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December 2000
Vol. 9, No. 12, pp. 45–47.
Chemistry Chronicles
The Long Road to “Organic Glass”

A 1901 Ph.D. thesis and a lot of lab work culminated in clear methacrylate polymers.

A dissertation, “On the Polymerization Products of Acrylic Acid”, completed in 1901, earned Otto Röhm a Ph.D. from the University of Tübingen in Southern Germany. Acrylic acid (CH2=CHCOOH) had been known since 1843, when it was prepared by oxidizing acrolein, and (after 1865) using the closely related methacrylic acid. Methyl and ethyl acrylates had first been prepared in 1873 and had been found to polymerize in 1880.

Röhm, who was greatly intrigued by the properties of the transparent polymers he could synthesize from acrylic esters, carried this work a step further. Acrylic acid was difficult to make, however, involving complex reactions that required expensive raw materials and resulted in low yields. Its derivatives would not be commercialized for a quarter of a century or more.

Röhm, meanwhile, needed to earn a living after receiving his doctorate. He worked in various chemical positions for a few years after 1901, at the same time undertaking research on his own in the chemistry of leather tanning. After the hair was removed and prior to tanning, hides had to be softened by a process known as bating. Typically, this was carried out by immersing them in a mixture of water and fermented dog (or bird) dung. It was a filthy, noxious, and unhygienic operation, and it raised a horrendous stench. Röhm figured there must be a better way to bate.

His research led him to conclude that hides were softened by the action of enzymes. From further study, he found that he could extract a suitable enzyme from ground animal pancreases. He prepared an extract of standard strength, which he called Oropon, and set out to market the product—one of the earliest industrial uses of enzymes. Meanwhile, he invited an old friend, Otto Haas, to join him as a partner in his new venture. Haas had emigrated to the United States in 1901. He went back to Germany, and they named their company, which they established in 1907, Röhm & Haas.

Once Röhm had overcome the resistance of tradition-bound German tanners, Oropon was a marked success and soon was selling well throughout Europe. In 1909, Haas, who had no background in chemistry, returned to the United States to set up a branch of the firm in Philadelphia. By 1914, he was producing Oropon (and later, other tanning chemicals) in Chicago. With exports from Germany cut off by World War I, his business thrived.

When the United States entered the war in 1917, the U.S. government moved to seize the Röhm & Haas American assets as enemy-alien property. In a series of legal gambits, Haas (although he was still a German citizen) staved off this attempt with the support of American tanners, who argued that the company’s products were essential to their war effort. In the process, though, Röhm’s interest in the U.S. business was sold off, and the Philadelphia firm became independent of its German parent (and dropped the umlaut from the company name). The U.S. government took over Röhm’s interest in the company (50%) and then auctioned it for $300,000.

Haas continued to expand his operations after the war. He acquired an old, run-down maker of basic industrial chemicals in Philadelphia. He added textile chemicals to his line of tannery items. Haas, at the same time, remained in close touch with his old friend Röhm and visited Germany often.

Röhm’s interest in the subject of his doctoral thesis had never waned. Prior to World War I, in fact, he had acquired a few patents for the use of acrylic ester polymers as substitutes for rubber or as drying oils for varnishes. By 1920, he rekindled his efforts. With the help of Walter Bauer, by 1926, he had developed an easier, cheaper process for making acrylic esters, based on heating ethylene cyanohydrin with sulfuric acid and an alcohol. In 1928, Röhm & Haas started to market poly(methyl acrylate) in Germany as a nonyellowing interlayer for laminated automotive safety glass, replacing nitrocellulose. Röhm kept Haas aware of his progress, and soon Haas’s chemists also were exploring acrylic polymers. The American company introduced its own safety glass interlayer, Plexigum, by 1931. At that time, it was still a relatively minor chemical firm, with sales of only about $3 million a year. Plexiglas dominated the market until it was beaten out by less expensive, better-performing polyvinyl acetal and butyral films in the late 1930s.

