parichehr
16th November 2010, 07:24 PM
Marvelous, mysterious macromolecules
By the early 20th century, chemists had learned that many materials were polymeric -- including such natural substances as proteins, cellulose, and rubber. Other polymers had been synthesized in the laboratory from smaller molecules like styrene, vinyl chloride, and acrylic acid. At least one synthetic polymer, Bakelite, a hard resin produced from phenol and formaldehyde by Leo H. Baekeland about 1907, was a big commercial success. Chemists knew, too, that polymers were molecules of high molecular weight (for example 40,000 or more) made up of huge numbers of smaller chemical units. But how these units were arranged and held together was not clear. Many eminent chemists believed that polymers were aggregates, perhaps colloids, consisting of relatively small molecules held together by some intermolecular force of uncertain nature.
In the early 1920s, the German organic chemist (and 1953 Nobel laureate) Hermann Staudinger postulated that polymers consisted of units linked together by the same covalent bonds found in smaller organic molecules. Throughout the 1920s, Staudinger supported his view with new experimental evidence, and other chemists, among them Karl Freudenberg, Michael Polanyi, Kurt Meyer, and Herman Mark, came up with additional evidence backing Staudinger. The subject, nevertheless, remained controversial well into the 1930s.
Carothers had no direct contact with these chemists, but his ideas were generally in line with those of Staudinger. His research approach, on the other hand, was quite different. Whereas Staudinger focused his study on the analysis of natural polymers, Carothers built up polymers by reacting small organic molecules by means of well-known reactions -- for example, by combining dicarboxylic acids with diols or diamines -- to form long, macromolecular chains.
In addition to the many experimental studies, Carothers believed that mathematics could be applied to understand the formation and properties of polymers. To this end, Paul J. Flory was hired in 1934 and introduced to polymers by Carothers. The seminal ideas they advanced provided the foundation of many of the theoretical methods for studying polymers used to this day. Flory's accomplishments were recognized with the 1974 Nobel Prize in chemistry.
The research accomplishments of Staudinger and Carothers, along with that of their colleagues, during the 1920s and 1930s laid the foundations of modern polymer science and today's plastics, synthetic fiber, and rubber industries. Today, approximately half of the industrial chemists in the United States work in some area of polymer chemistry.
A new synthetic rubber
Meanwhile, in 1930 Carothers had been asked by Elmer Bolton, the new head of DuPont's chemical department, to look into polymers based on acetylene. Unlike Stine, who emphasized pure science, Bolton believed that research should be aimed at clearly defined applications. The freewheeling days of fundamental research at DuPont were fading.
Bolton, who previously had headed DuPont's research on dyes, had long been interested in producing a synthetic rubber. In the late 1920s he had followed the research of Father Julius Nieuwland of Notre Dame University, who used a cuprous chloride catalyst to combine two or three acetylenes into mono- or divinylactetylene. Bolton realized that these compounds were similar to isoprene, the molecule that is the basic structural unit of natural rubber.
Carothers assigned Arnold Collins to make a very pure sample of divinylacetylene. While distilling the products of the acetylene reaction in March 1930, Collins obtained a small amount of an unknown liquid, which he put aside in stoppered test tubes. A few days later he found that the liquid had congealed into a clear homogenous mass. When Collins dislodged the mass from its container, it bounced. Analysis showed that the mass was a polymer of chloroprene, formed with chlorine from the cuprous chloride catalyst. Accidentally, Collins had prepared a new synthetic rubber.
DuPont began large-scale production of polychloroprene, marketed under the name Duprene (later changed to neoprene), in 1932. Neoprene was difficult and expensive to manufacture, however, and it didn't really rival natural rubber, which was selling for only a few cents per pound in the early 1930s. Neoprene -- which was resistant to weather, oil, chemicals, and heat -- found several relatively small but profitable uses.
