SAKURADA, ICHIRO

(b. Kyoto, Japan, 1 January 1904; d. Kyoto, Japan, 23 June 1986), polymer chemistry, fiber chemistry.

Sakurada was the pioneer in polymer chemistry and modern chemical fibers research in Japan. He also was the developer of vinylon, a lightweight, durable, weather-resistant fiber widely used in the agriculture, industrial, and fishing sectors.

Childhood and Education Sakurada was born, grew up, and spent most of his scientific career in the ancient city of Kyoto. His father, Bungo Sakurada, was a newspaperman and served as a war correspondent for the newspaper Nihon Shinbun (literally translated as “Japan newspaper”) during the Sino-Japanese War (1894–1895) and the Russo-Japanese War (1904–1905).

In 1920 Sakurada enrolled at the Third High School in Kyoto, a three-year national high school in prewar Japan that prepared elite students for the imperial universities. Influenced by his father, Ichiro Sakurada was fond of writing and thought about majoring in literature. However, his mother, Masa, unhappy with her husband’s unsettled occupation and advised her son to enter the engineering field, which he did.

Sakurada’s early interest in colloids arose when he was fascinated with the beauty of a red sol of gold in a chemistry class. At this time, when colloid chemistry was reaching at its zenith, the chemistry teacher was eager to include colloids as a subject for high school students.

In April 1923, Sakurada entered the Department of Industrial Chemistry in the Faculty of Engineering at Kyoto Imperial University (the forerunner of Kyoto University). There, he found his lifelong mentor in Gen-itsu Kita, who—holding great administrative power—was running the department and promoting research in such industrially important materials as fibers, petroleum, and rubber. Kita characteristically stressed the importance of basic research in industrial chemistry, a trait that Sakurada inherited.

As a college student, Sakurada became particularly interested in fibers. In the mid-1920s, the rayon industry was booming in Japan. Consequently, fibers and textiles drew much attention from academic chemists as a promising research subject. Kita was one of the active academics who directed research on cellulose acetate fibers. He sent many of his students to rayon companies upon their graduation. For his senior thesis, Sakurada chose to study the synthesis of cellulose derivatives, such as cellulose esters, under Kita’s supervision.

Colloids and Macromolecules After his graduation in 1926, Sakurada spent two years as a research fellow at Kita’s laboratory. Impressed by Sakurada’s ability, Kita sent him to Germany in 1928 to extend his study of cellulose. Sakurada spent half a year at the University of Leipzig, where he studied the swelling and dissolution of cellulose acetate in organic solvents under the renowned colloid chemist Wolfgang Ostwald. In the summer of 1929, he moved to the Kaiser Wilhelm Institute for Chemistry in Berlin-Dahlem, a suburb of Berlin, to study with the cellulose chemist Kurt Hess.

During the 1920s in Germany, there was a heated debate over the molecular structure of a class of substances called polymers, including cellulose, starch, proteins, rubber, and plastics. Hermann Staudinger proposed his theory that they were made up of enormously large molecules, for which he coined the word macromolecules. He argued that the properties of polymers, such as colloidal behaviors in solutions, elasticity of rubber, and the strength of fibers should stem from the largeness and shapes of macromolecules. On the other hand, many chemists supported the aggregate theory that polymers were physical aggregates of molecules of ordinary sizes. The properties of polymers, they insisted, came from physical forces between the aggregates. The debate

culminated in a symposium held in 1926 at the Düsseldorf meeting of the Gesellschaft Deutscher Naturforscher und Ärzte (Society of German Natural Scientists and Physicians), in which Staudinger’s macromolecular theory was severely criticized by most of the other speakers.

Both Ostwald and Hess were among the leading advocates of the aggregate theory. Ironically, Sakurada, Japan’s future leader in macromolecular chemistry, came to their laboratories without knowing about the debate and thus made his German debut as their loyal student. At Hess’s laboratory, Sakurada collected data that might support the aggregate structure of cellulose. For the first three months, he attempted to crystallize cellulose in various solvents in order to show that cellulose, like ordinary organic compounds, could be purified by crystallization. After that attempt failed, Sakurada examined how the swelling behavior of cellulose was affected by its impurities. Colloidal properties might be, he and Hess suspected, due not to the large size of cellulose molecules but to impurities in the cellulose. In his German papers, Sakurada criticized Staudinger’s work, a criticism that, Sakurada later recalled, was more or less faultfinding, or criticism for criticism’s sake.

