based on ic rubber in Italy. After World War II, I have dwelt on this project because, in this research was later implemented with polymers remained to be one of his main my opinion, it largely contributed to the the collaboration of I. Pasquon and G. research interests, even though after the extraordinary results that Natta achieved AIbanesi. As early as 1944 Natta real- end of the initial activity in the field of in the period from 1953 to 1963. These ized that the olefins hydroformylation synthetic rubber no experimental re- very results were obtained also because rate was independent of the total pres- search was in progress in his Institute till the Institute was provided not only with sure of the 1:1 carbon monoxide and hy- the end of the forties. modern equipments for x-ray and elec- drogen gaseous mixture. However, it In the early fifties Natta started to investi- tron diffraction studies (the traditional was only after ten years that Natta suc- gate some physical properties of the field of Natta’s research activity), but al- ceeded in demonstrating that the said in- polymers, e.g. the rate of ultra-sonic so with adequate equipment waves in melted polymers (with for Ir and Uv spectrography, M. Baccaredda [8]) and the which at the time were consid- structure of crystalline polyeth- ered pioneering techniques. ylene (with P. Corradini [9]). Various research teams and However, he never ceased to services were established be interested in the synthesis within the Institute, even if in- of macromolecular compounds. formally. An important step in His talk often turned to the the life of the Institute was the high-molecular-weight linear creation of the Plastics Test- paraffins of which, during a trip ing Laboratory, set up by Nat- to Germany, he had received a ta with the collaboration of sample produced by the Fisch- Prof. D. Pagani, and with the er-Tropsch reaction in the pres- financial support of Milanese ence of ruthenium catalysts. firms [2]. The space available Natta resumed his experimen- for the Institute was consider- tal activity in the field of macro- ably increased with the con- molecular syntheses after he struction of a new building and had attended the lecture that the acquisition of the building Figure 2 - Chain growth by monomer addition Professor K. Ziegler delivered formerly housing the “Stazione to an activated chain end (1, 2, 3) or by monomer in Frankfurt (1952) about the Sperimentale per i Combu- insertion into a metal-to-carbon bond [4] ethylene polymerization in the stibili”. The scientific activity presence of alkyl aluminum developed by Natta from 1948 onwards dependence was connected with a reac- compounds (Ziegler’s “Aufbaureaktion” followed two main trends of high theoret- tion of first order with respect to hydro- [10]). At the end of the above lecture, ical and practical interest, which are still gen and of order (-1) with respect to car- which I also attended, Natta asked for valid even if 30 years have elapsed, i.e. bon monoxide (with the late R. Ercoli, full my opinion about Ziegler’s research: I the chemistry of carbon monoxide and Professor of Industrial Chemistry, Paler- was most favorably impressed by the synthesis and properties of macro- mo University, and S. Castellano, Car- Ziegler’s research on such a difficult sub- molecular compounds. Natta’s early re- negie Mellon Institute, Pittsburgh, Pa. ject, but I felt doubtful about the commer- search on the chemistry of carbon mo- U.S.A. [5]). Natta’s interest in the chem- cial prospects for Ziegler’s results. noxide dates back to the twenties. In the istry of carbon monoxide remained alive On this last point Natta’s opinion was op- early forties he became acquainted with even in subsequent years. As a matter of posite to mine: being well acquainted, the “oxo-synthesis”, a reaction discov- fact, he investigated the preparation and thanks to his previous work on synthetic ered by Dr. RohIen of Ruhrchemie. reactivity of chromium hexacarbonyl and rubber, with radical polymerization, he at Realizing its commercial importance, its arenic derivatives, and synthesized once realised - probably even before Natta investigated this reaction after vanadium hexacarbonyl, thus obtaining Ziegler himself - that the German scien- 1943 (with E. Beati [3]) with the twofold the first carbonyl of a metal of the 5th tist had found a completely new principle purpose of extending the scope of this group of the periodic table and the first as far as the synthesis of polymer chains reaction - originally applied to ethylene paramagnetic metal carbonyl (with R. Er- was concerned. In fact the polymeriza- only - to various organic substrates, and coli and F. Calderazzo, now full Profes- tion of ethylene carried out by Ziegler did of studying the mechanism of the same sor of General Chemistry, Pisa Universi- not occur by monomer addition to a free as well as of analogous carbonylation re- ty [6, 7]). The above very important re- radical or to a free carbonium ion (Figure actions investigated by Reppe during sults obtained by Natta in the field of car- 2), located at the end of a growing chain, World War II. Being convinced that the bon monoxide chemistry correspond on- but by monomer insertion between a