The development of nylon
In the early 1930's, Stine was promoted to DuPont's management committee and Elmer K. Bolton succeeded him as chemical research director. Bolton's top research priority was the creation of a new synthetic fiber. Thus began the interplay of science and commerce that marks the development process - the "D" of R&D.
New technology was needed to make the raw materials and to form them into a fiber. The market had to be decided upon, an important choice for a material that could compete with cotton, silk, wool, and rayon. The decision to focus on hosiery was crucial. It was a limited, premium market. "When you want to develop a new fiber for fabrics you need thousands of pounds," said Crawford Greenewalt, a research supervisor during nylon development who later became company president and CEO. "All we needed to make was a few grams at a time, enough to knit one stocking." In addition, the technology had to be scaled up and a plant built that required materials of construction that were new at the time. And the time was the Great Depression, not the most propitious moment to take a $27 million gamble -- the cost of nylon from research through the start-up of the new plant at Seaford, Delaware.
Encouraged by Bolton, in 1934 Carothers began a renewed effort to make a polymer suitable for fibers. He chose an ester of a nine-carbon amino acid as the starting material and produced a polyamide with a high melting point, the first nylon. Carothers' group then looked at 81 polyamide compositions, including on February 28, 1935, the 66 polymer -- so called because each of the reacting chemicals, hexamethylene diamine and adipic acid, has six carbon atoms. Polymer 66 was selected for development in part because both of the raw materials could be made from benzene, readily available from coal.
The initial development took place in the laboratory with equipment that could produce 100 pounds of nylon a week. The operation was so temperamental that the technicians actually tip-toed in the spinning room. They cautioned visitors to give the operation only a sidewise glance, for a head-on look would stop the process completely. In 1938, a pilot plant was constructed that could produce 500 pounds of nylon a day. The pilot plant was critical to getting Seaford up and running in record time.
The technical tasks were many. Consider these examples:
Intermediate chemicals. New manufacturing processes for both adipic acid and hexamethylene diamine were developed at the Belle, West Virginia, plant, and new equipment was designed to keep the ingredients hot during transport over the Appalachians to Delaware.
Melt spinning. Before nylon, spinning -- the extrusion of polymer to form filaments (as a spider "spins" its web or a silkworm a cocoon) -- was done with a solvent. Nylon could be solution-spun, but it also could be spun by melting the polymer. While this offered advantages, it had never been done. "I had nightmares over melt spinning," said Greenewalt. "The problem was the melting point of nylon was very close to the decomposition point. We'd get bubbles, because the decomposition products were gases." The solution, simple in hindsight, was to keep the polymer under high pressure - 4,000 pounds per square inch. Special pumps were designed to operate at these pressures, with small clearances and with no lubricant other than the polymer itself. A new grade of stainless steel had to be used that was abrasion resistant.
The high temperatures, 550º F (285º C), posed other problems. Many types of spinning-cell melting grids were designed to find a candidate that would maintain heated surfaces in spite of the poor thermal conductivity of the polymer. To protect the hot polymer from oxidation, DuPont used a purified grade of nitrogen, which came to be known as "Seaford-grade nitrogen." In addition, the spinning assembly involved radically new engineering developments to produce fibers of the required uniformity. Before the plant was opened, eight different spinning assemblies were constructed, each one embodying the newest ideas.
High-speed spinning and cold drawing. Special equipment was designed for this crucial step. Generators were made to run the windup of the yarn at a speed of 2,000 feet per minute with virtually no variation. The draw rolls -- between which the yarn was stretched a uniform amount -- had to be manufactured to a tolerance of 1/100,000th of an inch.
