A Most Invented Invention

It is the fourth-largest-selling plastic in America. Last year nearly seven billion pounds of polypropylene were stretched, blown, extruded, or molded into thousands of different products. Chances are the wrapper on your candy bar, the food-storage container in your refrigerator, the lining in your baby’s diaper, and the webbing in your lawn furniture were all made of it. Car-battery cases, auto parts, disposable medical clothing, syringes, woven bags, and all kinds of toys are fashioned from the plastic, as are millions of yards a year of rope, carpeting, and upholstery fabric. But what sets polypropylene apart is not only its commercial ubiquity but also its curious origin three and a half decades ago. It was invented or discovered at least nine times in as many places around the world, and its history is one both of fiercely competitive technical development and application and of decades of battling over inventive priority and patent rights. Polypropylene may be the world’s most invented invention.

The substance’s awkward name reflects its composition. The molecule is a polymer, meaning many monomers, or simple molecules; it is formed by linking together thousands of individual propylene molecules into a giant, straight chain. Polymers are common in nature—they are the major constituents in plant fibers, hair, bones, and muscles; polypropylene is one of many man-made polymers.

During the 1920s Swedish and German scientists began to theorize that polymer chains could be made many thousands of times longer and heavier than any known. In 1933 researchers at Imperial Chemical Industries of England created the first man-made, high-molecular-weight polymer: polyethylene. Ethylene, like propylene, is a reactive hydrocarbon olefin—a by-product of petroleum refining. Polyethylene was created by melding long molecular chains of ethylene (in the presence of heat, a catalyst, and an oxidizing agent) under great pressure—as much as forty thousand pounds per square inch.

The high pressure used in making it caused its molecular chains to be branched rather than purely linear, making the plastic weak and soft, with a low melting temperature. Still, polyethylene stormed the marketplace. By 1958, fifteen years after its commercial introduction in the United States, three hundred million pounds were consumed in this country. Moreover, it was the largest-selling plastic in the world.

The rise of polyethylene inspired some of the world’s leading polymer scientists to try to eliminate the plastic’s weaknesses by finding a way to polymerize straight, unbranched chains, presumably by using less pressure in the process. One such scientist was Karl Ziegler, director of the esteemed Max Planck Institute for Coal Research, in M’fclheim an der Ruhr, West Germany. Ziegler had earned his doctorate at twenty-one and made important contributions to several fields of chemistry before becoming head of the institute in 1943, when he was forty-five. The institute was sponsored by the coal industry, but Ziegler saw to it that he had complete freedom to do any work of his own in areas unrelated to coal and to keep any patents and royalties that resulted. One such area was in polymers, where his researches paved the way for many of the inventors of polypropylene who followed.

During the 1940s Ziegler published and lectured widely about his ongoing efforts to synthesize the first true straightchain polymers. In many quarters, both academic and commercial, he encountered indifference and skepticism, but by the early 1950s representatives from leading European and American chemical firms were paying frequent visits to the Planck Institute. There they would find Ziegler and his everpresent patent attorney, Andreas von Kreisler, eager to license his know-how. Ziegler’s contemporaries remember him as a “perfect German gentleman,” taciturn during negotiations despite his strong command of English. He was decidedly entrepreneurial, but he valued personal rapport, trust, and integrity as highly as hard business contracts.

In 1950 E. T. Borrows, of Petrochemicals Ltd., forged a friendship with Ziegler and licensed exclusive United Kingdom rights to his chemistry. Two years later Giulio Natta, one of Italy’s leading polymer chemists, secured Italian rights to Ziegler’s polymer work relating to the “transformation of olefins” for his corporate sponsor, the Montecatini Chemical Company, of Milan. Natta, born in Imperia, Italy, in 1903, impressed acquaintances as a gentle and demure scientist absorbed in his work. Like Ziegler, he was an entrepreneur as well, but he was a more intense and calculating one than the German, and less given to personal, informal agreements. With their temperaments so different, a breach between the two was perhaps inevitable.

Ziegler’s licensing deals extended well beyond England and Italy; in the United States the Hercules Powder Company gained entrée to his work in 1952. Hercules had been created by a 1912 antitrust ruling that broke up the Du Pont explosives monopoly and had since moved into new chemical fields. Later that year Ziegler also sold a semiexclusive license for Germany to Farbwerke Hoechst, of Frankfurt. So by late 1952 four major chemical companies were banking on a breakthrough from Ziegler’s polymer team. A breakthrough occurred the following year.

