Page 45 - Carrahers_Polymer_Chemistry,_Eighth_Edition

8 Carraher’s Polymer Chemistry

fibers; the pulling helped in reorienting the mobile polyester chains. The polyester had a molecu-

lar weight of about 12,000. Additional strength was achieved by again pulling the cooled fi bers.
Further reorientation occurred. This process of “drawing” or pulling to produce stronger fi bers
is now known as “cold drawing” and is widely used in the formation of fibers today. The process

of “cold drawing” was discovered by Carothers’ group. Although interesting, the fibers were not
considered to be of commercial use. Carothers and his group then moved to look at the reaction of
diacids with diamines instead of diols. Again, fibers were formed but these initial materials were

deemed not to be particularly interesting.
In 1934, Paul Flory was hired to work with Carothers to help gain a mathematical understanding
of the polymerization process and relationships. Thus, there was an early association between the-
ory and practice or structure–property relationships.

In 1934, Donald Coffman, a member of the Carothers team, pulled a fiber from an aminoethy-

lester (polyamide) polymer. The fiber retained the elastic properties of the polyesters previously
investigated but had a higher melting point, which allowed it to be laundered and ironed. The fi eld
of candidates for further investigation was narrowed to two—polyamide 5,10 made from pentam-
ethylene diamine and sebacic acid, and polyamide 6,6 synthesized from hexamethylenediamine
and adipic acid. Polyamide 6,6 won because the monomers could be made from benzene, a readily
available feedstock from coal tar.
The polyamide fiber project was begun in earnest using the reaction of adipic acid with hexamethyl-

enediamine. They called the polyamide fiber 66 because each carbon-containing unit had six carbons.
It formed a strong, elastic, largely insoluble fiber with a relatively high melt temperature. DuPont chose

this material for production. These polyamides were given the name “nylons.” Thus was born nylon-6,6.

It was the first synthetic material whose properties equaled or exceeded the natural analog, namely silk.
(In reality, this may not be the truth, but at the time it was believed to be true.)
The researchers had several names for polyamide 6,6, including rayon 66, fiber 66, and Duparon

derived from “Dupont pulls a rabbit out [of] the hat nitrogen/nature/nature/nozzle/naphtha.” The

original “official” name was “Nuron,” which implied newness and also spelled “on run” backwards.
This name was too close to other trademarked names and was renamed “Nirton” and eventually to
what we know today as “Nylon.”
As women’s hem lines rose in the 1930s, silk stockings were in great demand but were very
expensive. Nylon changed this. Nylon could be woven into sheer hosiery. The initial presentation
of nylon hose to the public was by Stine at a forum of women’s club members in New York City on

October 24, 1938. Nearly 800,000 pairs were sold on May 15, 1940 alone—the first day they were
on the market. By 1941 nylon hosiery held 30% of the market but by December 1941 nylon was
diverted to make parachutes, and so on.
From these studies Carothers established several concepts. First, polymers could be formed by
employing already known organic reactions but with reactants that had more than one reactive
group per molecule. Second, the forces that bring together the individual polymer units are the
same as those that hold together the starting materials, namely, primary covalent bonds. Much of
the polymer chemistry names and ideas that permeate polymer science today were standardized
through his efforts.
Representing the true multidisciplinary nature of polymers, early important contributions were
also made by physicists, engineers, and those from biology, medicine, and mathematics, including
W. H. Bragg, Peter Debye, Albert Einstein, and R. Simha.
World War II helped shape the future of polymers. Wartime demands and shortages encour-
aged scientists to seek substitutes and materials that even excelled currently available materials.
Polycarbonate (Kevlar), which could stop a “speeding bullet,” was developed, as was polytetra-
fl uoroethylene (Teflon), which was super slick. New materials were developed spurred on by the

needs of the military, electronics industry, food industry, and so on. The creation of new materials
continues at an even accelerated pace brought on by the need for materials with specifi c properties
and the growing ability to tailor make giant molecule—macromolecule—polymers.

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