The rate of gel formation and color formation in poly(hexamethylene adipamide), nylon 66, is found to be dependent upon the rate of removal of the volatile products of degradation. If a sample of nylon is heated above its melting point in a sealed tube, the material will remain soluble for extended periods of time as the intrinsic viscosity first passes through a maximum, then a minimum, followed by the abrupt formation of insoluble material. The color remains reasonably white. On the other hand, if the volatile material is permitted to escape, rapid gelation and color formation will occur, even in the complete absence of oxygen. Intermediate rates of gelation and color formation can be obtained by control of the rate of volatile material distillation. The decrease in molecular weight evidenced in the sealed tubes is probably due to hydrolysis and ammonolysis of the amide groups which occur simultaneously with the formation of multifunctional crosslinking agents. The volatile material contains an intense absorption in the 290 mμ region. Analysis of the volatile material shows that it contains inter alia, water, carbon dioxide, ammonia, cyclic monomer, hexylamine, hexamethyl‐eneimine, hexamethylenediamine, cyclopentanone, 2‐cyclopentylcyclopentanone, 2‐cyclopentylidinecyclopentanone, and 1,2,3,5,6,7‐hexahydrodicyclopenta[b,e]pyridine, which has an intense absorption at 287 mμ, ε = 8.87 × 104l./mole‐cm, (methanol).