Sizing. The size, or surface coating, itself proved a major problem. The first choice corroded knitting needles and gummed up the machines. Candidate after candidate was tried and failed. The clock was ticking. DuPont eventually assigned 30 scientists to work on the problem, and they didn't come up with the answer until the structural steel was up at Seaford and much of the other equipment was
installed.
www.acs.org (http://njavan.com/forum/redirector.php?url=http%3A%2F%2Fwww.acs.org)
American Chemical Society
By the early 20th century, chemists had learned that many materials were polymeric -- including such natural substances as proteins, cellulose, and rubber. Other polymers had been synthesized in the laboratory from smaller molecules like styrene, vinyl chloride, and acrylic acid. At least one synthetic polymer, Bakelite, a hard resin produced from phenol and formaldehyde by Leo H. Baekeland about 1907, was a big commercial success. Chemists knew, too, that polymers were molecules of high molecular weight (for example 40,000 or more) made up of huge numbers of smaller chemical units. But how these units were arranged and held together was not clear. Many eminent chemists believed that polymers were aggregates, perhaps colloids, consisting of relatively small molecules held together by some intermolecular force of uncertain nature.
In the early 1920s, the German organic chemist (and 1953 Nobel laureate) Hermann Staudinger postulated that polymers consisted of units linked together by the same covalent bonds found in smaller organic molecules. Throughout the 1920s, Staudinger supported his view with new experimental evidence, and other chemists, among them Karl Freudenberg, Michael Polanyi, Kurt Meyer, and Herman Mark, came up with additional evidence backing Staudinger. The subject, nevertheless, remained controversial well into the 1930s.
Carothers had no direct contact with these chemists, but his ideas were generally in line with those of Staudinger. His research approach, on the other hand, was quite different. Whereas Staudinger focused his study on the analysis of natural polymers, Carothers built up polymers by reacting small organic molecules by means of well-known reactions -- for example, by combining dicarboxylic acids with diols or diamines -- to form long, macromolecular chains.
In addition to the many experimental studies, Carothers believed that mathematics could be applied to understand the formation and properties of polymers. To this end, Paul J. Flory was hired in 1934 and introduced to polymers by Carothers. The seminal ideas they advanced provided the foundation of many of the theoretical methods for studying polymers used to this day. Flory's accomplishments were recognized with the 1974 Nobel Prize in chemistry.
The research accomplishments of Staudinger and Carothers, along with that of their colleagues, during the 1920s and 1930s laid the foundations of modern polymer science and today's plastics, synthetic fiber, and rubber industries. Today, approximately half of the industrial chemists in the United States work in some area of polymer chemistry.
A new synthetic rubber
Meanwhile, in 1930 Carothers had been asked by Elmer Bolton, the new head of DuPont's chemical department, to look into polymers based on acetylene. Unlike Stine, who emphasized pure science, Bolton believed that research should be aimed at clearly defined applications. The freewheeling days of fundamental research at DuPont were fading.
Bolton, who previously had headed DuPont's research on dyes, had long been interested in producing a synthetic rubber. In the late 1920s he had followed the research of Father Julius Nieuwland of Notre Dame University, who used a cuprous chloride catalyst to combine two or three acetylenes into mono- or divinylactetylene. Bolton realized that these compounds were similar to isoprene, the molecule that is the basic structural unit of natural rubber.
Carothers assigned Arnold Collins to make a very pure sample of divinylacetylene. While distilling the products of the acetylene reaction in March 1930, Collins obtained a small amount of an unknown liquid, which he put aside in stoppered test tubes. A few days later he found that the liquid had congealed into a clear homogenous mass. When Collins dislodged the mass from its container, it bounced. Analysis showed that the mass was a polymer of chloroprene, formed with chlorine from the cuprous chloride catalyst. Accidentally, Collins had prepared a new synthetic rubber.
DuPont began large-scale production of polychloroprene, marketed under the name Duprene (later changed to neoprene), in 1932. Neoprene was difficult and expensive to manufacture, however, and it didn't really rival natural rubber, which was selling for only a few cents per pound in the early 1930s. Neoprene -- which was resistant to weather, oil, chemicals, and heat -- found several relatively small but profitable uses.
The development of nylon
In the early 1930's, Stine was promoted to DuPont's management committee and Elmer K. Bolton succeeded him as chemical research director. Bolton's top research priority was the creation of a new synthetic fiber. Thus began the interplay of science and commerce that marks the development process - the "D" of R&D.