During the summer of 1953 E. Halzkamp, a graduate student at the institute, accidentally polymerized a sample of ethylene but didn’t fully understand the unusual reaction. Then, in October, building on his work, Ziegler’s team used a zirconium catalyst to polymerize half a sample of ethylene into a solid piece of polyethylene. Ziegler wrote of the result that “it is impossible by my own hands to put it into two pieces.” Improvements in the strength of the product followed with the intro auction of new catalysts, especially titanium halides and aluminum alkyls.

The discovery was momentous for two reasons. First, the reaction took place at low pressure and mild temperature; thereafter polyethylene would be much safer and less expensive to make. Second, this new low-pressure polyethylene was composed of straight molecular chains—the catalytic reaction had caused the polypropylene molecules to attach themselves to the end of the chain only, creating an orderly linear structure. As expected, the new plastic was harder, stronger, and more rigid than its predecessor.

Ziegler, having succeeded at the long-chain polymerization of ethylene, might sensibly have gone on to test other olefins, like propylene, for similar results. But he didn’t; he had long been skeptical about the possibility of polymerizing propylene and didn’t change his mind now. “ Es geht nicht! ” he once exclaimed to Natta. He proceeded to test other catalysts with ethylene, instead of other olefins.

Other polymer scientists were quick to do what Ziegler didn’t. Natta’s team of researchers learned of Ziegler’s catalyst system from three Montecatini chemists who were working at the Planck Institute. They immediately set to work with propylene and succeeded in polymerizing it on March 11, 1954. They kept their discovery secret pending patent applications and plans for commercialization. At a more leisurely pace Ziegler achieved the same result in May, sent a description and a sample to Natta, and applied for a patent in August—only to learn that the Italians had filed ten days earlier.

Ziegler felt betrayed. He believed that the technical-exchange agreement between the two institutions—as well as the code of honor between scientists—should have compelled Natta to keep him apprised of the experiments. Natta, however, believed that since money had flowed only toward Ziegler, knowledge should be expected to flow only the other way, and that in any case Montecatini’s license with Ziegler had been worded too narrowly to include polypropylene.

Relations between the two deteriorated. They fell into a licensing dispute that was worked out by lawyers—Ziegler would be allowed to license polyethylene and his catalysts; Natta had rights to polypropylene but would pay 30 percent of all the royalties on it to Ziegler. Years later, in 1963, the two shared a Nobel Prize for their contributions to polymer chemistry and, at least on that occasion, spoke kindly of each other. And it must have been some consolation to Ziegler that he had typically sold his licenses for a million dollars apiece.

As the months passed, it became clear that Natta and Ziegler were hardly the only two men who had created polypropylene. Unsurprisingly, given the importance of the Ziegler catalyst system, the other companies that had licensed his know-how followed fast. Hoechst chemists made polypropylene in a low-density polyethylene pilot plant as early as March 1954 but decided not to “usurp Ziegler’s research field” by rushing to the patent office. Petrochemicals Ltd., the British licensee, also achieved the reaction in its pilot plant during a temporary shortage of ethylene, not long after Natta’s patent and Ziegler’s discovery of the plastic.

And Hercules also discovered polypropylene. In early 1955 a team of scientists headed by Edwin J. Vandenberg at the Hercules Research Center in Wilmington, Delaware, began investigating polymerization with Ziegler catalysts. Scarcely a week into the work they polymerized propylene. Their initial sample had “so much amorphous or rubber polypropylene that the overall properties were no better than polyethylene,” according to a company report, but within a few months they were making polypropylene with “such outstanding physical properties that it would warrant a full-scale development program.” Hercules soon learned of the earlier breakthroughs by Natta and Ziegler.

Thus far the multiple invention of polypropylene seems logical and plausible: Ziegler developed a revolutionary catalyst system for polymerizing ethylene but failed to move as quickly in trying it with propylene as did several others with whom he was sharing his knowledge. But there were still many more inventors.

Chemists at Phillips Petroleum, in the United States, conducted intensive research in catalysis in the early 1940s, trying to improve fuel octanes and synthetic rubbers. Grant C. Bailey and James A. Reid discovered a promising nickeloxide olefin catalyst, but their work was then dropped during the war. In the late 1940s two other Phillips scientists, John P. Hogan and Robert L. Banks, picked up the line of inquiry.

By 1951 Hogan and Banks, both still in their early thirties, were attempting to oligomerize (make mid-size chains of) olefins such as propylene and ethylene, for high-performance gasoline additives. When they added chromium oxide to their nickel-oxide catalyst in a propylene mix, they observed an unusual effect: “A white solid material appeared in the product receiver and a large pressure differential occurred between the inlet and outlet of the reactor, forcing the termination of the experiment. When the reactor was dismantled, additional white solid material was found.” This white substance, they soon determined, was polypropylene, and chromium oxide was the key catalyst. Phillips quickly filed a patent application, on January 27, 1953—more than a year before either Natta or Ziegler made polypropylene.

