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Carothers, W

Name: Wallace Hume Carothers

Achievements: Nylon

Born: April 27, 1896; Burlington, Iowa

Died: April 29, 1937; Philadelphia, Pennsylvania (Aged 41)

Field & Discipline: Science; Chemistry; Synthetics; Chemist

Education: Capital City Commercial College (1914-15); Tarkio (Missouri) College (1915-20); University of Illinois (1920-24)

Major Work:

“Collected Papers of Wallace Hume Carothers on High Polymeric Substances” (1940)

Life & Times:

In 1924 Carothers was appointed professor of organic chemistry at the University of Illinois, where he remained for two years.  His real passion was for research, and in the early 1920s his interest in both chemistry and physics led him to investigate the theory -- first proposed by Gilbert N. Lewis in 1916 -- that chemical bonds could be formed by the sharing of electrons as well as by their transfer.  These investigations led Carothers to publish in 1924 a paper concerning the nature of the double covalent bond, by which the atoms of certain organic molecules share two pairs of electrons instead of only one.

In 1926, Carothers moved to Harvard University as a professor of chemistry, but the following year, on the strength of his 1924 paper, he was offered a job the [hired by] E.I. du Pont de Nemours Company*.   In 1927, the company had decided to promote fundamental research in colloid chemistry, catalysis and organic synthesis, and offered Carothers the opportunity to devote himself to pure research as Du Pont's director of research in organic chemistry. 

Before leaving Harvard, Carothers began investigating the construction of polymers - the class of natural or synthetic substances composed of very large complex molecules (called macromolecules), made up of long chains of simple molecules (called monomers) arranged in repetitive configurations - as his ultimate aim was to synthesize many useful organic compounds through molecular bonding.

In 1928, Carothers moved to the Du Pont laboratory at Wilmington, Delaware where he and an eight-man research team began to investigate the nature of polymers by making long chains of polyesters, through reactions between alcohols and acids which combined in such a way that the molecule on one end of the chain was always capable of further reaction. By 1929 he and his team had demonstrated conclusively that polymeric molecules were held together by simple covalent bonds (instead of by some unknown force peculiar to polymers, as had been suspected), and that there was no theoretical limit to the length of a polymeric chain.

Meanwhile, other researchers in the Du Pont laboratories had been working with the chemist [work related to] Nieuwland* at the University of Notre Dame on research into the production of synthesized rubber. In 1920, Nieuwland had discovered that the reaction of acetylene (a colorless gas and the simplest and best known member of the hydrocarbon series containing one or more pairs of carbon atoms linked by triple bonds) and a cuprous chloride-ammonium chloride catalyst produced a new gas and a new liquid, which he identified (1921) as a mixture of polymers of which monovinylacetylene and divinylacetylene (DVA) were the main constituents.  In 1929, this project was passed on to Carothers and his team, who were asked to investigate the chemical structure of the short-chain polymer DVA and, while producing high-grade DVA, a member of the team had recovered a liquid by-product that emulsified into a white, rubbery mass a few days later. This substance was named "chloroprene" by Carothers, and on analysis the liquid was found to have a molecular structure like that of isoprene, the chemical constituent of rubber.

Further investigations revealed that chloroprene (or 2-chlorobutadiene) was the result of the reaction between monovinylacetylene, a derivative of DVA, and a hydrochloric acid solution of cuprous chloride.  Chloroprene was then given to Du Pont's Jackson Laboratory in 1930, and developed commercially into neoprene (1931), an oil-resistant synthetic rubber compound used to make wetsuits, shoe soles, industrial hoses, and adhesives.

In April 1930, Carothers and his team then turned their efforts towards the invention of a synthetic fiber that could replace silk. Their first step was to try and make the longest polymeric chain ever produced in a laboratory by combining a dibasic acid and a dihydric alcohol to create a new fiber formed by the polymerization process. (When a dibasic acid and an organic diamine are heated together, the product produced by the reaction is called an amide; this reaction results in the formation of relatively small molecules which, when heated, unite to form long chains in which a dibasic acid molelcule links up with a diamine molecule - the resulting product is called a polyamide, and a long chain of these is known as a superpolymer).

During this experiment, Carothers discovered that the water formed during the production of polyesters was dripping back into the mixture, blocking the reaction between dibasic acids and dihydric alcohols, and weakening the fibers and limiting the length of the polymeric chain. Carothers refined the process by developing a "molecular still,”  the water was distilled and removed from the process. The result was a molten polyester that could be drawn into pliable filaments and that, when cooled, could be stretched to form very strong fibers.

However, despite their strength, these fibers were not commercially viable because their melting temperature was too low, and Carothers spent the next four years testing the properties of fibers produced by combining various dibasic acids and diamines, from which he obtained many different types of polyamides (ammonia-acid compounds that can be moulded while hot, but adopt a permanent shape when cooled).

Finally, in February 1935, Carothers and his co-workers found that, by polymerizing a mixture of six carbon adipic acid and six carbon 1,6-diaminohexane (also known as hexamethylenediamine), they were able to produce a tough, elastic, heat-resistant synthetic material that could be drawn out into strong and silky fibers - the product known today as nylon.

During the early 1930s, Carothers and his group had produced over 100 different specimens of polyamides coded according to the number of carbon atoms in each of their monomers. The one produced from 1,6-diaminohexane and the adipic acid (each containing six carbon atoms) became known first as "66 polyamide,” then as "nylon-6,6,” and finally as nylon, a new organic textile fiber, derived essentially basically from coal (benzine), water (hydrogen) and air (oxygen and nitrogen).  Nylon is a long-chain synthetic polyamide which has repeating amide groups,  and was the first completely synthetic fiber, produced entirely from mineral sources.

During his nine years with Du Pont, Carothers published his findings concerning polymers in more than 30 journals, and the work of his research group resulted in the filing of more than 70 patents. He served as associate editor of the “Journal of the American Chemical Society” (1929-37), as an editor of the journal “Organic Synthesis” (1930-37), and was a member of the American Academy for the Advancement of Science.

In 1936, Carothers was elected to National Academy of Sciences and the same year he married Helen Sweetman, a fellow employee at Du Pont, with whom he had one child.    Carothers committed suicide by taking cyanide in April 1937 two weeks after filing the basic nylon patent application, and not long before the birth of his only child.  It seems that Carothers was a severe manic-depressive and that a combination of managerial changes at Du Pont and the untimely death of his sister, Isobel, in January 1936, added to his depression.

Assessment: The invention of nylon marked the beginning of a new era of synthetic fibers and  it is today used in a extremely wide variety of applications.

Oneliner: Wallace Carothers, inventor of nylon

Bibliography:

Wikipedia

Language: English

Father: Ira Hume Carothers

Mother: Mary Evalina McMullin

Siblings: Three younger siblings

Spouse: Helen Everett Sweetman (m. 1936)

Children: Jane (b. 1937)