Page 151 - Carrahers_Polymer_Chemistry,_Eighth_Edition

114 Carraher’s Polymer Chemistry

A beam from a semiconductor diode laser “interrogates” the undersides of both recordable and
recorded CDs seeking out areas of reflected, corresponding to the binary “one,” and unrefl ected,

corresponding to the binary “zero” light. The ability to “read” information is dependent on the
wavelength of the laser. Today, most of the CD players use a near-infrared laser because of the
stability of such lasers. Efforts are underway to develop stable and inexpensive lasers of shorter
wavelengths that will allow the holding of more information within the same space.
There is concern that BPA may cause neural and behavioral changes in infants and children. A
major line of exposure to infants is in baby bottles. In our modern age, the composition of baby bottles
has evolved from glass to polyethylene to PC and now back to glass and other newer materials such as
Tritan, which is a proprietary copolyester developed by Eastman with properties similar to PC. While
the use of most PC will continue, the “better to be safe than sorry” motto is best used for products that
come in intimate contact with infants that are more susceptible than adults to various agents.

4.7 SYNTHETIC POLYAMIDES
Wallace Hume Carothers was brought to DuPont because his fellow researchers at Harvard and the
University of Illinois called him the best synthetic chemist they knew. He started a program aimed
at understanding the composition of natural polymers such as silk, cellulose, and rubber. Many of
his efforts related to condensation polymers were based on his belief that if a monofunctional reac-
tant reacted in a certain manner forming a small molecule (Equation 4.58) and that similar reac-
tions except employing reactants with two reactive groups would form polymers (Equation 4.59).
O
||
R − OH + HOOC − R R − O − C − R + HOH (4.58)
Small ester

O O
|| ||
HO − R − OH + HOOC − R − COOH − ( − O − R − O − C − R − C − ) − + H O (4.59)
2
Polyester

While the Carothers’ group had made both polyesters and polyamides, they initially emphasized
work on the polyesters since they were more soluble and easier to work with. One of Carothers’

coworkers, Julian Hill, noticed that he could form fibers if he took a soft polyester material on a
glass stirring rod and pulled some of it away from the clump. Because the polyesters had too low
softening points for use as textiles, the group returned to work with the polyamides. They found
that fibers could also be formed by the polyamides similar to those formed by the polyesters.

These polyamides allowed the formation of fibers that approached, and in some cases surpassed,

the strength of natural fibers. This new miracle fiber was introduced at the 1939 New York World’s

Fair in an exhibit that announced the synthesis of this wonder fiber from “coal, air, and water”—an
exaggeration—but nevertheless eye catching. When the polyamides, nylons were fi rst offered for
sale in New York City, on May 15, 1940, nearly a million pairs were sold in the first few hours.

Nylon sales took a large drop when it was noted that nylon was needed to produce the parachute
material so critical to World War II.
The first polyesters produced by Carothers had relatively low molecular weights because of low

fractional conversions. Carothers was successful in producing higher molecular weight polymers by
shifting the equilibrium by removing the water produced. Equation 4.59 is an equilibrium process
with the removal of water driving it toward polymer formation. However, these aliphatic polyesters,
which he called “super polymers,” lacked stiffening groups in the chain and thus had melting points
that were too low for laundering and ironing.

9/14/2010 3:38:22 PM
K10478.indb 114
K10478.indb 114 9/14/2010 3:38:22 PM