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metal atom and the growing chain bound the case of ethylene, propylene high tra of the amorphous and crystalline to it. In Natta’s opinion this offered greater polymers, which would be suitable for polymers were found to be similar, ex- possibilities for controlling the polymer application in the field of synthetic rubber cept for some bands, present in the latter chain structure during the synthesis. Ex- with which he was so well acquainted. which disappeared upon melting. F. cited by this idea, Natta suggested to the Somewhat reluctantly - we were all en- Danusso and G. Moraglio investigated Montecatini Company to enter into a col- gaged in research in other fields - we the behavior of the various polypropy- laboration agreement with K. Ziegler, and started to prepare and purify propylene lene fractions in solution and found that charged me to establish at his Institute a to be used in the polymerization experi- they had substantially different molecular research team entrusted with the task of ments. At the beginning of March 1954, weights. Natta’s early idea was to use repeating Ziegler’s experiments, of sepa- P. Chini obtained a small quantity of a propylene for the production of synthetic rating ethylene polymers with as high as yellow-brown gummy product which rubber: in March 1954 he insisted on possible a molecular weight, and of in- clearly was nonhomogeneous. The poly- copolymerizing propylene with butadiene vestigating the kinetics of polymeriza- merization of propylene immediately be- with the idea of obtaining a vulcanizable tion. It was also envisaged to send a few came the most important subject of our product. However as soon as the crys- members of the new team to Ziegler’s research; in particular, G. Mazzanti, who taline polypropylene was isolated, he re- Institute. Thanks to the collaboration of a at the time was at the head of Montecati- alized that the new polymer, being a high number of chemists of exceptional ca- ni’s trainees, dealt with the problem with melting one, could be used as a plastic pacity (it is enough to mention the late P. Longi and E. Giachetti. material in many fields, different from Prof. P. Chini, M. Farina, now full Pro- fessor at the Milan University, R. Magri, L. Luciani, E. Giachetti), Ziegler’s tests were repeated, ethylene polymers were fractionated by solvent extraction, and the study of the “Aufbaureaktion” kinet- ics was started. Under the agreement between Monteca- tini and K. Ziegler, at the beginning of 1954 Prof. Natta was given the text of Ziegler’s patent on the preparation of ethylene high polymers in the presence of catalysts obtained by causing TiCl4 and alkyl aluminum compounds to react. Thanks to the extensive knowledge of the aluminum alkyl chemistry already ex- isting at the Institute, the research in the new area could immediately be started. At this point, Natta was able to give full proof of his extremely great creative tal- ent. After learning of Ziegler’s results, and using his great experience in the field of heterogeneous catalysis and rad- ical polymerization, he assumed as a working hypothesis that the formation of ethylene high polymers was due to a higher rate of growth of the polymer Figure 3 - Chain growth and chain termination in ethylene polymerization chains, caused by the presence of a het- and propylene dimerization with organometallic catalysts erogeneous catalyst activating the ethyl- ene molecule before it is inserted in the All resources Natta had at his Institute those for polyethylene. By availing him- aluminum-carbon bond (Figure 3). were employed for the characterization self of very simple apparatus, and with Thinking that Ziegler could rapidly pro- of the new polymers. P. Corradini per- the help of Mr C. Origgi, a technician of gress in his research on polyethylene formed x-ray investigations, and a high exceptional skill who directed the work- Natta decided to prepare small quantities crystallinity was found in the less soluble shop of the Institute, in May 1954 Natta of the new polyethylene for the purpose polymer fractions. succeeded in making the first fibre from of studying its structure, but at the same Furthermore, after determining the poly- polypropylene. time, he decided to start