Chemists in the laboratories of Standard Oil of Indiana had also been experimenting with the polymerization of olefins. While trying to catalyze alkylation reactions with ethylene (using cobalt on charcoal) Alex Zletz discovered low-pressure polyethylene and then polymerized propylene, sometime between April and July 1953. Standard Oil filed for a patent on the process in October 1954 but remained hesitant about getting involved in plastics. Du Pont also independently made the breakthrough. Du Pont had acquired the U.S. rights to high-pressure polyethylene, and in 1954 a group of researchers there led by W. Frank Gresham began seeking to improve that product. Nicholas G. Merckling soon discovered linear polyethylene, and then on May 21, 1954, he synthesized a “solid, coarse, free flowing powdery material“—polypropylene. The company filed for patents in August, only to learn of the “remarkably parallel” concurrent work of Ziegler. Du Pont went on to fight for the priority of its discoveries, but intense competition kept it from ever becoming a producer of either plastic.

And there were yet more discoveries of polypropylene that weren’t pursued. Before the war, chemists at Shell Development Company, in California, observed something quite similar to Phillips’s mysterious white solid while likewise attempting to synthesize hydrocarbons, but paid little heed. And in February 1955 S. B. Lippincott of Standard Oil of New Jersey polymerized propylene. Lippincott’s work languished after he was transferred to another project two months later.

Thus polypropylene was discovered by Ziegler; by scientists at Hoechst, Montecatini, and Hercules who built on his earlier research; and separately by Phillips Petroleum, Standard Oil of Indiana, Du Pont, and others who didn’t seek patents. To put it mildly, the situation had possibilities for patent attorneys.

In 1958 the U.S. Patent Office declared an interference involving five patent applicants—Phillips, Standard Oil of Indiana, Du Pont, Montecatini, and Hercules. Each was asked to present evidence that it had invented, in the key wording that was agreed on four years later, “normally solid polypropylene, consisting essentially of recurring polypropylene units, having a substantial crystalline polypropylene content.” Meanwhile several corporations sued one another over specific aspects of the new process—for instance, the Ethyl Corporation in 1959 charged that Texas Alkyls (a joint venture between Hercules and Stauffer Chemical) was infringing on its process for manufacturing aluminum-alkyl catalysts. And scores of companies around the world made improvements on the processes, catalysts, engineering, and uses for polypropylene. By 1960 more than a dozen U.S. firms and as many in Europe were claiming rights to 278 polypropylene-related patents all around the world.

The melee took decades to resolve, but the production and sale of the plastic went ahead. Hoechst, Montecatini, and Hercules all built pilot plants to work out the intricacies of manufacturing polypropylene and began full-scale production in 1957. As the American case, that of Hercules, shows, the road to commercial success with polypropylene was just as rocky as the legal path.

Hercules began scaling up the Ziegler process in early 1955, when it sent a technical team to M’fclheim to bring back expertise and apparatus. Like other Ziegler licensees, they returned with little more than the scientist’s laboratory notebook. In the words of Elmer Hinner, who managed the division of Hercules in charge of its polypropylene work, “There we were with a patent, not knowing what to do with it.”

First Hercules forged a technical-exchange agreement with Hoechst, which was progressing well with its own scaling-up operation. The deal saved months, perhaps years, of critical development time. So did an important breakthrough by Edwin Vandenberg. Vandenberg discovered what became known as the “hydrogen effect,” a method of closely controlling the molecular weight of polymers through the controlled use of hydrogen. Then Hercules got its first real factory for polypropylene by default. In 1955 the company began building a ten-million-dollar polyethylene plant in Parlin, New Jersey. The site was close to a promising source of raw materials, a new ethylene plant being built by the Enjay Company, a predecessor of Exxon Chemical. But by the summer of 1957 Enjay had failed to deliver, and “there we sat,” as Hinner later recalled, “with a plant and no ethylene to put in it.” The problem turned out to be propitious: several managers persuaded the directors of Hercules to convert a portion of the idle plant to make polypropylene.

It was a risky move. Hercules had yet to commercially produce its first pound of polyethylene, yet now the company was to make an additional investment in an unproven related product. As Hinner recalled, “We [were selling] the Hercules Board on a handful of ugly gunk that the market development people told us had real market potential. … That crazy thing of not being able to get the ethylene really got us on in the [polypropylene] ball game.”

