Question

why did nylon 6-6 polymer form only at the interface of the two liquid phases?

Answer 1

Making nylon 6,6 is even easier if you use a diamine and a diacid chloride instead of a diacid. This is because acid chlorides are much more reactive than acids. The reaction is done in a two-phase system. The amine is dissolved in water, and the diacid chloride in an organic solvent. The two solutions are placed in the same beaker. Of course, the two solutions are immiscible, so there will be two phases in the beaker. At the interface of the two phases, the diacid chloride and diamine can meet each other, and will polymerize there. There is special way to do this called the "Nylon Rope Trick"⁴, and we'll show you how to do that in just a minute