Page 40 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Introduction to Polymers 3

celluloid, could be made into the usual rubber-like products, but also solid pieces like boxes, wipe-
clean linen, collars, cuffs, and ping-pong balls. Celluloid could also, like the shellac–wood pulp
mixture, be worked—cut, drilled, and sawed. But celluloid was flammable, and did not stand up well

in hot water. The wearers of celluloid dentures truly could have their “teeth curled” when drinking a
hot cup of coffee. One of its best qualities was that it could be made to “look like” other materials—it
could be dyed to look like marble, swirled to mimic tortoiseshell and mother of pearl, and even look
and feel like ivory. It did not make good billiard balls. One account had billiard balls hitting and
exploding like a shot that caused cowboys to draw their guns.
Both cellulose and cellulose nitrate are linear or two-dimensional polymers, but the former can-
not be softened because of the presence of multitudinous hydrogen bonds between the chainlike
molecules. When used as an explosive the cellulose nitrate is essentially completely nitrated, but the
material used by Parks and Hyatt was a dinitrate, still potentially explosive, but less so. Parks added
castor oil and Hyatt added camphor to plasticize—to reduce the effect of the hydrogen bonding—
the cellulose nitrate, allowing it some fl exibility.
Worldwide, rubber gained in importance with the invention of the air-filled or pneumatic tires by

a Scotsman, John Dunlop, in 1888. He had a successful veterinarian practice in Belfast. In his off
time he worked to improve the ride of his son’s tricycle. His invention happened at the right time.
The automobile industry was emerging, and the air-fi lled tires offered a gentler ride. Thus the tire
industry came into being.
All of these inventions utilized natural materials as at least one ingredient. After years of work
in his chemistry labs in Yonkers, New York, Leo Baekeland, in 1907, announced in an American

Chemical Society meeting the synthesis of the first truly synthetic polymeric material latter dubbed
Bakelite.
Baekeland was born in Belgium in 1863; he was the son of an illiterate shoe repairman and
a maid. He was bright, and he received, with highest honors, his doctorate at the age of 20. He
could have spent the remaining part of his life in academics in Europe, but following the words of
Benjamin Franklin, he sailed to America. In the 1890s, he developed the first photographic paper,

called Velox, which could be developed in synthetic light rather than sunlight. George Eastman saw
the importance of this discovery and paid Bakeland $750,000 for the rights to use this invention.
It was generally recognized by the leading organic chemists of the nineteenth century that phenol
would condense with formaldehyde. Since they did not recognize the concept of functionality, Baeyer,
Michael, and Kleeberg produced useless cross-linked goos, gunks, and messes and then returned to
their research on reactions of monofunctional reactants. However, by the use of a large excess of phe-
nol, Smith, Luft, and Blumer were able to obtain a hard, but meltable thermoplastic material.
With his $750,000, Baekeland set up a lab next to his home. He then sought to solve the problem
of making the hard material made from phenol and formaldehyde soluble. After many failures, he
thought about circumventing the problem by placing the reactants in a mold of the desired shape
and allowing them to form the intractable solid material. After much effort he found the conditions
under which a hard, clear solid could be made—Bakelite was discovered. Bakelite could be worked:
it was resistant to acids and organic liquids, stood up well to heat and electrical charge, and could be
dyed to give colorful products. It was used to make bowling balls, phonograph records, telephone
housings, gears, and cookware. His materials also made excellent billiard balls. Bakelite also acted
as a binder for sawdust, textiles, and paper, forming a wide range of composites including Formica
laminates, many of which are still used. It was also used as an adhesive giving us plywood.
While there is no evidence that Baekeland recognized what polymers were, he appeared to have
a grasp on functionality and how to “use” it to produce thermoplastic materials that could later be
converted to thermosets. Through control of the ratio of phenol to formaldehyde he was able to form
a material that was a thermoplastic. He coined the term A-stage resole resin to describe this thermo-
plastic. This A-stage resole resin was converted to a thermoset cross-link, C-stage Bakelite, by addi-
tional heating. Baekeland also prepared thermoplastic resins called novolacs by the condensation of
phenol with a lesser amount of formaldehyde under acidic conditions. The thermoplastic novolacs

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