Page 700 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Selected Topics 663

does not contribute to the lack of distortion necessary for many PC products. Some polymers such as
polyimides and polysulfones have the necessary high T but they are more expensive than PC.
g
Several substitute materials are coming onto the marketplace that have similar properties to PC.
Tritan, a copolyester made by Eastman, is one such material. While the precise structure of Tritan
is not currently public, it is based on tetramethylcyclobutanediol and a derivative of cyclobutane-
diol. Tritan has good heat tolerance and resistance to hydrolysis and chemical decomposition in
comparison to PC. Another material is based on adjusting the ratio of tetramethylcyclobutanediol
and DPO in dimethyl terephthalate-based copolyesters. The material is touted as being green since
it can use bacterially produced PDO and because no solvent is needed for their synthesis creating
less waste.

19.18 SUMMARY

1. Polymers are major materials in the nanotechnology revolution, including as conductive (photo
and electronic) materials. Delocalization of electrons throughout a polymer chain or matrix is
important for electronic conductance. This is often accomplished through doping that encour-

ages flow of electrons. Doping provides a ready mechanism for delocalization to occur. Doping

is the mode of creating electron sinks or deficiencies and electron excesses that are necessary to
breach, or get to, the conductive band.
2. Polymers are also major materials in the biomedical areas as materials and in the delivery of

drugs. Polymeric drugs can act as control agents to deliver specific biologically active agents or
can act as drugs themselves. Polymeric drugs have advantages over smaller drugs because of
their size, which have begun to be taken advantage of in the medical area.

3. Polymers are used extensively in dentistry as composites, fillings, dental bases, teeth, cements,
and as adhesives.
4. Sutures are the largest group of devices implanted into humans. Sutures are employed to hold

together parts of the body generally through the use of fibers. There is a wide variety of materials
available today, each with known advantages and limitations and essentially all are polymeric.
5. Smart materials are materials that react to applied force—electrical, stress–strain (includ-
ing pressure), thermal, light, and magnetic. A smart material is not smart simply because it
responds to external stimuli, but it becomes smart when the interaction is used to achieve a

defined engineering or scientifi c goal.
6. Engineering plastics are also referred to as high-performance thermoplastics or advanced ther-
moplastics. An engineering plastic is simply one that can be cut, sawed, drilled, or similarly
worked with. Many of those today must have a relatively high use temperature generally in
o
excess of 200 C. Many of these polymers are being utilized as light-weight replacements for
metal because of their strength, high-dimensional stability and resistance to chemicals and
weathering. Illustrations of high-performance thermoplastics are a number of nylons and poly-
esters, PC, polyimides, PPO, and polysulfones.
7. The use of polymeric materials as basic structural materials is widespread and of ancient origin.
These materials include concrete, wood, glass, and a wide variety of plastics and elastomers. In
fact, with the exception of steel, most of a house is polymeric.
8. Polymers form the basis for fire resistant textiles. For instance, many of the fi refighters and race

car drivers wear clothing made from aromatic nylons because these materials resist melting,
dripping, supporting combustion in air, or burning.
9. For new polymeric materials to enter the marketplace, many things must be in place, including
a “flagship” property that meets a particular market need, ready availability, and money. It takes

about $1 billion to introduce and establish a new polymer into the marketplace.
10. There is an increased awareness and much activity involving the development of green materials
and green practices. This awareness involves public awareness, increased petroleum cost, recog-
nition that the petroleum reserves are limited, and increased ability to employ microorganisms to

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