Hercules began producing high-density polyethylene (marketed as Hi-fax) in September 1957 and polypropylene (Profax) three months later. Hi-fax found use in housewares, wire coatings, bottles, fibers (for seat covers, ropes, fishing nets, and the like), toys, chemical ware, and especially housewares and bottles. The Hula Hoop craze alone boosted sales by some two and a half million pounds in 1958. Pro-fax also caught on quickly. Although polypropylene cost more than polyethylene, its low specific gravity (0.9) made it one of the lightest durable plastics; its higher melting temperature (above 300 degrees Fahrenheit) meant it could withstand boiling water; and its flexible strength made it suitable for household goods with hinges.

So Hercules decided to take a plunge with polypropylene. Late in 1959 the company’s board authorized the construction of a $16.2 million, 50-million-pound-per-year polypropylene plant in Lake Charles, Louisiana. And before that plant was even open, construction was started on a second plant. This was by far the biggest gamble in the company’s history. Unluckily, intense competition soon sapped the profitability of polypropylene. By 1961 there were at least nine American producers of the plastic, with a total capacity of 470 million pounds, and the market price of polypropylene had dropped in two years from sixty-five cents a pound to only forty-two cents. Some companies decided to enter the field by selling polypropylene made by others rather than by building their own plants.

Hercules responded by integrating forward into polypropylene fibers and films, hoping to provide an internal market for its raw product and to replace its declining sales of cellulose-based fibers and films, which were being superseded by some of the new plastics. The company spent ten million dollars to buy a nylon- and rayon-fiber plant in Virginia in 1960, adapted part of it to make polypropylene film, and acquired rights to a European-developed process for making super-thin sheets of film by literally blowing big bubbles of it, rather than by stretching it, the then conventional method. That year, according to a Hercules general manager, “our entry into the plastics business came of age.”

As fast as the market for polypropylene grew during these years, production capacity seemed always to stay ahead- the industry maintained persistent overcapacity. There were several reasons for this. First, petrochemical technology flowed quickly and easily among companies, partly because of the importation of German chemical expertise after World War II and the demise of the cartellike structure of the pre-war world chemical industry. Second, the raw materials were inexpensive, particularly in the United States, thanks to breakthroughs in petroleum refining from thermal to catalytic to steam cracking. And third, the glamour of new products made large investments in petrochemical plants especially attractive. Ever since Du Pont had developed nylon in the 1930s, people had believed that synthetic “miracle” fibers would replace the natural fibers that had fueled the Industrial Revolution—cotton, wool, and silk.

With supply growing even faster than demand, profitability in petrochemicals began to decline in the 1960s, and it was further dampened by the oil shocks of the early 1970s. Still, U.S. companies have generally remained starryeyed about the future for polypropylene; at various times as many as seventeen companies have manufactured the plastic on a large scale.

Hercules remained the leading U.S. producer of polypropylene until 1983, when it created the firm of Himont in a joint venture with Montedison (formerly Montecatini) to take advantage of a new, advanced manufacturing process, called Spheripol, that Montedison had developed. Montedison now owns all of Himont, and Himont is the world’s dominant polypropylene producer. Last year it manufactured nearly four billion pounds of the plastic at a dozen plants throughout the world (Lake Charles is still its biggest in the United States), and other polypropylene makers who license its processes are responsible for nearly two-thirds of the world’s supply.

Altogether more than twenty-two billion pounds of polypropylene are produced worldwide each year. In the early 1980s producers were still losing money on it, but for now, at least, profit margins are healthy and American plants are running at near capacity. Plastics are viewed with more popular respect than ever, and among engineers they are seen as a leading material of the future.

In one sense that future may be far too long. The big problem with petroleum-based plastics—apart from their dependence on future oil supplies—is their remarkable persistence in the environment. They take from generations to centuries to decompose. Petroleum based plastics such as low- and high-density polyethylene, polypropylene, and polyvinyl chloride still constitute less than 10 percent of municipal landfills, but the proportion is growing rapidly. When dumped, they foul the land and sea; when burned, they convert into poisonous fumes and ashes. The solutions to these problems so far seem woefully inadequate. Exposure to solvents and sunlight can speed decomposition, but harmful residues remain. The new “biodegradable” plastic products, such as trash bags, are actually composites of plastics and nonplastic materials that degrade into millions of tiny plastic particles. Perhaps polypropylene and its chemical cousins will someday be replaced by insect-produced bacterial plastics or by plastics made of cellulose, a harmless constituent of plant fiber, which reigned before the petrochemical revolution. For now the most promising trend is a limited one—recycling, as encouraged by public awareness and new municipal laws.