the investigation mer chain identity period, he observed The mechanical characteristics of the of the polymerization of propylene. As a that there existed no planar zig-zag con- fiber were studied at the Plastics Testing matter of fact, as he knew that by react- formation of the type found in linear Laboratory with G. Lutzu. At the same ing propylene in the presence of alu- paraffin, at least in the crystal state. E. time, Natta and his collaborators started minum alkyls, dimers or at most trimers Mantica with M. Peraldo and L. Bicelli to discuss the structure of polypropylene of propylene could be obtained, he carried out the Ir analyses and found that and the reasons for the crystallinity of hoped that the new heterogeneous cata- the methyl to methylene ratio in the poly- the heptane-insoluble fractions. At first, lysts found by Ziegler might give, as in mer was about 1. Furthermore, the spec- the difference between the crystalline

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and noncrystalline fractions was as- Corradini had found for polypropylene. only three months elapsed from the first sumed to depend on the different molec- Schildknecht’s work focused the atten- synthesis of crude polypropylene to the ular weights. However, Natta was not ful- tion of Natta and his group on the rele- first patent application conveying all da- ly satisfied with this explanation: as a vance of the steric regularity in the poly- ta about isotactic polypropylene. matter of fact, the molecular weights did mer main chain to the physical proper- To give a few examples, Ziegler obtained not undergo a regular variation with the ties of the vinyl polymers. After count- his first crude nonfractionated polypropy- decreasing of the fractions solubility in less discussions the hypothesis was for- lene eight-nine months after his first the organic solvents, but were consider- mulated that the crystalline and non- patent on polyethylene. Some U.S.A. in- ably different in the crystalline and the crystalline polypropylene fractions were dustrial laboratories (e.g. Standard Oil of non-crystalline fractions. Natta liked re- different because of the existence in the Indiana and Phillips Petroleum), suc- peating the saying “Natura non facit crystalline polymer of steric regularity in ceeded in obtaining from propylene, by saltus” and urged us to look for other the main chains of the macromolecules. methods other than Natta’s, mixtures of reasons on which the said differences In his first paper on the topic [17], Natta polypropylenes with different stereoregu- might be based. From a thorough biblio- stated that in the crystalline fractions the larities but they did not fully understand the structure even after years of research. Finally, the DuPont Compa- ny that in August 1954 - ap- proximately two months af- ter the first patent of Natta - had filed a patent on the preparation of a polypropy- lene mixture with catalysts similar to Ziegler’s, only ob- tained isotactic polypropy- lene from the said mixture in 1955, i.e. after becoming acquainted with Natta’s pa- pers. After submitting his first patent application on polypropylene [12], Natta decided to develop re- search on the polymeriza- tion of other alpha olefins. These studies resulted in the patenting of many new isotactic polymers. He then focused his atten- tion on the factors determin- ing the stereospecificity of ZiegIer’s catalytic systems. On the basis of the hypoth- Figure 4 - First representation Figure 5 - First representation of 3/1 esis that it is a transition of an isotactic polymer chain helix of isotactic polypropylene metal solid compound that activates the olefin before graphic investigation we were able to as- asymmetric carbon atoms may have the the occurrence of the insertion in the certain that some crystallinity had been same steric configuration at least for metal-alkyl bond, Natta assumed that previously observed in a vinyl polymer, long chain portions, and proposed to stereospecificity was caused by the sur- the poly(isobutylvinylether), obtained by calI the said carbon atoms, and conse- face regularity of the solid. With the aim C.E. Schildknecht in 1948 by cationic quently the polymers containing them, of obtaining more regular catalytic sur- polymerization in heterogeneous phase. “isotactic” (Figures 4 and 5). The deter- faces, Natta decided to prepare the cata-

