The re‐equilibration of polycaproamide

The polymerization of caprolactam and the depolymerization of polycaproamide at equilibrium lead to an identical mixture of linear polymer, caprolactam and its cyclic oligomers. In this work the depolymerization reaction has been studied. The postulated reaction mechanism is based on hydrolysis and inter‐ and intramolecular segment interchange reactions (acidolysis and aminolysis), according to which the concentrations of water and end groups (—NH 2 and —COOH) determine the rate of depolymerization. In an attempt to elucidate the mechanism of depolymerization, the effect of these variables on the rate has been determined. Depolymerizations were carried out at 230, 250, and 270°C. in sealed tubes, using dry polymers of different initial molecular weights, polymers containing various amounts of water up to 30% by weight, and polymers in which the amine end groups had been acetylated to preclude aminolysis. Comparable chemical blocking of the acid end groups could only be partially achieved. The reaction product was analyzed for lactams by boiling water extraction, for caprolactam by a sublimation method, and for end group concentrations by titration. It has been found that: ( 1 ) an increase in molecular weight, i.e. , a decrease in active end group concentration, causes a decrease in the rate of depolymerization of dry polymer; ( 2 ) the equilibrium lactam content as well as the rate of depolymerization are increased by ( a ) the addition of water and ( b ) increasing temperature; ( 3 ) acetylation causes a decrease in the rate of depolymerization of dry polymer; the lower the molecular weight of the acetylated polymer ( i.e. , the higher the —COOH concentration), the more rapid is its depolymerization. These results are discussed in terms of the proposed reaction mechanism.