polyester (thing)

In the early 1900's, Wallace Carothers discovered that using condensation reactions to hook up long chains of organic molecules would be an inexpensive way to generate high-quality polymers. One of his ideas for carrying this out was to create a polyester. Esters consist of two hydrocarbon groups linked by a COO group. Polyesters would consist of many hydrocarbon groups linked together in a chain by many COO groups.

.....-Hydrocarbon Group-COO-Hydrocarbon Group-COO-Hydrocarbon Group-COO-Hydrocarbon Group-COO-Hydrocarbon Group-COO-.....

To generate a polyester, two different monomers are required. One of the monomers must be a non-branching carbon chain with two primary alcohol groups. The other monomer must be a non-branching carbon chain with two carboxylic acid groups. Solutions of these two monomers are mixed together and then heated in the presence of an inorganic acid. This causes a condensation reaction to occur, alternately linking the monomers together in long chains.

Dacron, a commercial polyester invented by DuPont for use in textiles, is a product of the condensation reaction between the alcohol ethylene glycol (commonly know as anti-freeze) and terephthalic acid. The molecular structures of these molecules look like this:

      Ethylene glycol             Terephthalic Acid
           H   H                          __
           |   |                    O    /  \    O
   H - O - C - C - O - H            ||  / /\ \  ||
           |   |            H - O - C - \ \/ / - C - O - H
           H   H                         \__/

During the condensation reaction, the H atom on an alcohol group and the OH atoms on a carboxylic acid group split off their parent molecules and join together to form water. At the same time, the parent molecules unite at the points of the split to form an ester.

                      H - O - H                  H - O - H
                     /\     /\        __        /\     /\
           H   H     /       \  O    /  \    O  /       \     H   H
           |   |    /         \ ||  / /\ \  || /         \    |   |
   H - O - C - C - O ----><---- C - \ \/ / - C ----><---- O - C - C - O - H
           |   |                     \__/                     |   |
           H   H                                              H   H

Because both ends of each monomer have an attached alcohol or carboxylic acid group, long chains of multiple esters (otherwise known as polyester) form.

                             __                               __
           H   H       O    /  \    O       H   H       O    /  \    O
           |   |       ||  / /\ \  ||       |   |       ||  / /\ \  ||
   H - O - C - C - O - C - \ \/ / - C - O - C - C - O - C - \ \/ / - C - O - H
           |   |            \__/            |   |            \__/
           H   H                            H   H

These polyester chains, once formed, isolated, and purified, can be refined into fabric for use in clothing and other textiles.