When the autoclave was heated, heat flowed from the outside inward. The nylon salt closest to the walls of the autoclave became hot first. Then, as heat flowed inward, the nylon salt in the middle of the autoclave became hot. If the autoclave was small, the heat didn't have very far to travel. It wouldn't take long for the heat to reach all the nylon salt in the autoclave.

When DuPont's scientists and engineers wanted to make larger amounts of nylon, things became more complicated. To make fifty pounds of nylon polymer required a much larger autoclave than making two-pounds. In order for all the nylon salt inside the autoclave to become hot, the heat must travel a longer distance through more nylon salt than in a two-pound autoclave. The result was that the nylon salt near the walls of the autoclave became very hot before the nylon salt in the middle of the autoclave could even become warm. This was problematic, because by the time the nylon salt in the middle of the autoclave became hot, the nylon salt near the walls had already polymerized.

This was the problem facing DuPont's scientists and engineers when they were trying to make large batches of nylon. They needed a way to improve heat transfer, that is, to make heat travel faster to all the nylon salt inside the autoclave.

The answer was very simple. Instead of placing solid crystals of nylon salt into the autoclave, the nylon salt was dissolved in water. The nylon salt solution was then placed in the autoclave. When the solution boiled, it churned violently. This mixed the nylon salt solution, which resulted in uniform polymerization.

Making nylon polymer in water may sound problematic, if one remembers that nylon polymer is not soluble in water. One might expect nylon oligomers to precipitate from solution before they can grow into polymers. But this did not happen. The polymerization took place very quickly before precipitation could occur.

The final process developed worked something like this: A solution of the nylon salt in water was heated gradually in the sealed autoclave to 285 ^oC. At this temperature the nylon salt would instantaneously polymerize. Of course, since the water was above its normal boiling temperature, it will became steam. When the pressure of the steam reached 250 psi, and the temperature reached 285 ^oC, the steam was allowed to escape slowly from the autoclave. In this way the pressure was bled off slowly until all the steam had escaped and the pressure returned to normal atmospheric level. In this way the water was removed from the autoclave, leaving nylon polymer behind. If the water were not removed in this way, it would have reacted with the nylon polymer, turning it back into nylon salt.