While in Germany, Sakurada had an opportunity to attend what became known as a historic symposium on colloid-polymers, titled “Organische Chemie und Kolloidchemie” (Organic chemistry and colloid chemistry), which the Kolloid Gesellschaft (Colloid Society) arranged at its annual meeting in Frankfurt in September 1930. Wolfgang Ostwald, the founder of the society, presided over the meeting. Such notable polymer researchers as Staudinger, Kurt Meyer, Herman Mark, Reginald O. Herzog, Hess, and Rudolf Pummerer were invited as principal speakers. After hearing their presentations, Sakurada sensed that the aggregate theory was now on the verge of falling apart. Nonetheless, Hess would remain as Staudinger’s formidable opponent in German scientific circles until the late 1930s.

Research on Fibers Back in Japan in 1931, Sakurada received his doctor of engineering degree from his alma mater for his study of cellulose, “Ueber die Cellulose und ihre Substitutionsprodukte” (On cellulose and its substitution products). That year he married Chiyoko Okumura. They had three children, including their only son, Yutaka Sakurada, who would later work on synthetic polymers for medical use at Kuraray Company.

Sakurada was appointed associate professor at Kyoto Imperial University in 1934 and full professor the following year. Although he was reluctant to give up his German teacher’s aggregate view for years, he turned into the most active propagator of the macromolecular theory of polymers in Japan’s chemical community after the mid-1930s. At that time, he must have thought that the macromolecular theory was definitively gaining significant acceptance in Europe and America. His involvement in the German macromolecular debate no doubt enriched his later scientific career in Japan. All of his fruitful research, which he would carry out in Japan, used the macromolecular theory as its guiding principle.

At Kyoto, Sakurada, together with his colleagues and students, carried out both basic and applied study of cellulose and other polymers. His study on the viscosity of polymer solutions helped to alter the Staudinger law of viscosity, which expressed a linear relationship between viscosity and molecular weight (or degree of polymerization) of polymers in dilute solutions. From this simple linear relationship, Staudinger had drawn a conclusion that macromolecules had a thin, rigid rod shape, like a glass fiber in solution. Sakurada, on the other hand, thought that they should be flexible chain molecules, a concept that gave rise to a new interpretation of the viscosity mechanism. By 1940, refined general formulas had been proposed independently by Werner Kuhn in Switzerland; Herman Mark, then in United States; Roelof Houwink in the Netherlands; and Sakurada. To put the viscosity formula in a general way, consider η_sp/c = constant x Pn where η_sp = the specific viscosity, c = the concentration, P = the degree of polymerization, and “n” is a characteristic value for a given type of macromolecule. According to Staudinger, “n” should always be 1. Sakurada and others suggested that if the exponent “n” was numerically large, then the molecular chain was less folded; if it was small, the chain was highly folded and did not have a strong influence on viscosity. Sakurada and others assumed different values of “n.” Werner Kuhn thought that it should be between 0.6 and 0.9; Mark between two-thirds and three halves; Houwink, 0.6; and Sakurada between 0 and 2.0. They indicated that Staudinger’s empirical viscosity-molecular weight relationship was valid for only a few specific systems and not for many important high polymers such as rubber, polystyrene, and polyamides.

Sakurada proposed his general formula in a Kyoto journal article, “Yoekichu ni okeru itojo-bunshi no katachi narabini yoeki-nendo to bunshiryo no kankei” (The shape of threadlike molecules in solution and the relationship between the solution viscosity and the molecular weight) in 1940, but for years it remained little known to Western scientists. Today, the general formula is often called the Mark-Houwing viscosity formula rather than the Kuhn-Mark-Houwing-Sakurada viscosity formula.

The technique of x-ray diffraction of cellulose, which he had learned from Carl Trogus while in Germany, played an important role in Sakurada’s fiber research. Analyzing the structure of cellulose by this technique, he and his student, Keiroku Fuchino, discovered a new crystalline cellulose named “water cellulose,” which contained water molecules in the crystal lattice. His other basic research included such topics as the chemical reactions of macromolecules and their mechanism (for example, the mechanism of chain transfer and the relationship between monomer feed ratio and copolymer composition), the permittivity and diffusion of polymers in solutions, and the mechanical properties of fibers.