This polymer exhibited a very low crys- mination of the molecular structure of lysts using crystalline TiCI3, insoluble in tallinity, lower than that of non-fractionat- polypropylene paved the way for the the reaction medium, instead of TiCl4. ed polypropylene [11]. discovery that some catalysts based on Once again Natta’s intuition proved true: On the basis of the x-ray diffraction titanium halides and aluminium alkyls - the isotactic poIymer content in the spectra, whose interpretation was diffi- found by Ziegler - had a very important crude poIymer was increased from 40% cult just because of the low crystallinity and quite unexpected property: the to 85%. The way was paved for the com- of the samples, Schildknecht and col- stereospecificity, which we now know to mercial production of the isotactic poly- laborators had set forth the hypothesis be exceptionally high, i.e. equal to or mer. I have dwelt on the discovery of iso- that the polymer chains in the crystals even higher than that of enzymes. To tactic polypropylene as being Natta’s had a planar zig-zag conformation, fully appreciate the level of Natta’s cre- masterpiece. In this research - more which was inconsistent with what P. ative skill, it is enough to point out that than in any other - Natta’s imagination,

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deep and wide scientific In 1960 he succeeded in knowledge, decisiveness persuading CNR (Italian perseverance, and in- National Council for Re- credible skill blended search) to establish a harmonically. After this National Center of Ma- discovery, Natta devel- cromolecular Chemistry, oped a series of research consisting of eight sec- projects of outstanding tions located in Milan, importance in the new Padua, Turin, Genoa, field. Indeed, Sir Robert Pisa (two sections), Ro- Robinson wrote that Nat- me and Naples. ta “developed the theme In the sixties, thanks to of polymerization as a this Centre, macromole- grandiose fugue” [13]. cular chemistry in Italy The results that Natta reached a high level on and his collaborators ob- an international scale. tained concerning the The former Sections stereospecific polymer- were later replaced by ization and related fields an Institute, some labo- can hardly be listed. ratories, and some Re- However, the develop- search Centres. The ac- ment of this research tivity of Giulio Natta as may be inferred from Fig- Figure 6 - Development of the research of Natta an educator over almost ure 6, drawn from a sum- and co-workers on stereospecific polymerization 40 years has been so marizing paper that Natta successful that it seems published in 1963 [14]. The research that lene has been impressive: the present unnecessary to recall it here. Natta developed in the sixties followed production amounts to more than 3 mil- While he was convinced that the formal the main trends described above. He lion tons per year (Figure 7). Concerning lectures were of little use for the educa- continued to direct the research at his In- the rapid development of stereospecific tion of the young students, Natta deeply stitute till 1973, when having reached re- polymerization, he was very proud of the believed in the formative value of discus- tirement age, Natta left the Institute he number of patents that researchers all sions on specific research topics, and in had directed for more than 35 years. over the world had applied for, in the particular in the formative value of the The importance of Natta’s discoveries for field, in the period from 1954 to 1960 experimental research work and of the the progress of polymer science was im- [13]: 4 in 1954 (when the discovery took mastering of the theory necessarily con- mediately understood on an international place), 25 in 1955, approx. 150 in 1956, nected to it. He had an admirable faith in scale. As early as in January 1955, Pro- about 200 in 1957, 1958, 1959, 1960, for research: “Scientific research is truly fas- fessor P.J. Flory made the following a total of about 1.000 patents in six cinating, and those who do it are inter- comments on Natta’s first paper on iso- years! Now, I wish to briefly hint at the ested in every new application”, he wrote tactic polymers submitted to JACS [17a]: activity of Prof. Natta as an educator and [16] to conclude his last paper dated “The results described in your manu- at the impetus he gave to the progress of 1972. “As far as I am concerned, should script are of extraordinary interest; per- macromolecular chemistry in Italy. I begin anew, I would devote my life to haps one should call them revolu- research”. He followed his schol- tionary in significance” [15]. ars with the greatest interest, and This was also the opinion of Prof. although he was somewhat critical Tobolsky of Princeton University of their work, particularly from the when he published his paper “Rev- point of view of the practical im- olution in Polymer Chemistry” in portance of their research, he was 1957 [19]. In addition to a large very proud and happy for their number of international awards, in success. It was his opinion that U.S.A., Soviet Union and Europe, success in research may be in 1963 