The kinetics of hydrolytic polymerization of ε‐caprolactam. II. Determination of the kinetic and thermodynamic constants by least‐squares curve fitting

Abstract

SynopsisThe kinetic and thermodynamic constants of the hydrolytic polymerization of c-caprolactam were determined by least-squares curve fitting. The calculations were carried out using observed kinetic data such as concentrations of c-caprolactam ([CL]), endgroup ([EG]), and e-aminocaproic acid ([ACA]) and time derivatives of each concentration (rates) d[CL]Idt, d[EG]/dt, and d[ACA]Idt.The sets of the converged constants are obtained for the initial water concentrations of 0.42,0.82, and 1.18 molekg. An averaged set of the constants applicable for this range of the initial composition was also evaluated. The compatibility between observed and calculated concentration and rate curves was improved by the use of the newly developed sets of the constants. The mechanism of the polycondensation reaction is also discussed, based on the rate and kinetic constants obtained by this work. HYDROLYTIC POLYMERIZATIONThe hydrolytic polymerization of e-caprolactam (CL) has been studied by variousThe proposed reaction mechanism, the set of the rate equations derived from the mechanism, and the kinetic and thermodynamic constants are summarized in Table I. Here, x , y , z, and w are the concentrations of CL, endgroup (EG), e-aminocaproic acid (ACA), and water, respectively; kj is the rate constant; Ki is the equilibrium constant; A{ is the frequency factor;

Polyamides

“…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.…”

“…Their K eq at 2 wt % water (using concentrations) is about 600 at 240 C and 450-500 at 270 C. Values of 519 and 377 for comparable conditions can be Figure 1. Dependence of monomer on temperature in polycaprolactam (data from [19, 38, 39]) calculated from the data of TAI and coworkers [56]. These variations are typical of the data available on the hydrolytic polymerization of caprolactam, most of which have been generated at water contents much higher than practical for melt processing.…”

“…Kinetic and thermodynamic constants for the polymerization of caprolactam have been summarized ( [56], Table 3) and have been said to correlate with manufacturing experience with a deviation of less than 12 wt% [58]. The data in Table 3 are averaged for initial water contents of 0.82 and 1.18 mol/ kg (1.48 and 2.12 wt%).…”

Stabilization of High Molecular Weight Nylon 6 Synthesized by Anionic Polymerization of ε-Caprolactam

“…The concentration of water at equilibrium state was calculated from eq viii in Scheme 3 in terms of K expressed by AS and AH (eq iii in Scheme 3). 32 We used the following values, a 0 = 0, c 0 = 0.03 mo!% (Figure 8) or 0.07mol% (Figure 9), z 0 = 100mol% and w0 =0.1 mo!%, AS=0.9437 e.u., AH= -5945.8calmol-1 , 32 T=473 K.…”

“…32 Here, k 0 is the rate constant of the uncatalyzed reaction by the carboxyl end group and kc is that of catalyzed reaction by the carboxyl end group. The following values were obtained; k(c 0 = 0mol¾)=0.335 (kgmo1-1 h-1 ), k(c 0 =0.03mo1%)= 0.344 (kgmol-1 h-1 ), k(c 0 =0.07mo1%)=0.356 (kg mol-1 h-1 ), and k(c 0 =0.7mo1%)=0.546 (kgmol-1 h-1 ).…”