On the applied side, his work on synthetic fibers was extremely important. Japan’s boycott of Australian wool in 1936, which signaled the beginnings of its autarky program, resulted in the establishment of the Nihon Kagaku Sen-i Kenkyusho (Japanese Institute for Chemical Fibers Research) at Kyoto Imperial University. With an ample donation from the mercer and trader Mansuke Ito to the institute, Sakurada and his coworkers, including Seizo Okamura, began to study the synthesis of artificial wool from cellulose acetate. Even though he was aware of some of Wallace Carothers’s ongoing research on polymerization at DuPont through the latter’s publications and patents, Sakurada predicted that completely synthetic fibers, which would excel existing natural and semisynthetic fibers, would not be feasible. Thus, he focused his investigative efforts on modified natural fibers such as cellulose acetate.

DuPont’s announcement of the invention of nylon in October 1938 dashed Sakurada’s optimism regarding modified natural fibers and led him to take a hard look at completely synthetic fibers. Japan’s industrialists were now concerned that nylon would deal a fatal blow to the Japanese silk industry. Silk was Japan’s major export. In 1938 Japan had some 79 percent of the world’s export share of silk. The exports depended heavily on the American market: The United States was then buying nearly 80 percent of Japan’s silk exports. About 70 percent of the American consumption of silk was for women’s stockings. Fabricated into stockings from the outset, nylon appeared ready to replace silk almost immediately in this dominant field of hosiery. A newspaper article reported that the United States intended to shut out silk within ten years, which would be a matter of grave concern to forty million Japanese farmers.

By January 1939, U.S. representatives of two Japanese companies had managed to obtain a few milligrams of nylon, and they immediately sent them to Sakurada and other chemists. Sakurada conducted an x-ray diffraction analysis to determine the starting materials of nylon. Their analyses quickly showed that nylon was a surprisingly good fiber, except that it was too elastic and soft when compared with silk, the only weakness which Sakurada could find—and that one flaw was ameliorated by DuPont by 1940. In February, an emergency symposium on nylon was held in Osaka, the center of Japan’s fiber and textile business, where Sakurada and other fiber chemists reported on the properties and possible starting materials of nylon. They also praised Carothers’s scientific work as well as DuPont’s well-planned fundamental research program, while criticizing the backwardness of Japan’s industrial research.

The Development of Vinylon The “nylon shock” triggered the institutionalization of fiber chemistry in Japan. Owing to the efforts of Kita and Sakurada, Kyoto Imperial University in April 1941 opened the Department of Fiber Chemistry in which Sakurada, Okamura, Masao Horio, and Kiyohisa Fujino began teaching fiber and polymer chemistry. In the same year, government, industry, and academe in Japan joined to create Nihon Gosei Sen‘i Kyokai (Japanese Research Association of Synthetic Fibers) to promote research on and the development of synthetic fibers. Under its umbrella, Sakurada’s group decided to study polyvinyl alcohol (PVA), while another group at the Tokyo Institute of Technology worked on nylon and polyurethane fibers.

PVA was readily available to Sakurada, as in the previous year he had assigned Seung Ki Li and Hiroshi Kawakami to investigate the hydrolysis rate of poly(vinyl acetate) as a part of his basic research on polymers. Sakurada thought that a cellulose-like fiber could be made from PVA, as it appeared to resemble cellulose in that both had many hydroxyl groups in their macromolecules. Many attempts were needed to solve practical problems. For example, they had to develop the so-called three-step hardening method by using a formalin treatment to make the PVA fiber insoluble in water during its synthesis process. In October 1939, just one year after DuPont’s announcement of nylon, Li announced a new PVA fiber, tentatively named the Synthetic No.1.

The Synthetic No. 1 still had a practical flaw for use as a fiber. When wet, its softening point dropped to 50 to 60 degrees centigrade (122°F–140°F). After attempts to solve this problem failed, Sakurada recalled his prior study on water cellulose. Water cellulose was formed by washing alkali cellulose with low-temperature water. It contained water molecules in the crystallization. When it was dried at 100 degrees centigrade (212°F) for a few minutes, it was transformed into cellulose II (mercered cellulose) by losing the water molecules. The drawn PVA fiber, Sakurada reasoned, should contain water, and thus it should be susceptible to water. If water molecules were eliminated by heat, the distance between the PVA molecules would be shortened and the combining power between the PVA macromolecules would increase. Hence, heat resistance would be improved. The result was exactly what he anticipated. In this way, his group was able to establish the process of giving hot-water resistance to the fiber by means of a high temperature treatment.