Bauer also began experimenting with methacrylic ester polymers, which form harder plastics than the acrylates. In 1932, he and Röhm poured methyl methacrylate between two vertical, parallel sheets of glass to polymerize. When they pulled away the glass sheets, they found they had a rigid, crystal clear, colorless sheet of polymer. Röhm called it an “organic glass” and branded the product Plexiglas.

The Plexiglas sheets softened at about 110 °C and were easy to shape when heated, as well as to saw or drill. Although relatively expensive, they were shatterproof, weather-resistant, and lightweight. Röhm went looking for applications: in windows, spectacle lenses, lighting fixtures, and dentures. As the world geared up for World War II, demand for Plexiglas boomed for use in military aircraft as cockpit canopies, windows, gun turrets, and bombardier enclosures. Haas sent one of his chemists to Germany to learn the techniques for casting sheets of Plexiglas, and by 1936, Röhm & Haas was turning them out at Bristol, PA.

While Röhm was developing methacrylate polymers in Germany, chemists at Britain’s giant Imperial Chemical Industries (ICI) in the early 1930s had come up with a better method for making the monomer, based on acetone or propanone and hydrogen cyanide. ICI began manufacturing cast methacrylate sheets in 1933. It trade named its product Perspex and sold it as a safety glass. The German Röhm & Haas and ICI exchanged licenses for their technology.

In the United States, Du Pont, too, started to work on methyl methacrylate plastics in the early 1930s, seeking an outlet for its surplus isobutanol. Under its long-standing patent and technology exchange agreement with ICI, Du Pont licensed ICI’s process for making methacrylate ester. It began selling the plastic, initially under the brand name Pontalite and later Lucite, in 1937, the year Otto Röhm died. Unlike its American competitor Röhm & Haas, however, Du Pont focused on small shapes, such as rods and tubes.

Consumption of methacrylate plastic rose dramatically as the output of warplanes soared during World War II. In the United States, for example, sales of Plexiglas by Röhm & Haas climbed from $430,000 in 1938 to $4.5 million in 1941 (despite lower prices) and then to more than $22 million in 1944. The company expanded its capacity rapidly, bringing a second Plexiglas plant on-line in Knoxville, TN, in 1943.

As the war wound down in 1945, however, sales of Plexiglas plummeted by 75%. Röhm & Haas found itself in a position of making far more of the plastic than it had an outlet for. Business revived briefly in 1946, fed by pent-up consumer demand, as Plexiglas found uses in a variety of novelty items, including cigarette cases, doll furniture, and jewelry. But the fad did not last out the year.

Röhm & Haas managed to open up other applications, though. Lenses for car taillights proved to be a lucrative market. Illuminated signs for outdoor advertising were even more important. Faced with the same problem in Britain, ICI found markets for its Perspex in lighting, skylights, architectural shapes, signs, and even bathtubs.

Because it is remarkably clear, shatter- and weatherproof, dimensionally stable, and easy to shape, poly(methyl methacrylate) continues to be widely used for signs, lighting fixtures, protective panels and windows, and construction. Additional applications include dentures and other dental appliances, contact lenses, and optical fibers.

Polyacrylates also have a diverse array of uses. Since the early 1950s, they have been important in formulating water-based paints and industrial coatings. They also go into textile and leather finishes and paper coatings. During the 1930s, Röhm & Haas chemists found that esters of methacrylic acid with some of the higher alcohols produced additives for lubricating oils and hydraulic fluids that kept viscosity low at low temperatures. These additives, which the company named Acryloids, are credited with keeping Russian military equipment in operation during the bitter winter campaigns of World War II while German equipment froze solid.

David M. Kiefer, assistant managing editor of Chemical & Engineering News until his retirement in 1991, is a consulting editor for Today’s Chemist at Work. Comments and questions for the author can be addressed to the Editorial Office by e-mail at tcaw@acs.org, by fax at 202-776-8166 or by post at 1155 16th Street, NW; Washington, DC 20036.

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