Hydrolytic polymerization of caprolactam. I. Hydrolysis—polycondensation kinetics

Abstract

In a study aimed at process optimization of caprolactam polymerization, particular reference has been paid to the competing role of water in caprolactam hydrolysis and endgroup polycondensation. The dependence of the apparent equilibrium constant for polycondensation on water concentration indicated that there is a strong effect of the medium on the activities of the reacting species which can not be neglected in a kinetic study of the polycondensation reaction. The effect of a variation of the medium was taken into account by using a polycondensation rate constant which included a function of the water present at any given time. With the aid of analog computer curve‐fitting techniques, good agreement with second‐order kinetics was found. The validity of a second‐order mechanism was confirmed in a kinetic study of the chain amide linkage hydrolysis. The hydrolysis of caprolactam follows substantially different kinetics, where the generation of carboxyl groups reduces the activation energy of the reaction, which follows predominantly a third‐order mechanism.

Aliphatic Polyamides

“…113-115 esterify Poly-THF diol + [nylon 11 diacid prepolymer]~'Pebax' poly(ether ester amide) (Ato Chimie) (20) Poly(oxypropylene)diamine + caprolactam + diacid~'Arnitel A' poly(ether amide) (Akzo) (21) Using amine/acyl chloride solutions or interface polymerization technology one can prepare various block copolymers.I!" High molecular weight materials were proposed as elastomers'P?…”

Polyamides

“…The dependence of conventionally calculated equilibrium constants K eq on water content, which can affect ionization, hydration, and activities, has been observed many times [49][50][51][52][53]; these K eq values are thus apparent equilibrium constants. GIORI and HAYES [54] showed for PA 6 that the apparent equilibrium constant for polycondensation increased with water content up to about 2 wt% and decreased thereafter (Fig. 2).…”

“…C by GIORI and HAYES [54] gives K eq ¼ 280 at 280 C. TAI's data [56] yield K eq ¼ 410 at 280 C at the lowest water content studied (0.42 mol/kg or 0.76 wt%). ZIMMERMAN [57] used a reported moisture content of 0.16 wt%, an end product of 3000, and an amide concentration of 8850 g equivalents/10 6 g at 101.3 kPa steam for PA 66 at 280 C to calculate a K eq of 260.…”

Determination of the weight-average molecular weight of polyamide-6 on the basis of melt viscosity

“…where k 1 is the reaction rate constant, [M] the instantaneous concentration of active end groups of the polymer chains, and [c] the concentration of an active agent (depending mainly on the moisture content in the polymer sample [14,15,.…”