Natta was awarded the achieved by those who make a Nobel Prize, shared with K. Zie- careful choice of the research sub- gler. However he considered the jects and who never neglect the best acknowledgments for his re- possible application for the results search to be the data he often re- obtained. The research subjects ceived about the commercial pro- chosen should be dealt with duction of the new polymers, and through hard work, utmost scientif- the news about the progress of the ic exactitude, and criticism. “In this scientific and industrial research in way only”, he used to say smiling, the area he had started. In twenty “if fortune smiles on us, any suc- years the rise in the commercial cess is possible”. The importance production of isotactic polypropy- Figure 7 - World production of isotactic polypropylene of Natta’s school for the Italian uni-

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versity and industry may be inferred from ammonia - on which industry of fertilizers Chim. Ind. (Milan), 1955, 37, 6. the following. Of his scholars, about is based - through which the ever in- [6] G. Natta, R. Ercoli, F. Calderazzo, twenty have been appointed as full uni- creasing world population may be pro- A. Rabizzoni, J. Am. Chem. Soc., 1957, versity Professors in Italy and abroad. vided with food; the progress achieved is 79, 3611. The number of those who attained out- certainly higher; I only recall the few with [7] G. Natta, R. Ercoli, F. Calderazzo, standing positions in the industry is cer- whom I was more closely in the knowl- A. Alberola, P. Corradini, G. Allegra, tainly higher; I only recall the few with edge of biochemical mechanisms on Rend. Accad. Naz. Lincei, 1959, whom I was more closely acquainted: G. which life in our world is based; of the 27[8],109. Mazzanti, the former President of Eni; M. discovery of new materials, often useful [8] G. Natta, M. Baccaredda, Rubber Bruzzone and W. Marconi, heading As- and sometimes necessary for the sort of Chem. Technol., 1950, 23, 151; Kolloid soreni’s laboratories; G. Crespi, coordi- life mankind wants to lead at the present Z., 1951, 120, 190. nator of Montedison‘s research; G. Pre- time. Natta’s message should especially [9] G. Natta, P. Corradini, Ric. Sci., gaglia, head research and technology of be considered by all those who seek any 1955, 695. Montedison Petrolchimica, and former opportunity to attack research and the [10] K. Ziegler, Angew. Chem., 1952, President of the Italian Chemical Soci- chemical industry under the guise of 64, 323. ety; A. Valvassori, Managing Director of philosophical and ecological motivations [11] C.E. Schildknecht, S.T. Gross, Donegani Institute SpA; A. Palvarini, that they do not care to analyse in a criti- H.R. Davidson, J.M. Lambert, A.O. head of Farmoplant’s research; B. cal and conscious way. Zoss, Ind. Eng. Chem., 1948, 40, 2104. Calcagno, of the Pirelli Company; G. [12] G. Natta, P. Pino, G. Mazzanti, Dall’Asta, former head of Snia Viscosa’s Acknowledgement U.S. Patent 3 112 300, 1963. research Center of Colleferro; P. Longi, [13] R. Robinson, Rubber Plastics Age M. Ragazzini, E. Giachetti, G. Paleari, G. I wish to thank Mrs R. Lamma Fontani, 1961, 42, 1194. Negri, I. Ronzoni, U. Soldano, and many who for many years was Prof. Natta’s [14] G. Natta, Chim. Ind. (Paris), 1963, others. Their professional and human faithful secretary, for her help in finding 89, 545. qualities hold in honour the School in the documentation necessary for this [15] P.J. Flory’s letter to G. Natta dated which they were formed. commemorative paper. Jan. 1, 1955. By his example and work, Giulio Natta [16] “G. Natta Impact”, Science et So- left a message that everybody should References ciété, 1972, 22, 325. ponder and convey to the young re- [17] a) G. Natta, P. Pino, P. Corradini, searcher who did not have the luck to [1] G. Natta, Chim. Ind. (Milan), 1948, F. Danusso, E. Mantica, G. Mazzanti, meet him a message of faith in research 30, 63. G. Moraglio, J. Am. Chem. Soc., 1955, and in the benefits deriving to mankind [2] G. Natta, Materie Plastiche, 1953, 77, 1708; b) G. Natta, Rend. Accad. from science and technology. 19, 161. Naz. Lincei Mem., 1955, 4(8), 73. Natta’s optimism about the beneficial ef- [3] G. Natta, E. Beati, Chim. Ind. (Mi- [18] G. Natta, Reale Accademia d’Italia, fects of science and technology for the lan), 1945, 27, 84. Viaggi di studio promossi dalla fon- future of mankind was the result of the [4] G. Natta, P. Pino, U.S. Patent 2 dazione Volta, 1935, 2, 6. events he had witnessed and of the suc- 851 456, 1955. [19] A.V. Tobolsky, American Scientist, cesses he had attained: the synthesis of [5] G. Natta, R. Ercoli, S. Castellano, 1957, 45(1), 35.

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