The uses of polypropylene are bound to keep growing for some time, as its engineered properties are improved and as naturally occurring materials become scarce. Tellingly, Americans used more plastics than iron and steel in the last decade. When the world finally exhausts its oil and gas supplies, we will feel the impact not only through crushing fuel shortages but also through the absence of thousands of products we now take largely for granted.

The patent battles over polypropylene appear to have finally ended, but only in the past year or so. The saga may have been the most expensive, complicated, and long-lasting patent dispute ever. The first major turning point came on November 29, 1971, when the 1958 patent interference was settled. Having heard some eighteen thousand pages of testimony, the U.S. Patent Office awarded priority of invention to Montedison, with the patent to be issued February 6, 1973. Du Pont, Phillips, and Standard Oil appealed the decision (Hercules had been dropped from the suit in 1964 because of its late invention date), resulting in a civil trial in the Federal District Court of Delaware during 1977 and 1978, which consumed another fifteen thousand pages of testimony and thousands of exhibits. Judge Caleb M. Wright, who heard this case, awarded priority to Phillips on January 11, 1980, overturning the Patent Office’s decision in favor of Montedison.

In his two-hundred-page decision, Wright ruled that Phillips had made polypropylene at least four times between October 9, 1951, and April 16, 1952, and that the company’s patent application, dated January 27, 1953, was a “constructive reduction to practice.” That is, Phillips had discovered the material, recognized a practical use for it, and adequately described it in the patent application. The judge rejected the Patent Office’s conclusion that Phillips hadn’t discovered the material until 1956; also he found that Montedison had committed fraud before patent examiners in 1958 by failing to disclose it had used a Phillips catalyst to produce the plastic. (Montedison countered by saying Phillips didn’t recognize the crystalline structure of polypropylene until learning of Natta’s work; Phillips replied that the crystallinity could not be determined until x-ray techniques became available in the 1960s.)

The court’s decision reaffirmed that patenting was paramount in establishing a discovery. It found that Phillips had discovered the plastic first, then Standard, then Du Pont and Montedison. But on legal grounds—weighing when patents were applied for—it established the order as Phillips, Montedison, Du Pont, and Standard Oil.

Nor did the struggle end there. The losers appealed, and their case was heard in Philadelphia starting in the spring of 1981. Du Pont argued that Montedison was disqualified because it had committed fraud and that Phillips hadn’t demonstrated polypropylene’s usefulness in 1953. Montedison disputed the fraud charge and reasserted that it deserved the patent. Standard Oil argued for its priority on the basis that it was the first to use x-ray techniques to determine the crystallinity of polypropylene and correctly describe the product and its uses.

The federal appeals court upheld the decision of the lower court, and the three companies appealed to the United States Supreme Court. The high court refused to hear the case. Hogan and Banks, of Phillips, were granted a patent on crystalline polypropylene on March 15, 1983—more than thirty years after their discovery. In 1987 they became the first multiple recipients of the chemical industry’s prestigious Perkin Medal. And just last year, in January 1989, the last legal appeal ended, and the Court of Appeals for the Federal Circuit affirmed again the decision in favor of Banks and Hogan. So far this is the final decision in the battles over the patent.

Throughout the patent dispute, other lawsuits, over license and royalty fees, swirled like molecules in a crucible. When Montedison’s patent was struck down, Hercules and Phillips sued the company for a total of more than a hundred million dollars, representing triple damages on the royalties they had paid to Montedison, but they temporarily withdrew these suits pending the outcome of the appeal. Scores of other companies that had paid handsomely for licenses and royalties later jumped into the fray; these matters have now been settled, but by agreements so complicated that their practical outcome is difficult to calculate. One thing is clear: Phillips stands to benefit by tens of millions of dollars during the life of its hard-won patent.

In retrospect the 1950s were an astonishingly fertile period in polymer chemistry. Watson and Crick unlocked the secrets of DNA (another complex polymer) in that decade, and important breakthroughs were made with synthetic rubbers, plastics, fuels, and other materials. Ziegler’s findings in linear polyethylene spawned related breakthroughs in polyisoprene, polybutadiene, and other long-chain polymers. But the rise of crystalline polypropylene was unique among these developments with its multiple, nearly simultaneous discovery (or invention, for who can say which word better applies here?) at separate laboratories around the world, some the result of work on completely unrelated projects but all occurring within a period of months in the early 1950s. Clearly it was an idea whose time had come, an invention that may have been, if any ever was, inevitable.