After Stine hired him, Carothers decided to concentrate on polymers, those giant molecules that are the building blocks of
such familiar substances as rubber and cotton. At that time, most scientists believed polymers were aggregates of small
molecules bound by unknown or undefined forces, and not by ordinary chemical bonds. Carothers believed that polymers were
molecules hooked together end-to-end in long chains by ordinary bonds. To test his theory, he proposed to create polymers by
using well-known chemical reactions to join together many small molecules. A few days after starting work, he wrote that
to study the reactions of substances xAx on yBy where A and B are divalent radicals and x and y are functional groups capable
of reacting with each other. Where A nd B are quite short, such reactions lead to simple rings of which many have been
synthesized by this method. Where they are long, formation of small rings is not possible. Hence reaction must lead either to
large rings or long chains.
Using dibasic acids and glycols, he was successful in producing polyesters with molecular weights of 2300 to 5000. He then introduced
the molecular still, a laboratory tool that made it possible to produce polyesters with molecular weights as high as 25,000.
Carothers called these materials "superpolymers." They were tough, opaque solids which became transparent, viscous liquids when heated.
Two important observations were made by his chief associate, Dr. Julian Hill: first, that filaments could be obtained by pulling threads
like taffy from the molten polymer; second, that these filaments when cooled could be drawn many times their original length, enhancing
their properties Whether dry or wet, they became strong and elastic -- the characteristics of a promising textile fiber. Filaments could
also be produced by dissolving the polymer in chloroform and passing the viscous solution through a standard rayon spinneret.
In 1931 the company applied for a patent on linear condensation polymers, and Carothers and Hill presented a paper to the American
Chemical Society in which they disclosed superpolyesters that could be extruded and drawn into a fiber with properties superior to silk.
Carothers' group experimented with many compositions, but none was a suitable candidate for a textile fiber. Their melting points were too
low, and they were too sensitive to solvents. Though his research continued, by 1933 work on fully synthetic fibers had come to a halt.