In January 1941 a pilot plant was constructed in the city of Takatsuki in Osaka Prefecture to produce the Synthetic No. 1. The scale-up work was, however, hampered by the outbreak of war and ended with Japan’s surrender in August 1945. It was not until 1950 that a large-scale industrial production of the PVA fiber, named vinylon, started at Kurashiki Rayon Company (later Kuraray Company) in Okayama Prefecture. The industrialization required hard effort by Tsukumo Tomonari (another student of Hess) and his coworkers at Kurashiki Rayon. As Japan’s original synthetic fiber, the vinylon fiber has been used for clothes, ropes, and a wide variety of industrial materials. A few years later, Li began the production of vinylon in North Korea.

In retrospect, Sakurada prided himself on the vinylon fiber as an industrial fruit that stemmed from his academic polymer research. After all, the research and development of vinylon was a big project involving several hundred chemists and chemical engineers. With Kita in charge, Sakurada directed a number of eminent academic chemists, including Seung Ki Li, Hiroshi Kawakami, Masakatsu Taniguchi, Keiroku Fuchino, Tetsuro Osugi, Hidenari Toyama, Seizo Okamura, Shoichi Matsumoto, Waichiro Tsuji, Kiyoshi Hirabayashi, Michiharu Negishi, Iwao Tsukahara, Akio Ueno, Masao Hosono, and Takeo Morita. Invented in response to the emergence of America’s nylon, the “made-in-Japan” fiber vinylon ignited Japan’s polymer research.

Postwar Polymer Chemistry As has been seen, Japanese polymer research arose first from studies of fibers rather than rubber or plastics. Yet in the midst of war, the activities of the Research Association of Synthetic Fibers were extended to synthetic rubber and plastics. In early 1943, the association was transformed into Kobunshi Kagaku Kyokai (Association of Polymer Chemistry), the world’s first independent scholarly society in this field. It published the first issue of its journal, Kobunshi Kagaku (Polymer chemistry), in October 1944, one and a half years earlier than the appearance of Mark’s Journal of Polymer Science and three years before Staudinger’s Die makromolekulare Chemie (Macromolecular chemistry). In 1951, the association was reorganized as the Kobunshi Gakkai (Society of Polymer Science). One of its founders, Sakurada served as the third president from 1961 to 1968. The society played an indispensable role in the phenomenal growth of the polymer community in postwar Japan.

In 1961 Kyoto’s Department of Fiber Chemistry was renamed the Department of Polymer Chemistry, where Sakurada served as a professor until his retirement in 1967. Succeeding Kita’s tradition of industrial chemistry, the Kyoto school, to which Sakurada was central, was the major site of Japan’s polymer research and education. As an educator, he was charismatic, strict, and punctual, yet he took good care of his students. About 210 students were trained as polymer chemists at his laboratory. Many of them occupied leading academic and industrial positions.

Upon retiring from Kyoto University in 1967, Sakurada assumed a professorship at Doshisha University in the city of Kyoto, which he held until 1974. He played a pivotal role in founding the Nihon Hoshasen Kobunshi Kagaku Kenkyu Kyokai (Japan Radiation Polymer Research Institute) in 1956. He also served as the president of the Chemical Society of Japan from 1968 to 1969. For his work on vinylon and polymers, he was awarded many prizes, including the Japan Academy Award in 1955, the Kun Nito Kyokujitsu Juko-Sho (Gold and Silver Star of the Order of the Rising Sun) in 1974, and the Bunka Kunsho (Order of Culture) in 1977. A prolific writer, Sakurada published over twenty books and some 880 scientific papers and essays. He authored Japan’s first textbook on polymer chemistry, Kobunshi no kagaku(Chemistry of macromolecules) in 1940. He published a book about his scientific work as an English-language monograph, Polyvinyl Alcohol Fibers, in 1985, a year before dying of lung cancer at the age of eighty-two.

BIBLIOGRAPHY

WORK BY SAKURADA

“Yoekichu ni okeru itojo-bunshi no katachi narabini yoekinendo to bunshiryo no kankei” [The shape of threadlike molecules in solution and the relationship between the solution viscosity and the molecular weight]. Nihon Kagaku Sen’i Kenkyusho Koenshu [Collected lectures of the Japanese Institute for Chemical Fibers Research] 5 (1940): 33–44.

“Kobunshi no kagaku” [Chemistry of polymers]. Kogyo Kagakuzasshi[Journal of industrial chemistry] 22 (March 1940). A special issue comprising 191 pages.

Sen’i kagaku kyoshitsu yori [From laboratory of fiber chemistry]. Kyoto: Bunri-shoin, 1943.

With Seizo Okamura, eds. Ko-jugo hanno [The high polymerization reaction]. Kyoto: Sen-i bunken kankokai, 1943.