New technology was needed to make the raw materials and to form them into a fiber. The market had to be decided upon, an important choice for a material that could compete with cotton, silk, wool, and rayon. The decision to focus on hosiery was crucial. It was a limited, premium market. "When you want to develop a new fiber for fabrics you need thousands of pounds," said Crawford Greenewalt, a research supervisor during nylon development who later became company president and CEO. "All we needed to make was a few grams at a time, enough to knit one stocking." In addition, the technology had to be scaled up and a plant built that required materials of construction that were new at the time. And the time was the Great Depression, not the most propitious moment to take a $27 million gamble -- the cost of nylon from research through the start-up of the new plant at Seaford, Delaware.
Encouraged by Bolton, in 1934 Carothers began a renewed effort to make a polymer suitable for fibers. He chose an ester of a nine-carbon amino acid as the starting material and produced a polyamide with a high melting point, the first nylon. Carothers' group then looked at 81 polyamide compositions, including on February 28, 1935, the 66 polymer -- so called because each of the reacting chemicals, hexamethylene diamine and adipic acid, has six carbon atoms. Polymer 66 was selected for development in part because both of the raw materials could be made from benzene, readily available from coal.
The initial development took place in the laboratory with equipment that could produce 100 pounds of nylon a week. The operation was so temperamental that the technicians actually tip-toed in the spinning room. They cautioned visitors to give the operation only a sidewise glance, for a head-on look would stop the process completely. In 1938, a pilot plant was constructed that could produce 500 pounds of nylon a day. The pilot plant was critical to getting Seaford up and running in record time.
The technical tasks were many. Consider these examples:
Intermediate chemicals. New manufacturing processes for both adipic acid and hexamethylene diamine were developed at the Belle, West Virginia, plant, and new equipment was designed to keep the ingredients hot during transport over the Appalachians to Delaware.
Melt spinning. Before nylon, spinning -- the extrusion of polymer to form filaments (as a spider "spins" its web or a silkworm a cocoon) -- was done with a solvent. Nylon could be solution-spun, but it also could be spun by melting the polymer. While this offered advantages, it had never been done. "I had nightmares over melt spinning," said Greenewalt. "The problem was the melting point of nylon was very close to the decomposition point. We'd get bubbles, because the decomposition products were gases." The solution, simple in hindsight, was to keep the polymer under high pressure - 4,000 pounds per square inch. Special pumps were designed to operate at these pressures, with small clearances and with no lubricant other than the polymer itself. A new grade of stainless steel had to be used that was abrasion resistant.
The high temperatures, 550º F (285º C), posed other problems. Many types of spinning-cell melting grids were designed to find a candidate that would maintain heated surfaces in spite of the poor thermal conductivity of the polymer. To protect the hot polymer from oxidation, DuPont used a purified grade of nitrogen, which came to be known as "Seaford-grade nitrogen." In addition, the spinning assembly involved radically new engineering developments to produce fibers of the required uniformity. Before the plant was opened, eight different spinning assemblies were constructed, each one embodying the newest ideas.
High-speed spinning and cold drawing. Special equipment was designed for this crucial step. Generators were made to run the windup of the yarn at a speed of 2,000 feet per minute with virtually no variation. The draw rolls -- between which the yarn was stretched a uniform amount -- had to be manufactured to a tolerance of 1/100,000th of an inch.
Sizing. The size, or surface coating, itself proved a major problem. The first choice corroded knitting needles and gummed up the machines. Candidate after candidate was tried and failed. The clock was ticking. DuPont eventually assigned 30 scientists to work on the problem, and they didn't come up with the answer until the structural steel was up at Seaford and much of the other equipment was
installed.
www.acs.org (http://njavan.com/forum/redirector.php?url=http%3A%2F%2Fwww.acs.org)
American Chemical Society