The Foundations of Chemistry

More than 2 million tons of this polymer is produced annually in the United States.
Dacron, the fiber produced from this polyester, accounts for approximately 50% of all
synthetic fibers. It absorbs very little moisture, and its properties are nearly the same
whether it is wet or dry. Additionally, it possesses exceptional elastic recovery properties
so it is used to make “permanent-press” fabrics. This polyester can also be made into films
of great strength (e.g., Mylar), which can be rolled into sheets 1/30 the thickness of a
human hair. Such films can be magnetically coated to make audio- and videotapes.
The polymeric amides, polyamides,are an especially important class of condensation
polymers. Nylonis the best known polyamide. It is prepared by heating anhydrous hexa-
methylenediamine with anhydrous adipic acid, a dicarboxylic acid. This substance is often
called nylon 66 because the parent diamine and dicarboxylic acid each contain six carbon
atoms.

Polymers have a wide range of

properties and uses. Mylar sheet

polymer (another polyethylene

terephthalate) is used to protect

documents, such as this photocopy

of a later version of the Declaration

of Independence (top). Another kind

of polymer coating is used to make

shatterproof covers on glass items

such as fluorescent light bulbs

(bottom).

27-19 Polymerization Reactions 1095

Molten nylon is drawn into threads (Figure 27-22). After cooling to room tempera-
ture, these can be stretched to about four times their original length. The “cold drawing”
process orients the polymer molecules so that their long axes are parallel to the fiber axis.
At regular intervals there are NXH,O hydrogen bonds that cross-linkadjacent chains to
give strength to the fiber.
Petroleum is the ultimate source of both adipic acid and hexamethylenediamine. We do
not mean that these compounds are present in petroleum, only that they are made from
it. The same is true for many other industrial chemicals. The cost of petroleum is an impor-
tant factor in our economy because so many products are derived from petroleum.

adipic acid

hexamethylenediamine

H 2 NNH(CH 2 ) 6 2

heat

H 2 O

HO (CH 2 ) 4 OH

O

C

O

C

 nylon 66

(a polyamide)

NH CCNH NHnC

O

(CH 2 ) 4 (CH 2 ) 6

O O

A patch made of Dacron polymer is used to close a defect in a human heart.

The molecular weight of the polymer

varies from about 10,000 to about

25,000. It melts at about 260–270°C.