Senso to kobunshi-kagaku [War and polymer chemistry]. Tokyo: Association of Polymer Chemistry, 1944.

Goseibutu no kagaku [Chemistry of synthetics]. Tokyo: Asahi shinbunsha, 1947. Sen-i no kagaku [Science of fibers]. Tokyo: Sankyo shuppan, 1948.

Sen’i monogatari [A fiber story]. Kyoto: Maki shoten, 1951.

Dai sanno sen’i [The third fiber]. Kyoto: Kobunshi kankokai, 1955.

With Masakatsu Taniguchi. Sen’i no kagaku [Chemistry of fibers]. Kyoto: Sankyo shuppan, 1956.

As editor. Poribiniru arukoru[Polyvinyl alcohol]. Kyoto: Kobunshi kankokai, 1956.

Sen-i, hoshasen, kobunshi [Fibers, radiations, and polymers]. Kyoto: Kobunshi kankokai, 1961.

With Hiroshi Sobue and Munenari Kushi, eds. Gosei sen’i [Synthetic fibers]. Tokyo: Asakura shoten, 1964.

Kobunshi-kagaku to tomoni [Together with polymer chemistry]. Tokyo: Kinokuniya shoten, 1969. An autobiography.”

Memoirs of My Research, 1–10” (in Japanese). Kagaku [Chemistry] 27 (1972): 12–17, 170–177, 284–291, 393–398, 478–483, 571–577, 657–663, 758–764, 867–873, 974–979.

Kagaku no michikusa [Loitering in chemistry]. Kyoto: Kobunshi kankokai, 1979.

Polyvinyl Alcohol Fibers. New York: M. Dekker, 1985. His only English book.

OTHER SOURCES

Furubayashi, Yuka. “The Formation of Polymer Chemistry in Japan: An Analysis of the Contributions of the Japanese Research Association of Synthetic Fibers” (in Japanese). Master’s thesis, Tokyo Institute of Technology, 2003.

Furukawa, Yasu. “Ichiro Sakurada” (in Japanese). Available from http://www.civic.ninohe.iwate.jp/100W/03/024/index.htm.

———. Inventing Polymer Science: Staudinger, Carothers, and the

Emergence of Macromolecular Chemistry. Philadelphia: University of Pennsylvania Press, 1998. See especially pp. 207–210.

Kim, Dong-Won. “Two Chemists in Two Koreas.” Ambix 52 (2005): 67–84.

Mark, Herman. “In Memory of Ichiro Sakurada (1904–1986).” Polymer Journal 19, no. 5 (1987): 439–440.

Morawetz, Herbert. Polymers: The Origins and Growth of a Science. 1985. Repr., New York: Dover, 1995. See especially pp. 103–110.

Okamura, Seizo. “Dedication to the Late Professor Ichiro Sakurada.” Polymer Journal 19, no. 5 (1987): 437–438.

———. “Polymer Chemistry: Ichiro Sakurada, Who Developed

Vinylon with Originality” (in Japanese). In Nihon no sozoryoku: Kindai gendai wo kaika saseta 470 nin [Creative powers in Japan: 470 people who cultivated the modern age]. Tokyo: Nihon hoso kyokai, 1993.

———. “Professor Ichiro Sakurada and Polymer Chemistry in Japan: A Perspective of Historical Study of Science” (in Japanese). In Nihon no kobunshi kagaku-gijutsu-shi [History of Japanese polymer chemistry and technology]. Tokyo: Japan Society of Polymer Science, 1998.

Shibatani, Kyoichiro. “Which Is Beautiful, the Girl or the Flower?” In The Chemical Society of Japan: A 125-Year Quest for Excellence 1878–2003, edited by Tadashi Watanabe. Tokyo: Chemical Society of Japan, 2003.

Tsuji, Waichiro. “The Giant in Fiber and Polymer Chemistry: Professor Ichiro Sakurada” (in Japanese). Sen’i to Kogyo [Fiber and Industry] 52, no. 6 (1996): 253–257.

———. “An Outline of Professor Ichiro Sakurada’s Works in Fiber and Polymer Chemistry” (in Japanese). Kagakushi[History of chemistry] 24 (1997): 205–217.

Yoshihara, Kenji. “Vinylon Is the Fiber That Japan Brought Up: Ichiro Sakurada, A Polymer Star” (in Japanese). Gendai Kagaku (Modern chemistry) no. 6 (2005): 16–21.

Yasu Furukawa