On the Hydrolytic Polymerization of Cyclic Dimer of ε-Caprolactam Catalyzed by Phosphoric Acid

Abstract

The hydrolytic polymerization of cyclic dimer of e-caprolactam with phosphoric acid catalyst was studied.
As cyclic dimer has very high melting point (347-348° C), the initial reaction proceeded as a heterogeneous system. The conversion of cyclic dimer and the formation of e-caprolactam proceeded according to the zero-order kinetics and the both rate constants were directly proportional to the amounts of phosphoric acid and water. From the concentration of the amino-end groups of the formed polycaproamide and the data for conversion of cyclic dimer, it was found that the concentration of the amino-end groups in the reaction system was kept constant during the reaction. Therefore, it was presumed that the hydrolysis of cyclic dimer catalyzed by phosphoric acid proceeded rapidly and cyclic dimer polymerized with the resultant amino-end groups by the amide exchange reaction.
After the con version of cyclic dimer exceeded about 50%, the polymerization of cyclic dimer proceeded according to the first order kinetics in a homogeneous system and the rate constant was directly proportional to the amount of water.